Mineralogical and geochemical characterization of the Old Tailings Dam,Australia: Evaluating the effectiveness of a water cover for long-term AMD control

Establishing a shallow water cover over tailings deposited in a designated storage facility is one option to limit oxygen diffusion and retard oxidation of sulfides which have the potential to form acid mine drainage (AMD). The Old Tailings Dam (OTD) located at the Savage River mine, western Tasmania contains 38 million tonnes of pyritic tailings deposited from 1967 to 1982, and is actively generating AMD. The OTD was constructed on a natural gradient, resulting in sub-aerial exposure of the southern area, with the northern area under a natural water cover. This physical contrast allowed for the examination of tailings mineralogy and geochemistry as a function of water cover depth across the OTD. Tailings samples (n = 144, depth: ≤ 1.5 m) were collected and subjected to a range of geochemical and mineralogical evaluations. Tailings from the southern and northern extents of the OTD showed similar AMD potential based on geochemical (NAG pH range: 2.1 to 4.2) and bulk mineralogical parameters, particularly at depth. However, sulfide alteration index (SAI) assessments highlighted the microscale contrast in oxidation. In the sub-aerial zone pyrite grains are moderately oxidized to a depth of 0.3 m (maximum SAI of 6/10), under both gravel fill and oxidized covers, with secondary minerals (e.g., ferrihydrite and goethite) developed along rims and fractures. Beneath this, mildly oxidized pyrite is seen in fresh tailings (SAI = 2.9/10 to 5.8/10). In the sub-aqueous zone, the degree of pyrite oxidation demonstrates a direct relationship with cover depth, with unoxidized, potentially reactive tailings identified from 2.5 m, directly beneath an organic-rich sediment layer (SAI = 0 to 1/10). These findings are broadly similar to other tailings storage facilities e.g., Fox Lake, Sherritt-Gordon ZnCu mine, Canada and Stekenjokk mine, Sweden where water covers up to 2 m have successfully reduced AMD. Whilst geotechnical properties of the OTD restrict the extension of the water cover, pyrite is enriched in cobalt (up to 2.6 wt%) indicating reprocessing of tailings as an alternative management option. Through adoption of an integrated mineralogical and geochemical characterization approach for tailings assessment robust management strategies after mine closure can be developed.     

A study on geotechnical characterization and stability of downstream slope of a tailings dam to improve its storage capacity (Turkey)

Tailings, waste products of the ore-dressing processes, are usually stored in a slurry form and pumped into sedimentation pond which is surrounded by natural heights and/or artificial walls. The database of International Commission of Large Dams and United Nations Environment Programme showed that several hundreds of tailings dam have failed since 1910. One of the reasons of these failures is slope instability. Construction of mine tailings dams in Turkey has started to increase, particularly in the recent decade. This paper focuses the study undertaken to assess the geotechnical characteristics and stability of downstream slope of a tailings dam at a copper-zinc mine in the Black Sea Region of Turkey. At the mine site there are two tailings dams located at two different elevations. The upper dam was completely filled and is out of service. Increasing amount of tailings filling the pond of the lower dam resulted in a limited storage, and therefore, it has been decided that heightening of the dam about 7 m to improve its storage facility would be necessary. For the purpose, a series of investigations in the vicinity of the tailings dam and some geomechanical laboratory tests were carried in conjunction with the use of empirical methods to determine mechanical properties of the current dam material, tailings and the rockfill material that will be used for heightening of the dam. The results of the static and pseudo-static stability analyses based on the methods of limit equilibrium and numerical modelling indicated that circular and non-circular failures are the most critical modes of failure for the dam and safety factor gradually decreases when the tailings rise up to a specific elevation in the pond. However, the ranges of the calculated safety factors from both methods are considerably similar and suitable for heightening of the dam by 7 m in terms of stability. The results suggest that any instability is not expected under both static and dynamic conditions after the current height of the tailings dam is increased by 7 m, if the slope geometry considered in the analyses is not changed and the tailings in the pond do not rise up to an elevation of about 475 m. In addition, magnitude of permanent settlement of the dam due to a probable earthquake was also assessed using two empirical methods and the results from both methods showed similar amount of settlements which were in tolerable limits.     

