ENVIRONMENTAL IMPACT OF MERCURY IN SMALL–SCALE GOLD MINE AREAS IN MANICA AND , .

Cornelio de Jesus Armindo UNGUANA Candidate for the Degree of Master of Engineering Supervisor: Tsutomu Sato Division of Sustainable Resources Engineering

I.INTRODUCTION II.MATERIALS AND METHODS gold (Au) ore in Mozambique is mainly extracted in Manica, Tete and Niassa provinces, the gold grade was 2.1. Methods of investigation reported to be 2.96g/t in 2007 [1]. More than 60000 This research was done in (Manica artisan miners have been involved in these activities, district) and Tete province (Macanga district), water including children and women. Mining activities are and sediment samples were collected in dry season mainly manual, low tech, indeed miners can lose 25%- from both study sites. 75% of gold at recovery stage, and the small scale artisanal mining covers more than 90% of gold 2.1.1. Water samples collection production in Mozambique [2] [3]. Mercury is used Water samples were collected from Munhena mine mainly for the processing of primary gold quartz veins. (drinking water and pond water), Chicamba dam Handling of mercury inappropriately may induce (Revue river and pond’s water) and Macanga mine water, sediments and atmosphere contamination. A (drinking water, tailing ponds, Maue river and Namazi number of study assessing exposure of mercury have river). been conducted, based on breath test samples from Water samples were collected in 50 ml polypropylene miners, it was found that the average level of mercury bottles and filtered in situ with a 0.45 µm and 0.20 µm in Munhena mine (Manica province) was 8.23µg/m3, disposable membrane filter and about 1% (v/v) of this value is eight times higher in comparison with HNO3, was added to avoid precipitation of calcite. Into WHO guideline (1 µg/m3) for public exposure to the samples which were used for total Mercury mercury. However the concentration of mercury in analyses, about 1% (v/v) of gold Standard solution water and sediments is unknown [2]. diluted in aqua regia (HCl:HNO3) was added to avoid Due to the occurrence of alluvial gold in the Maue and the reduction of Hg(II) to the elemental Mercury Namanzi rivers (Tete province) and the Revue river (Hg°). Water pH, dissolved oxygen (DO), Oxidation (Manica province), mining activities is ongoing, and reduction Potential (ORP) and Conductivity were these uncontrolled artisanal gold mining activities measured in situ together with alkalinity. Prior to the could increase the contamination of Hg in water and measurement, the pH and ORP meters were calibrated sediments. with KCl solution. All samples were stored at 4°C for Mercury coexist in main four chemical forms, further analyses in the laboratory. elemental mercury (Hg°), divalent inorganic mercury 2+ + (Hg ), dimethylmercury (CH3)2Hg and 2.1.2. Sediment samples collection + methylmercury (CH3Hg ) which is more toxic than Sediments samples were collected from Munhena Hg° and strongly accumulate on living organisms, mine (tailing and sediment ponds) and Revue river several studies show the techniques for sampling and (stream sediments and pond’s sediments). Only the measurement of the mercury concentration in aqueous upper 20-40 cm of sediments was collected and sealed and solid matrices [4] [5]. At the mining site, the ore in polyethylene bags frozen in the cooler bags, then material is processed with mercury, then discharged shipped to the laboratory and stored in a refrigerator at into tailing ponds and rivers. This study aims to assess 4° C until analysis. the environmental impact of mercury in water and sediment from the mining area in Manica province, 2.2. Water sample analysis Mozambique. Total mercury (Hg) and trace metal concentrations (As, Cd, Ba, Co, Cr, Cu, Pb, Zn, Mn) were measured on ICP- AES and ICP-MS. Samples for total Hg

1 analyses were prepared by using 10 ppm of Mercury standard solution.

2.3. Solid sample analysis Sediment samples were air dried in a fume hood at room temperature for 24h to 48h and ground, then sieved with a 2 mm siever before use [6]. Samples were not dried in the oven because of the presence of elemental mercury (Hg°), which would volatilize by increasing temperature. Following these procedures, analyses such as X-ray diffraction (XRD), were employed for samples characterization.

2.4. Water leaching experiment and Acid Fig 1: Measured mercury concentration in µg/l in Muenha mine and Revue river the water samples. digestion (MH-Muenha mine, RR-Revue river). Prior to the AAS analyses, mercury concentrations were estimated on leaching experiment following the Mercury concentration in Kassossole mining area Japanese Industrial Standard (JIS) method. After air were also measured and the results showed that drying at room temperature, 50g of sediment samples samples of tailings ponds, drinking water and from were diluted with ultra-pure water (18.2 MΩ.cm) in an Maue and Namanzi river were found to be less 500 ml polyethylene bottles. The aliquots were shaken contaminated. A different result was found on the for approximately 6 hours at room temperature, sample from bowl, in which the Hg concentration was samples were then centrifuged (3000 rpm, room 1.10 µg/l (Fig 2). The highest concentration in this temperature, 20 min) and the supernatant filtered sample is similar to the sample from bowl in Muenha through the 0.45 µm millipore membrane filter and mine. The results also showed that the sample from immediately 1% (v/v) of gold Standard was added to Maue river was below detection limits. the solution. The sample were then analyzed directly by Atomic Adsorption spectroscopy (AAS) for total mercury analyses. Total mercury analysis by acid digestion was performed, using samples that were digested following the procedure proposed by Japanese Industrial Standard (JIS). As experimental conditions, the liquid solid ratio was 3:100 and 6 g of sediment samples were diluted with 1M HCl in a 500 ml Polyethylene bottle followed by shaking at 200 rpm for 2h. The samples were then centrifuged 3000 rpm, room temperature for 20 min.

