Development of a textural index for the prediction of acid rock drainage

The acid rock drainage index (ARDI) was developed to predict acid formation based on intact rock texture. Five textural parameters which have direct control on acid formation are evaluated. The ARDI forms part of the geochemistry-mineralogy-texture (GMT) approach to undertaking acid rock drainage (ARD) predictive tests. This staged-approach involves parallel use of geochemical, mineralogical and textural analyses. Sample screening is performed at stage-one, and a general classification given. Stage-two involves the use of routine geochemical tests in order to cross-check stage-one results, and also to quantify the acid forming/neutralising potential. Stage-three uses advanced geochemical tests and microanalytical tools to cross-check any ambiguous results from the previous stages, and for detailed characterisation of acid forming sulphide phases.Samples were obtained from two mine sites in Queensland, Australia, from which seventeen mesotextural groups were identified (A-Q). The ARDI identified mesotextural groups J (quartz-pyrite) and H (quartz-arsenopyrite-pyrite) as extremely acid forming. Routinely used geochemical classifications also identified these as the most acid forming groups. Four mesotextural groups (K-O) were classified as having acid neutralising capacity after full GMT classification. The remainder of mesotextural groups were classified as not acid forming. Mesotextural groups G (quartz-galena-sphalerite), H and J only require kinetic testing to resolve the lag-time to, and longevity of acid formation, and to measure the concentration of potentially deleterious elements released. The ARDI was not able to confidently discern between samples with the capacity to neutralise acid, and those which are not acid forming. Therefore, further refinement of the ARDI is required. However, in its current form the ARDI is suitable for mineral deposits with low-carbonate contents. This paper demonstrates its use as part of stage-one of the GMT approach at both operational and abandoned mine sites to screen and classify acid forming potential.     

Using permeable reactive barriers for the treatment of acid rock drainage

Acid mine drainage (AMD) is the most serious environmental problem facing the Canadian mineral industry today. It results from oxidation of sulphide minerals (e.g. pyrite or pyrrhotite) contained in mine waste or mine tailings and is characterized by acid effluents rich in heavy metals that are released into the environment. A new acid remediation technology is presented, by which metallurgical residues from the aluminium extraction industry are used to construct permeable reactive barriers (PRBs) to treat acid mine effluents. This technology is very promising for treating acid mine effluents in order to decrease their harmful environmental effects.     

Sequential precipitation of Cu and Fe using a three-stage sulfidogenic fluidized-bed reactor system

The exposure of sulfides, such as pyrite (FeS₂) to water and air leads to the formation of acidic metal and sulfate containing waters, generally referred to as acid mine drainage (AMD). Under anaerobic conditions and in the presence of a suitable electron and carbon source, sulfate-reducing bacteria (SRB) can reduce sulfate to hydrogen sulfide which can precipitate metals as low-solubility sulfides. In the present study, a three-stage fluidized-bed reactor (FBR) system was operated at 35 °C with ethanol as an electron and carbon source for SRB to sequentially precipitate Cu and Fe from synthetic AMD. The system consisted of two pre-settling tanks before a sulfidogenic FBR for the sequential precipitation of Cu and Fe with biogenic H₂S gas and HS⁻ containing effluent, respectively. Cu and Fe precipitation efficiencies were over 99% and sulfate and COD removals 60-90%. Biologically produced alkalinity increased the initial pH of the AMD from 3.0 to neutral values.     

Effect of carbon coatings on gold dissolution in the presence of sulphide and lead

The role of sulphide and lead in gold dissolution in a cyanide medium has been investigated for pure gold with elemental carbon coatings. Sulphide reduced the dissolution of gold with or without carbon coatings to almost the same extent and this effect became more pronounced at a higher sulphide concentration. The carbon coating slightly reduced the negative effect of sulphide on gold dissolution at around 0.2–5 mg S²⁻/L. The negative effect of sulphide on gold dissolution decreased with increasing cyanide concentration. Lead increased the dissolution of gold with or without carbon coatings at a concentration up to 2 mg Pb²⁺/L with the beneficial effect declining over this concentration range. The carbon coating reduced the beneficial effect of lead on gold dissolution. Gold dissolution was retarded at around 5 mg Pb²⁺/L. The positive effect of lead on gold dissolution became more prominent with increasing cyanide concentration.SEM analysis revealed much less erosion of gold occurring with the addition of sulphide. The gold surface showed highly corroded spots scattered across relatively less corroded areas during leaching with the addition of lead, while the gold surface was smooth after leaching with a carbon coating. An XPS investigation indicated the formation of AuS_x at the gold surface with the addition of sulphide. Metallic lead or AuPb alloys and lead hydroxide were detected at the gold surface after leaching with the addition of lead. The carbon coating hindered the diffusion of lead to the gold surface and hence reduced the beneficial effect of lead on gold dissolution.     