Komatiites and nickel sulfide ores of the Black Swan area,Yilgarn Craton,Western Australia. 2: Geology and genesis of the orebodies

The Black Swan Ultramafic Succession hosts a number of magmatic Fe–Ni–Cu–PGE sulfide ore shoots, ranging from high grade massive ore to low grade disseminated sulfides. Of these, the most economically significant is the Silver Swan massive sulfide orebody, associated with the basal contact of the succession. The deposit varies in thickness between 5 and 20 m, reaches a N–S strike length of 75 m, extends for at least 1.2 km of vertical plunge and is open at depth. Overlying matrix (net-textured) ore is rare. Inclusions of dacite are abundant within the lower 5 m of the massive sulfide. They range from angular fragments through smooth sinuous and plumose morphologies to fine lace-like intergrowths with the sulfide matrix, and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts. Dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures, some well above their liquidus temperature. The composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30% komatiite. The consistent thickness of the inclusion-bearing basal layer within the massive sulphide is interpreted as the extent of 3-D physical connectivity between the inclusions and a partially molten underlying hybrid layer. Primary contacts between the Silver Swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse-grained chevron-textured chromites with skeletal textures. Compositions of these chromites match those from Kambalda, Perseverance and other localities, and are inconsistent with a metamorphic origin. They are interpreted as markers of primary magmatic contacts. The combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates. Taken together with observations on the internal fractionation of platinum group elements within the massive ores, these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube. The floor of the tube had been previously heated by passage of large volumes of lava, such that it had reached its melting range. The felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma. This constitutes strong evidence for the operation of thermo-mechanical erosion during ore emplacement. The disseminated Cygnet and Black Swan orebodies show a number of distinctive features. Cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip-up, transport and redeposition of sulfides from a pre-existing massive sulfide orebody, of which Black Duck may be a remnant. The Black Swan orebody, by contrast, does not show xenolithic features, but is characterised by an association of sulfide blebs with segregation vesicles, and by unusually coarse-grained olivine. The Black Swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals.Editorial handling: Peter Lightfoot     

Mineralogical and geochemical alteration of Hitura sulphide mine tailings with emphasis on nickel mobility and retention

Weathering of Hitura (W Finland) nickel sulphide mine tailings and release of heavy metals into pore water was studied with mineralogical (optical and electron microscopy, X-ray diffraction) and geochemical methods (selective extractions). Tailings were composed largely of serpentine, micas and amphiboles with only minor carbonates and sulphides. Sulphides, especially pyrrhotite, have oxidized intensively in the shallow tailings in 10–15 years, but a majority of the tailings have remained unchanged. Oxidation has resulted in depletion of carbonates, slightly decreased pH, and heavy metal (Ni, Zn) release in pore water as well as in the precipitation of secondary Fe precipitates. Nevertheless, in the middle of the tailings area, where the oxidation front moves primarily downward, released heavy metals have been adsorbed and immobilized with these precipitates deeper in the oxidation zone. In contrast to what was seen in pore water pH, but in accordance with static tests of the previous studies, the neutralisation potential ratio (NPR) calculated based on the mineralogical composition and the total sulphur content suggested that tailings are ‘not potentially acid mine drainage (AMD) generating’. However, the calculated buffering capacity of the tailings resulted largely from the abundant serpentine because of the low carbonate content. Despite its slow weathering rate, serpentine may buffer the acidity to some extent through ion exchange processes in fine ground tailings. Nevertheless, in practice, acid production capacity of the tailings depends primarily on the balance between Ca–Mg carbonates and iron sulphides. NPR calculation based on carbonate and sulphur contents suggested, that the Hitura tailings are ‘likely AMD generating’. The study shows that sulphide oxidation can be significant in mobilisation of heavy metals even in apparently non-acid producing, low sulphide tailings. Therefore, prevention of oxygen diffusion into tailings is also essential in this type of sulphide tailings.     

