Arsenic Speciation in the Tailings Impoundment of a Gold Recovery Plant in Siberia

Downloaded from http://geea.lyellcollection.org/ by Michael David Campbell on December 4, 2018

Arsenic speciation in the tailings impoundment of a gold recovery plant in Siberia

Elena V. Lazareva1, Olga V. Shuvaeva2 & Valentina G. Tsimbalist 1United Institute of Geology, Geophysics and Mineralogy, RAS SB, Ac Koptug, 3, Novosibirsk 630090, Russian Federation 2Institute of Inorganic Chemistry, RAS, SB, Ac Lavrentyev, 3, Novosibirsk 630090, Russian Federation (e-mail: [email protected])

ABSTRACT: The recovery of gold from ores containing arsenopyrite releases signiﬁcant amounts of arsenic into the environment. Arsenic releases primarily result from the processing and oxidation of stored mine tailings. This investigation examines: (1) the distribution of arsenic, iron, manganese and their chemical species in sediment cores extracted from a tailings impoundment in the Kemerovo region of southwestern Siberia; and (2) the weathering of arsenic minerals collected from its tailings dam. The data demonstrate that during storage of the sediments within the impoundment, arsenic is predominantly present as residual arsenopyrite and, to a lesser degree, as substances co-precipitated with iron hydroxide. The arsenic released from the sediment results from an oxidative dissolution of arsenopyrite and reductive dissolution of Fe oxides.

KEYWORDS: arsenic, gold mine, tailings, speciation, transformation

INTRODUCTION an average depth of approximately 2 m. Thus, the total volume 6 3 The processing of ore deposits is an important source of metals of the impoundment is about 1.1 10 m (Gaskova et al. to the environment. Arsenic is typically released during the 2000). The primary sulphide minerals involved in the cyanid- oxidative leaching of the sulphide-containing wastes and, once ation of these particular ores include pyrite, pyrrotite, magnetite, released to the environment, it is one of the most dangerous elements in terms of its potential impacts on both human and ecosystem health. The scale of its dispersion depends on the type of mineral processing that has occurred at the mine site and the storage conditions within the tailings impoundment. The processes of chemical weathering in tailings impoundments are signiﬁcantly diﬀerent from those in natural aquatic systems. The rate of elemental release from the particulate phase is primarily a function of the Eh–pH conditions in the impoundment as well as the chemical interactions of the available constituents. In sediments and soils, iron oxy-hydroxides are considered to be the phases of preferable adsorption for arsenic (Bowell et al. 1994). The objectives of this investigation were to: (1) document the distribution of arsenic in the solid waste materials of a tailings impoundment; (2) determine the chemical speciation of arsenic in its sediments and (3) examine the nature of arsenic transformations in the tailings impoundment.

THE SITE DESCRIPTION This study focuses on the Komsomolsk tailings impoundment (or depository) located in the Kemerovo region of southwestern Siberia. The tailings impoundment (or depository) contains waste materials produced by the cyanidation of gold–arsenopyrite ores, the processing of which began between 1937 and 1940. The facility is located 800 m above sea-level and is conﬁned on three sides by the local topography (Fig. 1). On the downslope side, the impoundment is conﬁned by a tailings dam. Fig. 1. Location of the Komsomolsky tailings impoundment and of The surface area of the impoundment is 146 000 m2 and it has sediment core sites.

Geochemistry: Exploration, Environment, Analysis, Vol. 2 2002, pp. 263–268 1467-7873/02/$15.00 2002 AEG/Geological Society, London Downloaded from http://geea.lyellcollection.org/ by Michael David Campbell on December 4, 2018

