Investigating the effect of acid stress on selected mesophilic micro-organisms implicated in bioleaching

During start-up of heap bioleaching, low grade ores may be treated with acid for agglomeration and to combat the acid neutralising capacity of the gangue minerals. This may stress the bioleaching inocula, particularly upon inoculation during ore agglomeration. Acid addition for agglomeration varies across operations, ore types and their neutralising capacity, with limited information published on recommended concentrations. The initial pH in the agglomeration mix is typically below pH 1.0 and may be as low as pH 0.5.This paper investigates the effect of acid stress in terms of initial acid concentration and duration of exposure in submerged culture on mesophilic micro-organisms typically implicated in mineral sulphide bioleaching and critical for heap colonisation at start-up. Following acid stress, cultures were returned to standard operating conditions in batch stirred slurry reactors and their performance assessed in terms of mineral leach rates, ferrous oxidation and the rate of microbial growth. Increasing acid stress resulted in an increase in the lag period before onset of microbial growth and iron oxidation due to decreased viable cell numbers, specific metabolic activity or both. Following adaptation, typical growth and ferrous iron oxidation rates were observed under low stress conditions while reduction in the rate and extent of microbial growth and ferrous iron oxidation persisted at extreme conditions. A reduction in yield (microbial cells produced per kg iron oxidised) was observed with increased acid concentration over comparative times. Microbial speciation analysis indicated a substantial decrease in the diversity of the microbial species surviving.     

Effects of dissolved oxygen and carbon dioxide under oxygen-rich conditions on the biooxidation process of refractory gold concentrate and the microbial community

Biomining microorganisms obtain energy from the oxidation of reduced sulfur and iron (II) by using dissolved oxygen (DO) as the electron acceptor. Carbon dioxide, the carbon source for biomining microorganisms, is essential for biooxidation. However, to date, no published reports exist regarding the effect of reactive oxygen species (ROS) and the CO₂ content in an oxygen-rich condition (when oxygen is sufficient) on the biooxidation process. In this study, a microbial community was used to oxidize refractory sulfide gold concentrate in a 1.5 L experimental stirred tank reactor. The effects of DO in a slurry and the CO₂ content in the intake gas on the biooxidation process, bacterial growth and microbial community were investigated. It was found that the biooxidation efficiency increased at first and then decreased as the DO level elevated, while the content of ROS significantly increased within the bacteria cells. Under an oxygen-rich condition, the biomass increased as the CO₂ content increased, while the biooxidation efficiency first increased and then decreased. These changes revealed that the oxidation activity of biomining microorganisms was inhibited by a high CO₂ content and that bacterial growth and energy utilization were decoupled. Leptospirillum ferriphilum-like bacteria and Sulfobacillus thermosulfidooxidans were the dominate strains in the experiment. As the DO increased, the relative proportion of L. ferriphilum-like bacteria in the bacteria community first increased and then decreased, while S. thermosulfidooxidans showed the opposite trend. With an increasing CO₂ content in the intake gas, the relative proportion of S. thermosulfidooxidans increased, while that of L. ferriphilum-like bacteria decreased.     

Bioleaching of chalcopyrite by Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans (A. ferrooxidans) was selected to experimentally study the effects of bacteria on the oxidation of chalcopyrite. The results indicated that A. ferrooxidans remarkably promoted the oxidation of chalcopyrite. The pH of the cell broth medium was observed to increase and then decrease during the bioleaching experiment. The number of suspended bacteria in the bio-oxidation process could be divided into three stages: the initial 4 days, in which the bacteria attached to the chalcopyrite surface and the number of suspended bacteria slightly decreased; day 5 to day 52, in which the suspended bacteria clearly increased with time and reached a maximum of 3.58 × 10⁷ cells/L on day 52; and day 53 to day 80, in which the number of suspended bacteria decreased. Other parameters such as redox potential (Eh) and iron ion concentrations increased with time. SEM micrographs showed that the cells were directly attached to the erosion pits on the smooth surfaces of the chalcopyrite. The erosion pits were similar to the bacteria in shape and size, and thus, the pits were likely products of dissolution by organic acids secreted by the attached cells. Compared to the unoxidized chalcopyrite, the elemental sulfur of the eroded chalcopyrite was clearly reduced, and the elemental oxygen was slightly increased. Moreover, a biofilm was present on the surfaces of the chalcopyrite particles. Therefore, the adherence of the cells to the mineral surfaces played a predominant role in altering the mineral appearance, which is important during the leaching of chalcopyrite.     

