Discrete element simulation of mine tailings stabilized with biopolymer

This paper presents a series of numerical simulations using discrete element method (DEM) to study the behavior of biopolymer-stabilized mine tailings (MT). Validation is conducted by comparing the DEM results with the experimental data. The macro-behavior comparison shows that the DEM simulations are in good agreement with experimental results. Analysis of the micro-parameters indicates more biopolymer induces larger tensile and shear strengths, confirming the experimental results which show that the strength of MT increases with higher biopolymer concentration. Analysis of the bond breakage pattern suggests that at the same strain level MT stabilized with higher biopolymer concentration show less bond breakage percentage. MT specimen under greater confining pressure develops larger shear band than that under lower confining pressure. Higher biopolymer concentration induces the increase in larger inter-particle bonding strength and thus larger cracking resistance and greater macro-strength.     

Hydro-mechanical evaluation of soil stabilized with cement-kiln dust in arid lands

This study evaluates the potential use of cement-kiln dust (CKD), a waste product from the cement industry, for enhancing the mechanical as well as the hydraulic properties of soils in arid lands. Stabilized products will play a major role in reducing slope failures, pavement damage and the design of containment barriers for hazardous waste in arid lands. Various tests to determine the different physical properties of the stabilized matrix were conducted and the optimum mixture that produces maximum internal energy and minimum hydraulic conductivity was selected. The effect of soaking and unsoaking of the treated specimens on the mechanical properties was also evaluated. The effect of metal ion concentration and conjugate anions on the resultant hydraulic conductivity was evaluated. The optimum percentage of CKD was calculated by using stress-strain data, Newton's divided difference and Simpson's integration technique. The analyses have shown that 6% by weight of CKD is the optimum mix design, which increases the shear strength and decreases the hydraulic conductivity to less than 10^-9 m/s. Therefore, the treated soil could be used as a soil-based barrier layer for containment of hazardous waste.     

An evaluation of copper remobilization from mine tailings in sulfidic environments

A laboratory-based assessment of copper remobilization from Cu-rich mine tailings exposed to anoxic, sulfide rich waters was performed. The results from incubation experiments, conducted over a 20 day period, were compared to thermodynamic modelling calculations of copper speciation in sulfidic waters. The tailings materials were observed to react rapidly with added sulfide, consuming 159 μmol HS⁻ g⁻¹ (dry wt) within a 24 h period. The consumption of sulfide was attributed to a two stage process involving the reduction of Fe-hydroxy phases by sulfide followed by reaction with available Fe²⁺ and Cu²⁺ resulting in the formation Fe- and Cu-sulfide phases. During incubation experiments, the dissolved copper concentrations in the absence of sulfide were approximately 0.31 μmol l⁻¹, whereas in the presence of sulfide (0.5–5 mM) concentrations were typically 0.24 μmol l⁻¹. The experiments did not indicate enhanced solubility owing to the formation of soluble copper sulfide species. The predictions (based on the most recent thermodynamic data for aqueous Cu-sulfide and Cu-polysulfide species) did not accurately explain the laboratory observations. Model predictions were greatly influenced by the assumptions made about the oxidation state of copper under anoxic conditions and the solid sulfide phase controlling copper solubility. The study emphasizes the limitations of modelling copper speciation in sulfidic waters and the need for laboratory or field verification of predictions.     

Phosphorus retention by phlogopite-rich mine tailings

Sewage water rich in P poses a threat to natural water systems. In households that are not connected to a sewer network, an easily maintained purification technique is needed to remove P from domestic waste waters. In the present study, the P retention properties of phlogopite-rich mine tailings were studied to determine whether the untapped tailings can be utilised in wastewater treatment for this purpose. On the basis of its chemical and mineralogical properties, this material, produced in the enrichment process of apatite ore in Siilinjärvi, Finland, can be assumed to act as a P sorbent. The P retention capacity and the P sorption mechanisms of phlogopite-rich tailings were studied with desorption–sorption isotherms and various chemical extractions. The impact of the artificial weathering of the material as well as the reaction time and particle size on P retention were also investigated. The fluctuating shape of the isotherm determined for the untreated material suggests the operation of several sorption mechanisms. The results imply that phlogopite-rich tailings retain P efficiently through specific sorption by amorphous Al and Fe oxides and possibly also by calcite present as an accessory mineral. Acidification of the material, extended reaction time and decrease in particle-size markedly increased the P retention.     