264 E. V. Lazareva et al.

Table 1. The sequential leaching procedure used for arsenic speciation

Arsenic fraction Procedure

1 1. Water soluble H2O double distilled, 1:100 , 1 h shaking 1 2. Exchangeable 1 mol l NH4 acetate, pH 7, 1:20, 20 C, 5 h shaking 3. Carbonate 1 mol l1 Na acetate, pH 5, 1:20, 20C, 5 h 1 1 4. Easily reducible 0.1 mol l , hydroxylamine hydrochloride, 0.1 mol l HNO3, pH 2, 1:100, 12 h 1 1 5. Moderately reducible 0.2 mol l NH4 oxalate, 0.2 mol l oxalic acid, pH 3, 1:100, 24 h 6. Residual mineral HNO3 (conc.), 1:5 stand 12 h add HCl, 1:10, slow evaporation under heating, addition with HNO3 (0.2%)

1The ratio sample (solid) : solution (g:ml). ilmenite, arsenopyrite, sphalerite and galena; the gangue ion determination. Sulphate-anion was determined turbidi- minerals include quartz, plagioclase, micas and calcite. metrically with barium chloride. The reaction of yellow to As is typical of many flooded impoundments, granulometric brown mixed arsenic/mercury bromide formation was used to fractionation of the tailings materials by processes of hydraulic determine arsenic. sorting is clearly visible within the Komsomolsk depository The laboratory determination of total arsenic, zinc, copper, (Robertson 1994). The eastern part of the site, close to the iron and manganese concentrations in water and sediment pipeline through which the tailings (or pulp) is pumped and leachate solutions was performed using flame and furnace dispersed, is enriched in relatively heavy, sand-sized atomic-absorption spectrometry following the procedures of (0.05–0.1 mm) particles. Grain size decreases with distance The Guide to Techniques and Applications of Atomic Spectroscopy.A from the pipeline so that the bed of the impoundment opposite model SP-9 (BYE-UNICAM) was used for flame analysis and a the tailings dam consists of silt. Similar inhomogeneities in grain Perkin Elmer Zeeman 3030 with HGA 600 set for electro- size and particle mineralogy also occur as a function of depth thermal determinations. The total elemental concentrations in below the surface of the impoundment. the sediments were determined after a wet digestion procedure using a mixture of nitric and hydrochloric acids, as for the METHODS residual mineral digestion (see Table 1). Standard water solutions for calibration were prepared by stepwise dilution of Sampling 1gl1 stock solutions (Merck, Germany) in 0.5 mol l1 Sediment cores were taken from the bed of the tailings HNO3. impoundment along lateral and vertical profiles as shown in The sequential leaching procedure (Table 1) developed by Figure 1. The coring sites were located: (1) adjacent to the Bombach et al. (1994) was used to determine arsenic speciation tailings pipeline; (2) within the shallow part of the impound- in the tailings sediments. However, the method was slightly ment opposite the pipeline; and (3) near the natural hillslope in modified to exclude the extraction of sulphide bound to organic an area with abundant aquatic vegetation. Samples were col- matter because it is not a significant component of the analysed lected layer by layer from the vertical columns. Samples from sediment. The initial ore material – (arsenopyrite, pyrite) + the prospecting pit wall were taken in special containers for quartz (1:3) – was also analysed using this leaching procedure. slides and polished sections. Upon extraction, the sediment To control the accuracy of the analytical results the following cores were cut into sections on the basis of the natural, quality assurance programme was applied: (1) stepwise dilution stratigraphic layering that existed within the cores. Pore waters of the leachate (preparation procedure is presented in Table 1) were subsequently extracted from the layers (100 Pa) in the solutions under consideration to reduce the matrix effect; (2) field. The samples were then frozen until they were analysed. ‘added-found’ method for water solutions; and (3) the balance Surface water samples were taken from different locations of correlation of the sum of element's species and the total the impoundment to provide a better estimation of the average element’s content (Table 5). dissolved arsenic concentrations. All water samples were filtered Thermodynamic calculations of saturation indices and spe- through a 0.45 µm filter immediately after sampling. Waters cies in solutions were performed with the aid of WATEQ4F were immediately analysed in the field according to procedures (Ball & Nordstrom 1991). Saturation index is defined as: outlined below to gain an initial estimate of arsenic concentra- SI=log10~IAP/Ksp~T!!, where IAP is the calculated ion-activity tions. Additional water samples were analysed in the laboratory. product and Ksp is the equilibrium constant for the solid. The These samples were preserved by acidification with nitric acid saturation index is approximately equal to zero when water is at (pH <2) after filtration prior to shipment to the laboratory. equilibrium with a solid. When SI is above zero the water is supersaturated with that mineral, and the mineral would tend to precipitate. When SI is less than zero the water is unsaturated Analytical procedures with respect to the mineral, and the mineral would tend to be The analytical procedures used in this investigation consisted dissolved. of field determinations, the laboratory measurement of total arsenic and other elements in waters and sediments of the impoundment and a determination of the speciation of arsenic RESULTS AND DISCUSSION in the tailings materials. Field experiments included the analysis As mentioned above, the main sulphide minerals involved in of surface waters in the tailings impoundment. These analyses ore processing are pyrite and arsenopyrite. The gold cyanidation were conducted using rapid test kits (Merck, Germany) and procedure used at Komsomolsk included the following steps mobile spectrophotometry (Photometer SQ-118, Merck, (Bortnikova et al. 1999; Shuvaeva et al. 2000): Germany) to determine major anions (SO2 ,CN) and to 4 < 3 2 3 provide an initial estimate of arsenic concentrations in water. A FeAsS + 6CN +8O2 Fe~CN!6 +SO4 + AsO4 (1) colour reaction, a violet polymethine dye formation in the < presence of barbituric acid and pyridine, was used for cyanide- 2Au + 4NaCN + 2H2O+O2 2Au~CN!2 + 4NaOH (2) Downloaded from http://geea.lyellcollection.org/ by Michael David Campbell on December 4, 2018

