Master's Thesis

2008:081 MASTER'S THESIS

Pulping Wastes and Abandoned Mine Remediation Application of green liquor dregs and other pulping by-products to the solidification/stabilisation of copper mine tailings

Lucile Villain

Luleå University of Technology D Master thesis Chemistry Department of Civil and Environmental Engineering Division of Architecture and Infrastructure

2008:081 - ISSN: 1402-1552 - ISRN: LTU-DUPP--08/081--SE Luleå University of Technology

MASTER THESIS

Pulping Wastes and Abandoned Mine Remediation

Application of green liquor dregs and other pulping by-products to the solidification/stabilisation of copper mine tailings

Lucile Villain

June 2008

Department of Civil, Mining and Environmental Engineering Division of Architecture and Infrastructure ACKNOWLEDGEMENTS

This master thesis was realised in Luleå University of Technology and in Ramböll Sverige AB consultancy in Luleå (Northern Sweden).

I would like to express my gratitude to my supervisor Christian Maurice who made the project possible and who guided me throughout this work while granting me autonomy as well. I am also grateful to Ramböll team who nicely welcomed me in spite of my poor Swedish, and helped in practical issues. I would like to thank Nils Hoffner for his useful information, Tomas Forsberg for his valuable help in the laboratory, Ulla-Britt Uvemo for her kind and constant assistance, and Lea Rastas Amofah for her friendly company and wise advice.

I am also thankful towards my family who encouraged me and sent me motivation from France; many thanks to my friends in Luleå who gave me support and joy during these days.

ABSTRACT

Green liquor dregs are one type of chemical by-products produced by the pulp and paper industry which are usually landfilled, and cause concern to the pulp mills due to the cost of landfilling. Their alkaline and impermeable properties render however their re-utilisation possible in several domains. Solidification/stabilisation of sulphide ore mine tailings is one type of potential application of green liquor dregs which is considered in this work.

The project aimed at assessing the efficiency of green liquor dregs associated with other pulping wastes (fly ash, bark sludge) in decreasing the permeability and release of metal contaminants in copper mine tailings from an abandoned mine site. The possibility to use these pulping wastes as a hydraulic barrier to cover tailings or traditional landfills was also considered. To achieve this objective, 2 types of permeability tests were performed, as well as an adapted Column Leaching test and a modified Batch Leaching in oxidising conditions. Tailings alone, different combinations of pulping wastes, and tailings treated with these combinations of pulping wastes were tested.

Addition of pulping wastes to tailings proved efficient in immobilising copper, in particular when one type of green liquor dregs was added to tailings in the proportion of 10%. Copper release was reduced at least 4 times by all the admixtures. Permeability of tailings was decreased to various extents with the addition of different proportions of pulping wastes. The best result was obtained with a combination of green liquor dregs, fly ash and bark sludge mixed with tailings. Hydraulic conductivities of pulping wastes were not as low as to guarantee their efficiency as a hydraulic barrier. It was suggested that moistening the materials may improve their impermeability.

Variability of the wastes produced by the mill was judged as the major problem if their re- utilisation became effective, and increased green liquor dregs quality control was suggested.

TABLE OF CONTENTS

1 INTRODUCTION...... 4 1.1 Research questions – Aim of the project...... 4 1.1.1 Background...... 4 1.1.2 Objectives of the project ...... 5 1.2 Scope of the study...... 6 2 MATERIALS AND METHODS ...... 8 2.1 Materials ...... 8 2.2 Methods ...... 9 2.2.1 Permeability tests...... 10 2.2.2 Leaching tests...... 12 2.3 Samples characterisation ...... 15 2.3.1 Mine tailings from Nautanen abandoned copper mine...... 15 2.3.2 Green liquor dregs from Billerud Karlsborg pulp and paper mill...... 16 3 RESULTS...... 17 3.1 Permeability tests...... 17 3.1.1 Constant Head Permeability Test ...... 17 3.1.2 Constant Rate of Strain test ...... 18 3.1.3 Results of hydraulic conductivities ...... 19 3.1.4 Evolution of HC in CRS test after saturation of samples in CHP test...... 21 3.2 Leaching tests ...... 22 3.2.1 Adapted Column Leaching test...... 22 3.2.2 Batch Leaching test in oxidising conditions ...... 25 4 DISCUSSION ...... 33 4.1 Permeability tests...... 33 4.2 Leaching tests ...... 34 4.3 Discussion on tailings treatment with pulping wastes...... 36 4.3.1 Green liquor dregs and pulping wastes as tailings/landfill hydraulic cover ...... 36 4.3.2 Green liquor dregs and pulping wastes as tailings chemical stabilising agent ... 38 4.3.3 Green liquor dregs and pulping wastes in solidification/stabilisation of tailings...... 38 5 Conclusions ...... 40 5.1 Future works...... 40 6 REFERENCES...... 42 I: Detailed Methodology ...... 45 II: Green Liquor Dregs...... 50 III: Nautanen Abandoned Copper Mine...... 60 IV: Solidification/Stabilisation Method ...... 63 V: Results of Metal Analysis ...... 73 VI: Results of CRS Test...... 89

1 INTRODUCTION

The pulp and paper industry in Sweden generates large quantities of waste, around 6.4 million tonnes in 2004 (Swedish Environmental Protection Agency). It consists mostly of wood waste and slurries generated by manufacturing processes. Most of this waste can be recycled or used for energy production by the industry. But some fractions are simply landfilled at the industries own facilities. An important part of the landfilled pulping waste is constituted by chemical residues that mainly comprise green liquor dregs (=grönlutsslam in Swedish) from sulphate pulping process mills. Currently, the European policy encourages the recovery of waste by means of recycling, re-use or reclamation or any other process with a view to extracting secondary raw materials (European Council directive 91/156/EEC on waste). Within this framework and considering the costs of landfilling, there is a growing interest in re-utilising the green liquor dregs. Due to their alkaline and impermeable properties, several applications (acidic wastewater treatment, landfill cover, agricultural and forest land applications…) have been considered. Mining is the industry that generates the greatest volume of waste in Sweden, which mainly consists of waste rocks (rocks to remove to reach the ore) and mine tailings (waste left after the ore has been extracted). The volume of waste rocks generated in Sweden in 2004 was over 32 million tonnes and the volume of tailings over 25 million tonnes (Swedish Environmental Protection Agency). The main environmental problem associated with sulphidic mine waste is known as acid mine drainage (AMD), a metal-rich acidic solution produced when sulphides are in contact with water and oxygen, and spread into the environment. Remediation of sulphidic mine waste is a potential application for green liquor dregs used as a cover preventing intrusion of water and oxygen in the waste, or as a mixture with mine residues aiming at immobilising the metals. This possibility has received little attention so far and is examined in this work. With green liquor dregs samples provided by Billerud Karlsborg pulp and paper mill (Kalix, Northern Sweden) as well as other pulping wastes on the one hand, and mine tailings sampled in the abandoned copper mining area of Nautanen (region of Gällivare, Northern Sweden) on the other, experiments were carried out to assess the beneficial effects of green liquor dregs (combined with other pulping by-products) on mine waste. Two fields were investigated: the hydraulic properties and the chemical effects.

1.1 Research questions – Aim of the project

1.1.1 Background

Solidification/stabilisation technique is a method used to chemically and/or physically bind the contaminants in a waste to prevent their leaching into the environment. A common stabilising agent is Portland cement which helps to lower the permeability of waste and the mobility of inorganic contaminants. As a consequence, the transport of water through the waste is reduced as well as the release of contaminants. In the natural environment, the most important factor controlling the distribution of inorganic compounds between stable and mobile phases is pH. This is also true in wastes treated by solidification/stabilisation, because precipitation, adsorption and redox reactions immobilising the metals are strongly influenced by pH. Therefore, the success of solidification/stabilisation 4 is really dependent on binder reactions which will impact the pH of the treated waste (Batchelor, 2006). Most of the metals are immobilised in neutral to alkaline conditions.

Green liquor dregs consist in a sludge exhibiting in general low permeability and high alkalinity, which could make them an interesting binding agent in solidification/stabilisation of metal-bearing wastes. They contain sodium carbonate, sodium hydroxide at the origin of high pH value, calcium carbonate, unburned carbon and traces of other elements.

Wastes from metal mines consist mainly of waste rocks, ore rests, slags and tailings (processing wastes from a mill, washery or concentrator). These by-products are usually rich in sulphide minerals containing heavy metals. The main environmental problem associated with these sulphide minerals is the exposition to air and water which leads to oxidation of the sulphides into sulphates and generation of hydrogen ions. The production of hydrogen ions with sulphate anions results in an acidic solution, which is known as Acid Mine Drainage (AMD). The oxidation of sulphide minerals does not only create acid, but it also liberates metals and sulphate into waters and accelerates the leaching of other elements from gangue minerals. As a consequence, AMD is associated with the release of sulphate, heavy metals (Fe, Cu, Pb, Zn, Cd, Co, Cr, Ni, Hg), metalloids (As, Sb), and other elements (Al, Mn, Si, Ca, Na, K, Mg, Ba) (Lottermoser, 2003). The whole ecosystem is at risk in such a situation. To meet environmental quality requirements, mining companies must make sure that the prevention or treatment of AMD will be done.

In mine sites in current exploitation, one way used to avoid this AMD generation is to control the sulphide oxidation with one or more of the following strategies: exclusion of water, exclusion of oxygen, pH control, control of Fe3+ generation, control of bacterial action, removal and/or isolation of sulphides. This can be achieved through covering of wate rocks and tailings with wet/dry covers, encapsulation, in-pit disposal and mixing, co-disposal and blending with benign or alkaline material, addition of organic wastes or bactericides (Lottermoser, 2003). Treatment of AMD may also be required (neutralisation of the acidic water with an alkaline agent or other chemical treatments, anoxic limestone drains, wetlands...). Generally speaking, in abandoned mines, the outcome of a sulphidic mine waste which is considered as dangerous for the environment is excavation followed by landfilling. This drastic method is becoming more and more costly, and solidification/stabilisation of the mining wastes could be used as a milder alternative. Several studies have already been carried out with cementitious materials and/or recycled alkaline by-products, in order to increase cohesiveness, reduce water transport through the mine waste and increase pH.

1.1.2 Objectives of the project

A potential solution to avoid the landfilling of green liquor dregs and treat sulphidic mine waste as well is to apply solidification/stabilisation with green liquor dregs on tailings. Green liquor dregs are expected to decrease the flow of water and act as a good stabilising agent to counter the generation of acidity and release of metals from mine waste. The objective of the present work is to evaluate the efficiency of green liquor dregs from Billerud Karlsborg mill in solidifying/stabilising copper mine tailings from Nautanen

5 abandoned copper mine. To achieve this, hydraulic and chemical properties of the wastes will be evaluated with two types of experiments:

• Permeability tests • Leaching tests

According to a previous study (Hargelius, Ramböll, 2008) the properties of green liquor dregs as a hydraulic barrier in landfills were enhanced when two other by-products – fly ash and organic sludge – were added. Fly ash has a high content of lime CaO and can exhibit cementitious properties during the reaction of carbonation (cf. equation 1). The addition of fly ash to GLD is expected to lower its permeability.

Equation 1: Carbonation reaction, occuring only in the presence of water (hydrated lime) Ca(OH)2 + CO2 → CaCO3 + H2O

Organic sludge turned out to retard the hardening of the mixture green liquor dregs with fly ash and increase its plasticity during the previous study. That is why fly ash and bark sludge (organic sludge made of bark and wood waste) from Karlsborg mill were used as additives to green liquor dregs in the experiments, and their effect on the properties of green liquor dregs in solidification/stabilisation were assessed. Thus, permeability tests and leaching tests were conducted on tailings alone, on green liquor dregs alone or combined with fly ash and bark sludge (pulping wastes), and on the mixture of tailings and pulping wastes.

From the results obtained, we tried to answer the following questions:

• How to select a suitable utilisation for green liquor dregs (called GLD in the work) based on the hydraulic and chemical properties of these GLD associated with the other pulping wastes and tailings? 9 If the permeability of the pulping wastes is low enough (~10-9 m/s), they could be used as a hydraulic barrier covering tailings or landfills. 9 If their alkaline properties allow a chemical immobilisation of the metals in the tailings, they would be suitable as tailings stabilising agent. 9 If both permeability and alkalinity give relevant results, they could be used as a binder in solidification/stabilisation of mine tailings. The mixture could be placed back in situ if the whole pile of tailings is treated or used as an impermeable cover on the rest of the tailings if only a part is mixed with pulping wastes. • Does the addition of fly ash and organic sludge improve the properties of the green liquor dregs in these applications? Which combinations are most efficient in each case?

1.2 Scope of the study

The research work is carried out in the framework of a master thesis consisting in a semester internship in Ramböll Sverige AB consultancy in Luleå and Luleå University of Technology (LTU). The experiments are set in two laboratories of the university: the geotechnical laboratory, and the environmental laboratory. The work may be considered as a preliminary

6 study to potential field tests since no such study of application of green liquor dregs to mine tailings was published before as far as we know.

2 MATERIALS AND METHODS

2.1 Materials

The experiments were carried out using mine tailings from the mining area of Nautanen (province of Lappland, Northern Sweden) on the one hand, and wastes from Billerud Karlsborg pulp and paper mill (Kalix, province of Norrbotten, Northern Sweden) consisting of green liquor dregs, fly ash and bark sludge on the other. Fly ash from Stora Enso Hylte mill (province of Småland, Southern Sweden) and sewage sludge from Uddebo waste water treatment plant (Luleå, province of Norrbotten, Northern Sweden) were also used in some experiments.

Mine tailings from Nautanen abandoned copper mine

The tailings used for the experiments consist in a composite sample formed with 55 subsamples collected at different points of the abandoned copper mine of Nautanen, in the area of Gällivare, in October 2007. The subsamples were dried and 2 mm sieved. They were sorted; those containing more than 2000 mg/kg copper (55 of them) were selected and mixed together. Tailings in the area of Nautanen contain a high amount of copper (table 2), which leaching is currently the main threat for the environment (cf. appendix III).

Figure 1 Copper mine tailings dried and 2 mm sieved. The aspect is sand-like.

Wastes from Billerud Karlsborg pulp and paper mill

The main by-product from the pulp and paper industry used in the experiments consist in green liquor dregs – named GLD in the work–, which are produced in the process of causticization (recovery of pulping chemicals). They form a basic and rather impermeable sludge composed of sodium carbonate, sodium hydroxide, calcium carbonate, unburned carbon, sulfides and traces of heavy metals and other elements. Three samples of GLD (GLS 30, GLS 30 EM, GLS 31) were provided by Billerud Karlsborg mill, collected over 2 days. They were sampled in the location right before the GLD are spilt in a tank before being landfilled.

Figure 2 Green liquor dregs GLS 30 (left), GLS 30 EM (middle), GLS 31 (right)

The mill also supplied fly ash (FA and FA1) from the electrostatic filter placed after the fluidized bed boiler, which is formed of residues from the combustion of bark and wood waste. Fly ash is composed of inorganic nutrients, silicon dioxide, calcium oxide and heavy metals. It is used here to cement the material with which it is mixed. In addition, bark sludge (BS) was provided by the mill, which was sampled from the debarking process and mainly composed of bark compost from pine trees, sand and NaOH added to bark in order to increase pH and avoid corrosion of the machines. It aims at moistening the mixtures and increasing their plasticity.

Figure 3 Fly ash FA which was moistened in the mill (left), dry fly ash FA1 (middle) and bark sludge BS (right) from Billerud Karlsborg pulp and paper mill (Kalix, Norbotten, Sweden)

Fly ash from Hylte mill (FA2a) and sewage sludge from Uddebo waste water treatment plant (SS) were used in some tests to broaden the source of wastes. FA2a was of the same type as FA1, and sewage sludge, though not a pulping waste, was used as an organic sludge with the same role as bark sludge.

The wastes were tested either separately or in combinations which are listed in table 1.

2.2 Methods

The experiments aimed at assessing the properties of GLD and pulping wastes, and their influence on stabilisation of mine tailings in two main domains: the hydraulic aspect and the

9 chemical one. To achieve this, two types of experiments were conducted: permeability tests and leaching tests.

Important note: all the proportions given for mixtures were calculated on the basis of the dry matter weight.

2.2.1 Permeability tests

Constant Head Permeability test

The Constant Head Permeability test (CHP test) was carried out in the geotechnical laboratory of LTU, on four series of two to four samples. For each series, the quantity of water discharging from a constant level tank through the sample in a 5 cm diameter cell in a saturated up-flow mode was measured regularly during approximately two weeks, and the hydraulic conductivity was calculated for each interval. The two weeks duration of the test aimed at reaching the saturation of the samples with water. Thus, after stabilisation of the measured values, saturated hydraulic conductivity (HC) was obtained. For more details about the CHP test, see appendix I.

Figure 4 Picture of the Constant Head Permeability apparatus (left) and scheme of the device (right)

First series of tests: hydraulic conductivity of green liquor dregs

The three samples of GLD provided by Billerud Karlsborg mill – GLS 30, GLS 30 EM and GLS 31 – were tested in the first series. Based on the results of the first series, GLS 30 EM, the most impermeable GLD, was selected for the permeability tests on mixtures with other pulping by-products.