Effect of SDS on planctonic Acidithiobacillus thiooxidans and bioleaching of sand samples

The inhibition of bioleaching by sodium dodecyl sulphate (SDS), previously used in large scale percolators in Romania (Schippers et al., 2001), was shown for pure cultures of sulphur-oxidizing Acidithiobacillus thiooxidans DSM 622 or German sand samples.A decrease of 25-75% in planctonic cell number from an initial 10¹⁰A. thiooxidans cells, counted with a Thoma-chamber 30 min after exposure to SDS concentrations from 0.5 to 10 g/L, suggested a cell lysis. Additionally a release of nucleic acids was found.To apply these results in a more complex habitat, columns filled with aquifer material from an East German lignite mining area containing 1% pyrite were treated. Columns were washed once with 2 g/L SDS and afterwards with rainwater. Most-probable-number determinations of flow-through revealed no growth of iron- and sulphur-oxidizing microorganisms within 26 weeks, while up to 10⁶ cells per millilitre were determined in the control. Elution of sulphate dropped to 25%.     

The effect of ionic strength of plant water on valuable mineral and gangue recovery in a platinum bearing ore from the Merensky reef

As the restrictions on water usage become more prevalent throughout the world, mining operations are required to understand the impact that water recycling will have on them. Not only owing to operational needs, but also from an environmental stand point. As would be expected recycling is likely to lead to increased dissolved ions, increasing the ionic strength, which may impact plant performance. By conducting flotation tests under varying degrees of ionic strength of synthetic plant water it is possible to better understand the effect that water recycling could have on the recovery of a mining operation. The effect of such an increase in ionic strength is discussed.     

弓长岭井下铁矿中央区岩移规律及残矿回收安全性分析

通过对弓长岭井下铁矿中央区岩移活动规律进行分析,在保证安全的前提下,使岩移损失的残矿资源得到开发利用.     

Determination of the relative leaching kinetics of Cu, Rh, Ru and Ir during the sulphuric acid pressure leaching of leach residue derived from Ni-Cu converter matte enriched in platinum group metals

Hydrometallurgical process routes are typically used for separation of platinum group metals (PGMs) from base metals in Ni-Cu converter matte. Nickel dissolution is primarily achieved in the first stage leach (high pressure or atmospheric leaching, or a combination of the two), which is followed by second stage high pressure sulphuric acid/oxygen leaching to dissolve copper and the remaining nickel. PGMs are recovered from the leaching residue, and their dissolution must hence be limited. The leaching of base metals in the first stage has been characterised, but there is a limited understanding of the behaviour of metals, and more specifically PGMs, in the second stage pressure leach. This research presents the results of laboratory work performed to investigate the kinetics of leaching in the second stage pressure leach. The influence of key operating parameters such as the temperature, pressure, and initial acid concentration on PGM dissolution was investigated.     

Biosorption of heavy metals by algal communities in water streams affected by the acid mine drainage in the coal-mining region of Santa Catarina state, Brazil

In the coal-mining region of Santa Catarina state, Brazil, the water streams affected by acid mine drainage are inhabited by a few algae groups, including the genera Microspora, Eunotia, Euglena, Mougeotia, and Frustulia. The aim of this work was to study the accumulation of metals by these algal communities (periphyton) and their contribution to water decontamination. The results showed that the algal biomass contains high concentrations of metals, especially iron. The inorganic composition of the biomass correlated with the water chemistry.     

Diagnostic pre-treatment procedure for simultaneous cyanide leaching of gold and silver from a refractory gold/silver ore

This study investigates the optimization of simultaneous dissolution of gold and silver from a refractory gold ore through determination of pre-treatment stages. Based on the mineralogical studies (thin layer and polished section) and chemical analysis on the ore sample, a “diagnostic leaching” procedure was designed. Results from diagnostic leaching suggest that the most effective pre-treatment agents for gold and silver are ferric chloride and sulfuric acid media, respectively. Optimum conditions for the simultaneous dissolution of gold and silver were determined using a two factorial design technique. Pre-treatments with sulfuric acid and ferric chloride reagents increased the efficiency of the dissolution of gold from 54.7% to 82% and silver from 37.4% to 81.6%.     

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.     

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.     