Arsenic speciation of a Siberian gold recovery plant 265

Table 2. Composition of water in the Komsomolsky pond (µg l1) database and the computer code WATEQ4F. The modelling was also based on the measured composition of the water Year Sample pH CN As Zn Cu Fe within the impoundment. The modelling results show that 1997 Fresh pulp water 10.2 530 250 47 800 2800 660 within the fresh pulp, the main copper and zinc containing Pond nd 273 100 21 10 <10 phases are present as hydroxides (Table 3). Arsenic originates 1998 Pond 8.6 111 180 440 20 180 both from arsenopyrite oxidation during the gold recovery 1999 Fresh pulp water 11.0 534 75 2600 1220 750 procedure (Eq. 1) and during storage (Eq. 4) by oxygen- Pond 9.0 99 140 <20 260 <50 containing anions (Shuvaeva et al. 2000). Calcium arsenate precipitation may be the primary means through which arsenic nd, not determined. is removed from the solution. Removal would occur through the following reaction: 2Au~CN! +Zn<@Zn~CN! #2 + 2Au (3) 2 4 3 < 3CaO + 3AsO4 +3H2O Ca3~AsO4!2 + 6OH (5) Calcium oxide is also used in the process to maintain alkaline conditions. Given the high sulphate content in the pond water, However, the results of the thermodynamic modelling using any residual arsenopyrite is probably oxidized in the aeration WATEQ4F (Gaskova et al. 2000) suggest that the saturation zone according to the following reaction: index for calcium arsenate is not achieved (Table 4). Similar calculations for the adsorption and co-precipitation of selected < arsenic phases showed that iron and manganese hydroxides FeAsS + 3.5O2 +4H2O Fe~OH!3solid + (goethite, hematite, magnetite, psilomelane, todorokite etc.), HAsO2 +SO2 +H+ (4) 4 4 carbonates, clay minerals (sepiolite) and chlorites were present in the pulp and impoundment waters. It has also been estab- The resulting composition of the water in the impoundment lished via a mineralogical examination of a solid sample from is given in Table 2 (Lazareva et al. 1999). Table 2 shows that the impoundment (Lazareva et al. 1999) that arsenic containing signiﬁcant amounts of copper and zinc are present in the waters secondary mineralization phases are present and consist of iron of the impoundment. It is likely that zinc is produced in step 3, oxides (0.8% As) and calcium–iron–arsenate–hydrate (15% As). whereas copper is probably released from sphalerite and These data suggest that calcium plays a signiﬁcant role in the chalcopyrite as a result of their transformation in the cyanide removal of arsenic from the tailings impoundment waters medium (Scott & Ingles 1987). The pulp is diluted by the water (Pactunc et al. 1998; Lazareva et al. 1999). within the impoundment, thereby causing copper and zinc contents to sharply decrease. However, decreases in copper and zinc concentrations may also be related to the formation of (1) Arsenic distribution in core sediments insoluble iron-cyanide—Cu2Fe(CN)6,Cu3@Fe~CN!6#2·14H2O, It should be noted that the term ‘sediment’ used here refers to Zn2Fe(CN)6 (Huiatt et al. 1982), or (2) unstable copper and zinc the tailings within the water-covered portions of the impound- cyanide complexes. ment. Sediment Cores 1 and 2 consist of interbedded layers of Thermodynamic calculations of the possible species of sand and silt-sized material. Core 1, located close to the copper and zinc in the impoundment were performed using the pipeline, consists mainly of coarse sand particles. Only the