Second series of tests: hydraulic conductivity of tailings, tailings+GLD, and GLD+fly ash

In the second series, HC of tailings was evaluated as a reference for the mixtures involving tailings. Tailings mixed with GLS 30 in the proportion 90:10 (90 TAIL+10 GLS 30) were also tested, in order to evaluate the evolution of permeability when adding a small proportion of GLD (with the aim of chemical stabilisation only). The most permeable GLD was chosen in this case since the interest is then focused on chemical properties and not on impermeability. Two other samples were tested: GLS 30 EM + FA and GLS 31 + FA, which are mixtures of the most impermeable GLD with fly ash (in the proportion 70:30). The addition of fly ash, which exhibits cementitious properties through the reaction of carbonation in humid conditions, was expected to decrease the permeability of the GLD. Yet it was acknowledged during the experiment that FA had been watered in the mill and carbonation had probably already taken place before mixing with GLD. New fly ashes which were not watered (FA1, FA2a) were ordered and used in the next series of test.

Third series of tests : hydraulic conductivity of GLD+fly ash, GLD+fly ash+bark sludge/ sewage sludge, tailings+GLD+fly ash

FA1 from Billerud Karlsborg - 99.5% dry matter content - and FA2a from Hylte mill - 99.8% dry matter content – were tested, which dryness ensured that the carbonation didn not already take place before mixing with GLD. The mixture of GLD with fly ash was tested in the proportion 70:30 with FA1. Based on the comments of K. Hargelius (Ramböll Gothenburg) according to which organic matter like sewage sludge or fiber sludge should be added to the mixture to facilitate the blending, bark sludge (BS) and sewage sludge (SS) were added to GLD and fly ash in two other samples. The following proportions were chosen:

60% GLS 30 EM + 30% FA1 + 10% BS 60% GLS 30 EM + 30% FA2a + 10% SS

A fourth sample was tested in this series: 70% Tailings + 30% (GLS 30 EM + FA1), which aimed at assessing the evolution of the HC of tailings when mixed with this combination of pulping wastes.

Fourth series of tests : hydraulic conductivity of tailings mixed with 30%/60% GLD+fly ash+bark sludge

The fourth series was tested to evaluate the evolution of the HC of tailings with different proportions of one of the most impermeable admixtures according to results of the previous series (GLS 30 EM + FA1 + BS). The proportions 30% and 60% of admixture were chosen:

70 TAIL + 30 (GLS 30 EM + FA1 + BS) 40 TAIL + 60 (GLS 30 EM + FA1 + BS)

Constant Rate of Strain test

Several samples (cf. table 1) tested with CHP test were duplicated and sent to Ramböll Sverige AB Region Väst laboratory in Gothenburg. There, Constant Rate of Strain (CRS) test using an oedometer was conducted. The samples were compressed during several hours and drainage was allowed from their top surface. Hydraulic conductivity was calculated from the deformation and the pore pressure at the lower undrained surface (cf. appendix I for more details). 3 samples – GLS 30 EM + FA1 + BS bis, GLS 30 EM + FA2a + SS bis and 70 TAIL + 30 (GLS 30 EM + FA1) bis– were sent to Gothenburg for CRS test after being submitted to the CHP test during 18 days, so as to evaluate the evolution of the HC measured by CRS test between the initial sample and the sample saturated with CHP test.

2.2.2 Leaching tests

Adapted Column Leaching test

Constant Head Permeability test apparatus was used to perform an adapted Column Leaching test as well (cf. appendix I). The first leachates obtained from each sample – for a liquid/solid ratio of ~0,2 L/kg dry weight – were analysed for pH and electrical conductivity (EC). pH was measured with a WTW pH 330/ SET-1 pH meter, EC with a WTW inolab EC meter. The samples tested were those submitted to CHP test, and the role of this leaching test was to characterise the chemical properties of the different combinations of pulping wastes on the one hand, and the evolution of the tailings chemical properties when mixed with pulping wastes on an other.

Batch Leaching test in oxidising conditions

Batch Leaching test in oxidising conditions was adapted from the standard Batch Leaching test at L/S = 10L/kg (ISO/DIS 21268-2). It aimed at allowing leaching of tailings alone or treated with pulping wastes in oxygenated conditions to artificially favour the oxidation of sulphides and assess the release of metals in this situation. The Batch test consisted in mixing the material and distilled water in a ratio L/S=10 into plastic bottles and let them interact during two weeks. Oxygen was regularly injected (3 days a week) in order to keep oxidising conditions during the whole test period judged as long enough to let the oxidation reaction of sulphides happen. After each injection the bottles were shaken ten times by hand so as to accelerate the intrusion of oxygen into the water and to increase contacts between the material and the water. After 15 days of experiments, about 80 mL of the supernatant liquid was taken out from each bottle and filtered so as to determine pH and electrical conductivity. Metal concentrations in the leachate were determined by a commercial laboratory with the EPA method (modified) 200.8 (ICP-SFMS). A more detailed protocol of the test is proposed in appendix I.

This leaching test aimed at characterising the evolution of tailings chemical properties and release of metals when they were mixed with different combinations of pulping wastes. To achieve this, the following samples were tested:

9 Distilled water ( blank) 9 GLS 30 EM (reference)

9 TAILINGS 9 90 TAIL+ 10 GLS 30 9 90 TAIL + 10 GLS 30 EM 9 90 TAIL + 10 (GLS30 EM + FA1) 9 90 TAIL + 10 (GLS 30 EM + FA1 + BS) 9 70 TAIL + 30 (GLS 30 EM + FA1 + BS)

Figure 5 Samples of TAILINGS and TAILINGS + GLS 30 in Batch Leaching test in oxidising conditions. On the left, bottles after injection of oxygen and shaking; on the right, bottles after decantation.

The characteristics of the different combinations of wastes and the tests they were submitted to are summarised in table 1.

Table 1 Different combinations of pulping wastes and tailings used in the experiments. Content with proportions in dry matter weight and tests associated to each combination are indicated.

Content Permeability tests Leaching tests (% in dry matter weight) Sample name Green Constant Constant Batch Fly Bark/Sewage Column Tailings liquor Head Rate of Leaching test ash sludge Leaching test dregs Permeability Strain in O2 GLS 30 100 X X GLS 30 EM 100 X X X X GLS 31 100 X X GLS 30 EM + FA 70 30 X X GLS 31 + FA 70 30 X X GLS 30 EM + FA1 70 30 X X X GLS 30 EM + FA1 + BS 60 30 10 X X X GLS 30 EM + FA1 + SS 60 30 10 X GLS 30 EM + FA2a 70 30 X GLS 30 EM + FA2a + BS 60 30 10 X GLS 30 EM + FA2a + SS 60 30 10 X X X TAILINGS 100 X X X 90 TAIL + 10 GLS 30 90 10 X X X 90 TAIL + 10 GLS 30 EM 90 10 X 90 TAIL + 10 (GLS30 EM + FA1) 90 7 3 X 90 TAIL + 10 (GLS 30 EM + FA1+ BS) 90 6 3 1 X 70 TAIL + 30 (GLS 30 EM + FA1) 70 21 9 X X X 70 TAIL + 30 (GLS 30 EM + FA1 + BS) 70 18 9 3 X X X X 40 TAIL + 60 (GLS 30 EM + FA1 + BS) 40 36 18 6 X X

2.3 Samples characterisation

2.3.1 Mine tailings from Nautanen abandoned copper mine

A part of the tailings selected for the experiments was sieved and separated into 3 fractions according to grain size: 0-0.125 mm; 0.125-0.5 mm and 0.5-2 mm. Figure 6 illustrates the distribution of the particle size. The 3 fractions were analysed for their metal content by a commercial laboratory. The procedure comprised drying of the samples at 50°C and leaching in nitric acid/hydrogen peroxide in closed teflon vessels in a microwave oven (concentrations were corrected to dry weight 105°C). Analysis was realised according to EPA method (modified) 200.7 (ICP-AES). The results are given in table 2.

0.5-2 mm 0.125-0.5 mm 0-0.125 mm

Figure 6 Distribution of particle size in the tailings.

Table 2 Metal content of the tailings according to the particle size intervals.

ELEMENT (mg/kg TS) 0.5-2 mm 0.125-0.5 mm 0-0.125 mm TOTAL As 8.97 <3 5.5 5.3 Ba 125 206 246 200 Be 0.311 0.287 0.403 0.333 Cd 0.254 0.356 0.741 0.464 Co 18.3 23.5 22.1 21.7 Cr 2.09 0.368 1.31 1.12 Cu 1250 2700 3910 2760 Fe 30400 33300 44500 36451 Hg <1 <1 1.34 1 Li 4.19 7.47 8.63 7.06 Mn 1620 1010 918 1128 Mo 10.2 11.5 22.8 15.1 Ni 3.49 6.3 7.63 6.1 P 728 1150 1780 1263 Pb 21.3 30.5 59 38 Sr 4.52 5.77 8.83 6.52 V 23.2 28.3 40.4 31.2 Zn 82 116 199 136 TS (%) 99.7 99.8 99.7 99.7

2.3.2 Green liquor dregs from Billerud Karlsborg pulp and paper mill

Dry matter content of the GLD was evaluated. The GLD were analysed with the Constant Head Permeability test and the adapted Column Leaching test. Hydraulic conductivity was measured as well as pH and electrical conductivity of the leachate, giving the following results:

Table 3 Dry matter content and hydraulic conductivity of the GLD, and pH and EC of their leachates obtained in the adapted Column Leaching test.

Sample Dry content Hydraulic conductivity pH of EC of leachate (%) (m/s) leachate (mS/cm) GLS 30 72 1.2 E-06 12.6 2.3 GLS 30 EM 55 2.2 E-08 12.1 31.3 GLS 31 65 2.5 E-07 13.0 177.5

The characterisation indicates that green liquor dregs, sampled within only several hours of interval in the pulp and paper mill, show very different properties. In particular, hydraulic conductivity varies on three orders of magnitude. A correlation is suggested between the dry matter content and the hydraulic conductivity, i.e. the drier the GLD, the more permeable.

A Batch Leaching test in oxidising conditions (cf. 2.2.2) was performed on GLS 30 EM in triplicates during one week. The metal concentrations (as well as chloride content) in the leachate are provided in table 4:

Table 4 Metal concentrations in the leachate from the triplicates of GLS 30 EM in the Batch Leaching test in oxidising conditions, and limit values for non-hazardous waste with standard Batch Leaching test L/S = 10 L/kg. Chloride content is indicated as well. mg/kg TS GLS 30 EM 1 GLS 30 EM 2 GLS 30 EM 3 Limit non- hazardous waste As <0.011 <0.011 <0.011 2 Cd <0.001 <0.001 <0.001 1 Co <0.001 <0.001 <0.001 Cr 0.272 0.302 0.270 10 Cu <0.011 <0.011 <0.011 50 Mo 0.097 0.099 0.101 10 Ni <0.005 <0.005 0.007 10 Pb <0.002 <0.002 <0.002 10 V 0.012 0.015 0.021 Zn 0.072 0.047 0.050 50 Cl 89.8 248.8 96.3 15000 Data for other green liquor dregs sampled in 1999 and 2005 in the same mill Billerud Karlsborg are provided in appendix II.

3 RESULTS

3.1 Permeability tests

3.1.1 Constant Head Permeability Test

The three GLD samples provided by Billerud Karlsborg mill – GLS 30, GLS 30 EM and GLS 31 – were tested in the first series. 18 measurements were done during 15 days from which the following hydraulic conductivities were calculated (figure 7):

1,6E‐06 1,4E‐06 (m/s)

1,2E‐06 1,0E‐06 GLS 30 8,0E‐07 GLS 30 EM Conductivity 6,0E‐07 GLS 31 4,0E‐07 2,0E‐07

Hydraulic 1,0E‐09 0 5 10 15 20 Calculation points over 15 days

Figure 7 Hydraulic conductivity of GLS 30, GLS 30 EM, and GLS 31 with time. Each point represents a calculation of HC from the flow of water measured in an interval of time.

The results of this first series led to the following observations: • The 3 GLD show different hydraulic conductivities (HC): o HC of GLS 30 EM varies in the interval 3.7E-09 – 2.6E-08 m/s o HC of GLS 31 varies in the interval 8.4E-08 – 2.7E-07 m/s o HC of GLS 30 varies in the interval 6.4E-07 – 1.4E-06 m/s • The HC vary on different magnitudes for each GLD during the two weeks. GLS 30 shows the largest variation. • A total stabilisation of HC after 15 days was not observed, but a tendency appeared. The saturated hydraulic conductivity was calculated as an average from the last six points (the 15th point was excluded for GLS 30).

The other series of samples tested with CHP test were analysed in the same way, and HC was calculated from the average of the values exhibiting a near stabilisation. The results of this analysis are given in table 5, in which duration of the test, number of HC values selected for the calculation of average saturated HC and days associated to these values are indicated.

Table 5 Duration of CHP test, number of HC values selected for calculation of average saturated HC and days associated to these values for each sample submitted to CHP test.

Duration of Number of HC Days of Sample name the CHP test values for Comment selected values (days) average HC GLS 30 15 5 4-15 GLS 30 EM 15 6 4-15 GLS 31 15 6 4-15 GLS 30 EM + FA 11 5 6-11 GLS 31 + FA 11 4 3-7 HC rise from d 7 TAILINGS 11 5 6-11 90 TAIL + 10 GLS 30 11 4 3-7 Pbs on d 7-11 GLS 30 EM + FA1 14 10 4-14 GLS 30 EM + FA1 + BS 14 10 4-14 GLS 30 EM + FA2a 14 10 4-14 70 TAIL + 30 (GLS30EM+FA1) 14 9 4-14 70 TAIL + 30 (GLS30EM+FA1+BS) 15 7 9-15 40 TAIL + 60 (GLS30EM+FA1+BS) 15 8 11-15

Average saturated hydraulic conductivities of the samples with CHP test are given in table 6.

3.1.2 Constant Rate of Strain test

Results were obtained in the form of a curve of hydraulic conductivity function of deformation of the sample (figure 8). A trend line was drawn from the curve, which intersection with horizontal axis (0 deformation) gave the saturated hydraulic conductivity. When the curve presented a significant change in the slope of HC with deformation two extreme trend lines were drawn and HC was given in an interval (figure 8).

Hydraulic Conductivity (m/s) Hydraulic Conductivity (m/s)

Deformation (%) Deformation (%)

Hydraulic Conductivity (m/s)

Deformation (%)

Figure 8 Determination of the hydraulic conductivity from the curve HC function of deformation in CRS test: 3 examples (GLS 30 EM + FA1 + SS and GLS 30 EM + FA2a above, GLS 30 EM + FA2a + BS below). Intersection of trend lines with horizontal axis gives the saturated hydraulic conductivity.

Results of saturated hydraulic conductivities with CRS test are given in table 6.

3.1.3 Results of hydraulic conductivities

Table 6 Results of hydraulic conductivities with CHP and CRS tests for the different combinations of pulping wastes and tailings. Content of the combinations is also indicated.

Content Constant Head Permeability test Constant Rate of Strain test (% in dry matter weight) Sample name Green Dry Hydraulic Dry Hydraulic Fly Bark/Sewage Density Density Tailings liquor content conductivity content conductivity ash sludge (g/cm3) (g/cm3) dregs (%) (m/s) (%) (m/s) GLS 30 100 1.29 72 1.2 E-06 GLS 30 EM 100 1.38 55 2.2 E-08 1.53 58 1-1.5 E-08 GLS 31 100 1.83 65 2.5 E-07 GLS 30 EM + FA 70 30 1.35 60 2.0 E-07 GLS 31 + FA 70 30 1.52 69 2.5 E-07 GLS 30 EM + FA1 70 30 1.09 66 1.6 E-06 1.35 66 4.0 E-08 GLS 30 EM + FA1 + BS 60 30 10 1.40 57 1.4 E-08 1.47 58 2.0 E-09 GLS 30 EM + FA1 + SS 60 30 10 1.46 60 5.0 E-09 GLS 30 EM + FA2a 70 30 1.40 66 2.0 E-09 GLS 30 EM + FA2a + BS 60 30 10 1.45 59 1-2 E-08 GLS 30 EM + FA2a + SS 60 30 10 1.13 ~58 1.4 E-07 1.47 58 1-4 E-08 TAILINGS 100 1.84 100 5.8 E-07 90 TAIL + 10 GLS 30 90 10 1.97 97 2.8 E-07 70 TAIL + 30 (GLS30EM+FA1) 70 21 9 1.91 ~87 6.4 E-08 2.11 87 1.5-4 E-08 70 TAIL + 30 (GLS30EM+FA1+BS) 70 18 9 3 1.99 82 7.7 E-10 40 TAIL + 60 (GLS30EM+FA1+BS) 40 36 18 6 1.51 68 9.7 E-09

Two samples gave consistent results between the CHP test and the CRS test: GLS 30 EM and 70 TAIL + 30 (GLS 30 EM + FA1). All the other duplicates gave significantly different hydraulic conductivity results between CHP and CRS tests. In this case, HC is always lower with CRS test, on 1 order of magnitude for GLS 30 EM + FA1 + BS and GLS 30 EM + FA2a + SS, 2 orders of magnitude for GLS 30 EM + FA1.

