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.     

金属矿山场地人工土壤特征研究

根据金属矿山的露天采场、浸矿场、废石场、排土场、尾矿库等场地的地表物质特征,将金属矿山场地人工土壤分为基岩型土壤、废石型土壤、尾砂型土壤、尾泥型土壤、岩土型土壤、土岩型土壤、风化土壤和表土共八种类型,对每种类型人工土壤的地表物质特征、颗粒特征、污染特征和土地复垦特征进行系统分析,供从事矿山场地修复、土地复垦、生态恢复等专业的研究人员和管理人员参考。     

Laboratory Evaluation of the Use of Alkaline Phosphate Wastes for the Control of Acidic Mine Drainage

Pyrrhotite tailings at the abandoned Kettara mine site in Morocco are producing acid mine drainage (AMD). We investigated the use of alkaline phosphate waste (APW) rock from a nearby operating open-pit phosphate mine to control the AMD. The neutralizing potential of the APW, using the Paktunc method, was estimated between 500 and 680 kg CaCO₃/t. In laboratory column tests, the addition of 15 wt% APW to the coarse Kettara tailings produced leachates with significantly lower acidities and metal concentrations than unamended controls. The high calcium concentration in the flushed solutions indicates that calcite was responsible for the neutralization. Dolomite dissolution seems to be negligible and fluorapatite was stable under the testing conditions. It was also observed that when the treated solution comes in contact with unweathered Kettara coarse tailings, the pH becomes acidic, although the metal concentrations remain low.     

Integrating sulfidization with neutralization treatment for selective recovery of copper and zinc over iron from acid mine drainage

The most commonly used commercial process for acid mine drainage (AMD) treatment today is lime neutralization. However, it is accompanied by the treatment of produced metal hydroxide precipitate. Because of the decrease in the capacity of landfill disposal site and the increase in the price of base metals such as copper (Cu) in recent years, it is expected that not only to treat but also to recover these base metals from AMD. For the subsequent smelting process, the major issue is how to separate the Cu and zinc (Zn) over iron (Fe) from AMD as selectively as possible.In this work, we attempted to achieve this objective by modifying the present lime neutralization treatment process with sodium hydrosulfide (NaHS) sulfidization. An AMD sample generated from an abandoned copper mine located in east Japan was utilized in this study. At first, lime neutralization was applied to the AMD to find the precipitation behaviors of Cu, Zn, and Fe. Next, NaHS sulfidization as well as the integration with lime neutralization were conducted to separately precipitate Cu, Zn, and Fe from the AMD. Finally, two modified treatment approaches for selectively recovering Cu and Zn over Fe from the AMD were proposed. The results of consecutive experiments for the two proposed approaches showed that Cu, Zn, and Fe in the AMD were removed and separated into individual precipitates, and that the concentrations of each heavy metal in the final effluent were also able to meet the Japanese effluent standards.     

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.     

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.     

Kinetic Testing and Sorption Studies by Modified Weathering Cells to Characterize the Potential to Generate Contaminated Neutral Drainage

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.     

Mitigating the generation of acid mine drainage from copper sulfide tailings impoundments in perpetuity: A case study for an integrated management strategy

Acid mine drainage (AMD) is one of the most serious and pervasive challenges facing the minerals industry. Current philosophy in sulfide tailings management takes an end-of-pipe approach which is yet to be shown to be sufficient to prevent post-closure impacts from AMD and guarantee “walk-away” status. An improved, integrated approach to tailings management and AMD mitigation is proposed, whereby conventional tailings are separated with the use of flotation into a largely benign tailings stream and a sulfide-rich product. The key features of this conceptual approach are outlined and partly demonstrated for the case of porphyry-type copper sulfide tailings. The significance of this approach is that it provides a basis for the identification of opportunities for the development of new process designs incorporating waste management systems for mitigating AMD in a manner consistent with the principles of cleaner production and sustainable development.     

金川矿山废石与酸浸尾砂最优配合比的研究

为了找出金川矿山废石与酸浸尾砂的最优配合比,即二者混合后达到最大堆积密实度,应用两种骨料堆积密实度模型计算出理论最大值,同时使用试验测量的方法得到了最优组,最终结合两种结果得到:废石∶酸浸尾砂应控制在7∶3与8∶2之间为最优范围。这为矿山后续强度的要求与管道输送提供了保证,同时可为同类矿山的设计提供参考。     

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.     

Engineering Closure of an Open Pit Gold Operation in a Semi-Arid Climate

Along with material characteristics and geometry, the climate in which a mine is located can have a dramatic effect on the appropriate options for rehabilitation. The paper outlines the setting, mining, milling and waste disposal at Kidston Gold Mine's open pit operations in the semi-arid climate of North Queensland, Australia, before focusing on the engineering aspects of the rehabilitation of Kidston. The mine took a holistic and proactive approach to rehabilitation, and was prepared to demonstrate a number of innovative approaches, which are described in the paper. Engineering issues that had to be addressed included the geotechnical stability and deformation of waste rock dumps, including a 240 m high in-pit dump: the construction and performance monitoring of a “store and release” cover over potentially acid forming mineralised waste rock; erosion from the side slopes of the waste rock dumps; the in-pit co-disposal of waste rock and thickened tailings; the geotechnical stability of the tailings dam wall; the potential for erosion of bare tailings; the water balance of the tailings dam; direct revegetation of the tailings; and the pit hydrology. The rehabilitation of the mine represents an important benchmark in mine site rehabilitation best practice, from which lessons applicable worldwide can be shared.     