Sorption of lead by phlogopite-rich mine tailings

The Pb sorption capacity of apatite ore mine tailings and its potential to act as a remediation agent in a Pb polluted areas were investigated. The tailings, originating from the Siilinjärvi carbonatite complex in Finland, consist mainly of phlogopite and calcite accompanied by apatite residues. The ability of the tailings to retain Pb from an aqueous solution was investigated using an isotherm technique. Furthermore, in a 3-month incubation experiment, uncontaminated mineral soil was amended with untreated tailings and with tailings artificially weathered with acid to increase the quantity of Al and Fe (hydr)oxides. Tailings of two particle-sizes (∅ > 0.2 mm and ∅ < 0.2 mm) somewhat differing in their mineralogical composition were investigated as separate amendments. All tailings materials were added to the soil in two dosages (5 g and 10 g of tailings per 125 g of soil). Following incubation, tailings-induced changes in the Pb sorption capacity of the soil were investigated with the isotherm technique. Finally, to investigate the distribution of sorbed Pb among various chemical pools, the soil samples amended with tailings were contaminated with Pb and then subjected to sequential fractionation analysis. The results revealed efficient removal of Pb from an aqueous solution by the tailings, presumably through precipitation and surface complexation mechanisms. Amending the soil with the tailings increased the mass-based maximum Pb sorption capacity from 10.8 mg kg⁻¹ of the control soil to 14–20.5 mg kg⁻¹ for the untreated tailings and to 32.1–72.1 mg kg⁻¹ for the acid-treated material. The tailings transferred Pb from the exchangeable pool to the non-extracted one and thereby substantially decreased its bioavailability. The material with a particle diameter of less than 0.2 mm had a higher mass-based Pb sorption capacity than the large-sized material. The results suggest that the tailings may potentially serve as an immobilizing agent in polluted areas.     

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.     

吉林红旗岭镍矿区尾矿地球化学特征研究

文章通过对红旗岭矿区尾砂数据的分析研究,对矿产资源的再度利用提出合理有效的方案,为矿产资源的二次开发开辟新的道路.在红旗岭尾矿库进行尾矿取样研究分析,测试尾砂中的元素含量,分析尾砂中元素的分布规律,依据工业品位要求,以及尾矿含水率等数据初步估算红旗岭矿区尾矿镍金属储量;对镍高品位值地段分析以及尾砂抽稀试验,为红旗岭尾矿...     

Mercury speciation in tailings of the Idrija mercury mine

Five hundred years of mercury (Hg) mining activity in Idrija, Slovenia caused widespread Hg contamination. Besides Hg emissions from the ore smelter, tailings have been found to be the major source of river sediment contamination. In the present study, solid phase binding forms and the aqueous mobility of Hg have been investigated in tailings of the Idrija Hg mine by means of a pyrolysis technique and aqueous Hg speciation. Results show that Hg binding forms differ with the age of the tailings due to the processing of different ores with different roasting techniques. In older tailings, the predominant Hg species is cinnabar (HgS), due to incomplete roasting, whereas in tailings of the 20th century the amount of cinnabar in the material decreased due to a higher efficiency of the roasting process and the increasing use of ores bearing native Hg. In younger tailings, metallic Hg (Hg⁰) sorbed to mineral matrix components such as dolomite and Fe-oxyhydroxides became the predominant Hg binding form in addition to unbound Hg⁰ and traces of HgO. Leaching tests show that in younger tailings high amounts of soluble Hg exist in reactive form. In older tailings most of the soluble Hg occurs bound to soluble complexes. It might be assumed that in the long term, matrix-bound Hg⁰ could be bound to humic acids derived from soils covering the tailings. This means that, despite the lower total Hg concentrations found in the younger tailings, the long-term risk potential of its mobile matrix-bound Hg⁰ is higher than that of older tailings bearing mostly immobile cinnabar.     