The HC of the three GLD vary on 3 orders of magnitude (E-06, E-07, E-08). The HC of the GLD is either increased or left unchanged when 30% fly ash is mixed with them (except with FA2a in CRS test). The largest increase is observed with FA1 in CHP test (HC of GLS 30 EM raised 70 times). The addition of BS or SS to the mixture GLD and fly ash tends to reduce the raise of HC of GLD due to fly ash or even decrease the HC (GLS 30 EM + FA1 + BS/SS in CRS test).

The addition of 10% GLS 30 to tailings reduces its HC by 50% in CHP test. The HC of tailings is reduced ~9 times when mixed with GLS 30 EM + FA1 in the proportion of 70:30 (tailings:GLS30EM+FA1) in CHP test. The HC of the tailings is reduced ~60 times with 60% GLS 30 EM + FA1 + BS and ~800 times with 30% GLS 30 EM + FA1 + BS in CHP test.

3.1.4 Evolution of HC in CRS test after saturation of samples in CHP test

Three samples were submitted to the CHP test during 18 days and then sent to Gothenburg for CRS test. The results are given as follows: samples called bis refer to the ones that were sent for CRS test after 18 days in CHP test, then results for the same samples in initial conditions are reminded (in italic) both with CRS and CHP tests.

Table 7 Hydraulic conductivities with CRS test of three samples (bis) after 18 days in CHP test. Hydraulic conductivities for the same samples in initial conditions with CRS and CHP tests are also reminded.

Density Dry content Hydraulic conductivity Sample (g/cm3) (%) (m/s) GLS 30EM + FA1 + BS bis 1.49 55 2.5 E-09 –1.5 E-08

GLS 30EM + FA1 + BS (CRS) 1.47 58 2.0 E-09

GLS 30 EM + FA1 + BS (CHP) 1.40 57 1.4 E-08

GLS 30EM + FA2a + SS bis 1.49 56 2.5 E-08

GLS 30EM + FA2a + SS (CRS) 1.47 58 1–4 E-08

GLS 30 EM + FA2a + SS (CHP) 1.13 ~58 1.4 E-07

70 TAIL + 30 (GLS 30EM + FA1) bis 2.03 80 3.5 E-08

70 TAIL + 30 (GLS 30EM + FA1) (CRS) 2.11 87 1.5–4 E-08

70 TAIL + 30 (GLS 30 EM + FA1) (CHP) 1.91 ~87 6.4 E-08

Comparing the HC of samples bis with the HC obtained on initial samples with CRS test, it is noticed that: • There is no significant evolution of HC measured with CRS test for GLS30EM+FA2a+SS and 70 TAIL+30 (GLS30EM+FA1) between sample in initial conditions and sample saturated with CHP test. • For GLS30EM+FA1+BS, the HC measured in CRS test after saturation in CHP test is more uncertain, but remains in the same order of magnitude as in initial conditions.

3.2 Leaching tests

3.2.1 Adapted Column Leaching test

Pulping wastes combinations

10 pH of leachate of pH (L/S~0.2) 9

8 GLS 30 GLS 30 EM GLS 31 GLS 31 + FA GLS 30 EM + GLS 30 EM + GLS 30 EM + GLS 30 EM + FA FA 1 FA 1 + BS FA 2a + SS Samples

Figure 9 pH of leachates from pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg) pH of the GLD and GLD mixed with FA ( fly ash watered in the mill) are between 12 and 13. pH of GLD mixed with FA1 (dry fly ash) and FA1 + BS are slightly above 13. pH of GLD with FA2a and sewage sludge is ~11. Thus the highest pH are obtained with the mixtures GLS 30 EM + FA1 (+ bark sludge).

EC (mS/cm) 250

200

150

100

EC of leachate (L/S~0.2) 50

0 GLS 30 GLS 30 EM GLS 31 GLS 31 + FA GLS 30 EM + GLS 30 EM + GLS 30 EM + GLS 30 EM + FA FA 1 FA 1 + BS FA 2a + SS Samples

Figure 10 Electrical conductivity of leachates from pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)

EC of the pulping wastes initial leachates vary between 2.3 mS/cm (GLS 30) and 216.7 mS/cm (GLS 31 + FA). • EC of leachates from GLD vary in an interval of about 2 orders of magnitude (2.3 mS/cm to 177.5 mS/cm). • Addition of fly ash increases the EC of leachates, especially with FA1. • Not only addition of fly ash can induce high EC. Leachate of GLS 31 alone exhibits a higher EC than leachates of 4 of the mixtures containing fly ash.

Tailings untreated and treated by pulping wastes

4 pH of leachateof pH (L/S~0.2) 2

0 TAILINGS 90 TAIL + 10 GLS 30 70 TAIL + 30 70 TAIL + 30 40 TAIL + 60 (GLS30EM +FA1) (GLS30EM +FA1+BS) (GLS30EM +FA1+BS) Sample

Figure 11 pH of leachates from tailings untreated and mixed with pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)

Initial leachate of tailings alone exhibits a low pH (4.7). The addition of all the pulping wastes tends to increase this pH. The addition of 10% GLD is enough to raise the pH up to 8.2. The largest increase (13.2) is when GLS 30 EM + FA1 + BS is added in the proportion of 60% to tailings, though it remains close to the pH obtained with addition of GLS 30 EM + FA1 (+BS) in the proportion of 30% (pH 12.8-12.9).

EC (mS/cm) 100

20 EC of theleachate (L/S~0.2) 10

0 TA ILINGS 90 TA IL + 10 GLS 30 70 TA IL + 30 70 TAIL + 30 40 TAIL + 60 (GLS30EM +FA1) (GLS30EM +FA1+BS) (GLS30EM +FA1+BS) Samples

Figure 12 Electrical conductivity of leachates from tailings untreated and mixed with pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)

The EC of the leachate from tailings (2.2 mS/cm) is increased with the addition of all pulping wastes. The highest rise is observed for the admixture GLS 30 EM + FA1 + BS in the proportion of 60%. Contrary to the values of pH, the difference of EC between 30% and 60% (GLS 30 EM + FA1 + BS) admixtures with tailings is sizeable (EC 1.7 times higher with 60% admixture).

3.2.2 Batch Leaching test in oxidising conditions

The samples were analysed each in triplicates, except for distilled water (blank) for which only one sample was tested. Average values were calculated from the triplicates, and the results fluctuations are indicated by vertical errors calculated with standard deviations.

25 pH and Electrical Conductivity

4 pH of leachates (L/S~10) 2

0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM EM +FA1) E M +F A 1+B S ) +F A 1+B S ) Samples

Figure 13 pH of leachates from samples tested in Batch Leaching test in oxidising conditions (L/S=10 L/kg).

EC (μS/cm) 3500

3000

2500

2000

1500

1000 EC of leachates (L/S~10) leachates of EC 500

0 Water TAILINGS 90 TAIL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM EM +FA1) EM +FA1+BS) +F A 1+B S ) Samples

Figure 14 Electrical conductivity of leachates from samples tested in Batch Leaching test in oxidising conditions (L/S=10 L/kg).

Note: 2 measurements of pH and EC were done for distilled water, one directly from the bottle, and one after filtration with the same filter used for the other samples. Average values and standard deviations were calculated from these 2 measurements.

Tailings leachate exhibits a low pH (4.7) and a low EC (128 µS/cm). The addition of GLD in the proportion of 10% increases the pH to 8, value superior to that of distilled water (6.5), and EC is increased to ~600-650 µS/cm. The two types of GLD (GLS 30 and GLS 30 EM) give close results. The addition of 10% fly ash FA1 along with GLD to tailings raises the pH of 2 units (10.4) and the EC up to 995 µS/cm. If bark sludge is added as well, the raises are more limited. In particular, pH remains at 8.6. The addition of GLS 30 EM +FA1 +BS in the proportion of 30% (mixture interesting for its low permeability, cf. section 3.1.3) highly raises the pH (11.9) and the EC (2733 µS/cm). The main contribution to such high pH is fly ash, since GLS 30 EM alone generates a leachate with lower pH -10.9- (and bark sludge is present only in a small proportion).

Metal release in the leachates

The metal concentrations directly reflect the release of the contaminants from each material since the same amount of material (30 g dry weight) was tested and the same amount of water (300 mL) was added. They are shown on the graphs in figure 15. Table 8 illustrates the metal release in mg/kg TS.

Table 8 Release of metals from the triplicates of tailings and tailings treated with the addition of different combinations of pulping wastes. Limit values for acceptance of non-hazardous wastes at landfills in standard Batch Leaching test L/S = 10 L/kg (European directive 2003/33/EC) are indicated as well.

mg/kg TS TAILINGS 90 TAIL+ 10 GLS 30 90 TAIL + 10 90 TAIL + 10 Limit non- GLS 30 EM (GLS30 EM + FA1) hazardous waste As <0.1 <0.02 <0.1 <0.02 <0.02 <0.02 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 2 Cd 0.05 0.06 0.06 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.002 <0.001 <0.001 1 Co 0.6 0.7 0.7 0.006 0.010 0.010 0.003 0.001 0.003 0.002 0.003 0.001 Cr <0.05 <0.01 <0.05 0.01 0.01 0.02 0.008 0.009 <0.005 0.5 0.4 0.3 10 Cu 39.6 46.7 50.4 5.6 7.2 8.1 0.4 0.4 0.4 6.2 4.9 4.1 50 Mo <0.05 <0.01 <0.05 0.5 0.5 0.5 0.3 0.3 0.3 1.6 1.3 1.2 10 Ni 0.1 0.2 0.2 <0.01 0.08 0.011 <0.005 <0.005 <0.005 0.008 0.005 <0.005 10 Pb <0.02 0.007 <0.02 0.03 0.05 0.05 <0.002 <0.002 <0.002 0.006 <0.002 <0.002 10 V <0.005 <0.001 <0.005 0.01 0.02 0.02 0.007 0.004 0.003 0.04 0.03 0.03 Zn 10.8 12.2 13.2 0.1 64.1 4.3 2.7 0.2 0.08 2.4 0.2 0.07 50

mg/kg TS 90 TAIL + 10 70 TAIL + 30 GLS 30 EM Limit non- (GLS 30 EM+FA1+BS) (GLS 30 EM +FA1+BS) hazardous waste As <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 2 Cd <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 1 Co 0.01 0.01 0.009 0.003 0.003 0.003 <0.001 <0.001 <0.001 Cr 0.2 0.2 0.2 0.3 0.4 0.3 0.3 0.3 0.3 10 Cu 4.0 5.3 2.8 11.7 12.4 12.2 <0.01 <0.01 <0.01 50 Mo 1.0 1.0 1.0 1.7 1.7 1.6 0.1 0.1 0.1 10 Ni 0.02 0.02 0.01 0.008 <0.005 0.009 <0.005 <0.005 0.007 10 Pb <0.002 <0.002 <0.002 0.005 0.003 0.003 <0.002 <0.002 <0.002 10 V 0.02 0.02 0.01 0.06 0.07 0.07 0.01 0.02 0.02 Zn 2.4 0.3 0.2 1.9 0.2 0.2 0.07 0.05 0.05 50

Cu concentrations in the leachates Co concentrations in the leachates

6000 80

70 5000 60 g/L) g/L) μ μ 4000 50

3000 40

30 2000 20 Concentration of Co ( Co of Concentration Concentration of Cu ( Cu of Concentration 1000 10

0 0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM Water TA ILINGS 90 TA IL+ 10 90 TA IL + 10 90 TAIL+ 10 90 TA IL+10 70 TA IL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM EM +FA1) E M +F A 1+B S) +F A 1+B S ) EM +FA1) E M +F A 1+B S ) +F A 1+B S ) Samples Samples

Ni concentrations in the leachates Cd concentrations in the leachates

20 7

18 6 16 g/L) g/L) 5 μ

μ 14

12 4 10 3 8

6 2 4 Concentration of Ni ( Ni of Concentration Concentration of Cd ( Cd of Concentration 1 2 0 0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM Water TA ILINGS 90 TA IL+ 10 90 TA IL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM EM +FA1) E M +F A 1+B S ) +F A 1+B S ) 29 EM +FA1) EM +FA1+BS) +F A 1+B S ) Samples Samples Cr concentrations in the leachates Mo concentrations in the leachates

60 200 180 50 160 g/L) g/L) μ

μ 140 40 120

30 100 80 20 60 40 Concentration of Cr ( Cr of Concentration 10 Mo ( of Concentration 20

0 0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TA IL+10 70 TAIL + 30 GLS 30 EM Water TA ILINGS 90 TA IL+ 10 90 TA IL + 10 90 TA IL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM EM +FA1) EM +F A 1+B S ) +F A 1+B S ) EM +FA1) E M +F A 1+B S ) +F A 1+B S ) Samples Samples

V concentrations in the leachates

6 g/L) μ 5

2 Concentration of V ( of Concentration 1

0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TA IL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM 30 EM +FA1) E M +F A 1+B S ) +F A 1+B S ) Samples 30 Pb concentrations in the leachates Pb concentrations in the leachates 2

6 0,8 0,7 5 0,6 g/L) g/L) μ 4 μ 0,5

3 0,4

0,3 2 0,2 Concentration of Pb ( of Concentration 1 Pb ( of Concentration 0,1

0 0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM Water TA ILINGS 90 TA IL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM EM +FA1) E M +F A 1+B S ) +F A 1+B S) EM +FA1) E M +F A 1+B S ) +F A 1+B S ) Samples Samples

Zn concentrations in the leachates ZnZn concentrations concentrations in in the the leachates leachates 2 2

6000 14001400

5000 12001200 g/L) g/L) g/L) μ 10001000 4000 μ μ

800800 3000 600600 2000 400400 Concentration of Zn ( of Concentration 1000 Concentration of Zn ( Concentration of Zn ( 200200

0 0 0 Water TA ILINGS 90 TA IL+ 10 90 TAIL + 10 90 TAIL+ 10 90 TAIL+10 70 TAIL + 30 GLS 30 EM WaterWater TA TA ILINGS ILINGS 90 90TA TA IL+ IL+10 10 9090 TAIL TAIL + 10 + 10 9090 TAIL+ TA IL+ 10 10 9090 TAIL+10 TA IL+10 7070 TAIL TAIL + 30 + 30 GLSGLS 30 30 EM EM GLS 30 GLS 30 EM (GLS30 (GLS 30 (GLS 30 EM GLSGLS 30 30 GLSGLS 30 30 EM EM (GLS30(GLS30 (GLS(GLS 30 30 (GLS(GLS 30 30 EM EM EM +FA1) EM +F A 1+B S) +F A 1+B S) EMEM +FA1) +FA1) EMEM +FA1+BS) +FA1+BS) +F+F A 1+B A 1+B S ) S ) Samples 3311 SamplesSamples

Figure 15 Concentrations of Cu, Co, Ni, Cd, Cr, Mo, V, Pb and Zn in the blank (distilled water), in the leachates from tailings with different admixtures, and from GLD alone. The concentrations are given in µg/L so that the results can be compared to the test performed with water only. Results in mg/kg are provided in table 8. The concentrations lower than the detection limit were not represented except for Pb. Standard deviation of Pb concentration is not shown for TAILINGS since the concentration is based only on one value measured above detection limit, and for 4 other samples which concentration was lower than this limit value (0.2 µg/L) in all triplicates. In « Pb concentrations in the leachates 2 » the result of 90 TAIL+ 10 GLS 30 is removed since it shows an abnormally high concentration of Zn. In « Zn concentrations in the leachates 2 » one of the 90 TAIL+ 10 GLS 30 triplicates which had suspiciously high Pb concentration was ignored.

The results of concentrations of As in the leachates are not shown since they were all under the detection limit.

Water was used as a blank, i.e. a reference for the results obtained, and GLS 30 EM as an indicator of the contribution of GLD to the release of metals. The other samples comprise 1 sample of tailings alone, and 4 samples of tailings mixed with different types and proportions of pulping combinations. According to the European directive 2003/33/EC establishing criteria and procedures for the acceptance of waste at landfills, As, Cd, Cr, Cu, Mo, Ni, Pb and Zn show lower average release than the limit values authorised for non-hazardous wastes (with a standard Batch Leaching test at a L/S ratio of 10 L/kg) in all cases.

