Showing papers on "Tailings published in 2003"

Mine Wastes: Characterization, Treatment and Environmental Impacts

Abstract: This book provides a thorough, up-to-date overview of wastes accumulating at mine sites. It deals comprehensively with sulfidic mine wastes, mine water, tailings, cyanidation wastes of gold-silver ores, radioactive wastes of uranium ores, and wastes of phosphate and potash ores. The book emphasizes the characterization, prediction, monitoring, disposal and treatment as well as environmental impacts of problematic mine wastes. The strong pedagogical framework is supported by case studies from around the world, end-of-chapter summaries as well as lists of resource materials and www sites for each waste type.

Chemical and Microbiological Characteristics of Mineral Spoils and Drainage Waters at Abandoned Coal and Metal Mines

Abstract: Mining is a long-established human activity. Abandonedmines, tailings, and mine spoils may have considerable impacton neighboring environments long after the sites are abandoned. Of greatest concern are derelict mines and wastes that generateacidic discharge waters that are enriched with iron and othermetals and metalloids. The chemistry and microbiology of thesesites are intricately intertwined. Whilst some indigenousmicroorganisms are responsible for accelerating sulfide mineraloxidation, thereby generating acidity and mobilizing metals,others catalyze reductive processes that essentially reversethese reactions and thereby ameliorate polluted mine waters.This article reviews current knowledge on the chemistry and microbiology of abandoned coal and metal mines, mine spoils and tailings.

Soil Contamination and Plant Uptake of Heavy Metals at Polluted Sites in China

Abstract: We investigated heavy metal contamination in soils and plants at polluted sites in China including some with heavy industries, metal mining, smelting and untreated wastewater irrigation areas. We report our main findings in this paper. The concentrations of heavy metals, including Cd and Zn, in the soils at the investigated sites were above the background levels, and generally exceeded the Government guidelines for metals in soil. The concentrations of metals in plants served to indicate the metal contamination status of the site, and also revealed the abilities of various plant species to take up and accumulate the metals from the soil. Substantial differences in the accumulation of heavy metals were observed among the plant species investigated. Polygonum hydropiper growing on contaminated soils in a sewage pond had accumulated 1061 mg kg(-1) of Zn in its shoots. Rumex acetosa L. growing near a smelter had accumulated more than 900 mg kg(-1) of Zn both in its shoots and roots. Therefore these species have potential for phytoremediation of metal-contaminated sites. Our results indicate the need to elucidate the dynamics of soil metal contamination of plants and the onward movement of metal contaminants into the food chain. Also our results indicate that the consumption of rice grown in paddy soils contaminated with Cd, Cr or Zn may pose a serious risk to human health, because from 24 to 22% of the total metal content in the rice biomass was concentrated in the rice grain. Platanus acerifolia growing on heavily contaminated soil accumulated only very low levels of heavy metals, and this mechanism for excluding metal uptake may have value in crop improvement. Sources of metal entering the environmental matrices studied included untreated wastewater, tailings or slurries and dust depositions from metal ore mining, and sewage sludge. Pb, Zn or Cd concentrations declined with the distance from metal smelter in accordance with a good exponential correlation (R2>0.9), and this shows that metal dust deposition is an important contributor to metal contamination of soils.

Effects of mining activities on heavy metal concentrations in water, sediment, and macroinvertebrates in different reaches of the Pilcomayo River, South America.

Abstract: From 1997 until 1999 the extent and the ecological effects of zinc, copper, lead, and cadmium pollution were studied in different reaches of the South American Pilcomayo River. A comparison of metal concentrations in water, sediment, and chironomid larvae, as well as the diversity of macroinvertebrate species, was made between sites near the origin of the Pilcomayo River, with hardly any mining activities, sites in the Potosi region, with intensive mining, and sites located 500 km or further downstream of Potosi, in the Chaco plain. Samples were also collected in an unpolluted river (Cachi Mayu River) and in the Tarapaya River, which is strongly contaminated by mine tailings (1000 tons a day). The upper parts of the Pilcomayo River are strongly affected by the release of mine tailings from the Potosi mines where mean concentrations of lead, cadmium, copper, and zinc in water, filtered water, sediment, and chironomid larvae were up to a thousand times higher than the local background levels. The diversity of the benthic macroinvertebrate community was strongly reduced in the contaminated parts; 97% of the benthic macroinvertebrates consisted of chironomid larvae. The degree of contamination in the lower reaches of the river, however, was fairly low because of sedimentation processes and the strong dilution of mine tailings with enormous amounts of clean sediment from erosion processes. Analysis of sediment cores from the Ibibobo floodplain, however, reveal an increase of the heavy metal concentrations in the lower reaches since the introduction of the contaminating flotation process in the mine industry in 1985.