Table 3. Saturation index @=log10IAP/Ksp~T!# values for compounds of copper and zinc calculated using the WATEQ4F program

Phase Pulp 1999 Pond 1999 Pond 1998 Pore water 1998 (Sh #3) Pore water 1998 (Sh #8) Cu(OH)2 0.133 0.537 1.158 2.356 2.953 Tenorite CuO 1.153 0.483 0.138 1.336 1.933 Willemite Zn2SiO4 4.001 2.558 1.355 2.779 2.148 Zincite ZnO 0.959 2.383 0.606 2.653 2.437 Zn(OH)2 amorph 0.078 3.42 1.642 3.69 3.474 Zn(OH)2 cryst 0.172 3.17 1.392 3.44 3.224 Zn(OH)2´ 0.872 2.47 0.692 2.74 2.524 Zn(OH)2 0.662 2.68 0.902 2.95 2.734 Zn(OH)2 0.622 2.72 0.942 2.99 2.774 ZnO amorph 1.062 2.279 0.502 2.55 2.333

ZnSiO3 4.218 1 3.136 1.049 1.464

Table 4. Saturation index @=log10IAP/Ksp~T!# values for arsenate calculated using the WATERQ4F program

Phase Pond 1998 Pore water 1998 Pore water 1999 Pulp 1999 Pond 1999

Ba3(AsO4)2 11.719 7.381 7.021 16.504 14.778 Scorodite FeAsO4 ·2H2O 7.537 6.51 6.854 13.584 12.88 AlAsO4 ·2H2O 8.902 8.225 17.673 14.351 Ca3(AsO4)2 ·4H2O 7.681 7.867 9.002 3.665 5.142 Cu3(AsO4)2 ·6H2O 11.319 13.857 17.277 17.844 15.175 Mn3(AsO4)2 ·8H2O 11.472 8.194 11.047 20.673 11.959 Ni3(AsO4)2 ·8H2O 17.2 16.253 17.14 16.706 Pb3(AsO4)2 13.069 16.101 15.746 16.797 18.563 Zn3(AsO4)22 ·5H2O 9.49 14.576 15.556 15.196 20.54 Downloaded from http://geea.lyellcollection.org/ by Michael David Campbell on December 4, 2018