The comparison of the metal concentration values between the samples leads to the following observations: • The admixtures were all efficient in reducing the release of Cu, Co, Ni and Cd. This is most important for Cu which is released by tailings in a concentration closed to the authorised value for non-hazardous waste (45.6 mg/kg~50 mg/kg). Cu concentration is reduced, at least 4 times, by all the admixtures. Co is almost totally immobilised, since its release is reduced to close to 0 µg/L. Ni is also significantly reduced by all the admixtures, though one of the triplicates TAIL + GLS 30 shows only a slight decrease in concentration. The concentration of Cd, already low in the tailings, is reduced to almost 0 µg/L with the admixtures. • The admixtures increased the release of Cr, Mo and V. In any case, the concentration of Cr and Mo remain well below the authorised limit value for non-hazardous waste. • Pb and Zn are more difficult to describe. The standard deviations are high, though not visible with Pb in tailings (two of the triplicates had value <2 µg/L without more precision). The concentrations in water and in leachates of 90 TAIL + 10 GLS 30 EM, 90 TAIL + 10 (GLS 30 EM+FA1+ BS), and GLS 30 EM remain unknown (<0.2 µg/L). Nevertheless, it can be noted that Pb concentration in the leachates was decreased from tailings leachate with all admixtures except GLS 30. The graph « Zn concentrations in the leachates 2 » ignoring one of the 90 TAIL+ 10 GLS 30 triplicates with suspiciously high Zn concentration shows that all the pulping

admixtures reduced Zn release from tailings, but the standard deviations are quite important as well. Anyhow, Pb concentration is always great below the limit for non-hazardous waste (more than 200 times lower), and Zn is 5 times lower than the limit for non-hazardous waste with tailings, and more than 10 times lower in all other conditions excluding the abnormal triplicate of 90 TAIL + 10 GLS 30.

4 DISCUSSION

4.1 Permeability tests

The HC of the three GLD – GLS 30, GLS 30 EM and GLS 31 – varied in a wide interval (3 orders of magnitude). It seems that there is a correlation between the HC and the dry matter content: the dryer the GLD, the more permeable. This fluctuation becomes a major problem when the re-use of the GLD is considered.

The results obtained with addition of fly ash to GLD did not follow the expected trend. Fly ash mixed with sulphidic mine tailings proved to reduce permeability of the material in previous studies (appendix IV table 16). While a decrease of the HC of GLD was expected with the addition of fly ash to GLD, it actually was either an increase (GLS 30 EM) or no evolution (GLS 31). FA presented a dry matter content of 71%, which indicates that it was collected after being watered, since dry fly ashes usely have a dry matter content around 97%. It was suggested that carbonation of fly ash had already occured and could not happen when mixed with GLD. Thus the cementation would not be achieved, which explained why HC was not decreased. However the addition of dry fly ash FA1 to GLD did not give the desired result either: the HC was highly increased instead of being decreased. Another suggestion was made based on the observations made during the CRS test. The samples with fly ash appeared dry and friable. The fly ash may have absorbed water from the GLD, thus drying it and creating fissures within it. These cracks may have generated an artificial pass for the flow of water, thus distorting the value of hydraulic conductivity. This drying effect is less important when BS or SS is added to the combination GLD anf fly ash, especially with BS. Considering the water content of BS (77%) and SS (72%) we can assume that the sludges moistened the mixture and reduced to some extent the effect of cracking by fly ash.

The addition of pulping wastes to tailings reduced their permeability to different degrees: • The addition of 10% GLS 30 to tailings reduced the HC only twice. It appears as a rather consistent result, since only a small amount of GLD was added. The conservation of tailings permeability is particularly interesting if the GLD are used as a binding agent in chemical stabilisation, while it is not desirable to prevent the flow of water through the waste. • The HC of tailings was reduced 9 times when mixed with GLD + FA1 in the proportion of 70:30 (tailings:GLD+FA1). The admixture helped to make the tailings more cohesive. It seems that the effect of drying and cracking by fly ash previously discussed did not appear when the admixture was added to tailings, or to a small extent. It could be explained because the mixture GLD+FA1 is in this case spread within the tailings.

• The HC of the tailings is reduced 60 times with 60% GLS 30 EM + FA1 + BS and 800 times with 30% GLS 30 EM + FA1 + BS. It shows that the admixtures are both efficient in solidifying the tailings. Result with 30% admixture is better than with 60% admixture (7.7 E-10 m/s instead of 9.7 E-09 m/s). This may appear unlogical since the decrease of HC of tailings is due to the pulping admixture, yet it is explainable if we consider the HC of GLS 30 EM + FA1 + BS alone: 1.4 E-08 m/s. The more the admixture within tailings, the closer to this value.

The difference between the results of CHP and CRS tests can be up to 1 order of magnitude (GLS 30EM + FA1 + BS, GLS 30 EM + FA2a + SS), or even 2 (GLS 30 EM + FA1). The permeability results are rather difficult to interpret since they vary significantly from one test to another and from one sample to his duplicate. CHP test is an easy and reliable test for permeable enough materials, e.g. gravel and sand of HC down to 10-6 m/s. When the material is more impermeable, like in this study, the test is less adapted. For example, in the conditions of experiment, only 4.5 g of water will take more than 17h to flow through a material with HC of 7.5 10-10 m/s. Even though a plastic film was placed to cover the top of the bottles collecting water, evaporation is still possible and may impact the result on such a period. Besides, any anomaly like cracks in the material may distort considerably the measurement. Likewise, stabilisation of the hydraulic conductivity may be difficult to recognise for such impermeable materials. In this situation, it seems easier to use the CRS test, which is actually most of the time used for its low cost and rapidity of execution. But the result is not fully guaranteed either since calculation of HC is not the first role of the oedometer used in CRS test. That is why the performance of both permeability tests highights the difficulty to assess HC in case of impermeable materials. A tendency in the HC of samples can be drawn from the results obtained, but no accurate value can be given in a reliable way.

4.2 Leaching tests pH and electrical conductivity were measured in both leaching tests. pH reflects the acidity/alkalinity of the samples. It is fundamental information since acidity is the main factor controlling the release of metals from the tailings, and a consequential rise in pH can immobilise the major part of the metals in a solid form. EC (measure of the ability of a material to conduct an electric current) of leachate is highly dependent on the concentration of dissolved chemical species which tend to ionise in the solution. EC is used as an indicator of how ion-free or impurity-free the leachate is: the purer the leachate, the lower the conductivity. Nevertheless it should be pointed out that different chemicals contribute in different proportions to the EC value, and no simple correlation between EC and the concentration of electrolyte in the solution can be made. That is why EC does not reflect directly the concentration of elements released from the leached material.

Column Leaching test and Batch Leaching test in oxidising conditions gave consistent pH and EC results. pH of tailings (~4) was raised to ~8 with addition of 10% GLD, and to more than 10 when the admixture contained fly ash (except for 90 TAIL + 10 (GLS 30 EM+FA1+BS)). EC of tailings was raised less than 5 times with addition of 10% GLD, around 8 times with 10% pulping wastes containing fly ash, and more than 20 times with 30%/60% pulping admixtures with fly ash. Fly ash contributes considerably to the rise in pH because of its high content in lime. Fly ash also increases EC because it is a concentrate of inorganic nutrients and it is very rich in chloride.

From pH and EC results, 10% GLD turned out to be the most interesting admixture for tailings, raising pH to a little bit more than neutral, and not increasing EC considerably.

Release of metals in the Batch Leaching test in oxidising conditions

The effect of the pulping wastes addition on the metal release from tailings depends on the metal considered:

• The admixtures were all efficient in reducing the release of Cu, Co, Ni and Cd from tailings. This is most important for Cu which leaching is the major environmental problem in Nautanen abandoned mine. Cu release is decreased at least 4 times by all the admixtures, and 100 times with addition of 10% GLS 30 EM. The decrease is explained by the rise in pH after addition of pulping wastes which immobilise the metals in solid forms. Note: The concentration of Cu is a little bit higher in 70 TAIL + 30 (GLS 30 EM+FA1+BS) compared to tailings with other admixtures. This could be explained by the relatively high content in organic matter (bark sludge BS) in the sample. Dissolved organic matter can act as a complexing agent for heavy metals and organic acids may dissolve stable metal phases. Thus organic matter can increase the mobility and release of metals, in this case Cu. That is why it appears preferable to use the admixture GLS 30 EM+FA1+BS in the proportion of 10% rather than 30%. • The admixtures increased the release of Cr, Mo and V. According to the values obtained with GLS 30 EM alone, it is suggested that the increase of Cr concentration is triggered by release from GLD, and to a greater proportion by fly ash. This suggestion is endorsed by the results of leaching tests on fly ash from the same mill (cf. appendix II table 13). The release of Mo and V with admixtures is contributed by GLD only to a small extent (cf. result with GLS 30 EM), more probably by fly ash (cf. fly ash composition in appendix II table 13 for Mo). It is also most probably released by tailings due to the rise in pH with pulping wastes, Mo and V being mobilised with higher pH (opposite pH effect to Cu, Co, Ni and Cd). The concentration rises are not so important though and the increased release should not be problematic. • Pb and Zn are more difficult to interpret. All the triplicates of 90 TAIL + 10 GLS 30 show significantly high Pb concentrations compared to other samples, which may be explained by a higher content of Pb in GLS 30 than GLS 30 EM. As for Zn, one of the triplicates of 90 TAIL+ 10 GLS 30 gave an abnormally high concentration in the leachate (6220 µg/L). This result was checked and confirmed, so it may have been triggered by contamination. The high Zn concentration in distilled water is not explained. The sample may also have been contaminated, but there is no reliable information to endorse this suggestion since water was not duplicated. • Cr, Mo, Pb and Zn concentrations remain anyway well below the limit values for non- hazardous waste in standard Batch Leaching test L/S=10 (excluding Zn for the abnormal triplicate of 90 TAIL + 10 GLS 30).

The best result in term of low release of metals is 90 TAIL + 10 GLS 30 EM. Thus the best admixture to immobilise heavy metals in the tailings turned out to be GLD added in the proportion of 10%. The results were not as satisfactory with GLS 30 as with GLS 30 EM (Zn,

Pb, V increased and Cu not reduced as much), which proves again that the variability of GLD can be problematic. Another good admixture for chemical stabilisation is GLS 30 EM + FA1 + BS in the proportion of 10%.

On the basis of the results of permeability tests and leaching tests, the potential applications of GLD (along with other pulping wastes) suggested in the beginning (1.1.2) will be discussed here.

4.3 Discussion on tailings treatment with pulping wastes

4.3.1 Green liquor dregs and pulping wastes as tailings/landfill hydraulic cover

The CHP test gave 3 different HC results for the three types of GLD: 1.2 E-06 m/s, 2.2 E-08 m/s and 2.5 E-07 m/s. CRS test indicated a HC of the same order as with CHP test for GLS 30 EM. It seemed that the more humid the GLD, the more impermeable. Results for GLD from the same mill in 2000 and 2007 were:

Table 9 Results of hydraulic conductivity of green liquor dregs from Billerud Karlsborg mill with CHP test in 2000 and CRS test in 2007. Results for GLD in the present work are reminded in italic.

Hydraulic conductivity Sample Density (g/cm3) Dry content (%) (m/s)

Karlsborg 2000 (CHP) 1.46 38 4 E-09

Karlsborg 2000 (CHP) 1.57 - 2 E-09

Karlsborg 2007 (CRS) 1,45 49 2 E-08

Karlsborg 2007 (CRS) 1.51 56 4 E-08

Karlsborg 2007 (CRS) 1.45 62 4 E-08

GLS 30 1.29 72 1.2 E-06

GLS 30 EM (CHP) 1.38 55 2.2 E-08

GLS 30 EM (CRS) 1.53 58 1– 1.5 E-08

GLS 31 (CHP) 1.83 65 2.5 E-07

Considering that a material should exhibit a low to very low HC (at least ~10-9 m/s) to be used as a hydraulic barrier, the results for GLD are not fully satisfactory. The main problem is the variation of HC among the GLD, which comes from a great variability of the waste when it is produced at the mill. If the HC of GLD is actually mainly dependent on the moisture content, as suggested in this work, it could be a criterion to select the GLD which are suitable as hydraulic barriers. The impermeability might also be improved by moistening the GLD before compaction and covering in that case. 36

The addition of 30% fly ash to GLD increased the permeability of GLD with CHP test, all the more so as fly ash was dryer. This was probably due to the drying of GLD by fly ash and subsequent cracking. With CRS test this effect did not appear such problematic. Result obtained with 70% GLD + 30% fly ash in January 2008 at Ramböll Gothenburg with CRS test (K. Hargelius) is given in table 10:

Table 10 Result of hydraulic conductivity for 70% GLD + 30% fly ash in january 2008 at Ramböll Gothenburg with CRS test. Results for GLS 30 EM + FA1 and GLS 30 EM + FA2a with CRS test are reminded in italic.

Density Hydraulic conductivity Sample Dry content (%) (g/cm3) (m/s)

GLD + fly ash Gothenburg 01/08 (CRS) - - 7 E-09

GLS 30 EM + FA1 (CRS) 1.35 66 4.0 E-08

GLS 30EM + FA2a (CRS) 1.40 66 2.0 E-09

Overall the addition of 30% fly ash alone to GLD did not prove efficient in lowering its HC, probably due to the drying of GLD.

When 10% bark sludge/sewage sludge was added to GLD with fly ash (60% GLD + 30% fly ash + 10% BS/SS), it seemed to lower the drying effect of fly ash on GLD with CHP test, but not so obviously with CRS test. Results from January 2008 in Ramböll Gothenburg (K. Hargelius) gave the same range of HC with CRS test.

Table 11 Results of hydraulic conductivity for GLD + fly ash (Fa) + organic material in January 2008 at Ramböll Gothenburg with CRS test. Results for GLS 30 EM + fly ash + BS/SS with CRS test are reminded in italic.

Density Dry content Hydraulic conductivity Sample (g/cm3) (%) (m/s) 65% GLS + 25% Fa + 10% compost (CRS) - - 8.0 E-09 (after 11 days)

70% GLS + 20% Fa + 10% SS (CRS) - - 5.0 E-09 (after 11 days)

60% GLS + 30% Fa + 10% compost (CRS) - - 4.0 E-08 (after 10 days)

60% GLS + 30% Fa + 10% compost (CRS) - - 4.0 E-09 (after 7 days)

GLS 30EM + FA1 + BS (CRS) 1.47 58 2.0 E-09

GLS 30EM + FA2a + BS (CRS) 1.45 59 1-2 E-08

GLS 30EM + FA1 + SS (CRS) 1.46 60 5.0 E-09

GLS 30EM + FA2a + SS (CRS) 1.47 58 1-4 E-08

From the trends of HC obtained for the different combinations of pulping wastes, two solutions are suggested to obtain sufficiently impermeable materials with GLD and make them suitable as a hydraulic barrier: • Mixing GLD, fly ash and an organic sludge, and increasing the content of organic sludge to more than 10% to make the material more humid (e.g. 60% GLD + 20% fly ash + 20% organic sludge) • Using GLD alone or 70% GLD + 30% fly ash, and adding water to the mixture before compaction and covering. Yet the efficiency of this solution should be examined thorougly since it has not been tested in this work.

4.3.2 Green liquor dregs and pulping wastes as tailings chemical stabilising agent

GLD added to tailings in the proportion of 10% turned out to generate the best immobilisation of metals in the tailings. The results varied between the GLD (e.g. Cu concentration was reduced 7 times with GLS 30 and 100 times with GLS 30 EM), which raise again the problem of variability of GLD in case of re-utilisation. But the effect was beneficial in both cases anyway. 60% GLS 30 EM + 30% FA1 + 10% BS added in the proportion of 10% gave positive results as well. The same mixture in the proportion of 30% was not as good. It might be explained by the mobilisation of metals by organic matter present in the mixture in a greater content. All the admixtures showed positive results in stabilising Cu and reduced its release from tailings at least 4 times. This is a promising result since the release of copper from tailings is the most worrying problem in Nautanen mine. They increased the release of Cr, Mo and V, but the concentrations remained low anyhow.

4.3.3 Green liquor dregs and pulping wastes in solidification/ stabilisation of tailings

If impermeability and chemical stabilisation can be achieved at the same time when pulping wastes are mixed with tailings, solidification/stabilisation of the tailings may be applied, and the mixture tailings + pulping wastes either placed back in situ or as a cover on tailings left. The best solidification (decrease of permeability) of tailings is obtained with the admixture 60% GLS 30 EM + 30% FA1 + 10% BS. HC of tailings is reduced by 2 orders of magnitude with a 60% addition, and 3 orders with a 30% addition of this combination. Thus the best candidate for solidification/stabilisation of tailings is this combination added in the proportion of 30%. Yet chemical stabilisation is not as satisfactory in that case. Cr, Mo and V are leached to a greater extent, and Cu concentration is decreased about 4 times only, possibly because of its mobilisation by organic matter. Nonetheless Cu release is decreased significantly even in this situation and the release of the other metals remain well below the authorised limit for non-hazardous waste. Thus a part of the tailings could be mixed with 30% (GLD + fly ash + bark sludge), and the mixture used as a cover on the tailings left because it presents a very low permeability.

In the case of solidification/stabilisation of the whole pile of tailings and not only the cover, we could think about GLD alone or a mixture of GLD and fly ash added in the proportion of 30% to tailings. The HC would not be lowered too much, so that water can still flow through 38 the waste. But leaching tests on these two solutions should be carried out to evaluate the chemical stabilisation efficiency in these situations, since only 10% addition to tailings was tested here.