Komatiites and nickel sulfide ores of the Black Swan area,Yilgarn Craton,Western Australia. 3: Komatiite geochemistry,and implications for ore forming processes

The Black Swan komatiite sequence is a package of dominantly olivine-rich cumulates with lesser volumes of spinifex textured rocks, interpreted as a section through an extensive komatiite lava flow field. The sequence hosts a number of nickel sulfide orebodies, including the Silver Swan massive shoot and the Cygnet and Black Swan disseminated orebodies. A large body of whole rock analyses on komatiitic rocks from the Black Swan area has been filtered for metasomatic effects. With the exception of mobile elements such as Ca and alkalis, most samples retain residual igneous geochemistry, and can be modelled predominantly by fractionation and accumulation of olivine. Whole rock MgO–FeO relationships imply a relatively restricted range of olivine compositions, more primitive than the olivine which would have been in equilibrium with the transporting komatiite lavas, and together with textural data indicate that much of the cumulus olivine in the sequence was transported. Flow top compositions show evidence for chromite saturation, but the cumulates are deficient in accumulated chromite. Chromite compositions are typical of those found in compound flow-facies komatiites, and are distinct from those in komatiitic dunite bodies. Incompatible trace element abundances show three superimposed influences: control by the relative proportion of olivine to liquid; a signature of crustal contamination and an overprint of metasomatic introduction of LREE, Zr and Th. This overprint is most evident in cumulates, and relatively insignificant in the spinifex rocks. Platinum and palladium behaved as incompatible elements and are negatively correlated with MgO. They show no evidence for wholesale depletion due to sulfide extraction, which was evidently restricted to specific lava tubes or pathways. The lack of correspondence between PGE depletion and contamination by siliceous material implies that contamination alone is insufficient to generate S-saturation and ore formation in the absence of sulfide in the assimilant. Contamination signatures in spinifex-textured rocks may be a guide to Ni-sulfide mineralisation, but are not entirely reliable in the absence of other evidence. The widespread vesicularity of the sequence may be attributable to assimilated water rather than to primary mantle-derived volatiles, and cannot be taken as evidence for primary volatile-rich magmas. The characteristic signature of the Black Swan Succession is the presence of highly localised disseminated sulfide within a sequence showing more widespread evidence for crustal contamination and interaction with its immediate substrate. This has important implications for the applicability of trace element geochemistry in exploration for komatiite-hosted nickel deposits.Electronic Supplementary Material Supplementary material is available in the online version of this article at Editorial handling: Peter Lightfoot     

Identifying calcium-containing mineral species in the JEB Tailings Management Facility at McClean Lake,Saskatchewan

The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the McClean Lake uranium mill facility that is operated by AREVA Resources Canada. This facility has been designed around the idea that elements of concern (e.g., U, As, Ni, Se, Mo) will be controlled through equilibrium with precipitants. Confirming the presence of calcium-containing carbonates in the JEB TMF is the first step in determining if gypsum (CaSO₄·2H₂O) controls the concentration of HCO₃⁻ (aq), limiting the formation of soluble uranyl bicarbonate complexes. A combination of X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and microprobe X-ray fluorescence (XRF) mapping was used to analyze a series of tailings samples from the JEB TMF. Calcium carbonate in the form of calcite (CaCO₃), aragonite (CaCO₃), and dolomite (CaMg(CO₃)₂) were identified by analysing Ca K-edge μ-XANES spectra coupled with microprobe XRF mapping. This is the first observation of these phases in the JEB TMF. The combination of μ-XANES and XRF mapping provided a greater sensitivity to low concentration calcium species compared to the other techniques used, which were only sensitive to the major species present (e.g., gypsum).     