Stabilization of available arsenic in highly contaminated mine tailings using iron.

Abstract: To evaluate the stabilization of available As in contaminated tailings from two abandoned metal mines of South Korea (the Myoungbong and Daduck Mines, 6670 and 56,600 mg/kg total As, respectively), characteristics of the tailings were investigated, and the tailings were treated through precipitation of amorphous iron compounds. Steep decreasing trends of extractable (5% NaOCl) As with increasing initial Fe(III) additions were observed in both treated tailings. In general, the treated tailings had the lowest extractable As concentration at pH 6. Available As, defined as the sum of As concentrations for the first four steps of a sequential extraction, was reduced from 2090 to 428 mg/kg (80% reduction) in the Myoungbong tailings and from 1320 to 395 mg/kg (70% reduction) in the Daduck tailings. As levels in the treated tailings decreased even more after a 1-month dormant period. Adsorption/coprecipitation tests performed with mixed As(III) and Fe(III) solutions demonstrated dramatically increased As sequestration via interaction with amorphous iron compounds with increasing pH. The bulk of the As appeared to be affiliated with stable Fe precipitates.

Speciation and characterization of arsenic in Ketza River mine tailings using x-ray absorption spectroscopy

Abstract: Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A for the exposed tailings and 3.33-3.35 A for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentate-binuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.

Bioremediation of metal contamination.

Abstract: A study was initiated to evaluate the use of the fungus Aspergillus niger for bioleaching and then todetermine the effect of process steps, the tailingsconcentration and type of substrate. An oxidized miningtailing containing mainly copper (7240 mg kg-1 tailings) was studied. A sucrose and mineral salts medium was initially used to produce citric and gluconic acids by A. niger atvarious concentrations of tailings (1, 5, 7, 10 and 15% w/v).Maximal removal of up to 60% of the copper was obtained forthe 5% tailings when the organic acid supernatant was addedto the tailings. In a single step process, A. niger wasthen grown in the presence of mining tailings at variousconcentrations. Maximum copper solubilization (63%) occurredwith 10% mining tailings using sucrose as the substrate.Other substrates were then evaluated including molasses, corncobs and brewery waste (10% mining tailings). Sucrose gavethe best results for copper removal, followed by molasses,corn cobs and brewery waste. Other experiments usingultrasound as a pretreatment showed that 80% removal of thecopper could be obtained for a 5% tailings concentration. Inconclusion, leaching of copper from mining tailings istechnically feasible using A. niger but furtherresearch will be required to increase the economic feasibilityof the process.

Mineralogical characterization of arsenic in uranium mine tailings precipitated from iron-rich hydrometallurgical solutions.

Abstract: Arsenic-rich uranium mine tailings from the Rabbit Lake in-pit tailings management facility (RLITMF) in northern Saskatchewan, Canada, were investigated to determine the mineralogy and long-term stability of secondary arsenic precipitates formed from iron-rich hydrometallurgical solutions. Total arsenic and iron concentrations in six iron-rich samples of the mine tailings ranged from 56 to 6000 μg/g and from 12 600 to 30 200 μg/g, respectively (Fe/As molar ratios of 5.3−303). On the basis of stability field diagrams generated from pH, Eh, and temperature measurements on tailings samples (mean values of 9.79, +162 mV, and 2.8 °C, respectively), it was concluded that arsenic and iron in the tailings were stable as As5+ and Fe3+. Synchrotron-based X-ray absorption spectroscopic studies of tailings samples, fresh mill precipitates, and reference compounds showed that the arsenic in iron-rich areas of the tailings existed as the stable As5+ and was adsorbed to 2-line ferrihydrite through inner-sphere bidentate...

Geochemical distribution of arsenic in waters, sediments and weathered gold mineralized rocks from Iron Quadrangle, Brazil