A consideration of the volume of GLD required to solidify/stabilise tailings from Nautanen abandoned copper mine gives the following results: • ~8900 gross tonnes of GLD (average TS of 60%) to solidify/stabilise ~12500 tonnes1 of tailings with a 30% proportion. (70% TAIL + 30% GLD) • ~2300 gross tonnes of GLD to stabilise tailings with a 10% proportion. (90% TAIL + 10% GLD) As 11980 gross tonnes of GLD were produced in 2007 in Billerud Karlsborg pulp and paper mill (Nils Hoffner, personal communication), this could be an interesting alternative to landfilling if several abandoned mines were to be treated in that way. But if a mixture 70% TAIL + 30% (GLD + fly ash + bark sludge) is used only as a cover on tailings left, it might not be so interesting for the mill. It is worth noting that the remediation of tailings with GLD was in the present work imagined for abandoned mine tailings with limited volume and high metal content. The volume estimation of GLD required is relevant in this domain, but it is inadequate in the case of tailings from a currently exploited mine which waste volume would be disproportionately higher.

1 Estimation of tailings amount in Nautanen mine from MRM Konsult AB Luleå report, 2005. TS of tailings is considered as 100% to simplify the calculation. 39

5 Conclusions

Re-use of green liquor dregs associated with other pulping wastes proved efficient in the solidification/stabilisation of Nautanen copper mine tailings:

• The hydraulic conductivity of the tailings was reduced with the addition of pulping wastes. The best result was obtained when tailings were mixed with the combination 60% green liquor dregs + 30% fly ash + 10% bark sludge in the proportion 70:30 (tailings:pulping wastes). Hydraulic conductivity of tailings was reduced 800 times in this case. It is suggested that a part of the tailings pile could be mixed with this combination, and the impermeable material obtained placed back as a hydraulic barrier covering the rest of the tailings. • Chemical immobilisation of copper in tailings treated by pulping wastes was achieved with all combinations tested (Cu release was reduced at least 4 times). The best stabilisation was observed with the addition of one type of green liquor dregs in the proportion 90:10 (tailings:green liquor dregs). Immobilisation of Cu, Co, Ni and Cd was favoured by the pH raise due to pulping wastes. Cr, Mo and V release was increased on the contrary, though to a limited extent.

The results of permeability tests on combinations of green liquor dregs and pulping wastes did not clearly argue for the re-use of these materials as a hydraulic barrier. The hydraulic conductivities were in the range of 10-8-10-7 m/s with CHP test and 10-9-10-8 m/s with CRS test (rather low hydraulic conductivities though not very low), and the variation between duplicates and between the tests were quite high. This variation was explained by the uncertainty of permeability tests as materials are more impermeable, and by the variability of wastes.

The quality fluctuation of the pulping wastes produced in the mill appeared as the major problem for their re-utilisation. Chemical and hydraulic properties of green liquor dregs in particular varied considerably, affecting the efficiency of the treatment of tailings. The quality management of pulping wastes will not be realised as long as it is not necessary or profitable for the mill. However it is suggested to increase quality controls on the green liquor dregs to be able to select the most suitable fractions for re-utilisation. Studies in field scales are also recommended.

5.1 Future works

Here are some suggestions to complete the experiments carried out in the present work: • A hypothesis was expressed that the drawback of the combination green liquor dregs + fly ash was the absorption of humidity from green liquor dregs by fly ash and

subsequent cracking of the material increasing its permeability. To assess this hypothesis, it is suggested to perform permeability tests on fly ash alone and compare the hydraulic conductivity with the one of green liquor dregs mixed with fly ash. • It was observed that the dryer the green liquor dregs, the more permeable. Thus it would also be interesting to evaluate the hydraulic conductivities of green liquor dregs alone or with fly ash moistened by the addition of more organic sludge or water. If permeability is such dependent on the moisture content, adding water to pulping wastes before their compaction and use as a cover or before their addition to tailings might be an easy way to improve their impermeability. • As for chemical immobilisation of metals, long-term leaching tests (e.g. long-term Column test) of tailings treated by pulping wastes would be interesting. • The repetition of the experiments with pulping by-products and tailings from other origins would be relevant as well.

6 REFERENCES

Avfall i Sverige 2004. Svenska MiljöEmissionsData (SMED) på uppdrag av Naturvårdsverket, Augusti 2006. BATCHELOR. B., 2006. Overview of waste stabilization with cement. Waste Management 26 (2006). 689–698. BATTAGLIA. A., CALACE. N., NARDI. E., PETRONIO. B.M., PIETROLETTI. M., 2007. Reduction of Pb and Zn bioavailable forms in metal polluted soil due to paper mill sludge addition. Effects on Pb and Zn transferability to barley. Bioresource Technology 98 (2007). 2993–2999. Beneficial Use of Industrial By-Products. Identification and Review of Material Specifications, Performance Standards, and Technical Guidance. December 2003. Prepared For NCASI. CALACE. N., CAMPISI. T., IACONDINI. A., LEONI. M., PETRONIO. B.M., PIETROLETTI. M., 2005. Metal-contaminated soil remediation by means of paper mill sludges addition: chemical and ecotoxicological evaluation. Environmental Pollution 136 (2005). 485-492. CARLSSON. E., 2002. Sulphide-Rich Tailings Remediated by Soil Cover – Evaluation of cover efficiency and tailings geochemistry, Kristineberg, northern Sweden. Doctoral Thesis. CONNER. J.R., 1990. Chemical Fixation and Solidification of Hazardous Wastes. Van Nostrand Reinhold, NY, USA. COUNCIL DECISION of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC (2003/33/EC). DRAFT INTERNATIONAL STANDARD ISO/DIS 21268-2. Soil quality — Leaching procedures for subsequent chemical and ecotoxicological testing of soil and soil materials — Part 2: Batch test using a liquid to solid ratio of 10 l/kg dry matter. Efterbehandling av Nautanens gruvområde MKB, 2005-04-28. MRM Konsult AB Luleå GULLICHSEN. J., FOGELHOLM. C-J, 1999. Chemical Pulping book 6B. Papermaking Science and Technology. Chapters 11 and 14. HÖCKERT. L., 2007. Chemical stabilization of mine waste with sewage sludge and calcium carbonate residues. Master Thesis. JONES. H.R., 1973. Pollution Control and Chemical Recovery in the Pulp and Paper Industry. Pollution Technology Review n°3. p 46-49. KIM. A.G. Leaching methods applied to the characterization of coal utilization by-products. National Energy Technology Laboratory, US Department of Energy, Pittsburgh. LOTTERMOSER. B., 2003. Mine Wastes. Characterization, Treatment and Environmental Impacts.

MOUTSATSOU. A., PROTONOTARIOS. V., 2006. Remediation of polluted soils by utilizing hydrothermally treated calcareous fly ashes. China Particuology Vol. 4, No. 2 (2006). 65-69. NEHDI. M., TARIQ. A., 2007. Stabilization of Sulphidic Mine Tailings for Prevention of Metal Release and Acid Drainage Using Cementitious Materials: a Review. J. Environ. Eng. Sci. 6 (2007), 423-436. NORDTEST Method, NT ENVIR 002 2 approved 1995-11. Solid waste, granular inorganic material: column test. NURMESNIEMI. H., PÖYKIÖ. R., KEISKI. R. L., 2007. A case study of waste management at the Northern Finnish pulp and paper mill complex of Stora Enso Veitsiluoto Mills. Waste Management 27 (2007), 1939–1948. NURMESNIEMI. H., PÖYKIÖ. R., PERÄMÄKI. P., KUOKKANEN. T., 2005. The use of a sequential leaching procedure for heavy metal fractionation in green liquor dregs from a causticizing process at a pulp mill. Chemosphere 61 (2005), 1475–1484. PÉREZ-SIRVENT. C., GARCÍA-LORENZO. M.L., MARTÍNEZ-SÁNCHEZ. M.J., NAVARRO. M.C., MARIMÓN. J., BECH. J., 2007. Metal-contaminated soil remediation by using sludges of the marble industry: Toxicological evaluation. Environment International 33 (2007). 502–504. Pilotyta med tätskikt på Ätrans Deponi, Fältförsök – Värö – FAVRAB – Hylte. K. Hargelius., 2008. Ramböll Sverige AB Region Väst, Gothenburg. PÖYKIÖ. R., NURMESNIEMI. H., KUOKKANEN. T., PERÄMÄKI. P., 2006. Green liquor dregs as an alternative neutralizing agent at a pulp mill. Environ Chem Lett 4 (2006), 37– 40. Second annual GEODE-Fennoscandian shield field workshop on Palaeoproterozoic and Archaean greenstone belts and VMS districts in the Fennoscandian Shield. 28 August to 1 September, 2000, Gällivare-Kiruna, Sweden. Abstract volume & Field trip guidebook. Edited by Pär Weihed & Olof Martinsson. SEPPÄLÄ. J., MELANEN. M., JOUTTIJÄRVI. T., KAUPPI. L., LEIKOLA. N., 1998. Forest industry and the environment: a life cycle assessment study from Finland. Resources, Conservation and Recycling 23, 87–105. THACKER. W. E., 2007. Beneficial use of by-product solids from the kraft recovery cycle. NCASI Northern Regional Center Technical Bulletin n 931, 1–36. YLMAZ. O., ÇOKÇA. E., ÜNLÜ. K., 2002. Comparison of Two Leaching Tests to Assess the Effectiveness of Cement-Based Hazardous Waste Solidification/Stabilization. Turkish J. Eng. Env. Sci. 27 (2003), 201-212.

Internet and communication references:

Billerud’s website. http://www.billerud.se and on-line Karlsborg's environmental report 2007 COUNCIL DIRECTIVE of 18 March 1991 amending Directive 75/442/EEC on waste (91/156/EEC).

http://eurlex.europa.eu/smartapi/cgi/sga_doc?smartapi!celexapi!prod!CELEXnumdoc&lg= EN&numdoc=31991L0156&model=guichett ELE International report on soil permeability testing. http://www.ele.co.uk/pdfs/36-41.pdf Engineer Manual 1110-1-4007, Safety and Health Aspects of Hazardous, Toxic, and Radioactive Waste Remediation Technologies, 15/08/03. http://www.usace.army.mil/publications/eng-manuals/em1110-1-4007/c-4.pdf Geo Denmark (Danish Geotechnical Institute) power point presentation. http://www.geo.dk/media/191ed79d-906e-47d4-a692-cd3ef980f5da- Continuous%20consolidation%20tests%20(CRS).pdf ICS Portal for Technology Transfer report on Solidification/Stabilisation. http://www.ics.trieste.it/Portal/InfoTech_Technology_Document.aspx?documentcid=21_1 66_28 Jurate Kumpiene, course “Risk Assessment of Contaminated Land”. Malin Angervall, Ramböll Sverige AB Region Väst laboratory in Gothenburg (personal communication).

I: Detailed Methodology

1 Measurement of the dry matter content

In order to carry out the leaching tests and to realise the mixture of by-products with specific proportions, the materials were analysed for their dry matter content. Small amounts of material (3.5 g to 20 g) were taken from three random areas of each material container and placed into aluminium crucibles. The subsamples obtained were weighed on an abnino lab Precisa scale of 0.01g accuracy. They were then placed into an oven under a temperature of 105 ºC during 24 hours at least. The weight of the materials was measured again.

2 Permeability tests

2.1 Constant Head Permeability test

Hydraulic conductivity, or K, is a property of soil, rock, or any material describing the ease with which water can move through pore spaces or fractures. It depends on the intrinsic permeability of the material and on the degree of saturation. In order to determine the hydraulic conductivity of the materials, permeability tests were performed with a Constant Head Permeability apparatus (figure 16). The principle is to let water flow through a material sample contained in a 5 cm diameter plastic tube from a constant level tank. Water flowing out of the sample is collected in a bottle (with the top covered by a plastic film to reduce evaporation) and weighed at certain intervals of time during approximately two weeks in order to reach saturation of the sample. As the amount of water passing throughout the material at each interval of time and the height of the water tank are known, hydraulic conductivity of the sample can be calculated from Darcy’s law.

Figure 16 Scheme of the Constant Head Permeability test apparatus

Darcy’s law: v= K×i v= volume of water crossing a unit sectional area per unit time (m/s) K= saturated hydraulic conductivity [m/s] i= hydraulic gradient

Q v= Q= ∆V/∆t volumic flow of water [m3/s] A A= area of the sample [m2]

H i= H= height of the tank l l= length of the material

v × lQ Δ × lV K= = = i A× H t A××Δ H

Samples preparation:

The materials tested were tailings, pulping wastes and mixtures of both. They were placed into the permeability tubes between two filters. Material fractions were accumulated in the tubes as increments of ~2 cm-layers which were each time compacted as much as possible. As for rather granular material, the compaction was made with 17 impacts on the top surface of the sample with a load metal stick (proctor compaction test standard). Finer materials were compacted with a plastic stick with enlarged ending. This compaction aimed at filling in any void that could let water pass through and induce errors in hydraulic conductivity. To take

46 into account this artificial compacted state, the density of the samples was calculated and indicated with the hydraulic conductivity. Totally, 10 centimetres of material were packed in each tube. An inlet pipe from the constant level tank was plugged into the bottom of the tube; an outlet pipe leading to a plastic bottle was inserted at the top of the tube.

2.2 Constant Rate of Strain test

Constant Rate of Strain test is a continuous consolidation test which is an alternative method to tests in ordinary oedometer cells (Terzaghi). It reduces the testing period from weeks to within a day or two, or even a few hours. This procedure makes use of a steady increase of effective stress, instead of applying stress increments.

The oedometer is placed in a compression test machine and the sample is compressed with a constant rate of deformation in water. Load is gradually applied to the sample by increasing the axial displacement at a constant rate. The resulting increase in vertical stress and pore water pressure at the base are monitored while drainage is allowed from the top surface only. During the compression of the sample, the deformation, the applied load and the pore pressure at the lower undrained end of the sample are continuously recorded.

Calculation The results of the CRS test are based on Wissa's solution. The saturated hydraulic conductivity can be determined from the following formula: k = where r=average internal strain (deformation) rate (s-1) H= height of the sample (m) 3 gw= volumic weight of water (kN/m ) ubottom= pore pressure at the bottom undrained surface (kPa)

3 Leaching tests

Leaching is the process by which inorganic or organic constituents are released from the solid phase (soil or soil-like material) into the water phase. It represents one of the major means of spreading of contaminants into the environment. Release of contaminants occurs due to mineral dissolution, desorption and complexation processes which are affected by several factors such as pH and redox potential of the medium, or the proportion of water phase with respect to solid phase (generally represented by L/S= Liquid/Solid ratio). Several tests reproduce natural leaching in laboratory conditions. They differ by experimental factors like pH, redox potential and L/S as well as the way to mix the water phase with the sample. They are “Batch Leaching tests”, “Column Leaching test”, “pH Dependence Leaching tests” (pH stat), “Availability tests”, “Diffusion Leaching tests”…

3.1 Column leaching test adapted for the project

Standard Column Leaching test

Column (or dynamic) Leaching test is one type that provides basic characterisation for short, medium and long term leaching behaviour of solid waste materials, simulating the flow of

47 percolating groundwater through a granular material. The Standard Test Method for Leaching Solid Material in a Column Apparatus (ASTM D-4874) is intended to maximise the leaching of metallic species from a solid. The aqueous fluid passes through particles of known mass in a saturated up-flow mode. The Dutch Standard Column Test (NEN 7343) is also an up-flow application, and the Nordtest Column Method (NORDTEST, 1995) is similar to the Dutch Column test, except that column dimensions are optional. The up-flow column procedures are designed to insure that the leachant solution (solution introduced into the sample) is equally distributed throughout the column (A. G. Kim). Leachate (solution obtained after leaching) fractions are collected at different time periods and analysed for their pH and electrical conductivity.

Modifications to the standard test

Due to practical reasons (limitation in time), the Column test is not applicable to materials with low water permeability e.g. less than 10-8 m/s. As the study is concerned with materials of expected low permeability (the aim is precisely to obtain impermeable mixtures with pulping wastes), the standard Column Leaching test protocol had to be adapted. Instead of collecting five fractions of leachate until a L/S ratio of 2 (L/kg dry weight) as indicated by the standard, only the initial fraction of L/S ratio ~0.2 was collected. Likewise, instead of samples of 2 kg dry weight minimum, materials of about 200g – 400g dry weight were tested. Furthermore, the tests were performed with the Constant Head Permeability test apparatus instead of a Column Leaching test apparatus; firstly since the system is roughly the same: water is injected into a tube filled with the sample, in an up-flow mode; and secondly because permeability, which is the other parameter of interest in the present work, can be determined at the same time.

3.2 Batch leaching test in oxidising conditions

When the Column Leaching test described above was performed some weaknesses appeared in the realisation of the experiment: • Firstly, it was impossible to obtain the fractions of leachate at a specific L/S at the same time for each sample due to their significantly different permeabilities. This is not satisfactory since the standard indicate that the leachate fractions of each sample should be collected after the same time interval. • Secondly, only short-term leaching properties of the samples could be assessed with this method ( about 4 hours to four days leaching) To make up for these insufficiencies, it was decided to perform a Batch Leaching test in addition to the Column Leaching test. The main advantages of the Batch test are its ease of realisation and repeatability allowing convenient comparisons of the materials leachability. The main drawback is the non-respect of the natural leaching conditions (shaking and mixing with a leachant instead of water percolating). Yet it should be pointed out that no leaching test can satisfactorily reproduce natural leaching conditions anyway.

