Valorization of acid mine drainage treatment sludge as remediation component to control acid generation from mine wastes,part 2: Field experimentation

The possibility of using acid mine drainage (AMD) treatment sludge as a cover component to control AMD generation from mine wastes was investigated through laboratory characterization and kinetic column testing (companion paper). The results showed that mixtures of sludge and waste rock, and sludge and tailings, may be integrated in an AMD prevention and control strategy at Doyon mine site (northwestern Quebec, Canada). In order to further investigate these scenarios in realistic climatic conditions, instrumented field test cells were installed on site to evaluate the performance of the mixtures to control AMD generation from tailings and waste rock under natural field conditions. The main findings from two seasons of monitoring are presented in the paper. The waste rock-sludge mixture placed over waste rock was able to reduce the generation of AMD from the waste rock, therefore confirming lab results, and was able to produce a neutral effluent with low concentrations of dissolved metals. The tailings-sludge mixture placed over tailings, with an evaporation protection layer, maintained a high volumetric water content and reduced sulphide oxidation from the tailings as exhibited by a neutral effluent. Monitoring of the field cells will continue to provide valuable information on the possible sludge valorization options.     

Geophysical Diagnosis of Diversion Channel Infiltration in a Uranium Waste Rock Pile

The Osamu Utsumi mine was the first to economically mine uranium ore in Brazil. During its operation, a river valley was buried for the construction of the waste rock pile. The original stream was diverted to the northwest side of the pile and has since flowed into a diversion channel devoid of basal waterproofing, while an acid mine drainage (AMD) source flows at the base of this waste rock pile. This research aims to evaluate the possible relationship between water infiltration of the diversion channel and the AMD resurgence at the base of the pile using electrical resistivity tomography and induced polarization. 2D inversion models and pseudo-3D maps allowed the recognition of low resistivity zones (<?100 Ω·m) with high chargeability areas (10 mV/V). Some of these low-resistivity areas have been interpreted as infiltration zones in segments of the diversion channel into the pile, and in one of them, the flow intercepts a high chargeability area interpreted as a sulfide-rich zone that is expected to contribute to AMD at the base of the pile. Understanding the hydrogeochemical process will help select effective actions to mitigate the generation of AMD at the mine, which is currently in the decommissioning phase.

     

Valorisation of acid mine drainage treatment sludge as remediation component to control acid generation from mine wastes,part 1: Material characterization and laboratory kinetic testing

In operating mines, acid mine drainage (AMD) is often treated using lime treatment. This process generates a significant amount of sludge that contains metal hydroxide precipitates, gypsum, and unreacted lime. The sludge may have interesting geotechnical and geochemical properties to be used as a part of covers (oxygen barriers) to prevent AMD generation from waste rocks and tailings. The main results of a project aiming to evaluate the use of sludge from the Doyon mine site (Canada) as a material in mine site rehabilitation are presented. The first part of the project involved detailed characterization of sludge, waste rock, and tailings samples. Then, laboratory column leaching tests were performed to evaluate the performance of the mixtures to control AMD produced by tailings and waste rocks. It was found that a sludge–waste rock mixture placed over waste rock reduces the metal loads in the column effluent, which remained acidic, as well as a mixture of sludge and tailings deposited over tailings can reduce metal content in effluents from tailings.     

Effect of loess for preventing contamination of acid mine drainage from coal waste

Acid mine drainage (AMD) that releases highly acidic, sulfate and metals-rich drainage is a serious environmental problem in coal mining areas in China. In order to study the effect of using loess for preventing AMD and controlling heavy metals contamination from coal waste, the column leaching tests were conducted. The results come from experiment data analyses show that the loess can effectively immobilize cadmium, copper, iron, lead and zinc in AMD from coal waste, increase pH value, and decrease Eh, EC, and SO ₄ ^2? concentrations of AMD from coal waste. The oxidation of sulfide in coal waste is prevented by addition of the loess, which favors the generation and adsorption of the alkalinity, the decrease of the population of Thiobacillus ferrooxidans, the heavy metals immobilization by precipitation of sulfide and carbonate through biological sulfate reduction inside the column, and the halt of the oxidation process of sulfide through iron coating on the surface of sulfide in coal waste. The loess can effectively prevent AMD and heavy metals contamination from coal waste in in-situ treatment systems.     