III.RESULTS AND DISCUSION Fig 2: Measured mercury concentration in µg/l in Kassossole mine and Namazi river. 3. 1.Mercury in water samples Water samples were analyzed on ICP-MS and the 3.2. Concentration of Hg in the sediment highest mercury concentration was found in the samples in Muenha mine and Revue river samples collected on the bowl (0.51µg/l) in Munhena mine (Fig 1). This result is consistent with the fact that In order to estimate the concentration of Hg, sediment this sample was collected on the bowl which is used samples from Muenha and Revue river were leached for gold amalgamation. Therefore, the Hg in water and digested with hydrochloric acid (1M concentration of samples of bowl in Revue river (0.15 HCl). The results of acid digestion showed that the Hg µg/l) are less although these samples were collected concentration in sediments of tailings ponds in the under similar conditions. The concentration of Hg in gold processing plant and in the Muenha mine are 20 samples of river and drinking water was in agreement mg/l and 10 mg/l, respectively (Fig 3). with WHO standard (0.5µg/l).

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goethite formed under acid mining drainage can be identified by this extraction procedure [19]. The results of ICP-MS showed that the concentration of Fe=10 mg/l and the volume of Ferrihydrite was estimated to be 0.19%. The amount of mercury extractable by 1 M HCl and 0.2M of NH4 –oxalate were compared as the results suggested that too much amount of mercury was recovered with 1M HCl than with 0.2 M NH4 Oxalate. This results also suggested that the ferrihydrite is not Fig 3: Concentration of Hg in sediment samples the host mineral of mercury [Table 1]. digested with 1HCl and leaching with deionized water (Gold processing plant-GP, Muenha mine-MH, Revue Table 1: The extractable mercury with 1M HCl and river- RR). 0.2 M NH4 oxalate Solution Tailings ponds Tailings ponds The results of XRD (Fig 4) shows that the sediments (GP) (MH) of tailing ponds are mainly composed of clay minerals 0.2 M NH4 0.2% 0.4% such as pyrophyllite and kaolinite. Samples from oxalate tailing ponds indicate the occurrence of iron minerals 1 M HCl 99.8% 99.6% in amorphous phases, however iron (Fe) could also be identified by naked eye on the samples. There is no direct evidence of enrichment of mercury on pyrophyllite, but comparing the structure of kaolinite (1 tetrahedral and 1 octahedral sheet) and pyrophyllite (2 tetrahedral and 1 octahedral sheet), the structure suggest that both minerals can adsorb Hg (Fig 5). The structure of kaolinite and pyrophyllite suggest that mercury can adsorb on the AlOH⁻ or SiOH⁻ edges. Although there is limited edge site of OH⁻ on Pyrophyllite.

Fig 4: XRD pattern of sediments samples of Munhena mine and Revue river are mainly composed by pyrophyllite and kaolinite. Fig 5: Structure of a two layer clay kaolinite and pyrophyllite. The occurrence of Fe (III) oxihydroxides minerals on samples was investigated. The samples were subjected Although the water has low concentration of mercury to dissolution at room temperature in the absence of it can enrich in the sediments up to 20 ppm. The light with freshly prepared 0.2 M NH4-oxalate solution surface complexation modeling was used to check the pH 3.0 with 0.2M oxalic acid [8]. Solution samples amount of mercury accumulated in the sediments. was shaken for 1 h in darkness, at room temperature. Dissolution was done by shaking 2.5g of sample in 3.3. Surface complexation modeling 250 ml oxalate solution. After shaking for 1 hours the In order to understand the amount of mercury that can solution was filtered instantly with a 0.2µm Teflon accumulate in the sediment samples, surface inline filter for syringes. The dissolved Fe was complexation and 1D transport modeling were measured by inductively coupled plasma mass employed in this study. To simulate the system, the spectroscopy (ICP-MS). Schwertmannite, two line react program of “The geochemist’s workbench ferrihydrite, Mn-hydroxides, secondary jarosite and (GWB) was used.