The Batch Leaching test in oxidising conditions was inspired from the standard Batch Leaching test L/S=10 (ISO/DIS 21268-2) and modified to favour the oxidation of sulphides in the non-treated and treated tailings. The principle of the Batch test was to mix the material and distilled water at a ratio L/S=10 (L/kg dry weight) into plastic PE-HD polyethylene bottles and let them interact during two weeks. Oxygen was regularly injected (three days per week) in order to keep oxidising

48 conditions during the whole test period and allow the oxidation reaction of sulphides to occur. After each injection the bottles were shaken 10 times by hand so as to accelerate the intrusion of oxygen into the water and to increase contacts between the material and water.

Detailed protocol of the test:

30 g dry weight of tailings alone, green liquor dregs alone, and tailings mixed with different proportions of pulping by-products were introduced into 500 mL plastic bottles which were previously acid washed (HNO3 1 M acid bath) during at least 24 hours. 300 mL distilled water (pH ~6; EC ~20 μS/cm) were added in the bottles. 180 mL of oxygen was injected with a syringe through the top opening of the bottle in order to replace (at least partly) the air portion in the bottles with pure oxygen. The bottles were then shaken 10 times by hand. The same protocol of oxygen injection (120 mL thereafter) and shaking was applied three days a week during two weeks. After 15 days, the experiment was stopped. The material had sedimented and separated from the supernatant water – or leachate – the day before. About 80 mL of leachate were taken out from each bottle with a pipette and left to centrifuge during 15 min at 10000 g speed. Indeed, some of the materials did not sediment enough and a lot of particles were still in suspension in the leachate which did not allow its filtration. The centrifuged leachate was filtrated with a 45 μm filter on a 60mL syringe. The filtrate was divided into 3 parts: 40-50 mL were placed into a freezer (~-19°C) 2 to 6 days in order to be sent to a commercial laboratory for metal analysis; around 25 mL were stored in the freezer as a sample duplicate in case of need for further analysis, and the rest was analysed immediately for pH and electrical conductivity.

II: Green Liquor Dregs

1 Introduction

1.1 General information on waste management in Sweden

According to the definition provided in the European Council directive 91/156/EEC on Waste used in Sweden, “waste” in general shall mean any substance or object which the holder discards or intends or is required to discard. The directive also defines waste “management” as the collection, transport, recovery and disposal of waste, including the supervision of such operations and after-care of disposal sites. It is indicated that Member States shall take appropriate measures to encourage: firstly, the prevention or reduction of waste production and its harmfulness, secondly the recovery of waste by means of recycling, re-use or reclamation or any other process with a view to extracting secondary raw materials, or the use of waste as a source of energy. The environmental protection concern is expressed through legislative and regulative aspects. In particular, there have been regulations to increase the cost of landfill disposal and to make it more difficult to establish new sites for disposal. In addition, urecovered waste can represent a loss of valuable resources in the form of both materials and energy (Seppälä et al., 1998).

1.2 Utilisation of waste and industrial by-products from the pulp and paper industry in Sweden

(Naturvårdsverket, 2004)

The pulp and paper industry in Sweden generates large quantities of waste, around 6.4 million tonnes in 2004. It is mostly made up of wood waste and slurries generated by manufacturing processes. Most of these wastes can be recycled or used for energy production by the industry. Waste management within pulp and paper industry sector is shown in table 12. Waste management is dominated by recycling and incineration. A total of approximately 5 300 ktons wastes is recycled. It consists mainly of wood wastes and paper and cardboard wastes that are recovered as fiber raw material. Approximately 380 ktons are deposited at forest industries landfills. A large part of the wastes is composed of chemical residues that mainly comprise green liquor dregs from sulphate pulping process mills. Landfilling is however getting more and more costly, and pulp and paper industries show a growing interest in recycling and use of landfilled wastes.

Table 12 Waste management within the pulp and paper industry sector in Sweden. Note that these quantities are quantities that are handled at treatment plants within the sector. Wastes that are sent away to plants in other sectors, e.g. to municipal waste plants are not included here (Avfall i Sverige 2004, Naturvårdsverket).

Amount, thousand tons

Non-hazardous wastes

Recycling, total 5 330 of which • wood waste 3 510 • paper and cardboard wastes 1 650 • wastes from incineration (ash 86 and slag)

Incineration, total 3 750 of which • wood waste 2 820 • slurry (both industrial slurry 819 and common slurry) -gross weight- 92 • paper and cardboard wastes Landfilling, total 383 of which • chemical rests and sediments 160 (e.g.green liquor dregs) • paper and cardboard wastes 49 • slurry (both industrial slurry 41 and common slurry) • wastes from incineration (ash 78 and slag) Other outcomes, total 9

The present work is concerned with the outcome of pulping wastes from Billerud Karlsborg pulp and paper mill (Kalix, province of Norrbotten, Northern Sweden). Pulp production at Karlsborg dates back to the start of the 20th century. Today Billerud Karlsborg is one of the largest businesses in the region. The mill comprises a pulp line, a paper machine, a coating machine and a drying machine for market pulp. Wastes from Karlsborg are dominated by various sludges and calcic materials. The largest fraction is formed by green liquor dregs, an alkaline sludge generated in the kraft chemical recovery system. Up until now no satisfying way to use the green liquor dregs was found and they are therefore deposited at the factory’s own landfill approximately 2.5 km north of the site. However the high cost of landfilling (around 3 million Swedish crowns per year in the mill) incites the mill to consider the re-utilisation of their wastes. The focus of this study was to examine potential utilisations of different pulping wastes from Karlsborg mill, and above all green liquor dregs. Accordingly, a description of the processes producing green liquor

51 dregs and a characterisation of this waste is provided in this section, followed by a review of the various possible utilisations of green liquor dregs found in the literature.

2 Description of the causticizing process, part of the kraft recovery system

2.1 Pulping process

Pulp and paper mills like Billerud Karlsborg mill include the fundamental processes of wood preparation, pulping, screening, washing, thickening and bleaching, as well as paper machine operations. Pulping is the process of separating wood chips or recycled paper into individual fibres by either chemical, semichemical, or mechanical methods. The chemical process is the most common method used for wood chips (Nurmesniemi et al., 2007). Chemical pulping aims at dissolving the lignin that binds the cellulose fibres together in the wood, which is the major raw material used in the pulp and paper industry. The kraft (or sulphate) process is the most common one, in which the cooking chemicals consist of a solution of sodium sulphide in caustic soda. The different stages in pulping lead to the formation of a wide range of solid residues, both organic (sludge) and inorganic (ash, dregs and grits). Green liquor dregs and lime mud account for the major portion of wastes from the causticizing process.

2.2 Causticizing process

Causticization is a part of the kraft pulp mill chemical recovery system, in which the cooking chemicals used in pulping are recovered. The purpose is to convert inactive sodium carbonate (Na2CO3) generated by the combustion process into active cooking chemical sodium hydroxide (NaOH), and to ensure that this conversion is as high as possible. The transformation is called causticization, wich comes from the fact that sodium hydroxide is also called caustic soda. The different units of the kraft recovery process are shown on figure 17: • Directly after the pulping process, evaporation of black liquor • Combustion of black liquor in a recovery furnace to form sodium sulphide and sodium carbonate • Causticization of sodium carbonate to sodium hydroxide • Regeneration of lime mud in a lime kiln (calcination) and return of white liquor to the pulping process

Spent “black” liquor from the digestion of wood chips, containing organic dissolved wood residues and inorganic cooking chemicals, is concentrated by evaporation and then burned in a special recovery boiler. This generates steam used as energy, and produces a flow of inorganic process chemicals consisting primarily of sodium carbonate and sodium sulphide (converted from sodium sulphate). The inorganic process chemicals are dissolved in water to form “green” liquor (named as such for its green colour). Insoluble impurities and non-reactive metals left from the black liquor, termed green liquor dregs, are washed and removed, usually by clarification. The green liquor is treated with

52 calcium hydroxide Ca(OH)2 (slaked lime), which converts sodium carbonate (Na2CO3) to sodium hydroxide (NaOH) producing “white” liquor , and lime mud (CaCO3). White liquor, mainly composed of sodium hydroxide and sodium sulphide, is returned to the digester to pulp more wood chips. Lime mud is calcined into reactive lime (CaO) in a lime kiln.

Figure 17 The causticizing process as a part of the pulp mill chemical recovery circuit (Nurmesniemi et al. 2006, modified from Järvensivu et al., 2001).

Non-reactive or non-process elements (NPEs) are elements that do not have a useful role in pulping, bleaching or recovery. NPEs include potassium, manganese, barium, iron, copper, nickel, chromium, zinc… They have to be taken out of the circuit to prevent operational damage. Therefore, the causticizing process acts as a ‘‘kidney’’ in the pulp mill in which non- process metals are purged from the process (Nurmesniemi et al., 2007). However, the total removal of metals should not be achieved, for a certain content of metals is required for effective peroxide bleaching. The removal of green liquor dregs from the recovery cycle participates in controlling non-process elements (NPEs) in kraft chemical recovery systems. Generally speaking, the green liquor dregs are washed to recover sodium and sulphur and to lower alkalinity, then dumped in landfills.

2.3 Characterisation of green liquor dregs

The NPEs in green liquor originate from wood raw material, bleaching, or makeup chemical or process water and enter the causticizing process through the recovery boiler (Chemical Pulping, 1999). Green liquor clarification concentrates on removing these impurities in solid form (green liquor dregs). Green liquor dregs are composed of sodium carbonate, sodium hydroxide (5 to 10 % in Karlsborg pulp and paper mill) at the origin of high pH values, calcium carbonate, unburned 53 carbon, sulfides and traces of heavy metals and other elements. They tend to have a very fine clay-like texture.

The characterisation of Karlsborg mill green liquor dregs by leaching tests (1999 and 2005) is provided in table 13. It gives the concentration of the main metals and elements to consider for acceptance in landfills. Data for fly ash from the fluidized bed boiler is shown as well, since it was used in the experiments of the present work.

Table 13 Results of leaching tests on green liquor dregs and fly ash from Billerud Karlsborg mill, Northern Sweden (1999, 2005 and 2006). From Nils Hoffner in Billerud Karlsborg (personal communication).

Green liquor dregs Green liquor dregs Fly ash Fly ash Fly ash spring Limit non hazardous 1999 2006 1999 2005 2006 waste L/S in L/kg L/S = 10 L/S =0,1 L/S = 10 L/S = 10 L/S =0,1 L/S = 10 L/S =0,1 L/S = 10 L/S =0,1 L/S = 10 (C0) (C0) (C0) Unit mg/kg TS mg/l mg/kg TS mg/kg TS mg/l mg/kg TS mg/l mg/kg TS mg/l mg/kg TS Arsenic <0.05 <0.001 0.0060 <0.05 0.084 0.047 0.018 0.035 0.3 2 Barium 0.05 <0.002 <0.01 3.44 0.60 11.0 0.48 14.9 20 100 Cadmium 0.002 0.00058 <0.001 0.006 0.00068 0.018 0.0030 0.0088 0.3 1 Chromium tot 0.16 0.015 0.049 3.35 14.41 3.36.31 0.4 2.5 10 Copper 0.05 0.040 0.058 0.15 0.080 0.055 0.048 <0.01 30 50 Mercury <0.001 <0.0003 <0.001 0.013 <0.0004 <0.01 <0.0003 <0.001 0.03 0.2 Molybdenum 0.096 0.17 4.8 4.94 1.92 3.86 3.5 10 Nickel <0.03 0.0042 0.014 0.06 0.010 0.17 0.0063 0.1 3 10 Lead <0.03 0.0014 <0.005 0.42 0.11 0.39 0.11 0.30 3 10 Antimony <0.002 <0.01 <0.004 <0.01 <0.003 <0.01 0.15 0.7 Selenium 0.020 0.081 0.96 1.01 0.63 0,88 0.2 0.5 Zinc 0.2 0.048 0.24 8.8 12.8 13.2 10.2 10.2 15 50 Chloride 28.0 45.4 6000 6936 3600 4023 8500 15000 Fluoride 7.80 <2 36.4 7.70 6.6 4.42 40 150 Sulphate 220 62.6 360 45576 23100 21120 7000 20000 DOC(*) 56.0 74.9 236 43.4 66 98 250 800 TS dissolved 16060 138146 90600 134790 60000 substances TOC % of TS 5 % 1,9 % 1,3 % >5 %

Notes: Data in bold exceed the limits on non-hazardous waste. Fly ash in 2006 was mixed with bark sludge and fibre sludge.

3 Utilisations of green liquor dregs

Green liquor dregs, as stated earlier, generally contain a significant amount of calcium that may be mostly in the carbonate form. They also exhibit in general a rather low permeability (hydraulic conductivity around 10-8 m/s). This renders numerous uses of green liquor dregs proven or possible. Several actual applications or studies on potential ones are listed here.

3.1 Utilisation in pollution control

3.1.1 Treatment of Reduced Sulphur Compounds in Waste Gases (Thacker, 2007)

Recent research exhibited some promising results of green liquor dregs used as a material for removing odorous total reduced sulfur (TRS) compounds from waste gas streams. Thacker reports that Fenske, Empie, and Heedick (2000) investigated the ability of dried green liquor dregs to eliminate hydrogen sulphide (H2S) from a laboratory packed-bed reactor. Dregs from three different mills were analysed for their removal efficiencies. Preliminary process calculations indicated that the daily production of green liquor dregs could satisfactorily reduce H2S emissions from a kraft recovery boiler provided that the dregs could be regenerated and re-used in a second cycle of H2S removal. A difference was observed in the ability of the three dregs types to remove hydrogen sulphide and it was assumed to be due to a variation in composition (especially calcium and organic carbon contents) of the materials. Thacker reports that in subsequent work, Lane and Empie (2003) studied the removal of H2S, dimethyl sulphide (DMS), dimethyl disulfide (DMDS), and methyl mercaptan (MeSH) by green liquor dregs under a variety of laboratory conditions. The results obtained were verified by a mill trial. In the mill setting, H2S and MeSH were reduced to immeasurable levels by green liquor dregs treatment, DMS and DMDS concentrations were unchanged, and total TRS was reduced from 2.1 to 1.6 ppm.

3.1.2 Utilisation of green liquor dregs as a neutralising agent for acidic wastewaters

Case study of Stora Enso Oyj Veitsiluoto Mills at Kemi, Finland (Pöykiö et al., 2006; Nurmesniemi et al., 2007)

Landfill treatment of green liquor dregs is considered problematic at Stora Enso Oyj Veitsiluoto Mills in Finland, and utilisation of green liquor dregs as a neutralising agent for acidic wastewaters began in the beginning of 1990. After carrying out a number of case studies, the continuous use of green liquor dregs for neutralising purposes started in 1995, and in 2004 the mill used half of the total amount of green liquor dregs produced at mill as a neutralising agent for acidic wastewaters (Pöykiö et al., 2006). The green liquor dregs are mixed with water in a tank and added into acidic wastewater prior to the biological wastewater treatment plant (i.e., the activated sludge plant). As green liquor dregs contain NPEs, it was important to determine whether the metals concentrations both in the biosludge and in the effluent treated by the green liquor dregs were affected. Mill scale studies were carried out which concluded that there has been an increase 56 in the concentrations of Ca, Cr and Ni in the biosludge, and Ca, Al, Cr and Ni in the effluent purged from the mills. Nevertheless, it is worth mentioning that the metal concentrations, especially in the effluent, were low. It was concluded that the neutralisation of acidic wastewaters by green liquor dregs in Stora Enso Oyj Veitsiluoto Mills during these 10 years proved successful: no problem arose in the incineration of the dregs-treated biosludge for the production of energy, this re-use permitted considerable cost savings by the reduction of transport to the disposal sites, and it saved the limited space available for other wastes. The mill intends to increase the utilisation of dregs by improving dregs clarification and treatment process.

3.2 Land-based uses (Thacker, 2007)

3.2.1 Agricultural land application

Agricultural land application is probably the most common beneficial use for causticizing by- products – lime mud, green liquor dregs and slaker grits2 –. It is mostly the case for excess lime mud, but green liquor dregs can also be applied. The by-products can serve as a liming agent, replacing agricultural limestone as a means to raise soil pH into a range that enhances crop production. The efficiency of a liming agent is often expressed as its calcium carbonate equivalence (CCE), which is the relative acid-neutralising capacity of the material, on a weight basis. The reference is pure calcium carbonate which value is 100%. Green liquor dregs tend to have values in the range of about 75% to 85%. Agricultural limestone generally presents CCE of 90% to 98%. Another important factor is the liming rate which controls the speed with which soil pH is increased and depends on the particle size of the liming agent. Green liquor dregs would show good reaction rates due to their small particle size, compared to limestone. In addition to their liming effect, green liquor dregs may represent a source of nutrients for crops. Apart from calcium, green liquor dregs provide phosphorus and magnesium. As for the results obtained with causticizing by-products as liming agents, published information, though limited, shows yield improvements comparable to those obtained with commercial limestone. More specifically, Thacker reports an example of study involving green liquor dregs demonstrating this improvement by Lickacz et al. (1998) for barley and alfalfa in soil treated with lime mud, slaker grits, or green liquor dregs.

Causticizing residues are applied on agricultural soils alone or mixed with another alkaline by-product such as wood ash to create the liming product.