Geochemical and mineralogical aspects of sulfide mine tailings

Tailings generated during processing of sulfide ores represent a substantial risk to water resources. The oxidation of sulfide minerals within tailings deposits can generate low-quality water containing elevated concentrations of SO₄, Fe, and associated metal(loid)s. Acid generated during the oxidation of pyrite [FeS₂], pyrrhotite [Fe_(1−x)S] and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate, (oxy)hydroxide, and silicate minerals. The extent of acid neutralization and, therefore, pore-water pH is a principal control on the mobility of sulfide-oxidation products within tailings deposits. Metals including Fe(III), Cu, Zn, and Ni often occur at high concentrations and exhibit greater mobility at low pH characteristic of acid mine drainage (AMD). In contrast, (hydr)oxyanion-forming elements including As, Sb, Se, and Mo commonly exhibit greater mobility at circumneutral pH associated with neutral mine drainage (NMD). These differences in mobility largely result from the pH-dependence of mineral precipitation–dissolution and sorption–desorption reactions. Cemented layers of secondary (oxy)hydroxide and (hydroxy)sulfate minerals, referred to as hardpans, may promote attenuation of sulfide-mineral oxidation products within and below the oxidation zone. Hardpans may also limit oxygen ingress and pore-water migration within sulfide tailings deposits. Reduction–oxidation (redox) processes are another important control on metal(loid) mobility within sulfide tailings deposits. Reductive dissolution or transformation of secondary (oxy)hydroxide phases can enhance Fe, Mn, and As mobility within sulfide tailings. Production of H₂S via microbial sulfate reduction may promote attenuation of sulfide-oxidation products, including Fe, Zn, Ni, and Tl, via metal-sulfide precipitation. Understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings.     

Origin of abnormal substances discharged from Baozhusi Dam Base, Sichuan, China

Baozhusi reservoir is a large-scale hydropower engineering project in Sichuan Province, China. After drainage wells were drilled in the dam base, white flocculent and black gel substances, accompanied by a rotten-egg odor, were found in some of the drainage water wells. On the basis of a brief introduction of the geological setting in Baozhusi Dam area, the origin of the abnormal substances were analyzed and discussed through the following procedures: (1) the abnormal substances were sampled and their chemical and mineral compositions were analyzed; (2) the origin of drainage waters were determined using the isotope method and well flux measurement results; (3) characteristics of chemical composition of drainage waters were discussed relative to other kinds of waters in the area; (4) process of formation of the abnormal substances were determined using hydrogeochemical methods; (5) laboratory immersion experiment was carried out to verify the conclusions. Results showed that the abnormal substances were formed by interactions between recharging water from the reservoir and dam base rock as well as dam building materials. Among these, the precipitation of calcite and dolomite, the dissolution of calcium hydroxide and anhydrite as well as the reduction of SO₄^–2 to H₂S by organic matter are the most important processes.     

尾矿堆积坝透镜体分布状态研究

尾矿堆积坝中尾砂透镜体具有复杂的分布状态，对坝体的稳定状况有极大影响。根据工程地质勘察所揭露出的透镜体长度信息，定义了一个分布系数米描述透镜体分布状态，并对德兴铜矿2^#尾矿坝、永平铜矿1^#尾矿坝、安徽某铜矿尾矿坝及银山铅锌矿尾矿坝主剖面进行了分析。结果表明，分布系数能较好地反映出尾矿堆积坝的沉积状况，即分布系数值越大，尾矿坝的沉积状况越好：分布系数与尾矿土的不均匀系数成正相关，与粉砂不均匀系数有定量的关系。这些结果对尾矿坝工程地质勘察资料的分析及尾砂沉积规律的认识可能会有重要意义。     

龙井市天宝山矿立山尾矿库地质环境恢复治理方案

龙井市天宝山立山尾矿库,由于企业破产尾矿库对周围环境造成严重危害,需对尾矿库、尾矿坝、排水工程、尾矿碴粉尘污染、水污染进行治理。     

Channel adjustments to reservoir construction and gravel extraction along Stony Creek, California

Stony Creek (drainage area 1920 km²), a tributary to the Sacramento River 200 km north of San Francisco, has experienced channel adjustments to both dam construction and instream gravel extraction. Black Butte Dam, constructed in 1963, reduced flood peaks and trapped the annual 100,000 m³ of bedload sediment formerly delivered from the upper watershed. The reach below the dam changed from an active braided channel to an incised, single-thread channel shortly after dam construction. About 25 km downstream of the dam, large instream gravel mines annually extract 230,000–580,000 m{su3} and have induced channel incision of over 5 m, necessitating bridge repairs costing US$1.4 million.     