Numerical modelling of transfer processes in a waste rock pile undergoing the temporal evolution of its heterogeneous material properties

Waste rock piles producing acid mine drainage (AMD) are complex and heterogeneous unsaturated systems in which multiple coupled processes are involved: multiphase flow of fluids (liquid and gas), heat transfer and mass transport. Numerical modelling is required to consider together these processes. Such modelling was used to evaluate the effects of closing options for a waste rock pile, including resloping and the placement of a cover, on AMD production from the South Dump of the Doyon Mine (Quebec, Canada). The thermal data recorded within the pile during 15?years show a steady reduction of temperature over the last 10?years. The objective of this study was to numerically reproduce the temporal evolution of thermal conditions to answer two key questions: (1) Can the evolution of material properties over time explain observed changes in thermal conditions? (2) If waste rock properties have evolved, is it effective to cover the pile to mitigate AMD production? Modelling showed that reducing the permeability of materials in the model can reproduce observed temperature changes over time, which cannot be achieved by reducing the reactivity of materials. Results also show that the evolution of hydraulic properties of the waste rock pile can have a direct effect on the global oxidation rate because of their control over the supply of atmospheric air and oxygen in the pile. When the production of AMD is already in decline, simulations also show that a simple remodelling of the surface may be sufficient to significantly decrease the oxidation rate and provide immediate environmental gains, without a cover. However, there may be other benefits related to cover placement that have not been evaluated by our study, especially in relation to the management of water runoff and leachate.     

Preparation of immobilized sulfate reducing bacteria (SRB) granules for effective bioremediation of acid mine drainage and bacterial community analysis

Heavy metal-resistant immobilized sulfate-reducing bacteria (SRB) granules were prepared to treat acid mine drainage (AMD) containing high concentrations of multiple heavy metal ions using an up-flow anaerobic packed-bed bioreactor. The bioreactor demonstrated satisfactory performance at influent pH 2.8 and high concentrations of metals (Fe 463 mg/L, Mn 79 mg/L, Cu 76 mg/L, Cd 58 mg/L and Zn 118 mg/L). The effluent pH ranged from 7.8 to 8.3 and the removal efficiencies of Fe, Cu, Zn and Cd were over 99.9% except for Mn (42.1–99.3%). The bacterial community in the bioreactor was diverse and included fermentative bacteria and SRB (Desulfovibrio desulfiricans) involved in sulfate reduction. The co-existing anaerobic fermentative bacteria (Clostridia bacterium, etc.) with the ability to use lactate as electron donor could explain the differences between actual lactate consumption and what would be expected based solely on sulfate reduction.     

Geochemistry and Mineralogy of Mill Tailings Impoundments from the Panasqueira Mine (Portugal): Implications for the Surrounding Environment

Selected geochemical results are presented from a study of the Panasqueira mine (Sn–W mineralization), which is one of the Portuguese test sites for the e-EcoRisk project (). These data permit a better understanding of the dynamics inherent to leaching, transport, and accumulation of some elements (mainly As, but also Cu, Pb, Zn, and Cd) in different sampling media and their environmental relevance. Stream sediment and water samples were found to be contaminated by the stored waste material in the tailing ponds; this effect could be observed for a considerable distance downstream.     

广西某铀矿山露天采场及废石场的退役治理

广西某铀矿山露天采场及废石场退役治理的项目包括露天采场,东、西部废石场,转运站,工业场地,建(构)筑物,运矿公路,以及设备器材等。介绍露天采场、废石堆环境贯穿辐射剂量率,222 Rn析出率,土壤中226 Ra比活度,以及个人剂量等的治理限值,详细论述了治理目标和各项目的治理方案。对治理后的效果作了评价。     

危岩高陡边坡破坏模式及处理技术的研究

通过对索风营水电站Dr2高陡边坡的地质结构及稳定状况进行分析，给出了边坡可能发生的三种破坏模式：倾倒破坏，座滑（剪切）破坏和滑移破坏。并结合边坡的这些破坏模式对边坡进行了处理，取得了良好的施工效果。     

Bioleaching of gold and copper from waste mobile phone PCBs by using a cyanogenic bacterium

Chromobacterium violaceum (C. violaceum), a cyanide generating bacterium has been used to leach out gold and copper from the waste mobile phone printed circuit boards (PCBs) containing ∼34.5% Cu and 0.025% Au in YP (yeast extract and polypeptone with glycine) medium. The bioleaching was carried out in an incubator shaker (150 rpm) at 30 °C and 15 g/L pulp density in the pH range 8-11. Dissolution of gold and copper increased from 7.78% (0.225 ppm) to 10.8% (0.46 ppm) and 4.9% (419 ppm) to 11.4% (879 ppm) in 8 days with increase in pH from 8 to 11 and 8 to 10 respectively. Supplementing oxygen with 0.004% (v/v) H₂O₂ increased the copper leaching to 24.6% (1743 ppm) at pH 10 in 8 days whereas improvement in gold leaching was insignificant with the recovery of 11.31% Au at pH 11.0. The waste PCBs can thus be recycled in environmental friendly manner.