Applied Geochemistry 27 (2012) 2260–2270
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Arsenic mobility in two mine tailings drainage systems and its removal from solution by natural geochemical barriers Nataliya V. Yurkevich a,⇑, Olga P. Saeva a, Nadezhda A. Pal’chik b a b
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, ac. Koptyug av., 3, Novosibirsk 630090, Russia Institute of Geology and Mineralogy SB RAS, ac. Koptyug av., 3, Novosibirsk 630090, Russia
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Article history: Available online 29 May 2012
a b s t r a c t Sulfide-mineral-bearing mill wastes are sources of high concentrations of acid, soluble metals, and As. These are serious problems for ore mining areas such as the Kemerovo and Cheljabinsk regions in Russia. This study evaluated the distribution of the mill wastes, the mobility of As from the wastes, and the potential of natural materials to attenuate As dispersion in the broader environment. Arsenic contents in wastes of the Belovo Zn-processing (Kemerovo) and the Karabash Cu-smelting plants (Cheljabinsk) are 2–3 orders of magnitude higher than the content of continental crust. Main mineral forms of As in these wastes are arsenopyrite (FeAsS) and scorodite (FeAsO42H2O). High dissolved As concentrations are found in water draining the wastes and in rivers adjacent to the mill sites. The water concentrations commonly exceed drinking water standards. High As concentrations in bottom sediments of the affected rivers extend a 100 m downstream of the waste drainage input. These sediments are also a source of river water contamination. Experiments were conducted to evaluate the ability of natural water to mobilize As from the wastes. The Belovo tailings released 86% of their contained As to the infiltrating water, whereas the less reactive Karabash tailings released only 22% of total As. The experimental leachates were used as influent to columns that tested the ability of limestone and natural clay to reduce the concentration of dissolved As and associated metals. Some dissolved As was precipitated with Fe, Pb and Sb initially in the limestone column. The decrease in dissolved As is consistent with the accumulation of As in yellow ferriferous sediments in the Belovo settling pond. In the pond and wetland sediments, As mobility is also decreased by the formation of sulfides and arsenides. Cubanite (CuFe2S3), klaprothite (Cu3BiS3), rammelsbergite (NiAs2), maucherite (Ni11As8), semseyite (Cu9Sb8S21), and skutterudite (CoAs3) were found in the chemically reducing lower sediments of the Belovo settling pond. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Acid drainage and metal migration are severe problems in ore mining regions all over the world. Examples of areas impacted by these conditions include the Kemerovo and Cheljabinsk regions in Russia where more than 5 and 15 million tons, respectively, of metal recovery wastes accumulate annually (Sidenko et al., 2001). Copper and Zn mining industry wastes in the towns Belovo (Kemerovo region) and Karabash (Cheljabinsk region) are considered in this work. Tailings at both sites contain large quantities of Fe, Cu, Zn and Pb sulfides, which host large amounts of Cd, Co, Ni, As, Sb and Be as impurities. In these wastes As is present in arsenopyrite (FeAsS), scorodite (FeAsO42H2O), orpiment (As2S3), realgar (AsS) and enargite (Cu3AsS4) (Ozherelieva and Bortnikova, 2006; Sidenko et al., 2001). Oxidation of the sulfide minerals results in the formation of acidic solutions with high concentrations of SO2 4 , Cu, Zn, Fe, As, Sb and other soluble species. These elements ⇑ Corresponding author. Tel.: +7 383 3309536; fax: +7 383 3332107. E-mail addresses:
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[email protected] (N.V. Yurkevich). 0883-2927/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apgeochem.2012.05.012
are transported in solution out of the tailing dumps into drainage streams that discharge into adjoining rivers and also seep into groundwater (Nordstrom and Alpers, 1999; Ozherelieva and Bortnikova, 2006; Bortnikova et al., 2011). Similar examples of element transport from wastes have been described by Stephane et al. (2005), Lei and Watkins (2005) and others. Natural and anthropogenic As sources, along with its mobility and toxicity have been extensively discussed in recent years because of the occurrence of As as a contaminant in many parts of the world. Up to 70,000 tons of As are extracted with ores annually in Russia (Ivanov, 1994). Only 2–2.5% is used beneficially, the remainder is considered waste and is discharged into the environment: 7% as gaseous discharges, 0.5% in industrial sewage, and 90% in other waste products. The total amount of As-containing wastes is approximately 107 tons and is increasing annually at a rate of 8–10%. Typical As concentrations in mine tailings are 0.04–0.59% (Kopylov and Kaminsky, 2004). The average amount of As in Belovo and Karabash wastes is about 0.01–0.34%. Arsenic concentrations in mine drainage and contaminated river waters can reach levels thousands of times higher than those in