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React is a flexible program that models equilibrium VI.CONCLUSION, RECOMMENDATION states and geochemical processes in systems that contain an aqueous fluid. This program can calculate 4.1. Conclusion the equilibrium distribution of aqueous species in a At Manica and Tete gold mining operations, mercury fluid, a fluid’s saturation state with respect to minerals, concentration in water samples were assessed. The and the fugacities of gases dissolved in a fluid. concentration of Mercury in Muenha mine and Revue We model the contamination by dissolved Hg, Ni, Pb river were 0.51µg/l and 0.14µg/l respectively, and in and Zn in tailing ponds containing sorbing mineral, Kassossole mining area Hg concentration varies from and effects of attempting to remediate the tailings 0.03 µg/l in pond water of tailings to 1.10 µg/l in the ponds. bowl water. The tailings, which includes Kaolinite, contains The results of this study confirmed high contamination initially uncontaminated ground water of the same of arsenic (0.3 µg/l) and lead (0.19 mg/l) in drinking composition as the flushing fluid. water in Muenha mine and Kassossole mining area Plotting the Hg, Zn, Pb and Ni content of the fluid in respectively. the domain versus position for 5 years of the model, The results of acid digestion showed that the Hg we see that the concentration of Hg increase up to 20 concentration in sediments of tailing ponds of gold ppm, in 5 years. Even flushing the system with fresh processing plant and Muenha mine are 20 µg/g and 10 water, Hg concentration remains well in excess in µg/g, respectively. However, the amount of Hg comparison with Pb, Ni and Zn concentration which extractable in the sediments of tailing ponds of gold decrease after flushing with fresh water (Fig 6). processing plant is less than that in the pond sediments While mercury concentration remains stable during of Muenha mine. the flushing Pb, Ni and Zn reflects the gradual Results of sequential extraction with NH4 oxalate desorption of the metals from kaolinite in the tailing suggested that ferrihydrite is not the host mineral for ponds sediment. Hg. because the amount of mercury extractable by This results suggested that Pb, Ni and Zn have low NH4 oxalate was much less than with HCl. Combining affinity to be adsorbed onto Kaolinite. the results of XRD, mercury extraction (with acid and 100 NH4 oxalate) and surface complexation modeling it Mercury was found that the kaolinite and pyrophyllite are the 10 host minerals for Hg.

1 The results of this study confirms the great importance of clay minerals to immobilize mercury in the .1 Zinc environment. Nickel .01 Lead 4.2. Recommendations .001 Because the sediments in the mining area have significant impact to the environment, these sediments 1e-4 must remain in tailings ponds with water to avoid the

Partial sorbate comp. (mg/kg), x comp. = .5 m sorbate Partial 1e-5 evaporation of Hg. It is also important to not use these 0 +.5 +1 +1.5 +2 +2.5 +3 +3.5 +4 +4.5 +5 sediments for farming activities because there is high Time (yr) possibility of contamination of plants with mercury. Fig 6: Partial sorbate component of Hg, Zn, Pb and Ni. Comparing the results of extractable of Hg, Ni, Pb, Zn Reference and Fe with 0.2 NH4 oxalate on table 2 the results 1. Pekkala, Y.; Letho, T.; Mäkitie, H. Special Paper 48 suggest that the host mineral of Ni, Pb and Zn is GTK Consortium Geological Surveys in Ferrihydrite. Mozambique. Report of Geological survey of Finland, 2008. Table 2: The extractable Hg, Zn, Ni, Pb and Fe with 2. Veiga, M. M.; Shoko, D.; Spiegel, S.J.; Savornin, 0.2 M NH4-Oxalate O.; Raphael, P.; Castigo, P.; N’dunguru, E.; Element Tailings ponds Tailings ponds Sandramo, R.; Jantar, P. Pilot Project for the (GP) (MH) Reduction of Mercury Contamination Resulting From Hg 2.4 μg/l 1.5 μg/l Artisanal Gold Mining Fields in the of Zn 9.04 mg/l 6.66 mg/l Mozambique, Report of the UNIDO, CDS-RN and Ni 0.19 mg/l 0.11 mg/l MICOA Mozambique, 2005. Pb 8.33 mg/l 7.12 mg/l 3. Shandro, J.A.; Veiga, M.M; Chouinard, R. Fe 9.8 mg/l 9.9 mg/l Reducing mercury pollution from artisanal gold

4 mining in Munhena, Mozambique. Journal of Cleaner production 2009, 17, 525-532. 4. Bank.S.M. Mercury in the Environment: pattern and process, University of California Press, London, England, 2012. 5. Ebinghaus. R.; Turner. R. R.; Lacerda. L. D.; Vasiliev. O.; Salomons. W. Mercury Contaminated Sites: Characterization, Risk Assessment and Remediation, Springer-Verlag berlin Heidelberg New York, 1999. 6. Miller, C.L.; Watson, D.B.; Lester, B.P.; Lowe, K.A.; Pierce, E.M.; Liang, L. Characterization of soils from an industrial complex contaminated with elemental mercury: Environmental Research 2013, 125, 20-29. 7. USGS. Geochemistry of Mercury and other Trace Elements in Fluvial Tailings Upstream of Daguerre point Dam Yuba River, California, august 2001, Scientific investigation report 2004-5165,2004. 8. Bernhard Dold, Speciation of the most soluble phases in a sequential extraction procedure adapted for geological studies of copper sulfide mine waste. Journal of Geochemical exploration 2003, 80, 55-68.

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