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.     

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.     

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.     

Column leach study III: Effects of sampling location,sampling methods,and chemical abatement treatments on the dissolution of metals in gold-copper mine tailings

Metal dissolution from tailings collected at a gold-copper mine mill site was examined by researchers from the U.S. Bureau of Mines using column leaching procedures and on-site field monitoring wells. The 3-year laboratory study reviewed effects of column waste depths, dry cycles, waste sampling locations, and metal dissolution abatement techniques. Results of the laboratory testing indicated that the concentrations of metals in the leachate gradually decreased with each leaching and that metal release from unsaturated tailings was enhanced in most, but not all, samples. Sulphide-rich tailings produced leachates with a pH in the range of 2 to 4, sulphate concentrations as high as 40,000 mg/L, and copper concentrations in the range of 0.2 to 2,400 mg/L. The effects of abatement treatments using phosphate, lime, and sodium lauryl sulphate were also examined, but the treatments were demonstrated to be of only marginal value. The interaction between tailings and wood chips, and tailings and a compost-peat moss mixture was also studied.     

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。     

Column leach study 1: Heavy metal dissolution characteristics from selected copper mine tailings

Mill tailings collected from seven copper mine mill sites in the western United States were examined by researchers from the Bureau of Mines for metal dissolution properties using a column leaching procedure involving a formulated “western rain” leachant. Studies investigated effects of height of waste column, wet/dry cycle, and maximum leachability of waste tailings. Further studies on selected samples indicated that treatment of acid-producing tailings with chemical stabilizers such as phosphates and carbonates did not greatly affect mobilization of heavy metals leached from these samples. Increased metal mobilization from unsaturated columns was often associated with decreased leachate pH and increased sulfate production, but was not observed in all samples examined. Results from these and other studies suggest that the driving force for metal dissolution and/or acid formation in unsaturated mine tailings is the oxidation of metal sulfides by atmospheric oxygen. The maintenance of tailings at or near saturation or the exclusion of atmospheric oxygen appear to produce leachates of nearly constant to slowly decreasing metal concentrations with each subsequent leaching.     

Column leach study II: Heavy metal dissolution characteristics from selected lead-zinc mine tailings

Metal dissolution from tailings from six lead-zinc mine and milling sites in the western United States was examined by researchers from the Bureau of Mines using a column leaching procedure involving a formulated “western rain” leachant. This 2-year laboratory study included the effects of column waste depth, dry cycles with and without oxygen, and pore water evaporation. The results indicated that leachate metal concentrations gradually decreased with each leaching, but that the degree of enhanced metal mobilization from unsaturated tailings varied widely from waste to waste. Further studies on selected samples from this group of tailings demonstrated that the driving force behind enhanced metal dissolution is the oxidation of sulphide minerals by atmospheric oxygen during the evaporation of pore water from the columns of tailings. Leachates from water-saturated columns of these tailings gave pH values from 6.5 to 8.5; acid production and dissolved metal concentrations were enhanced by alternating wet and dry cycles. All studies to date indicate that maintaining tailings at or near saturation and/or excluding atmospheric oxygen produce leachates of nearly constant to slowly decreasing metal concentrations with each subsequent leaching.     

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。     

The application of wood ash as a reagent in acid mine drainage treatment

The paper deals with a possible utilisation of wood ash as a reagent in treating acid mine drainage (AMD) from opencast mining of brown coal. Wood ash samples were obtained having combusted deciduous and coniferous tree wood in a household furnace. The dominant mineral phases in wood ash are calcite, quartz, lime and periclase. The used AMD is characteristic of high contents of sulphates, iron, manganese, heavy metals and low pH. The AMD treatment process included dosing of wood ash to adjust pH values about 8.3 (a dose of 0.5 g l⁻¹) or calcium hydroxide (a dose of 0.2 g l⁻¹) for comparison. The reaction time was 20 min. Dosing of wood ash in AMD resulted in an increase of pH in solution from 3.5 to 8.3, which caused the removal of metal ions mainly by precipitation, co-precipitation and adsorption. Comparing the application of Ca(OH)₂ in AMD treatment, at an almost identical pH value the concentrations fell in both cases for Fe, Mn, As, Co, Cu, Ni, Zn, Mg, Al and Mo. Applying wood ash the drop was even more distinct in Mn, Zn and Mg. The results of sedimentation tests in an Imhoff cone confirm that the settling capacities of sludge using wood ash are significantly better than when using calcium hydroxide in acid mine drainage treatment.     