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natural streams (Smedley and Kinniburgh, 2002; Romero et al., 2003; Courtin-Nomade et al., 2005). Average As concentration in river water is 2 lg/L (Taylor and McLennan, 1985). The World Health Organization (WHO) and Russian Ministry of Health maximum contamination limit (MCL) in water reservoirs for domestic use is 10 lg/L (ATSDR, 2003; HN 2.1.5.1315-03, 2003; US EPA, 2009). In contrast, the concentration of As in AMD and the settling pond (Zn-processing plant, Kemerovo region, Russia) can reach 650 lg/L. Groundwater in this area contains only 3–10 lg/L (Bortnikova et al., 2003, 2006). Important factors affecting As mobility are its solution chemistry, pH, redox conditions, As-bearing phases, adsorption and desorption, and biological transformations (Yamauchi and Fowler, 1994; Sadiq, 1997). Greatest mobility of common contaminant metals is favored by low pH and an oxidizing environments. In contrast, As is mobile over a wide pH range (i.e. extremely acid to alkaline. Water draining from some mines that is oxidizing, and neutral to alkaline in pH can contain several mg L1 of As (Marszalek and Wasik, 2000; Williams, 2001; Roddick-Lanzilotta et al., 2002). Thus, contamination of mine waters by As is not limited to acid mine drainage (AMD) (Lottermoser, 2007). Dissolved As in natural waters is generally composed of the inorganic forms 2 3 arsenate AsO3 (H2 AsO 4 4 ðaqÞ, HAsO4 ðaqÞ H3AsO4(aq), AsO4 ðaqÞ) 3 and arsenite AsO3 ðH2 AsO3 ðaqÞ). Arsenate compounds are generally less soluble, less mobile, and less toxic than arsenite and usually predominate in aerobic waters, whereas As(III) compounds predominate in slightly reduced conditions (Goh and Lim, 2005). Until recently, mechanisms of As toxicity and in particular its carcinogenic influence on living organisms have been poorly understood. Particularly because of the known toxicity of several associated elements. Nevertheless, As compounds in water have been assigned as 1st class in terms of danger according to the Russian hygienic standards. Therefore, special attention is given to As in environments influenced by mining activity, particularly where drinking water is affected. In addition to total As concentrations in waste systems, drainage, river and ground water, it is necessary to identify its species and coexisting mineral phases to conduct a tailings risk assessment that considers As mobility and an understanding of migration mechanisms. Data on As speciation are also necessary for development of removal and purification methods.
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This investigation intended to develop information that would forecast the behavior of As in the environment affected by mine wastes by (i) determining the composition of oxidized mine wastes, water and sediments in drainage streams, and (ii) evaluating the distribution of As in transition between the solid and the dissolved fractions. The results, coupled with information gained from leaching tests and experiments on geochemical barriers, increase understanding of the spatial variations of As in the system of waste–drainage–river and constrain possible mitigation strategies to immobilize the As.
2. Site descriptions The Kemerovo region, also known as the Kuzbass, is located in Western Siberia, Russia (Fig. 1). The region shares a border with the Tomsk and Novosibirsk regions, Altai and Krasnoyarsk territories, the Altai Republic, and the Republic of Khakassia. The region is ringed by mountains, including the Salair Ridge, the Abakan Range and the Kuznetsky Alatau Mountains. The mountains surrounding the Kemerovo region contain Au placers, deposits of Fe, Cu and polymetallic ores, urtite–nepheline, bauxite, and phosphorite. Bedrock geology of the Belovo district is dominated by Upper Permian sandstones and shales (Report on the environmental protection of the Kemerovo region, 2010). The Belovo district is situated in a forest-steppe area with moderate humidity. The thickness of the active water exchange zone is 30–60 m. The groundwater flux through the area varies from 1 to 6 L/s km2 (Hydrogeology of the USSR, 1977). A Zn-processing plant is located in the town of Belovo (Fig. 1). Zinc was extracted from an ore concentrate obtained from a polymetallic sulfide deposit mined in the Salair ore field. Salair ore consists of fine-grained intergrowths of different sulfide minerals which results in an ore concentrate that contains high amounts of Cd, Co, Ni, As, and Sb. The waste material of the ore-processing plant is a clinker formed by pyrometallurgical smelting. Between 1950 and 1954, approximately 600–700,000 tons of waste accumulated on the grounds of the Zn plant. The clinker is a loose, coarse-grained and heterogeneous material, which consists primarily of silicate glass with inclusions of K-feldspar, olivine, spinel, alloys and some residual sulfides. Concentration of S in the clinker
Fig. 1. Map showing the location of the town of Belovo and Karabash in the Kemerovo and Cheljabinsk regions.