A Numerical Multi-Component Reactive Model for Pyrite Oxidation and Pollutant Transportation in a Pyritic,Carbonate-Rich Coal Waste Pile in Northern Iran

A one-dimensional numerical finite volume model is presented to simulate pyrite oxidation and reactive transportation of the oxidation products in a pyritic, carbonate-rich, coal waste pile. The proposed model incorporates the shrinking core concept for describing pyrite oxidation, pyrite surface area reduction, oxygen diffusion, and transport of the oxidation products through the waste pile. The model governing equations were solved using the PHOENICS computational fluid dynamics model. The accuracy of the model was verified with field data. Pyrite oxidation was more intense at shallower depths where oxygen decreased almost linearly from the pile surface to an approximate depth of 2 m. The lowest pH, 3.5, was predicted at a depth of 0.5 m. The waste pile has high neutralisation potential due to buffering by carbonate minerals. The maximum concentration of SO₄ ^2?, 31.6 mol/m³, was predicted at an approximate depth of 4 m and to remain constant throughout the rest of waste profile. Simulation of a scenario with a cap shows that iron and sulphate was removed from the upper parts of the pile; their peak concentrations shifted downward due to dilution. Oxygen source removal limited iron and sulphate production. These results will be useful for developing an appropriate remediation scheme.     

Effect of Dense Material Layers on Unsaturated Water Flow Inside a Large Waste Rock Pile: A Numerical Investigation

The construction method used to build waste rock piles influences their internal structure. Commonly used methods typically lead to the creation of compacted material layers within otherwise loose, coarse-grained waste rock. These dense layers, which typically have a finer grain size, affect the movement and distribution of water inside the pile. Long-term numerical simulations of unsaturated flow in a large pile were conducted to investigate the effect of such layers. The simulations led to various observations that provide a better understanding of the hydrogeological behaviour of the modeled pile (based on an actual case). The results show how water distribution and seepage within the pile are influenced by the presence of these layers. Other factors, including the magnitude of precipitation (or recharge) and pile size, were also investigated. This article presents the main results of the simulations, with some comments on their practical implications for pile design.     

Waste rock dumping optimisation using mixed integer programming (MIP)

Despite the fact that waste rock hauling and dumping comprises a large proportion of the cost of materials handling in an open pit mine, little detailed planning is devoted to optimising waste rock dumping. The lack of such planning could result in long-term exposure of potential acid forming (PAF) waste rock, causing acid mine drainage (AMD), which would incur ongoing collection and treatment costs. A waste rock dumping plan that not only minimises hauling costs, but also involves the encapsulation of PAF waste rock to minimise AMD, would benefit a mining operation economically and environmentally. In order to create such a plan, two new mixed integer programming (MIP) models are formulated and tested with a five-year mining schedule. Optimised dumping plans are automatically generated, which detail the dumping location for each mining block. A manual approach is also attempted, and comparison shows that the MIP models have obvious advantages in error prevention, faster solution time and cost saving, by up to 9.5%.     

淮南煤矸石山周边土壤中蚯蚓对重金属的富集特征

为研究蚯蚓对煤矸石周边土壤中重金属的富集作用,从不同堆积年限煤矸石山周边土壤采集蚯蚓,分析了蚯蚓中Zn,Pb,Cd,Ni,Cr,V,Cu与土壤中相应重金属浓度关系。结果表明：随煤矸石堆积时间的增加,蚯蚓体内Pb,Cd,Cu含量增加,Ni,Cr,V含量先增加再降低,而Zn含量变化规律不明显;蚯蚓体内Zn和Cd含量可较准确反映煤矸石周边土壤中重金属浓度,而蚯蚓体内Ni,Cr,V含量可在距离上显示与煤矸石山远近关系;蚯蚓只对Zn和Cd产生富集效应（富集系数大于1）,且对Cd富集作用最大。蚯蚓可作为煤矸石山周边土壤Cd和Zn的指示生物。     