266 E. V. Lazareva et al.

Table 5. Arsenic species distribution in the sediment cores

Sample Soluble Exchangeable Carbonate Easily reducible Moderately reducible Residual mineral Total Core cm ppm % ppm % ppm % ppm % ppm % ppm % ppm ppm Arsenopyrite+Quartz 3.2 0.1 1.8 0.1 5.2 0.1 134.3 3.8 15.0 0.4 3340 95.5 3500 3500 C-1 0–1 3.1 0.2 2.0 0.2 2.6 0.2 96.7 7.6 18.0 1.4 1160 90.7 1280 1410 17–24 1.0 0.1 0.5 0.0 1.0 0.1 29.0 2.1 22.0 1.6 1320 96.2 1380 1510 31–38 0.9 0.1 2.6 0.2 1.8 0.1 27.3 2.0 29.7 2.2 1310 95.5 1370 1620 50–51 3.3 0.2 1.0 0.1 4.3 0.3 48.7 3.3 30.5 2.1 1380 94.2 1470 1630 C-2 0–2 2.8 0.4 1.2 0.2 1.7 0.2 33.0 4.1 69.0 8.6 690 86.9 800 930 2–8 4.0 0.5 2.1 0.2 1.8 0.2 86.3 9.9 68.5 7.9 710 81.7 870 1000 16–18 4.2 0.6 1.5 0.2 3.6 0.5 57.5 7.6 98.5 12.9 600 78.8 760 1070 58–60 4.0 0.4 0.8 0.1 2.8 0.3 26.5 2.7 75.5 7.6 890 89.4 1000 1180 68–72 2.7 0.2 0.8 0.1 2.8 0.2 10.3 0.9 98.5 8.4 1060 90.4 1180 1360 C-3 0–3 3.4 0.5 1.1 0.2 3.6 0.6 30.5 4.7 59.5 9.2 550 85.4 650 840 3–8 3.2 0.6 0.6 0.1 2.6 0.5 26.7 5.0 44.0 8.2 460 86.2 530 620

Fig. 2. Distribution of arsenic, iron, copper and zinc in the solid phase and pore water in the sediment cores. 1, sand; 2, sand–silt; 3, silt; 4, water–sediment boundary; 5, detritus horizon; 6, underlying soil. lowest (deepest) part contains silt. Core 2 (extracted from a The distribution of elements within the sediments and pore shallow part of the tailings impoundment) is composed pri- waters of the cores is given as a function of depth in Figure 2. marily of silt. The stratigraphy of Core 3 is more complicated, Within Cores 1 and 2 copper and zinc concentrations are not presumably because of the eﬀects of abundant aquatic vege- dependent on the grain size of the material present. Thus, the tation on local depositional processes. The upper 4 cm of silt in distribution of copper and zinc does not follow trends in Core 3 is followed by detritus and a buried soil. particle size created by gravity diﬀerentiation (hydraulic sorting). Downloaded from http://geea.lyellcollection.org/ by Michael David Campbell on December 4, 2018

Arsenic speciation of a Siberian gold recovery plant 267

Fig. 3. Element species distribution in the sediment cores (% of the total element content). Fractions: 1, water soluble; 2, exchangeable; 3, carbonate; 4, easily reducible; 5, moderately reducible; 6, residual mineral.