Speciation and colloid transport of arsenic from mine tailings

In addition to affecting biogeochemical transformations, the speciation of As also influences its transport from tailings at inoperative mines. The speciation of As in tailings from the Sulfur Bank Mercury Mine site in Clear Lake, California (USA) (a hot-spring Hg deposit) and particles mobilized from these tailings have been examined during laboratory-column experiments. Solutions containing two common, plant-derived organic acids (oxalic and citric acid) were pumped at 13 pore volumes d⁻¹ through 25 by 500 mm columns of calcined Hg ore, analogous to the pedogenesis of tailings. Chemical analysis of column effluent indicated that all of the As mobilized was particulate (1.5 mg, or 6% of the total As in the column through 255 pore volumes of leaching). Arsenic speciation was evaluated using X-ray absorption spectroscopy (XAS), indicating the dominance of arsenate [As(V)] sorbed to poorly crystalline Fe(III)-(hydr)oxides and coprecipitated with jarosite [KFe₃(SO₄, AsO₄)₂(OH)₆] with no detectable primary or secondary minerals in the tailings and mobilized particles. Sequential chemical extractions (SCE) of <45 μm mine tailings fractions also suggest that As occurs adsorbed to Fe (hydr)oxides (35%) and coprecipitated within poorly crystalline phases (45%). In addition, SCEs suggest that As is associated with 1 N acid-soluble phases such as carbonate minerals (20%) and within crystalline Fe-(hydr)oxides (10%). The finding that As is transported from these mine tailings dominantly as As(V) adsorbed to Fe (hydr)oxides or coprecipitated within hydroxysulfates such as jarosite suggests that As release from soils and sediments contaminated with tailings will be controlled by either organic acid-promoted dissolution or reductive dissolution of host phases.     

Chemical characteristics and acid drainage assessment of mine tailings from Akara Gold mine in Thailand

Acid Mine Drainage (AMD) is a great concern in many abandoned mines because of its adverse effect on the environment. In mining processes, many kinds of wastes are produced. These wastes may become eventually sources of environmental degradation. The focus of this study is the geochemical characterization of the end-processed tailings generated by Akara Gold Mine, the biggest gold mine in Thailand. Tailing samples were systematically collected for analyses of chemical and mineralogical compositions. As a result, their quantitative chemical analyses are slightly different from place to place, but mineral components cannot be clearly differentiated. For instance, it may be assumed that the end-processed tailings, which were a mixture between high and low grade concentrates, would have similar mineral components. However, the little variation of chemical composition may be caused by the ore refining processes that are somehow varied in proportion to chemical additives, alkali cyanide and quick lime in particular. In addition, clay composition in ore-bearing layers may also influence alumina content of tailings, accordingly. Distribution of the tailings is not related to depth and distance of the tailing storage pond because the disposal has sped them over the pond during operation. Total heavy metals of the tailing samples were analyzed on the basis of the EPA 3052 method. Consequently, the most toxic elements (e.g., Co, Cu, Cd, Cr, Pb, Ni and Zn) were found falling within the standard of Thailand Soil Quality Standards for Habitat and Agriculture. Only Mn appears to have higher content than the standard. In addition, leaching tests proved that these tailings contain low metal concentrations. As a result, at pH 2, Mn can leach out exceeding the Thailand Surface Water Quality Standard for Agricultural (Mn <1 ppm) and the Thailand Industrial Effluent Standard (<5 ppm). Although leachate at pH 4 and neutral conditions contains lower Mn than the Industrial Effluent Standard it still exceeds the surface water quality standard. Interestingly, Pb can be leached out exceeding both standards (0.2 ppm for the industrial effluent standard and 0.05 ppm for the surface water quality standard). For Ni leaching, its concentration is lower than the Industrial Effluent Standard at all pH conditions but still exceeds the Surface Water Standard at pH 2 and 4. This information should be taken into consideration for further environmental monitoring. Acid generating potential of the tailings was estimated using acid–base accounting (ABA) and net acid generation (NAG) tests. The results of ABA and NAG tests show that the tailing samples contain a high amount of sulfur. However, they also contain high acid neutralization capacity. Consequently, these tailings may not have potential to generate acid drainage; in the other words, they can be classified as a non-acid forming (NAF) material. However, since these tailings contain some heavy metals (e.g., Ni, Mn and Pb) that are observed in leachates exceeding the standards at low pH, the AMD conditions may lead to heavy metal release. Therefore, prevention of oxidizing process and dissolution should be considered with great care. In addition, Mn and Pb can also be leached at neutral conditions. Barrier of air and water, clay layer for example, should be placed over the tailings pound before covering by topsoil for re-vegetation. Growing native grass is recommended for stabilization of the surface and reducing erosion rate. Monitoring of water quality should also be carried out annually.     

The concentration control of soluble copper in a mine tailings stream

Comparison of decreasing total copper content and increasing pH of an abandoned copper mine drainage stream to the stability fields of malachite, tenorite, and cupric hydroxide indicates that soluble copper is not lost by precipitation but by sorption on the stream sediments.     