Acid mine drainage and acid rock drainage processes in the environment of Herrerías Mine (Iberian Pyrite Belt, Huelva-Spain) and impact on the Andevalo Dam

The present work describes the process of acid water discharge into the Andévalo Dam (Iberian Pyrite Belt, Huelva-Spain) starting from the interpretation of rainfall data and chemical analyses regarding pH, conductivity, metal and sulphate content in water, from a time series corresponding to the sampling of two confluent channels that discharge water into the referred dam. Statistical data treatment allows us to conclude the existence of acid mine drainage processes in the Chorrito Stream, which are translated into very low pH values and high sulphate and metal concentrations in the water coming from Herrerías Mine. On the other hand, the Higuereta Stream shows, for the same parameters, much lower values that can be interpreted as the channel response to acid rock drainage processes in its drainage basin induced by the rocky outcrops of the Iberian Pyrite Belt.     

Characterization of Kolar gold field mine tailings for cyanide and acid drainage

The gold mining process at Kolar gold field (KGF) mines has generated about 32 million tons of tailings. Gold was extracted from the mined ores using cyanidation technique that involved dissolution of gold in the ore by water soluble alkali metal cyanides (example, sodium cyanide or potassium cyanide). Of the several dumps that received the mine tailings only the Kennedy’s Line dump was active prior to closure of the KGF mines in the year 2000. The Kennedy’s Line dump received sulfide bearing tailings in slurry form that comprised of spent ore and process water bearing soluble alkali metal cyanide. Depending on the pH of the tailing slurry, the free cyanides may exist as aqueous hydrogen cyanide that can escape to the atmosphere as hydrogen cyanide gas or occur as soluble cyanide (CN⁻) ions that can be leached by infiltrating water to the sub-surface environment. Additionally, the presence of pyrite minerals in the Kennedy’s Line dump makes them susceptible to acid drainage. This study examines the potential of gold tailings of Kennedy’s Line dump to release cyanide ions (CN⁻) and acid drainage to the sub-surface environment by performing physico-chemical and leaching tests with tailing samples collected from various depths of the dump, sub-surface soil samples beneath the dump and groundwater samples from vicinity of Kennedy’s Line dump. The chemical mechanisms responsible for the ambient cyanide and pH levels of the tailing dump, sub-surface soil samples and groundwater are also inferred from the laboratory results.     

Geochemistry and mineralogy of surface pyritic tailings impoundments at two mining sites of the Iberian Pyrite Belt (SW Spain)

Two pyritic tailings impoundments located in two mining areas of the Iberian Pyrite Belt (Cueva de la Mora and Minas de Ríotinto-Zarandas) were selected to asses their potential environmental impact. Mineralogical (XRD diffraction study), physico-chemical characterization (colour, particle size, pH, acid–base account, total Fe, As, Cu, Pb and Zn) as well as a speciation study (by means of a seven-step sequential extraction procedure) were performed in superficial (0–20 cm) tailings samples. Arsenic and metal contents in soils around the tailings impoundments were also studied. Zarandas dam, a reclaimed impoundment, which has been limed, partially topsoiled and planted, has supported and allowed the growth of pine trees and other plants for many years. The surface of this impoundment can be considered very acid but nonacid forming. Although total As and metal concentrations were relatively high, it is not possible to conclude that the Zarandas tailings have polluted the surrounding soils. Tailings in Cueva de la Mora showed high total and easily mobilizable concentration of toxic elements. The net neutralization potential was strongly negative as a consequence of the acid generation caused by the sulphide oxidation, the presence of secondary acid-generating minerals and the absence of neutralizing materials. Coquimbite and rhomboclase efflorescences formed during the Mediterranean dry summers on the surface of this impoundment contained very high levels of soluble As, Cu and Zn that were easily dissolved and released to the running water in the first rains of autumn.     