Abstract: The Iron Quadrangle has been the scenery of the most important gold production in Brazil. It is estimated that during the three centuries of gold mining in the Iron Quadrangle, at least 390,000 t of arsenic was discharged into the drainage system. This study presents geochemical data for the three river basins in the region, with focus on surface water and stream sediment monitoring. Samples of primary and oxidized sulfide ores as well as of tailings and groundwater from the major gold mines were also studied. The highest As concentrations in water and stream sediments occur in the vicinity of mining areas. In surface water, up to 300 g As/l were found whereas the As contents in stream sediments were in the range of 20 to 4,000 mg/kg. The As3+/As5+ concentration ratios obtained for some water samples range from 1.10−1 to 4.10−2. The As mobility associated with ore-deposit weathering could be traced in some closed gold mines by observation of in-situ pyrite and arsenopyrite oxidation, precipitation of scorodite and gippsite, As adsorption onto goethite, and final liberation of As into underground and surface waters. This process is likely to produce large volumes of mine effluents containing total As and trivalent As up to 1,960 and 60 g/l, respectively. River sediments and tailings pile samples were submitted to a leaching procedure showing maximal arsenic release from 1 to 4% of the original total As in the samples. There are potential risks for As hazards in some areas induced by, for instance, the dispersion of old tailings by flooding, occupation of poisoned soils for settlements, and occasional consumption of contaminated surface and groundwater.

Microbially-mediated fugitive gas production from oil sands tailings and increased tailings densification rates

Abstract: Oil sands in northeastern Alberta, Canada, are strip mined and bitumen is separated from sand and clay by an alkaline hot water extraction process leaving millions of cubic metres of tailings for disposal. These include mature fine tailings (MFT) collected in settling ponds and consolidated or composite tailings (CT) that are produced by the addition of sand and gypsum to hasten dewatering and densification. This laboratory investigation monitored the potential for fugitive gas production in 0.9-m high columns that contained MFT or CT samples from three oil sands companies. Methane was found in columns that contained aged MFT, but not in those that contained fresh MFT. Dissolved or entrapped methane was found in columns containing each of the MFT samples and two of the CT samples. Ethylene was detected in columns containing MFT or CT. This may affect future plans to re-vegetate disturbed areas of the oil sands operations because ethylene strongly influences many phases of plant development. The densificat...

Metal bioavailability and speciation in a wetland tailings repository amended with biosolids compost, wood ash, and sulfate.

Abstract: Lead poisoning of waterfowl from direct ingestion of wetland mine tailings has been reported at the Coeur d'Alene River basin in Idaho A greenhouse study was conducted to evaluate the effects of surface applications of amendments on lead bioavailability in the tailings Treatments included sediment only, and sediment with three different surface amendments: (i) biosolids compost plus wood ash, (ii) compost + wood ash + a low SO4(2-) addition as K2SO4, and (iii) compost + wood ash + a high SO4(2-) addition Measured variables included growth and tissue Pb, Zn, and Cd concentration of arrowhead (Sagittaria latifolia Willd) and cattail (Typha latifolia L) and soil pH, redox potential (Eh), pore water Pb, Pb speciation by X-ray absorption spectroscopy, and in vitro Pb bioavailability The compost + ash amendment alleviated phytotoxicity for both plant species Bioavailability of Pb as measured by a rapid in vitro extract decreased by 24 to 34% (over control) in the tailings directly below the amendment layer in the compost + SO4 treatments The ratio of acid volatile sulfide (AVS) to simultaneously extracted metals (SEM) also indicated a reduction in Pb bioavailability (1:40 control, 1:20 compost, 1:8 compost + low SO4, and 1:3 compost + high SO4) Extended X-ray adsorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy data indicated that lead sulfide was greater after 99 d in the treatments that included additions of sulfate These results indicated that, under reducing conditions, surface amendments of compost + wood ash (with or without sulfate) decreased the bioavailability of Pb in metal-contaminated mine tailings

Arsenic phase distribution in Zimapán mine tailings, Mexico

Abstract: Arsenic contamination of groundwater has been linked to natural and anthropogenic sources in Zimapan, Mexico. Leaching of mine tailings was identified as one of the man-made causes of environmental arsenic pollution. Arsenic mobility from four tailing piles was studied by chemical procedures. Conductivity, concentration of sulfates, and pH in aqueous leachates were used as indicators of the physico-chemical conditions influencing arsenic mobility. Arsenic geochemical fractionation was determined through sequential extraction from the tailings. High arsenic contents from 2550 mg/kg to 21 400 mg/kg were found in all the tailings. Most arsenic was contained in the residual considered more stable, and in iron and aluminium oxyhydroxides fractions. Arsenic found in the soluble and exchangeable fractions (up to 1560 mg/kg) may mobilize easily and pollute the environment. On the other hand, presence of calcite in the tailings may decrease arsenic leaching. Arsenic and sulfate contents, speciation, and pH, indicate that the recent pile is a major source of pollution. This shows that even stable forms of arsenic may mobilize and may represent an environmental risk. Higher pH is observed to prevent the dissolution of arsenic bound to carbonates. Hence, addition of calcium oxide or calcite to the tailings is recommended.