Stabilization of arsenic-contaminated mine tailings using natural and calcined oyster shells

Natural oyster shells (NOS) and calcined oyster shells (COS) were used to immobilize arsenic (As) from contaminated mine tailings. In addition, a blend of Portland cement (PC)/cement kiln dust (CKD) was used as a stabilizing agent. The Korean Standard Test (KST) method (1 N HCl extraction) was used to evaluate the effectiveness of the treatment. The experimental results showed that COS effectively immobilized As in treated mine tailings. Specifically, an As concentration less than 1 mg L⁻¹ was obtained following COS treatment at 25 and 30 wt%. However, all the samples subjected to NOS treatments failed the Korean warning standard of 1.2 mg L⁻¹ after 28 days of curing. All of the COS-PC treatments were successful meeting the Korean warning standard after 7 days of curing. However, the PC-only treatment failed to meet the Korean warning standard. Similarly, the CKD-only treatment was failed to meet the Korean warning standard after 7 days of curing. However, the COS-CKD treatment showed that when the COS content was greater than 20 wt%, less than 1 mg L⁻¹ of As leachability was obtained. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) showed needle-like and torpedo-like Ca–As phases in the COS-treated samples suggesting that As was strongly associated with Ca and O. X-ray absorption near edge structure (XANES) analyses confirmed that As(V) was prevalent in the tailings and that there were no changes in As speciation following NOS or COS treatment.     

Modeling and predicting of drainage quality for sulfide mine tailings impoundments

Effluent from tailings impoundments of sulfide mine is an important environmental problem. The oxidation of sulfide minerals in tailings impoundments and consequent release of acid and contaminants, including heavy metals and arsenic, to tailings pore-water can last for decades to centuries. Pollution of water bodies including surface water and groundwater occurs when infiltration of precipitation is unhindered, bottom liners are absent and no drainage collection is installed. So there is a great need to develop reliable modeling techniques for characterizing geochemical interactions taking place within the tailings and predicting potential future environmental hazard which favor further prevention and remediation of the acidic mine drainage （AMD）. In this paper, a comprehensive dynamic model for tailings-water interaction was established on the basis of considering the coupling and feedback among many factors and processes such as sulfide oxidation, gangue dissolution, oxygen diffusion, water flow and mass transport,     

Arsenic mobilization from mine tailings in the presence of a biosurfactant

Batch experiments were conducted to investigate As mobilization from mine tailings in the presence of a biosurfactant (JBR425, mixed rhamnolipids) and to evaluate the feasibility of using biosurfactant in remediating As contaminated mine tailings/soils. Introduction of the biosurfactant increased As mobilization greatly. When the mass ratio was 10 mg biosurfactant/g mine tailings at pH 11, As mobilization by the biosurfactant was greatest after 24 h, with a corresponding concentration ratio (the ratio of As mobilization by the biosurfactant to that by distilled water at same adjusted pH, wt/wt) of 21.6. Selective sequential extraction indicated that As was easily mobilized from the weakly bound and relatively more mobile fractions by washing with the biosurfactant. A mobilization isotherm was developed to predict As mobilization from the mine tailings in the presence of biosurfactant. It was shown that biosurfactant sorption to the mine tailings is essential for As mobilization. Arsenic mobilization was found to be positively correlated with the mobilization of Fe and other metals (i.e., Cu, Pb and Zn), which might further enhance As mobilization by helping incorporate it into soluble complexes or micelles. Capillary electrophoresis analyses indicated that As redox or methylation reactions had insignificant effect on As mobilization. Biosurfactants might be used potentially to remove bulk As from mine tailings or contaminated soils under alkaline conditions.     

大厂矿区尾矿稀散资源分布规律与潜力评价研究

许多矿山开采和选矿排放的尾砂中蕴藏丰富的伴生金属资源,随着这类矿产资源价格上涨,尾砂伴生资源越来越受到人们的关注。本文对大厂矿集区茶山、车河、长坡和绿荫塘四个尾矿库中铟、镉、镓、锗等稀散元素分布特征与变化规律进行了调查,以期评价其潜在经济价值。调查结果表明,解放前修建的绿荫塘老尾矿库尾砂稀散元素铟、镉、锗均远超过工业品位,具有一定开采价值。70年代修建的长坡尾矿库铟、镉达到工业品位;90年代修建的车河、茶山尾砂库只有铟达到工业品位。四个尾矿库中稀散元素含量与尾砂来源和选矿水平密切相关,并发生次生淋滤富集作用。对环境有毒害的稀散元素镉尽管含量较高,但其主要赋存在闪锌矿中并没有释放到土壤环境中产生污染。这些调查研究结果将为政府部门和矿山企业决策提供依据。     

Mercury mobility in unsaturated gold mine tailings,Murray Brook mine,New Brunswick,Canada