矿山酸性废水抑酸技术研究现状与展望

矿山开采及闭矿产生的酸性矿井水、固废堆场产生的酸性淋滤液对矿山生态环境造成了严重的影响，系统梳理与总结相关研究成果对进一步推动酸性矿山废水的治理具有重要意义。本文综述了阻氧覆盖、表面钝化、杀菌处理和微生物抑酸技术的方法原理与应用，分析了不同方法的优缺点和适应性。分析结果表明，抑制矿山废水酸化的方法主要包括物理化学法和微生物法；物理化学抑酸技术能够一定程度上从源头抑制AMD的产生，但存在适用条件限制、二次污染风险、材料易失效等缺点；目前微生物抑酸主要是通过铁还原菌、硫酸盐还原菌、复合型厌氧生物膜等抑酸微生物抑制AMD的产生，但大多处于研发和试验阶段。本研究基于金属硫化矿物微生物催化氧化产酸机理，提出利用“微生物间拮抗与竞争作用”筛选高效抑酸微生物，探索矿山酸性废水抑酸处理新方法。     

Mine Closure of Pit Lakes as Terminal Sinks: Best Available Practice When Options are Limited?

In an arid climate, pit lake evaporation rates can exceed influx rates, causing the lake to function as a hydraulic terminal sink, with water levels in the pit remaining below surrounding groundwater levels. We present case studies from Western Australia for two mines nearing closure. At the first site, modelling indicates that waste dump covers for the potentially acid forming (PAF) material would not be successful over the long term (1,000 years or more). The second site is a case study where PAF management is limited by the current waste rock dump location and suitable cover materials. Pit lake water balance modelling using Goldsim software indicated that both pit lakes would function as hydraulic terminal sinks if not backfilled above long-term equilibrium water levels. Poor water quality will likely develop as evapoconcentration increases contaminant concentrations, providing a potential threat to local wildlife. Even so, the best current opportunity to limit the risk of contaminant migration and protect regional groundwater environments may be to limit backfill and intentionally produce a terminal sink pit lake.     

Electrical and Seismic Tomography Used to Image the Structure of a Tailings Pond at the Abandoned Kettara Mine, Morocco

The Kettara site (Morocco) is an abandoned pyrrhotite ore mine in a semi-arid environment. The site contains more than 3 million tons of mine waste that were deposited on the surface without concern for environmental consequences. Tailings were stockpiled in a pond, in a dyke, and in piles over an area of approximately 16?ha and have generated acid mine drainage (AMD) for more than 29?years. Geophysical methods have been used at the Kettara mine site to determine the nature of the geological substrate of the tailings pond, the internal structure of the mine wastes, and to investigate the pollution zones associated with sulphide waste dumps. Electrical resistivity tomography (ERT) and seismic refraction data were acquired, processed, and interpreted; the results from ERT and seismic refraction were complementary. A topographical survey of the tailings disposal area was also undertaken to estimate the volume of wastes and quantify the AMD process. Two-dimensional inverse models were used to investigate the geophysical data and indicated alteration zones at depth. It was determined that the material could be classified into three categories: tailings, with low resistivity (5?C15??? m) and low velocity (500?C1,800?m/s); altered, black shales, with intermediate resistivity (20?C60??? m) and velocity (2,000?C3,500?m/s), and; materials with high resistivity and velocity (>60????m and >4,000?m/s, respectively), including unaltered shales associated with quartzite seams. The low-resistivity zone generates AMD, which migrates downward through fractures and micro-fractures. The substrate is composed of broken and altered shale, which facilitates AMD infiltration.     

辽宁鞍本地区某铁矿废石碎磨特性研究

为解决废石堆存造成的一系列环境及安全问题,明确铁矿废石制备砂石骨料工艺流程,以辽宁鞍本地区某铁矿废石为例,在对其性质进行分析的基础上,开展了基于Bond球磨功指数试验与JK落重试验的碎磨特性参数研究。Bond球磨功指数试验结果显示,该铁矿废石Bond球磨功指数Wib为12.05 kWh/t。JK落重试验结果显示,该铁矿废石抗冲击粉碎模型为t10=71.25(1-e-0.52ECS) ,其中冲击粉碎参数A×b的值为37.05;磨蚀系数ta的值为0.17;相对密度为3.06。试验结果表明,该铁矿废石抗冲击粉碎能力属于硬范畴,抗磨蚀粉碎能力属于极硬范畴。结合上述试验结果,最终确定了该铁矿废石的生产设备与利用工艺。     