The upper layer of Core 1 is characterized by elevated concen- Elements speciation in core sediments trations of Cu and Zn, whereas a similar layer with high Cu- and Zn-values in Core 2 is buried by sand. This Cu and Zn enriched Arsenic. The distribution of arsenic species in Cores 1, 2 and 3 unit is different from other brown-coloured sediments within has been studied using a sequential leaching procedure (Table 5; the cores and is considered to mark the boundary between the Fig. 3). The contribution of water-soluble, exchangeable and water and sediment. Core 3 has two layers with high metal carbonate-bonded species to the general arsenic balance is contents. High metal values in the upper layer are due to both negligible (0.6% of the total arsenic concentration). In the the direct precipitation of metals from solution and to the absence of the secondary phases only arsenopyrite is leaching deposition of metals by aquatic plants (Bortnikova et al. 1998). during the sequential leaching of the easily reducible fraction. Enrichment in the lower detritus layer is due to the binding of Arsenic content in the easily reducible fraction of the pulp metals by detrital organic matter (Lazareva et al. 1999). (2–8 cm depth for C-2) is 9.9%. No clear correlation in copper and zinc contents between the The easily reducible fraction of arsenic is uniformly sediments and the pore waters exists within Cores 1 and 2. The distributed in the weathered material: sand, sand–silt and silt lack of correlation is probably due to the existence of different (<5% of the total) and is elevated in the impoundment dissolution processes within the individual layers of the cores. sediments (about 7.6%) where the enrichment with secondary In Core 3, the metal contents are similar within the sediment phases takes place. and pore water of the upper layer. The moderately reducible arsenic species content is higher in Arsenic is almost uniformly distributed through Cores 1 and the silt than in the sand material due to intensive oxidation of 2. There is, however, a slight change in concentrations that is arsenopyrite. The sediments are primarily composed of residual dependent on the grain size of material within the core (average minerals with a depth profile similar to that observed for total arsenic concentrations in the solid phase are: 0.19% in sand, arsenic. If arsenic within the residual mineral is present as the 0.13% in sand–silt and 0.14% in the silt-sized material). initial mineral (arsenopyrite), it is evident that its contribution is Therefore, arsenic is distributed according to the depositional minimal in the layers determined earlier as impoundment pattern of arsenopyrite. Taking into account the high arsenic sediments, namely: 0–1 cm for Core 1; 16–18 cm for Core 2 content in the impoundment sediments, it may be concluded and 0–3 cm for Core 3. More than 20% of the total arsenic that arsenic is removed from solution through precipitation, a is concentrated as secondary phases in the 16–18 cm layer conclusion supported by the low arsenic values in the pore of Core 2. The value is about 15% in Core 3. This suggests water of the upper layer of Core 1. In pore waters of Core 2, that arsenic transformations occur within the impoundment arsenic is mainly concentrated in the upper layer (fresh material) during sediment storage resulting in re-precipitation with iron as a result of the oxidative dissolution of arsenopyrite. oxyhydroxides. Downloaded from http://geea.lyellcollection.org/ by Michael David Campbell on December 4, 2018