Elevated concentrations of Hg are present (averaging 36 μg/g), mainly as cinnabar, in the Murray Brook Au deposit, located in northern New Brunswick, Canada. After the mined ore was subjected to CN leaching, the tailings were deposited in an unsaturated pile, and 10 a after mine closure an estimated 4.7 × 10³ kg of CN and 1.1 × 10⁴ kg of Hg remain in the pile. Elevated Hg concentrations have been measured in the groundwater (up to 11,500 μg/L) and surface water (up to 32 μg/L) down-gradient of the tailings. To investigate the controls on Hg mobility and leaching persistence, laboratory experiments were conducted using unsaturated columns filled with tailings. Within the first 0.2 pore volumes (PV) eluted, the concentrations of Hg and CN increased to peak concentrations of 12,900 μg Hg/L and 16 mg CN/L, respectively. In the subsequent 0.9 PV, concentrations decreased to approximately 1300 μg Hg/L and 2.8 mg CN/L. Thermodynamic calculations demonstrate that >99.8% of the mobilized Hg in the tailings pore water is in the form of Hg–CN complexes, indicating that Hg mobility to the surrounding aquatic environment is directly dependent on the rate of CN leaching. One-dimensional transport simulations suggest that leached CN can be partitioned into conservative (24%) and non-conservative (76%) fractions. Extrapolation of simulation results to the field scale suggests that CN, and by extension Hg, will continue to elute from the tailings for at least an additional 130 a.     

Geochemistry of arsenic in uranium mine mill tailings,Saskatchewan, Canada

The Rabbit Lake U mine in-pit tailings management facility (TMF) (425 m long×300 m wide×91 m deep) is located in northern Saskatchewan, Canada. The objectives of this study were to quantify the distribution of As phases in the tailings and evaluate the present-day geochemical controls on dissolved As. These objectives were met by analyzing pore fluid samples collected from the tailings body for dissolved constituents, measuring Eh, pH, and temperature of tailings core and pore fluid samples, conducting sequential extractions on solid samples, conducting geochemical modeling of pore fluid chemistry using available thermodynamic data, and by reviewing historical chemical mill process records. Dissolved As concentrations in 5 monitoring wells installed within the tailings body ranged from 9.6 to 71 mg/l. Pore fluid in the wells had a pH between 9.3 and 10.3 and Eh between +58 and +213 mV. Sequential extraction analyses of tailings samples showed that the composition of the solid phase As changed at a depth of 34 m. The As above 34 m was primarily associated with amorphous Fe and metal hydroxides while the As below 34 m was associated with Ca, likely as amorphous poorly ordered calcium arsenate precipitates. The change in the dominant As solid phases at this depth was attributed to the differences in the molar ratio of Fe to As in the mill tailings. Below 34 m it was <2 whereas above 34 m it was >4. The high Ca/As ratio during tailings neutralization would likely precipitate Ca₄(OH)₂(AsO₄)₂:4H₂O type Ca arsenate minerals. Geochemical modeling suggested that if the pore fluids were brought to equilibrium with this Ca-arsenate, the long-term dissolved As concentrations would range between 13 and 126 mg/l.     

尾矿中硫化物风化氧化模拟实验研究

为防治矿山尾矿造成环境污染，对方铅矿，闪锌矿，磁黄铁矿、黄铜矿，黄铁矿进行了风化氧化实验研究，结果显示，硫化物的氧化速率顺序为：方铅矿＞闪锌矿＞磁黄铁矿＞黄铜矿＞黄铁矿，侵蚀液pH值越低，硫化物氧化速率越大，有机物存在对硫化物氧化起缓冲和抑制作用。     

Optimization of sample preparation method of total sulphur measurement in mine tailings

A sample preparation method of total sulphur measurement of reactive mine tailings was optimized. The total sulphur was measured by inductively coupled plasma optical emission spectroscopy, and ultrasound technique was used for sample digestion. The optimization process was adopted by a combined approach of experimental design and response surface methodology. The digestion time, temperature and acid-oxidant combination (i.e. effect of H₂O₂ with a fixed amount of acid mixture) were investigated. A two-level and three-factor (2³) full factorial design of experiment was applied to identify the most significant factors, and a central composite design was used to optimize the digestion procedure. KZK-1, a sericite schist, was selected as the certified reference material. The optimum methodology at 95 % confidence level (P < 0.05) was identified to be 10 min of digestion at 77 °C, with a solution of 1 ml HNO₃:1 ml HCl:1.35 ml H₂O₂. This combination resulted in 100 % sulphur recovery. The investigated method was verified by X-ray diffraction analysis. The optimum digestion level was applied to a reactive mine tailings, which achieved satisfactory results with a percentage relative standard deviation < 3 %.