鄂尔多斯盆地西缘延安组陆相页岩油气选区评价关键参数值的确定

对鄂尔多斯盆地西缘侏罗系延安组低成熟页岩样品进行热模拟实验和岩石热解实验,分析岩石热成熟度(R_o)与生烃率及热解烃率(S_2)之间的变化规律,以及热解烃量与生烃量的关系。研究表明,陆相低成熟页岩气态烃产率随R_o的升高呈线性增加,液态烃产率随R_o的升高先增加后下降。产烃率随R_o的上升呈指数增加,热解烃率随R_o上升呈指数减少。热解烃率与产烃率之间具有良好的线性负相关,产烃率在热解烃率下降的过程中呈线性增加。陆相页岩生烃演化可分为3个阶段:游离烃释放及初期热降解的未成熟阶段、热降解-热裂解的成熟阶段和热裂解的过成熟阶段。根据生烃模拟中气态烃增长率和液态烃产率突增,以及第一个生烃高峰时所对应的R_o值,确定了鄂尔多斯盆地西缘侏罗系延安组陆相页岩油气有利区和目标区的关键参数R_o和TOC的下限。     

A Geotechnical Solution to Reduce Acid Mine Drainage Generation at Recreio Mine

Coal mining is frequently associated with acid mine drainage (AMD) generated by tailings and waste dumps containing sulphide minerals. A practical and economical alternative to minimise AMD generation is to avoid the contact between water and waste dumps using a compacted soil cover. This study evaluates the use of distinct raw materials as cover layers. The study area was an open pit coal mine in the south of Brazil. Geotechnical characterization, physical, chemical and mineralogical analyses were carried out on two different soils from this mine. Hydraulic conductivity tests were performed using Flexible-Wall Permeameter. The results obtained from the hydraulic conductivity tests for two compacted soils suggest their applicability as impermeable layers. Considering the operational aspects at the mine and the characteristics determined for the soils a new construction scheme for the dump site was suggested.     

The Effect of Particle Size on Mine Waste Sulfide Oxidation Rates and Conceptual Treatment Costs

Mine Water and the Environment - Acid and metalliferous drainage (AMD) oxidation reaction rates were determined using oxygen consumption rates in a high sulfur overburden rock from the Australian...     

Phosphate coating on pyrite to prevent acid mine drainage

Abstract

Acid mine drainage (AMD) is a serious environmental problem that preoccupies the Canadian Mineral Industry. Considerable amounts of money are spent every year in an effort to prevent or reduce the acid mine drainage phenomenon. AMD occurs when sulfide minerals (ex. pyrite) contained in rock are exposed to air and water and subsequently oxidize to produce low pH water. This acid effluent has the potential to mobilize any heavy metals contained in the rock. Coating the sulfide minerals with iron phosphate is a new promising technology to reduce AMD.Pyrite is treated with a solution containing H₂O₂, KH₂PO₄ and sodium acetate (NaAc). H₂O₂ oxidizes a small part of pyrite producing ferric iron (Fe³⁺) anions. These cations subsequently react with the PO₄ ^3? anions to produce FePO₄ that precipitates on the pyrite surface producing a passive coating. This iron phosphate coating can protect the grains of pyrite from oxidation. This paper presents a series of experiments that confirm that iron phosphate coating can considerably reduce AMD.     

Numerical Modelling of Flow and Capillary Barrier Effects in Unsaturated Waste Rock Piles

Abstract  Flow systems in unsaturated waste rock piles were simulated using a two-dimensional numerical model (HYDRUS). The conceptual models are based on homogeneous (unstructured) waste piles, and on structured piles that include either horizontal or inclined fine-grained layers within a coarser host material, forming a capillary barrier system. The approach considers fully transient conditions and uses observed climatic data from a mine site in northern Quebec, Canada. All physical properties of the porous media, including the water retention curves, were obtained from measured data. Different geometric configurations were tested to determine their effect on moisture distribution and water flow, which ultimately control the potential for acid rock drainage (ARD). The simulations begin with a relatively dry initial condition under hydrostatic equilibrium. After an initial transient period, the simulated internal moisture distribution became periodic with a regular pattern of seasonal fluctuations. The simulations suggest that flow can be controlled in such systems using inclined fine-grained layers that retain and divert moisture due to capillary barrier effects. With horizontal layers, the local flow regimes become unstable, causing vertical preferential flow zones to develop below the barriers wherever the local water pressure first exceeds the entry pressure of the underlying coarser material. In this scenario, ARD production can remain high since a large fraction of the internal pile is being flushed. A shallow downward slope in the layers forces drainage toward the outer boundary and maintains lower saturation in the centre of the pile, thus potentially reducing the amount and mobility of ARD. NSERC Polytechnique/UQAT Industrial Chair: Env and Mine Waste Mgmt     