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is as much as 1.5 wt%. Large amounts of carbonaceous material occur in the clinker (20–25 wt%). The C represents coke breeze that was incompletely consumed in the smelting furnace. There is a ditch below the waste heaps, which collects drainage water and resulting flow passes into a wetland area. The drainage water then flows into a purifier, where it is diluted by urban wastewater. The mixture of urban waste and drainage water is discharged into the Bachat River (Sidenko et al., 2001). The Bachat River forms at the confluence of the Bolshoy Bachat River and Maliy Bachat. It is a lowland river with a steady flow and a meandering channel 0.5– 1.0 m deep. Typical flow rates are 0.8–1.5 m/s along the 86 km length. The drainage basin area is 1720 km2. The Bachat River flows into the Inya River. The city of Karabash is located in the Chelyabinsk region in the Southern Ural Mountains (Fig. 1). Karabash is one of the largest Cu smelting centers of Russia and is known for its severe environmental problems. The Karabash chalcopyrite deposits are hosted by a suite of highly metamorphosed Ordovician–Silurian and Devonian uralite porphyries, associated tuffs, and sandstones. The ores consist mainly of massive chalcopyrite, pyrite and other sulfide minerals (Kirin, 1964). The area of the Urals is characterized by poor ground water resources. The thickness of the active water exchange zone in the studied area is 30–50 m. The groundwater flux varies from 0.1 to 0.5 L/s km2 (Hydrogeology of the USSR, 1977). Copper was extracted at Karabash from ore supplied by deposits in the area and in Kazakhstan. Between 1910 and 1958, a finegrained slurry of processing wastes was dumped along and in the Sak-Elga River. It is a tributary of the Miass River (Tobol basin) and has a length of 19 km. The drainage basin is 135 km2. The SakElga flows into the river Miass on its western bank. The solid process wastes have been accumulated over a 3 km length of the river bed that covers an area of 2.1–2.5 km2 with a thickness from 0.3 to 2.0 m. When the river banks erode, sulfate minerals (such as gypsum (CaSO42H2O), barite (BaSO4), jarosite (NaFe3(SO4)2(OH)6), magnesiocopiapite (MgFe4(SO4)(OH)220H2O), aluminocopiapite ((Mg,Al)(Fe,Al)4(SO4)6(OH)220H2O) and antlerite (Cu3(SO4)(OH)4), together with scorodite (FeAsO42H2O) form on the exposed surfaces. These secondary minerals are dissolved and carried by the SakElga River into the Miass River, and Argazin Reservoir. Beginning in the middle of the twentieth century, wastes were stored in two tailings dumps. The Karabash tailings contain high contents of sulfide minerals, primarily pyrite (up to 25 wt%), chalcopyrite (3 wt%) and up to 1 wt% of sphalerite and galena. The amount of carbonaceous material in Karabash tailings is up to 10–15 wt%. The concentration of sulfide-S is much higher in the Karabash wastes at 6 wt% relative to the maximum of 1.5 wt% measured for the Belovo clinkers.
3. Sampling and analytical methods Fifteen samples of tailings were collected at each study site (Fig. 2 and 3b). The tailings were sampled at a depth of 50 cm along the dump (length of 300 m) in Belovo and along the bank of the Sak-Elga River (length of 300 m) in Karabash. The bottom sediments in drainage streams and the contaminated rivers Sak-Elga and Bachat were sampled from 1999 to 2008. The location of sediment sampling sites is shown in Figs. 2 and 3a. Solid samples were collected with a plastic scoop and transferred into a polyethylene bag. The drainage and contaminated river waters were sampled annually from 1999 to 2008 during the summer. The locations of the water sampling sites are shown in Figs. 2 and 3a. The water samples were collected in plastic bottles that were rinsed with
Fig. 2. Schematic map of the Belovo study area with location of sampling points of (1) both water and bottom sediments in settling pond and drainage ditch B-1–B-16; (2) water in the Bachat River BR-1–BR-3; (3) Belovo tailings BT-1–BT-15.
the sampled water. Samples to determine the background water composition and for leaching experiments were collected from the Gavrilov reservoir in the Kemerovo region and from the Argazin reservoir in the Cheljabinsk region (Fig. 3). These backgrounds sites are located beyond the extent of known industrial impact areas at distances of 1–5 km from the tailings. 3.1. Analytical methods for water The pH, Eh and temperature were measured in situ using calibrated meters. Water samples used to determine metal concentrations were filtered at the sampling site to