3.2.2 Forest land application

Causticizing by-products and especially green liquor dregs in our concern are rarely applied to forest land outside of research projects. However they could be beneficial when forest growth is limited by a soil with low pH or low nutrients Ca, Mg, P or K content. Although relatively high heavy metal contents restrict the use of green liquor dregs as a forest fertilizer if it is spread without any ameliorating agent, Österås et al. (2005) reported that a

2 By-products resulting from the hydration of calcium oxide (CaO) by green liquor, during the spent cooking solution recovery process in mills producing kraft pulp, that is composed primarily of calcium carbonate (CaCO3) and calcium hydroxide [Ca(OH)2] (BNQ, 2005).

57 mixture of green liquor dregs and wood ash may be suitable for forest fertilizer purposes (Nurmesniemi et al., 2007). Indeed, it counteracts nutrient depletion and the acidification of forest soils. The authors controlled that, in a long-term perspective, the spreading of this mixture would not result in elevated concentrations of heavy metals such as Cu, Zn and Cd in the tree stems.

3.2.3 Mine reclamation

The use of causticizing residues for mine reclamation is very limited and concerns mainly lime mud rather than green liquor dregs. Yet Thacker reports that according to Redmond (1997), the grits, dregs, and mud from a Northeastern USA mill were each declared by the state regulatory agency to be a co-product and marketed by a contractor for uses that included strip mine reclamation.

3.2.4 Soil stabilisation and hydraulic barrier

Thacker presents a research carried out in Sweden on geotechnical and environmental characteristics of one type of slaker grits and green liquor dregs in order to assess their potential use in landfill and road construction (Gustavsson, Wiberg, and Oberg-Hogsta 2000). The wastes were analysed for particle size distribution, optimal water content, maximum dry density, stress-strain characteristics, and hydraulic conductivity. The two by-products were mixed with soft clay, cement and lime. The presence of either grits or dregs triggered only minimal increases in strength, and the by-products were judged to be of limited utility for soil stabilisation. Even though green liquor dregs mixed with pulp mill ash have already been used as a road amendment to improve soil strength and reduce deformation (Nurmesniemi, 2005), the Swedish study on the other hand oriented towards hydraulic barrier layer of landfills as a more suitable application for green liquor dregs.

3.3 Other applications

3.3.1 Cement kiln feedstock (Thacker, 2007)

Major components of Portland cement are various oxides of calcium, silica, aluminium, and iron, with calcium being by far the predominant constituent. Hence causticizing by-products could be attractive feedstocks in the fabrication of cement due to their high calcium content. Thacker reports that Smith, Badar, and Hodge (1995) mentioned an early effort at evaluating possible uses for dregs and grits including their addition, along with the mill’s wood ash, to a cement kiln. Nevertheless the materials were judged to be unsuitable as cement kiln feed because of high levels of sodium, potassium, sulfur, and chloride. It was noted also that the quantity of all materials might not be sufficient to employ them in a cement plant.

3.3.2 Fine aggregate in asphalt paving (NCASI, 2003, Thacker 2007)

Lime mud, lime slaker grits, and green liquor dregs have been used successfully as a substitute for fine aggregate in HMA (hot-mixed asphalt, the most prevalent type of asphalt

58 paving material) although paving contractors expressed concerns regarding perceived environmental liability.

III: Nautanen Abandoned Copper Mine

The tailings samples used in the experiments come from Nautanen copper mine area in lappland (county of Norrbotten, Northern Sweden – figure 18 –) which was exploited in the beginning of the XXth century. Information about the geology of this area is provided here, followed by the description of the present environmental situation of the site.

Sampling of the tailings

Gällivare

1 Geology of Nautanen area

(Second annual GEODE-Fennoscandian shield field workshop)

Northern Norrbotten is an important mining county dominated by Fe- and Cu- deposits, with Au as a minor constituent in some of the Cu-deposits. Sweden’s largest sulphide mine, Aitik, is situated in the Gällivare area of Northern Norbotten. With an annual production of 18 Mt, it is one of the major Cu and Au producers in Western Europe. Already in 1902–1907 copper and gold were mined in the Gällivare area at Nautanen, Liikavaara, Ferrum and Fridhem mines.

The geology of the Northern Norrbotten region comprises an Archaean granitoid-gneiss basement, which is unconformably overlain by Palaeoproterozoic greenstones, porphyries and sedimentary successions. The Archaean basement is dominated by ~2.8 Ga tonalite- granodiorite intrusions. Minor constituents are mafic to intermediate volcanic rocks, clastic sediments and undeformed red ~2.7 Ga granites.

The iron deposits in Gällivare area were first recognised in the 18th century. When the railway from Luleå was built in 1888 to exploit the important iron resources, extensive exploration activities were initiated in the surroundings. In 1898, copper ore was discovered at Nautanen and within a few years a number of Cu-mineralizations had been found Northeast and East of Gällivare. Most of the Cu-deposits in the Gällivare area are hosted by volcaniclastic sediments varying in composition from arenites to pelites. These sediments are intruded by synorogenic diorites and late to postorogenic granites and pegmatites. The ore deposits occur within, or close to, a major shear zone running in a northwestern direction through the volcaniclastic belt.

During the period 1902 to 1907, 71835 tonnes of ore containing 1–1.5 % Cu and some Au were mined in open pits and underground at Nautanen. The deposit is hosted by strongly altered and deformed rocks within the major NW-SE directed shear zone. Less deformed clastic metasedimentary rocks of partly volcanogenic origin are found on both sides of the shear zone. Several lenses of Cu-ore have been mined. They consist mainly of chalcopyrite in association with magnetite and some pyrite. Minerals found in accessory amounts are sphalerite, galena, carrollite, bismuthinite, molybdenite and scheelite.

2 Present state of Nautanen mine

(MRM Konsult AB Luleå report)

2.1 Historical background

Nautanen mining areas were discovered in 1898 and mining activities started in 1902. Nautanen Kopparfält AB (Nautanen Copper Ore company, registered 12 December 1900) mined the area for copper and gold. Their findings soon turned out to be significantly less than expected and the company concluded its activities in 1908, after only about 6 years of activities, in bankruptcy. After closure of the mine, residues from mining activities were left in the form of waste rock piles, tailings, slags and various other wastes which have been exposed to weathering. The facilities were dismantled and the society was abandoned. In recent years, however, the site evolved to a touristy attraction. The area has been declared historical monument (number 81), and therefore benefits from a level of protection under the law on cultural heritage.

2.2 Environmental issues

The weathering of exposed residues has given rise to environmental problems, in particular with copper leaching from the decomposing wastes, tailings, slags and ore piles. Leaching from the mine is evaluated to represent 150-200 kg copper per year, only calculated on the

61 analysis of water in one stream (Imetjoki). Impact on the environment is visible through the absence of vegetation and reduction of species diversity in some areas (mainly along Imetjoki stream). MRM reports that in the main study carried out (Bothniakonsult AB, 2002) the area was classified according to the Swedish Environmental Protection Agency MIFO model. Since the risk for humans is judged as low, the location was placed at risk class 2 and not risk class 1. Yet the risk for the environment was judged as high enough that measures to reduce emissions of copper are necessary. It has been suggested that the leaching of copper has reached a level that is not likely to increase, but not to reduce either, i.e. it has attained a "steady state" proportion. This state is estimated to last the coming several hundred years, possibly some thousand years. There is theoretically a sufficient amount of copper for much longer periods of time than the leaching period achieved until here. An estimation of the copper content in the wastes (about 0.7% to 0.8% in about 80 000 tonnes) provides 560 to 640 tonnes of copper which can be leached up to about 30% (according to leaching tests), i.e. 170- 190 tonnes released. Tailings are located in the industrial area and present the largest leaching potential with about 72% of copper available. The average content is very uncertain, but with an estimated quantity of about 12 500 tonnes and a copper content of 0.1-0.2%, it provides 10 to 20 tonnes available for leaching. MRM adds that SGU (Swedish Geological Survey) indicates in PM 2003-11-24 a probably higher average copper content, about 0.5%, which would provide around 45 tonnes of copper available.

2.3 Targeted measures on cultural and environmental aspects

Measures have been proposed for the future treatment of the mine. The overall goal is to restore the natural environment in the area according to the conditions which prevail elsewhere in the surroundings. This means that in the long term, the flora and the fauna would again settle in the area and especially in the water. The area is classified as a cultural monument, which means that all interventions must be approved by the County Administrative Board Culture and Environment department (Länsstyrelsens kulturmiljöenhet). The area has a great value from a historical point of view. In that sense, some treatment actions are not fully consistent with the preservation of the cultural environment. The goal of the treatment plan is, to the largest extent possible, to take into account the unique cultural value and set interventions that above all would preserve the existing architectural foundations. A consultation has been held in Gällivare 2002-04-13, which has led the Regional Council of Norrbotten to recognise that the planned treatment activities are likely to have a significant environmental impact. The primary treatment option proposed is to transport the waste rocks to Aitik for reprocessing, and drop off the remaining contaminated soils within Nautanen mining areas, close to Max mine (used currently as a waste rock deposit) in which they would be stored in order to be landfilled. A second option put forward is the construction of a liming treatment station to remediate acidic contaminated water while preserving the cultural value of the site upstream.

IV: Solidification/Stabilisation Method

1 Definition and description of the method

"Solidification and Stabilisation" (S/S) refers to a generic set of technologies and/or processes that use binders and additives to remediate contaminated sites. The aim is to chemically and/or physically bind and immobilise contaminants, so as to reduce their leachability. This is generally achieved by the use of Portland cement, pozzolanic binders, kiln dust, and fly ash. There is a difference between solidification and stabilisation. Stabilisation attempts to reduce the solubility or chemical reactivity of a waste, by changing its chemical state or by physical entrapment (micro-encapsulation). Solidification systems aim at converting the waste into an easy handled solid with reduced hazards from volatilization, leaching or spillage. The two are often discussed together because they have the common purpose of improving the containment of potential pollutants in treated wastes. Combined processes are often termed “waste fixation” or “encapsulation” (Conner, 1990). S/S was used to treat nuclear wastes in the 1950s and was then widely applied to hazardous wastes in the early 1970s (Conner, 1990). The application of S/S process has proved successful for inorganic contaminants (metals) and radionuclides in the presence of low levels of organic matter. S/S methods can be practised in situ as well as ex situ.

Solidification/stabilisation method is usually performed using cement. That is why the following detailed description of the method mostly originates from the study of cement- based S/S of inorganic wastes.

1.1 Solidification

(from Batchelor, 2006)

Solidification consists in changes in primarily physical properties of the waste to obtain a well solidified waste without free liquids and improved strength. This will facilitate its handling, especially if the untreated waste is a liquid or sludge. Furthermore, no more free liquid will be transported into the ground. The waste can thus be disposed of or replaced in situ more safely for the environment. Usually, the treatment results in a bigger size of the waste particles, so the ratio area/volume of the waste will be reduced. This will decrease the leaching of the contaminants. Likewise, the permeability of the waste will be greatly reduced, inhibiting the advective flow through it. A major constraint in applying cement-based S/S to wastes is the extent to which components of the waste interfere with cement hydration reactions. Many of the compounds that are reported to accelerate or retard cement hydration are found to cause similar problems in wastes. These include organics, particularly polar organics, halides, metals and sulphate. Avoiding adverse waste-binder interactions is a major focus of developing S/S technologies for some wastes. Approaches to managing these problems include adding an accelerator to counteract a retarder and vice-versa. For example, soluble silicate has been used extensively as a S/S admixture to reduce effects of retarders.

Different tests are useful to determine the extent of the solidification:

• The major method is to measure the unconfined compressive strength of the treated material. The acceptable value depends on the disposal conditions, yet there are some specifications for S/S treatment provided by regulatory bodies. It is important to estimate the long-term stability of the waste. • Permeability to water must be considered. • Wet-dry and freeze-thaw durability tests can be used. • The knowledge of the pore structure in a waste treated by S/S allows to assess the extent of contaminant release. The evolution of the porosity through interaction of the waste with the environment (leading to leaching of the binder and waste constituents) should also be taken into account.

1.2 Stabilisation

(from Batchelor, 2006)

Waste stabilisation is the result of chemical changes in contaminants and their environment that cause the contaminants to be less mobile or less toxic. Changes in mobility are primarily due to a contaminant being converted from the dissolved phase to a solid phase. Diffusion of the contaminants through the pores is then limited. The major reaction occurring in cement-based stabilisation is precipitation. The high pH resulting from cement hydration results in many metal contaminants forming hydroxide or mixed hydroxide solids. Sulphide precipitates are also possible, particularly if sulphides are added directly or indirectly through the use of blast furnace slag or similar binders that can produce sulphides. Calcium and calcium hydroxide solid phases are possible for anionic contaminants. Although contaminant stabilisation is typically considered to be by formation of pure solids, solid solutions can also be formed. Thanks to the addition of cement, the pore structure of the S/S treated waste will show an increase of the specific surface area which will promote the adsorption of the contaminants. Furthermore, as adsorption of cationic metals on oxy-hydroxides is favoured by high pH, this mechanism is all the more important when pH is raised by cement hydration. Oxidation-reduction reactions can be important immobilisation mechanisms for those contaminants that exist in multiple redox states and have substantially different chemical or toxicological behaviours in the different redox states. The classic example is chromium, 2- which is much more toxic and more mobile in its oxidised state (CrO4 ) than in its reduced state (Cr3+). In contrast, arsenic is more toxic when it is in its more reduced state as arsenite than as arsenate. These redox reactions can significantly affect contaminants mobility. For instance, trivalent chromium is more likely to be precipitated or sorbed than hexavalent chromium. Cements generally provide a moderately oxidising environment, but the addition of blast furnace slag can produce reducing conditions by releasing sulphide and other reduced sulphur compounds. Reductants such as ferrous iron can also be added to create reducing conditions and thus promote immobilisation.

However, it is worth noting that the stabilisation reactions may be reversed by complexation of the metal contaminants with organic matter, by increasing the total concentration of the metal in the mobile phase. The organic complexing agents may either be present in the waste or enter it after disposal.

In the natural environment, the most important factor controlling the distribution of inorganic compounds between stable and mobile phases is pH. This is also true in wastes treated by S/S,

64 because precipitation, adsorption and redox reactions immobilising the metals are strongly influenced by pH. Therefore, the success of S/S is really dependent on binder reactions which will impact the pH of the treated waste. The ability of cement to control pH can be expressed by its acid neutralising capacity (ANC). The acid neutralising capacity is a measure of the amount of base present that can accept hydrogen ions from a strong acid. Since the extent of these acid base reactions is dependent on pH, the ANC is a function of pH. However, a single value of ANC is often reported by choosing a specific pH for determination. The ANC of a waste treated by cement-based S/S will depend on the acids and bases contained in the waste, as well as the ANC of the binders.

1.3 Description of the practical settings involved in solidification/stabilisation

1.3.1 Solidification/stabilisation ex-situ Methods

(from Engineer Manual 1110-1-4007, 2003)

Field processes comprise excavation of the waste, screening and removal of the particles too large in diameter to be effectively treated, blending the binding agents and water with solids, and stockpiling of the treated solids before their shipment off-site or placement back in the excavation. S/S can result in monolithic-formed blocks, or chunks, or in a soil-like matrix. A significant factor to consider when dealing with ex-situ techniques is the “swell factor” representing the volume created by the binding agent. This factor depends on the amount of binder that must be added, and can be close to 50%. Thus, not all the treated waste may fit in the excavation without altering the natural grade.

1.3.2 Solidification/stabilisation in-situ Methods

(from Engineer Manual 1110-1-4007, 2003)

The principle is about the same, yet it spares the excavation and material handling requirements are lower. The S/S in-situ methods involve injection of stabilising agents into subsurface soils. Typically, it consists in the addition of the binder with water if necessary, and then repeated in-place mixing. The additives are the same in ex-situ and in-situ methods, yet, due to better mixing, the ex- situ S/S gives generally more confidence in contaminants immobilisation and may require smaller amounts of reagents.