268 E. V. Lazareva et al.

Iron. Iron is also concentrated in the sediment cores. It occurs This work was financially supported by the RFBR # 99-05-64620. mainly as residual minerals (arsenopyrite, pyrite, pyrrotite), but also in the easily and moderately reducible fraction. According to redox potentials, manganese is considered as an easily REFERENCES reducible and iron as a moderately reducible element. In the case under consideration iron is present in core sediments in BALL,J.W.&NORDSTROM, D. K. 1991. User’s manual for WATEQ4F, with ff revised thermodynamic database. US Geological Survey, Menlo Park, California. both forms. This may be due to the existence of two di erent BOMBACH, G., PIERRA,A.&KLEMM, W. 1994. Arsenic in contaminated soil types of iron bonding in arsenopyrite or two different sources of and river sediment. Fresenius’ Journal of Analytical Chemistry, 35, A9–A53. iron (arsenopyrite and pyrite). However, the latter hypothesis is BORTNIKOVA,S.B.,LAZAREVA,E.V.,ANDROSOVA,N.V.,GASKOVA,O.L.& not supported by the species distribution within the core. Thus, ANDRE, L. 1999. The geochemical peculiarities of technogenic lake at the it is more likely that in core sediments, iron transformations Komsomolsk recovery plant. In: YILMAZER, I. (ed.) Proceedings of ISGS ff (GEOENV’97), Istanbul, Turkey. 1–5 September 1997, 59–66. take place and iron occurs in two di erent forms (iron oxides or BORTNIKOVA,S.B.,LAZAREVA,E.V.,SZERBIN,P.&HOZHINA,E.I.1998. oxy-hydrates). The oxidative dissolution of the initial minerals is Transformation of metal speciation under an action of the aquatic more intensive on the surface of the sediment. However, the vegetation in flooded tailings (wastes of gold-ore cyanidation). In: ATAK,O. &CELIK (eds) Proceedings of the 7th International Mineral Processing Symposium, decrease of the easily and moderately reducible forms of iron Istanbul, Turkey. 15–17 September, Balkema, Rotterdam, 793–797. with depth is negligible. It may be that iron exists in the BOWELL, R. J., MORLEY,N.H.&DIN, V. K. 1994. Arsenic speciation in soil sediment as oxides that result from the pulp-oxidizing process pore waters from the Ashanti Mine, Ghana. Applied Geochemistry, 9, 15–22. or from the re-distribution of oxides forming on the surface of GASKOVA,O.L.,BORTNIKOVA,S.B.,AIRIJANZ,A.A.,KOLMOGOROV,U.P.& the sediment. PASHKOV, M. V. 2000. Geochemical peculiarities of the technogenic lake containing the wastes of gold–arsenopyrite–quartz ores cyanidation. Manganese. Manganese in the carbonate-bound fraction of the Geokhimia (Rus), 3, 317–328. sediment may originate only from the gangue minerals because, HUIATT,J.L.,KERROGAN,J.E.,OLSON,F.A.&POTTER,G.L.1982. according to thermodynamic calculation, the formation of Processing of a cyanide workshop. In: Cyanide from Mineral Processing. US Bureau of Mines, Salt Lake City, Utah. Mn2(CO3)3 should not occur in the impoundment sediments LAZAREVA,E.V.&POSPELOVA, L. N. 1998. Peculiarities of the initial and (Table 3). The easily reducible fraction is likely to be present as secondary distribution of elements in the tailing body. Mineralogical manganese oxide which may originate either from initial or Magazine, 62A(1–3), 862–863. secondary minerals but plays a negligible role in arsenic LAZAREVA,E.V.,BORTNIKOVA, S. B., KOLMOGOROV,U.P.,KIREEV,A.G.& deposition. TSIMBALIST, V. G. 1999. Metal redistribution within the sulfide tailings body. In: BRANNSSON, H. (ed.) Geochemistry of the Earth’s Surface, Rotterdam, 195–198. CONCLUSIONS PACTUNC,A.D.,SZYMANSKY, J., LASTRA, R., LAFLAMME,J.H.G.,ENNS,V.& SOPROVICH, E. 1998. Assessment of potential arsenic mobilization from the It has been established that the primary form of arsenic in the Ketza River mine tailings, Yukon. In: Canada Proceedings of Waste tailings impoundment sediments is the mineral arsenopyrite. Characterisation and Treatment Symposium. Orlando, Florida. Society for Arsenopyrite distribution varies in the tailings impoundment as Mining, Metallurgy and Exploration Inc., 12–18. a function of particle size which, in turn, is controlled by the ROBERTSON, W. D. 1994. The physical hydrogeology of mill-tailings impoundment. In: BLOWES,D.W.&JAMBOR, J. L. (eds) The Environmental processes of hydraulic sorting. Only a very small amount of Geochemistry of Sulphide Mine Wastes. Short Course Handbook, Waterloo, arsenic dissolves during ore processing. Ontario, 1–17. During the storage of the waste materials in the tailings SCOTT,J.D.&INGLES, J. 1987. State-of-the-Art Processes for the Treatment of Gold impoundment, arsenic is redistributed between solid and dis- Mill Effluent. Mining In: Mineral and Metallurgical Processes Division, solved phases and arsenic content in pore waters may become Industrial Programs Branch, Environment, Ottawa, Ontario, Canada. 1 SHUVAEVA,O.V.,BORTNIKOVA,S.B.,KORDA,T.M.&LAZAREVA,E.V.2000. very high (1700 µg l ). The main secondary forms of arsenic Arsenic speciation in a contaminated gold processing tailing dam. in the sediments of the impoundment (more than 20% of the Geostandard Newsletters: The Journal of Geostandards and Geoanalysis, 24(2), total content) are associated with iron hydroxides. 247–252.