Tailings dam seepage at the rehabilitated Mary Kathleen uranium mine,Australia

This study reports on the seepage of metals, metalloids and radionuclides from the Mary Kathleen uranium mill tailings repository. Since rehabilitation in the 1980s, the capped tailings have developed a stratified hydrochemistry, with acid (pH 3.7), saline, metal-rich (Fe, Mn, Ni, U ± As, Pb, Zn), oxygenated (1.05 mg L⁻¹ DO), radioactive waters in the upper tailings pile and near-neutral pH (pH 7.57), metal-poor, reduced (0.08 mg L⁻¹ DO) waters at depth. Seepage (∼0.5 L s⁻¹) of acid (pH 5.5), metal-rich (Fe, Mn ± Ni, U, Zn), radioactive (U-235, U-238, Ra-226, Ra-228, Ac-227) waters occurs from the base of the tailings dam retaining wall into the former evaporation pond and local drainage system. Oxygenation of the seepage waters causes the precipitation of Fe and coprecipitation and adsorption of other metals (U, Y), metalloids (As), rare earth elements (Ce, La) and radionuclides (U-235, U-238). By contrast, alkalis and alkaline–earth elements (Ca, K, Mg, Na, Sr), Mn, sulfate and to some degree metals (U, Zn, Ni), rare earth elements (Ce, La) and radionuclides (U-235, U-238, Ra-226, Ra-228) remain in solution until pH neutralisation and evaporation lead to their precipitation in efflorescences and sulfate-rich evaporative sediments. While the release of contaminant loads from the waste repository through seepage is insignificant (e.g. ∼5 kg of U per year), surface waters downstream of the tailings impoundment possess TDS, U and SO₄ concentrations that exceed Australian water quality guideline values in livestock drinking water. Thus, in areas with a semi-arid climate, even insignificant load releases of contaminants from capped tailings repositories can still cause the deterioration of water quality in ephemeral creek systems.     

四川会东老虎岩尾矿坝地震反应分析

应用有效应力有限元法研究了老虎岩尾矿坝在不同坝高时的应力水平、变形和孔隙水压力分布,以及遭到Ⅶ度地震作用时的反应.分析结果表明:在当前坝高情况下,无地震作用时尾矿坝处于稳定状态.在受烈度为Ⅶ度的地震作用下,尾矿堆积坝坝外坡和沉积滩面的堆积尾矿砂土在局部已经发生液化破坏;在封库坝高情况下,无地震作用时尾矿坝处于极限状态.在受烈度为Ⅶ度的地震作用下,尾矿坝坝外坡和沉积滩面的堆积尾矿砂土已发生大面积液化破坏.在地震作用下,老虎岩尾矿坝堆积尾矿产生液化破坏的主要原因是堆积坝体内浸润线的埋深较浅.对老虎岩尾矿坝必须加强排渗措施,使坝体内浸润线下移.     

Effects of pH on arsenic mineralogy and stability in Poldice Valley,Cornwall, United Kingdom

