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. 1 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. 2 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 3 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