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.     

矿山排土场和尾矿库联合共建技术及其工程应用

尾矿库和排土场是矿山生产过程中的重大危险源,其安全性、经济性关系到矿山工程的成败,非常重要。在总结分析国内几种废石和尾矿联合处置经验的基础上,提出了一种排土场和尾矿库联合共建堆存的方法。为了解该方法的有效性及合理性,采用有限单元法和极限平衡法对该尾矿坝的应力变形和稳定性进行了分析。研究结果表明,排土场和尾矿库联合共建具有坝体稳定性好、安全性能高、经济效益好等优点,极端工况下坝体安全系数为1.21。研究成果对今后排土场和尾矿库共建相关的研究、设计和施工具有指导意义。     

清洁化无废矿山采矿工艺设计实践

在ENFI承担的云南驰宏公司深部资源矿山的开采设计中,采用了以全尾砂、水淬渣、废石和水泥为原料的膏体泵送充填采矿工艺,提出了将该矿建成尾砂不进库、废石不出坑的清洁化无废开采矿山的目标。     

司家营铁矿项目建设及采选系统介绍

介绍了河北钢铁集团矿业有限公司司家营铁矿自然概况、资源分布及项目规划建设情况,重点介绍了司家营铁矿一期工程采矿工艺、选矿工艺,供水、供电等公辅设施,以及废石填海造地、尾矿库易址采煤沉陷坑等情况。     

Use of activated silica sol as a flocculant in the treatment of acid mine drainage to promote sludge stability

The most common treatment for acidic drainage is lime neutralization. The process involves neutralization and precipitation of a metal hydroxide-gypsum sludge using a flocculant, generally Percol. In the short term, the sludge is stable, but in the long term, any tendency of pH to drop can re-dissolve metal hydroxides and contaminate the surrounding area and groundwater. The use of activated silica sol, an inorganic silicate polymer used in municipal water treatment, as a replacement to Percol is investigated to improve long term stability of sludge. Silica sol is an effective flocculant, has neutralization potential, and forms metal–silica bonds more resistant to pH variation than metal hydroxides. Various mine effluents and simulated solutions were treated with lime and silica sol or Percol to pH 9–10. Results show that settling characteristics with low dosages of silica sol and Percol are similar. Leachability tests showed that the stability of the sludge improved when silica sol was used for one cycle, and after 4 cycles results were similar to Percol. Activated silica sol, therefore, has the potential to increase sludge stability in a single stage lime treatment process.     

Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca²⁺. This resulted in increased removal of sulphate as CaSO₄·2H₂O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO₄·2H₂O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.     

有色金属矿山尾矿资源化利用研究进展

在有色金属开采利用过程中产生了大量尾矿,尾矿堆存不仅造成了有价资源浪费,还存在安全隐患和环境污染。有色金属尾矿具有成分复杂、共伴生金属多、资源利用率低的特点。绝大多数尾矿中含有硫化矿物及重金属离子,对人类健康和生态环境造成严重威胁。详述了有色金属尾矿的综合利用途径,主要包括尾矿再选回收、充填矿山采空区、生产建筑材料、用作土壤改良剂和微量元素肥料、复垦植被和处理废水。讨论了各综合利用途径的优势和局限性,总结了目前比较有效的利用途径,进一步阐述了有色金属尾矿在废水处理领域中的利用情况,可为有色金属尾矿的综合利用提供参考。     

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.     

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.