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.     

Biotreatment of As-containing simulated acid mine drainage using laboratory scale sulfate reducing upflow anaerobic sludge blanket reactor

Heavy metal contamination of water sources can occur from the discharge of acid mine drainage (AMD). This study assessed sulfidogenic treatment of As-, Fe-, Zn-, Ni- and Cu-containing AMD in an upflow anaerobic sludge blanket (UASB) reactor, operated for approximately 500 days. Sulfate reducing granules were successfully enriched with synthetic wastewater and sulfate concentration decreased from 2000 mg/L in the influent to 100–200 mg/L in the effluent. The pH increased from 3–4 to 6–8 as a result of biogenic alkalinity production. Arsenic removal was not detected in the absence of heavy metals, possibly due to the high dissolved sulfide concentration. In the presence of heavy metals, and at low dissolved sulfide concentrations, As removal efficiency increased to 98–100% likely due to the formation of arsenopyrite (FeAsS) or the adsorption of As on metal sulfide precipitates. Fe, Cu, Ni and Zn removal efficiencies approached 99% in the presence of dissolved sulfide. When hydrogen sulfide generation was insufficient to precipitate all of the metals, Fe was detected in the UASB effluent. The results showed that As-, Fe-, Zn-, Ni- and Cu-containing AMD can be effectively treated by sulfate reducing granules in UASB reactors.     

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.     

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.     

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.     

Start-up,adjustment and long-term performance of a two-stage bioremediation process,treating real acid mine drainage,coupled with biosynthesis of ZnS nanoparticles and ZnS/TiO2 nanocomposites

Acid mine drainage (AMD) generation is a widespread environmental problem in Europe, including Portugal. Previous experience has shown that a combined process consisting of an anaerobic sulphate-reducing bioreactor, following neutralization with calcite tailing, produces water complying with legal irrigation requirements from synthetic AMD. Aiming the treatment of real AMD a new bioreactor was inoculated with a SRB enrichment obtained from sludge from a local WWTP anaerobic lagoon. In the initial batch phase, sulphate supplementation was needed to achieve high sulphate-reducing bacteria counts before continuous feeding of AMD was started. The system quickly achieved good performance, proving it is easy to start-up. However, this time the neutralization step failed to keep bioreactor affluent pH higher than 5 for longer than three weeks. This was due to armouring of calcite by precipitates of various metals present in AMD. A new configuration, replacing a packed-bed column by a shallow contact basin, proved to be more robust, avoiding clogging, short-circuiting and providing long-term neutralization. The treated effluent, with excess of biologically generated sulphide, was successfully used to synthesize zinc sulphide nanoparticles, both in pure form and as a ZnS/TiO₂ nanocomposite, thus proving the feasibility of coupling an AMD bioremediation system with the synthesis of metal sulphide nanoparticles and nanocomposites.     

矿山废石全尾砂充填研究现状与发展趋势

矿产资源开发过程中产生的废石、尾砂和冶炼渣,等占我国工业固体废料排放量的85％左右.大量矿山固体废料堆放地表,易造成严重污染,诱发泥石流、尾矿溃坝事故.固体废料充填工艺是解决矿山废尾排放的最有效途径.本文介绍了低浓度分级尾砂充填、全尾砂高浓度充填、膏体似膏体充填、块石胶结充填工艺的研究与应用现状,并分析了矿山废石全尾砂充填技术的研究与发展方向.     

Kinetic Testing for Oxidation Acceleration and Passivation of Sulfides in Waste Rock Piles to Reduce Contaminated Neutral Drainage Generation Potential

Contaminated neutral drainage (CND), generated when metals are leached and enough neutralizing minerals are present to keep a near-neutral pH, is a growing environmental concern related to mine waste management. There is a need to find ways to reduce CND generation from mine waste to avoid perpetual effluent treatment. Nickel concentrations at the Lac Tio mine effluent have been sporadically higher than provincial environmental standards. In this project, three different treatment solutions were applied to Lac Tio mine waste rock samples in 70 kg waste rock columns in an attempt to reduce nickel CND generation potential by forcing sulfide oxidation and/or passivation. Following the applications, kinetic tests were used to determine any reduction in sulfide oxidation and nickel leaching. Hydrogen peroxide and sodium silicate were the main products tested, alone and in combination with a sodium bicarbonate buffer. Buffered hydrogen peroxide showed the best potential to reduce CND generation, with nickel release reduced from 1.4 × 10–3 mg/kg/day (untreated) to 4.0 × 10–5 mg/kg/day (treated) and near-neutral pH values. This passivation treatment also reduced the sulfur release rate by more than 50%. Optical and scanning electron microscopy observations supported the laboratory results. To conclude, this research project proposes a new way to reduce the CND generation potential of low sulfide waste rock.     

冶金矿山循环经济的研究

针对冶金矿山的废水、废石和尾矿进行了循环经济研究,为其建立循环经济模式提供了理论基础和技术保障。