1.3.3 Advantages and limitations of the solidification/stabilisation process

Advantages • Relatively inexpensive methods for treating soils contaminated with inorganic waste • Can be extremely simple to apply, using readily available equipment with high throughput rates • Contaminants mobility is reduced

Limitations • The pollutants are not removed, only rendered less mobile and sometimes less toxic • The volume of the final mass may generally be higher than that of the original contaminated soil • The resulting mass may still need to be controlled as a hazardous waste • Long-term environment conditions can affect the stability of the treated waste • Depth of contaminants as well as achieving uniform mixing may limit these processes • High content of water, clay or organics may limit the efficiency of the mixing process

2 Application of solidification/stabilisation to sulphidic mine wastes

2.1 Introduction: weathering of sulphidic mine wastes

Wastes from metal mines consist mainly of waste rocks, ore rests, slags and tailings (processing wastes from a mill, washery or concentrator). These by-products are usually rich in sulphide minerals containing heavy metals. Common sulphide minerals are listed in table 14. The main environmental problem associated with these sulphide minerals is the exposition to air and water which leads to oxidation of the sulphides into sulphates, and the release of metals into the environment. Oxidation is a complex process involving several steps. Oxidation of Fe-bearing sulphides can be described with the example of pyrite which reaction is commonly presented according to the following equation 1:

2+ + 2- 2FeS2 +2H2O +7O2 →2Fe +4H +4SO4 (1)

The Fe2+ formed and released may oxidise further and generate additional acid through the equations 2 and 3:

2+ + 3+ Fe +1/4O2 + H → Fe +1/2H2O (2) 3+ + Fe +3H2O →Fe(OH)3 +3H (3)

The ferric iron Fe3+ is itself a very strong oxidant which may oxidise Fe-rich sulphides (in absence of oxygen). This can be described by the following reaction represented by equation 4:

3+ 2+ 2- + FeS2 +14Fe +8H2O →15Fe +2SO4 +16H (4)

The production of hydrogen ions with the sulphate anions results in an acidic solution, which is known as Acid Mine Drainage (AMD). The oxidation of sulphide minerals does not only create acid, but it also liberates metals and sulphate into waters and accelerates the leaching of other elements from gangue minerals. As a consequence, AMD is associated with the release of sulphate, heavy metals (Fe, Cu, Pb, Zn, Cd, Co, Cr, Ni, Hg), metalloids (As, Sb), and other elements (Al, Mn, Si, Ca, Na, K, Mg, Ba) (Lottermoser, 2003). The whole ecosystem is at risk in such a situation. To meet environmental quality requirements, mining companies must make sure that the prevention or treatment of AMD will be done.

Table 14 List of common sulphide minerals and their reactivity with regard to oxidation as well as their capacity to generate acidity. Adapted from Lottermoser (2003) and Nehdi & Tariq (2007).

Element Sulphide mineral Reactivity to oxidation and acidity generation Iron FeS2 Pyrite or Marcasite Most reactive sulphides, generate Fe1-xS Pyrrhotite strong acidity Zinc ZnS Sphalerite Fe-poor sphalerite oxidation does not generate acidity (Zn,Fe)S Fe-rich Sphalerite Fe-rich sphalerite oxidation generates acidity Copper CuFeS2 Chalcopyrite Reactive sulphides, generate CuFeS4 Bornite acidity Cu2S Chalcocite Low reactivity, no generation of CuS Covellite acidity Arsenic FeAsS Arsenopyrite Reactive sulphide, generates acidity Lead PbS Galena Low reactivity, no generation of acidity

In mine sites in current exploitation, one way used to avoid this AMD generation is to control the sulphide oxidation with one or more of the following strategies: exclusion of water, exclusion of oxygen, pH control (most of the metals are immobilised with a neutralisation of acidic pH), control of Fe3+ generation, control of bacterial action, removal and/or isolation of sulphides. This can be achieved through covering of wate rocks and tailings with wet/dry covers, encapsulation, in-pit disposal and mixing, co-disposal and blending with benign or alkaline material, addition of organic wastes or bactericides (Lottermoser, 2003). Treatment of AMD may also be required (neutralisation of the acidic water with an alkaline agent or other chemical treatments, anoxic limestone drains, wetlands...). Generally speaking, in abandoned mines, the outcome of a sulphidic mine waste which is considered as dangerous for the environment is excavation followed by landfilling. This drastic method is becoming more and more costly, and solidification/stabilisation of the mining wastes could be used as a milder alternative. Several studies have already been carried out with cementitious materials and/or recycled alkaline by-products, in order to increase cohesiveness, reduce water transport through the mine waste and increase pH. A review of some of them was realised. On the basis of this study, different alkaline stabilising agents will be presented here, and some experiments of metal mine waste S/S with these alkaline materials will be listed.

2.2 Solidification/stabilisation of mine wastes with alkaline agents

2.2.1 Portland cement as a primary binder

Most applications of S/S use ordinary Portland cement (OPC) as a primary binder, which means that they are cement-based. Yet other materials like lime, fly ash or blast furnace slag can be added, to lower costs and/or to improve the efficiency of the stabilising agent. Portland cement is made by firing a mixture of limestone and clay (or other silicate) in a kiln at high temperatures (Ylmaz et al., 2002). The main chemical that composes hydrated cement is colloidal calcium silicate hydrate, known as C-S-H, and this gel product is formed at the cement particle surfaces. C-S-H has important implications for the mechanisms of fixation during solidification and is principally responsible for strength development (Ylmaz et al., 2002). C-S-H formation also favours interactions of heavy metals including adsorption, chemical precipitation, ion-exchange, surface complexation, micro-encapsulation… rendering stabilisation of metal- and metalloid- bearing waste effective. Cement-based stabilisation can efficiently stabilise certain compounds contained in the tailings and also slow the ingress of oxygen to the inside of the cemented matrix.

Table 15 Some applications of solidification/stabilisation of mine wastes with Portland cement (Nehdi & Tariq, 2007).

Reference Material stabilised Stabilisation technique Results

Benzaazoua et al. Sulphide-rich tailings OPC (type I) and sulphate OPC and fly ash binders (2002) from four Canadian resistant cement (type V); fly proved suitable for high mines. ash and blast furnace slag. sulphide tailings. Slag- 1 containing~ 40% Mixing water types (lake based binders exhibited sulphides water, municipal water, and hydration inhibition and 1 containing~ 30% sulphate-rich process water). were found appropriate sulphides Paste backfill preparation only for medium and low 1 containing~ 10% using binders and sulphidic sulphur-rich tailings. sulphides tailings.

Benzaazoua et al. Sulphidic mine tailings OPC, aluminous cement, The main factor in fixing (2004) from milled gold ore ground blast furnace slag arsenic was the calcium containing 60% cement. Paste backfill content of the binding sulphide. Fine-grained preparation by mixing agent. Cemented stabilised tailings containing hydraulic binders with matrix rich in Ca(OH)2 pyrite and arsenopyrite sulphidic tailings. maintained a neutral to in about equal amounts. alkaline environment with pH conditions and calcium activity favourable for the inhibition of arsenopyrite oxidation. While arsenopyrite becomes rapidly passivated in oxidised but cementitious environments, pyrite remains reactive.

Misra et al. (1996) 1: fine grained reactive Agglomerates preparation Tests on tailings mine tailings containing using OPC and fly ash with agglomerates prepared 4.33% iron and 8.5% tailings. Fly ash: 5% to 20% using fly ash and OPC sulphur. by mass, and OPC: 2.5%, 5%, resulted in much lower 2: tailings with 7.5% and 10%. level of extractable ions comparatively lower concentration and well fineness and having 3% below the regulatory level sulphur. than from agglomerates alone. Yilmaz et al. (2003) Metal enriched gold OPC (10% to 20%) mixture Unconfined compressive mining residue (Cr, Cu, with tailings. strength values were 1.1 to Pb, Zn) 3.3 MPa and hydraulic conductivities were in the range of 1.04 10-9 to 2.1 10- 9 m/s Metal retaining efficiencies were greater than 87%. Yukselen and Soil contaminated with Lime and OPC. Lime/soil and Leachability of the Alpasalan (2001) heavy metals (Pb, 153 cement/soil mixtures at ratios contaminated metals was mg/kg, Cu, 510 mg/kg, of 1/15, 1/20, and 1/25 by reduced. Additive to soil Fe, 15.3%, S, 14.63%) mass. ratio of 1/15 was found from an old mining and superior for both lime and smelting area. cement, giving rise to solubility reduction of Cu, Fe and Pb. When additive/soil mixture=1/15, TCLP3 solubility decreased by 94% for lime/soil mixture and 48% for cement/soil mixture in the case of Cu; for Fe, TCLP solubility decreased by 90% for lime/soil mixture and 71% for cement/soil mixture. Pb: Solubility found below the regulatory limit of 5mg/L.

2.2.2 Calcareous fly ash

Fly ash is one of the residues generated in the combustion of coal or organic matter in general. Fly ash is generally captured from the chimneys of power generation facilities. Depending upon the source and makeup of the material being burned, the components of the fly ash produced vary considerably, but all fly ashes include substantial amounts of silica (both amorphous and crystalline) and lime. Owing to its pozzolanic nature4, fly ash is commonly used to supplement Portland cement in concrete production. But it could also be considered as a binding agent in the S/S process. In particular class C fly ash, which is produced from burning bituminous coal, has cementitious properties in addition to its pozzolanic properties, and is capable to counteract the acid potential of mine waste due to its high Ca content (Nehdi & Tariq, 2007). Two mechanisms are involved; the first one is the addition of alkalinity and neutralisation of acidity. The second one consists in the reduction of hydraulic conductivity,

3 TCLP= Toxicity Characteristic Leaching Procedure 4 A pozzolanic material can exhibit cementitious properties when it is in a finely divided form in presence of moisture and calcium hydroxide.

69 resulting in the inhibition of water penetration into sulphidic tailings; therefore oxidation of sulphides is prevented (Nehdi and Tariq, 2007).

Table 16 Some applications of solidification/stabilisation of mine wastes with fly ash. Adapted from Nehdi & Tariq (2007).

Reference Material stabilised Stabilisation technique Results

Moutsatsou and Samples from Lavrion Fly ashes from lignite Solidification/Stabilisation Protonotarios Technology and Cultural power plants, subjected to results indicated the necessity of (2006) Park (LTCP) in Greece. an alkaline hydrothermal utilizing additional pozzolanic Slags, mixed with sulphur treatment at 90°C, using materials (such as lime and compounds waste and NaOH 1M as an cement), aiming to upgrade the low-grade lead activation solution physical and mechanical metallurgical condensates, properties of the retention agents all by-products of mining and the leaching behaviour of and metallurgical specific metals present in activities in the past. solidified/stabilised waste.

Ciccu et al. (2003) Contaminated soils from Addition of fly ash The addition of fly ash and a tailings pond of lead and containing 90.40% ash, mixture of 7.5% fly ash and zinc mine, containing Zn 7.08% fixed carbon, 7.5% red mud by mass to (3366 ppm), Pb (12245 2.50% volatile matter, and contaminated soil drastically ppm), Cu (444 ppm), and red mud from reduced the heavy metal Cd (25 ppm). metallurgical treatment of contents of the soil leachates. bauxite ores. Mohamed et al. High-sulphate content Lime, fly ash (class-C) 5% lime, 10% Type C fly ash in (2002) mine tailings Al2O3 and aluminium (110 ppm) combination with 110 ppm (6.6%), Fe2O3 (41.07%), were used as additives to aluminium resulted in formation MgO (1.31%). mine tailings. of a solid monolith capable of producing more than 1 MPa of unconfined compression strength and reduction in hydraulic conductivity to 1.96 × 10-6 cm/s. Xenidis et al. Sulphidic tailings Lignite fly ash (class-C) Fly ash addition at lower amount (2002) containing 27% sulphur. amount ranging from 10% (10%) increased pH of leachates to 63% by weight to values of 8.6-10 and decreased dissolved concentrations of contaminants, mainly Zn and Mn. Higher fly ash addition (31% and 63% w/w) reduced water permeability of the material from 1.2 × 10-5 cm/s to 3 × 10-7 cm/s and 2.5 × 10-8 cm/s, respectively. Long- term (600 days) laboratory column kinetic tests were performed.

2.2.3 Other calcic materials

Natural, by-product or manufactured calcic chemicals characterised by high ANC (Acid Neutralising Capacity) can be used as neutralising agents in the process of S/S. The high ANC buffers the acidity of the waste and precipitates metals mainly in the form of (oxy)- hydroxides. The most common calcic acid neutralising agent is calcium carbonate (CaCO3)

70 which advantages include low cost and ease of use. But other agents like quicklime (CaO) can be employed.

Table 17 Some applications of solidification/stabilisation of mine wastes with calcic materials. Adapted from Nehdi & Tariq (2007).

Reference Material stabilised Stabilisation technique Results

Pérez-Sirvent et al. Two sediments derived Addition of sludges left The process of (2006) from mining activities after the cutting of stabilisation/immobilisation of the in Portman Bay (SE, marble, made of fine heavy metal using calcium Spain) polluted by grained material with a carbonate-rich wastes was very heavy metals (Pb, Zn, CaCO3 content in effective and toxicity disappeared Cd…) excess of 95% (38% almost totally from the calcite and 60% corresponding lixiviates. dolomite). Addition was done in a 1:1 proportion. Catalan and Yin Zinc and copper Calcite (CaCO3) and Calcite was found preferable to (2003) sulphide ores with total quicklime (CaO) quicklime for maintaining long- sulfur (S) and sulphate addition to the tailings term neutral pH conditions in the 2- (SO4 ) contents of 96.3 treated tailings. With the exception and 18,9 mg S/g of of zinc, acceptable levels of tailings, respectively. dissolved metal concentrations The sulphide content were achieved with calcite treated was estimated to be tailings. 77.4 mg S/g tailings. Jang et al. (1998) Mine soils containing CaO and Na2S addition Quicklime and sodium sulphide Cu, Ni, Pb, etc. had good immobilisation efficiencies for Cu, Ni, and Pb. Höckert (2007) Mine waste from Addition of 6,6% pH of the leachate from the waste Ljusnarsbergsfältet in calcium carbonate increased from 3 to near neutral, Kopparberg, Sweden, residues and 3,3% and metals concentrations in the containing 26000 sewage sludge. leachate were lowered 40 to 4000 mg/kg S, 7710 mg/kg times. However the long-term Pb, 4810 mg/kg Zn, leaching properties were not 2200 mg/kg Cu. examined, and in case of a turn towards low pH values, organic matter could favour an increase in metal mobility.

2.2.4 Cement kiln dust

Cement kiln dust (CKD) is a by-product from cement manufacturing. CKD satisfies the requirements of a cementitious stabilizer. It behaves as a soil stabilizer in a similar way as Portland cement (Nehdi & Tariq, 2007).

Table 18 Some applications of solidification/stabilisation of mine wastes with cement kiln dust (Nehdi & Tariq, 2007).

Reference Material stabilised Stabilisation technique Results

Doye and Duchesne Reactive tailings rich Cement kiln dust 10% CKD and 10% mixture (2003) in Fe, S, Cu, Pb, and (CKD), red mud of CKD and RMB allowed Zn bauxite (RMB) neutral pH over 365 days of batch leaching tests. Fortin et al. (2000) Mine tailings from Cement kiln dust The compacted layers copper, zinc, silver addition (10% by containing CKD acted as a and gold mining. weight) using layered trap for different metals co-mingling technique. favoring precipitation in addition to the alkaline reservoir to neutralise acidity and reduction in bacterial activity.

2.2.5 Paper mill sludge

The use of paper mill sludges in S/S treatment of heavy metal contaminated soils showed promising results. The paper mill sludges should be effective because of their organic matter, silicate and carbonate content. The organic matter is able to form stable complexes with several metals; the silicates are materials of high cation exchange capacity (CEC) and the bicarbonate/carbonate system is able to increase the pH value of soil (Calace et al., 2005). It would be all the more interesting to use them as valuable resources such as binding agents in S/S that their increasing produced quantity makes their disposal a concern for pulp and paper industry.

Table 19 Some applications of solidification/stabilisation of mine wastes with paper mill sludge.

Reference Material stabilised Stabilisation technique Results

Calace et al. (2005) Acidic soil from the Addition of a paper mill The results obtained by means mining activity zone in sludge, consisting mainly of leaching tests showed that Sardinia (Italy), of carbonates, silicates the addition of a paper mill contaminated with Fe and organic matter. sludge to the heavy-metal (135990 mg/kg), Zn The soil to sludge ratio polluted soil produces a (1607 mg/kg), Mn (287 was 9:1 w/w. decrease of mobile metal mg/kg), Cu (42 mg/kg), forms. The carbonate content Ni (45 mg/kg), Pb (1587 seems to play a key role in the mg/kg), Cd (12.6 mg/kg). chemical stabilisation of metals and consequently in the decrease of toxicity in soil. Battaglia et al. Soil from a mining Addition of a paper mill The addition of paper mill (2007) activity in Sardinia (Italy). sludge with 16% organic sludge to soil contaminated by The metals exceeding the matter, and 84% inorganic Pb and Zn induces a decrease legal limits were Zn (4774 matter essentially in the mobile forms of both mg/kg) and Pb (2796 composed of carbonates metals. The shift in more mg/kg). and silicates in the form stable forms (oxidizable and of kaolinite. Soil-sludge non extractable) could be weight ratio was 9:1. explained by the presence in the sludge of organic matter and kaolinite which are able to bind the metals very strongly.

V: Results of Metal Analysis

TAILINGS

90 TAIL + 10 GLS 30

90 TAIL + 10 (GLS 30 EM + FA1)

90 TAIL + 10 (GLS 30 EM + FA1+ BS)

Water filtered

GLS 30 EM

90 TAIL + 10 GLS 30 EM

70 TAIL + 30 (GLS 30 EM + FA1+ BS)

VI: Results of CRS Test

GLS 30 EM

GLS 30 EM + FA1

GLS 30 EM + FA1 + BS

GLS 30 EM + FA1 + SS

GLS 30 EM + FA2a

GLS 30 EM + FA2a + BS

GLS 30 EM + FA2a + SS

70 TAIL + 30 (GLS 30 EM + FA1)

GLS 30 EM + FA1 + BS bis

GLS 30 EM + FA2a + SS bis

70 TAIL + 30 (GLS 30 EM + FA1) bis