Many abandoned mine sites in Cornwall, UK, are characterised by elevated concentrations of arsenic (As), which can cause contamination of surrounding soil and water resources. These sites have important historical value that requires access to be maintained, despite exposure of humans to toxins that may lead to health issues including hyperpigmentation keratosis (including skin cancers) and liver fibrosis. The abandoned mine tailings at Wheal Maid has been assessed for As-bearing mineralogy and stability taking into account the public footpaths made by the local council to areas of potential contamination.To assess the potential risk associated with these mine sites, the As concentration in waters along the tailings dam and Carnon River have been measured and range up to 3.6 ppm, which is 2 orders of magnitude above the WHO guideline value of 0.01 ppm for drinking water. Samples of water, rocks and soils from the mine tailings ponds and the Carnon River were analysed using Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) to determine the concentration of individual elements in each sample followed by mineral identification using X-Ray Diffraction (XRD). Mineralogical evaluation indicated that the majority of mine tailings consist of clay-rich rocks, with few associated As-bearing minerals. Scorodite (FeAsO₄·2H₂O) is observed in the mine tailings pond and appears critical to the As distribution and storage in this surface environment. Using the analysed water chemistry, a modified version of PHREEQC is used to calculate the saturation index of scorodite as a function of pH conditions. The strong variation of the solubility of this mineral with pH and oxidation state highlights potential risks for using scorodite for As fixation and storage.     

关于磷石膏尾矿库安全专篇的研究

磷石膏尾矿库是以磷石膏渣堆积起来形成的尾矿库,其安全问题一直是磷化工企业及安全生产管理部门非常关心的问题。根据《尾矿库安全监督管理规定》,尾矿库工程在设计阶段应该编写安全专篇,需要对尾矿库及尾矿坝稳定性、尾矿库防洪能力及排洪设施和安全观测设施的可靠性进行充分论证。3个方面的内容紧密联系,其是否安全可靠决定着尾矿库是否安全运行。针对磷石膏尾矿库的安全专篇问题,分析了专篇中的关键技术内容,对防洪计算、稳定性计算和安全监测分析等方面的本质问题进行了探讨,并将这三者作为一个系统进行分析总结。通过对湖北某磷石膏尾矿工程安全专篇的编写与分析,对具体的技术方法给出了说明。目前尾矿库工程安全问题受到了广泛的关注,其结果提供了比较完整的具体经验,采用的方法和得出的结论对相关工程可以起一定的借鉴作用。     

Modelling natural attenuation of heavy-metal groundwater contamination in the Selebi-Phikwe mining area,Botswana

Seepage from a tailings dam is the major source of groundwater pollution in the Selebi-Phikwe area, where mining of sulphidic nickel–copper–cobalt ore started in 1973 and will continue until 2014. The seepage water has a pH in the range of 1.7–2.8 and is strongly enriched in SO₄ ²⁻ (5,680 g/L) and heavy metals (6,230 μg/L Ni, 1,860 μg/L Cu and 410 μg/L Co). The fracture aquifer affected by pollution from the dam exhibits a remarkable capacity of heavy-metal sorption. Most of the Ni, Cu and Co is scavenged at less than 500 m distance downgradient from the polluting source, whereas SO₄ ²⁻ is not immobilized significantly. The heavy-metal sorption process is assumed to be due to surface complexation, which is supported by a relatively high groundwater pH (in the range of 6.2–7.8 at >200 m distance from the tailings dam). The objective of this study is to demonstrate that the sorption process can be incorporated into a realistic three-dimensional reactive-transport groundwater model that is implicitly charge-balanced. The simulations are performed with the PHAST1.2 program, which is based on the HST3D flow and transport code and the hydrochemical PHREEQC2.12 code.     

基于流固耦合作用的某尾矿坝渗流稳定性分析

尾矿坝是矿山重要设施之一,其内部含有大量的水和尾矿,一旦失稳造成的损失不可估量。尾矿坝失稳有众多因素影响,但是坝内浸润线是最活跃的影响因素。本文基于流固耦合理论,建立某尾矿坝有限元计算模型,考虑坝内排水井的存在。模拟坝内不同工况下浸润线分布,对其静力稳定性及流固耦合作用下尾矿坝应力应变场进行分析,并将浸润线模拟位置与实际监测结果进行对比。揭示库内不同工况下浸润线变化规律以及与坝体稳定性之间的关系,并分析评价不同工况下尾矿坝的稳定性。最后,将渗流场与应力场进行流固耦合,模拟出365 d坝内应力位移分布,为尾矿坝施工及安全运行提供可靠的依据及技术支持。