Use of permeable reactive barriers to treat acid mine effluents

Acid mine drainage (AMD) is one of the most serious environmental problems facing the Canadian Mineral Industry. The AMD results from oxidation of sulphide minerals (e.g. pyrite or pyrrhotite) contained in mine waste or mine tailings. It is characterised by acid effluents rich in heavy metals, which are released into the environment. A new acid remediation technology is presented in this article by which alkaline metallurgical residues (red mud) from the aluminum extraction industry are used to construct permeable reactive barriers (PRB) to treat acid mine effluents. This article describes column tests performed to simulate a PRB constructed using Bauxsol?, a chemically and physically treated bauxite refinery residue, as a reactive material. The results from these experiments show that these PRB are efficient in neutralising pH and removing metals from acidic mine effluents.     

Acid Mine Drainage at the Abandoned Kettara Mine (Morocco): 2. Mine Waste Geochemical Behavior

Weathering and humidity cell tests were used to predict the potential for acid mine drainage (AMD) and to estimate the mineral reaction rates and depletion of fine and coarse tailings from the abandoned Kettara mine, Morocco. The geochemistry of the fine and coarse mine wastes was similar and, as expected by static tests, the wastes produced significant amounts of AMD. The sulfate production rate of both fine and coarse tailings was very high (2,000–8,000 and 2,400–560 mg SO₄/kg/week, respectively) during the first weeks of kinetics tests. After 9 weeks, sulfate release became low, ranging between 600 and 78 mg SO₄/kg/week for fine tailings and 500–120 mg SO₄/kg/week for coarse tailings. Effluent water samples had low pH (2.9–4.2) and elevated concentrations of acidity, sulfate, iron, copper, and zinc. Most or all of the dissolved K, Na, Al, Mg, and Si in the AMD result from the acidic dissolution of silicates (chlorite, talc, muscovite, and albite). Fine tailings produce much higher concentrations of acidity and sulfate than coarse tailings. However, due to greater transport of oxygen and water within the coarse waste, coarse tailings could be of greater environmental significance than fine tailings. The coarse waste continued to release acid after 378 days of leaching, whereas the fine tailings naturally passivates. These laboratory results agree with field observations; the upper profile of the coarse waste rock dam is highly oxidized (75 cm) whereas oxidation in the fine tailings does not extend more than 5–15 cm beneath the surface. A comparison between weathering and humidity cell tests indicated that the general trend of dissolution of metals was essentially similar for both methods. However, sulfate depletion rates were higher for the weathering cell tests. These tests indicate that the Kettara tailings piles and dam will continue to release acid for a long time unless remedial action is taken.     

Predicting Geochemical Behaviour of Waste Rock with Low Acid Generating Potential Using Laboratory Kinetic Tests

Techniques developed for acid mine drainage (AMD) prediction might not be suitable for contaminated neutral drainage (CND) generating sites. The Tio mine waste is known to generate Ni contaminated neutral drainage in some of the piles, but humidity cell tests fail to generate the Ni concentrations observed in the field. Weathering cell tests (small-scale humidity cell tests) were performed on fresh and weathered (produced 25 years ago) waste rock samples from the Tio mine containing various levels of hemo-ilmenite ore, and results were compared to humidity cell results on similar samples. The main constituents of the waste rock are the hemo-ilmenite ore and the plagioclase gangue; these minerals were purified from the waste rocks and the purified fractions were also submitted to weathering cell tests. The fresh waste rock samples were also submitted to sorption cells (modified weathering cells), which showed that the waste rocks have an important Ni sorption potential and that the sorbed phases are stable under weathering cell conditions. Even though the Ni concentrations obtained from the laboratory tests remain significantly lower than those obtained in field conditions (from field test pads and from waste rock piles), the results from the present study give important insight into the geochemical processes implicated in CND generation.