Effect of pulp density on planktonic and attached community dynamics during bioleaching of chalcopyrite by a moderately thermophilic microbial culture under uncontrolled conditions

An enriched and adapted moderately thermophilic culture showed good performance during bioleaching of chalcopyrite under uncontrolled conditions. The copper extractions were up to 85.0%, 77.3% and 56.3% at pulp densities of 10%, 15% and 20% (w/v) within 22 days, respectively. The real-time quantitative PCR was employed to monitor planktonic and attached community dynamics during bioleaching of chalcopyrite by the moderately thermophilic microbial culture. Only three species, including Acidithiobacillus caldus, Sulfobacillus acidophilus and Ferroplasma thermophilum, were detected during the whole bioleaching process. The results show that pulp density had significant effects on planktonic and attached microbial community dynamics. The succession of attached cells was different from community dynamics of their planktonic counterparts. F. thermophilum and A. caldus preferred to attach to mineral surface, especially at pulp densities of 15% and 20%.     

Effect of fluidized-bed carrier material on biological ferric sulphate generation

High biomass hold-up and high iron oxidation rates of a biological ferric sulphate generating fluidized-bed reactor (FBR) requires a carrier material with high specific surface area, high porosity and inertness. In this work, the effect of activated carbon (AC), diatomaceous earth (Celite) and Al₂O₃ (Compalox) carrier materials on the ferric sulphate generation in FBRs were studied. Compalox dissolved during the experiments and formed an unfluidizable aggregate, and was therefore rejected. The slow dissolution of Celite resulted in a light, fine-grained, layer on top of the fluidized bed that had to be changed into fresh Celite. AC resisted well the friction caused by fluidization. The iron oxidation in the continuous-flow FBRs became limited by oxygen supply already at loading rates of 2.5 kg Fe²⁺ m⁻³ h⁻¹. Iron oxidation rates of 27.6 and 25.7 kg m⁻³ h⁻¹ were obtained in batch FBR experiments with AC and Celite, respectively.Biomass accumulation of 6.2 × 10¹⁰, 2.4 × 10¹⁰ and 8.0 × 10⁹ cells per g of carrier was detected on Celite, AC and Compalox, respectively. The bacterial community structures on the carrier materials were revealed by Polymerase Chain Reaction and Denaturating Gradient Gel Electrophoresis (PCR-DGGE) followed by partial sequencing of the 16S rRNA gene. Two bacterial strains, Leptospirillum ferriphilum and a strain similar to a strain unofficially named “Ferrimicrobium acidiphilum”, were detected. Examination of the carrier material surfaces with scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) revealed that all carrier materials were covered with jarosite precipitates and that the bacteria were mainly retained on the jarosite covered areas. In conclusion, AC was the most promising carrier material for a large-scale biological ferric sulphate generating FBR based on its availability, durability and the achieved high iron oxidation rates.     

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.     

Quantification of growth and colonisation of low grade sulphidic ores by acidophilic chemoautotrophs using a novel experimental system

Microbial colonisation of low grade sulphidic ores and subsequent growth in heap bioleaching systems has not been quantified rigorously. In this study, an experimental system simulating the sub-processes that occur at the agglomerate scale was used to quantify the colonisation, growth and propagation of Acidithiobacillus ferrooxidans in an unsaturated bed of crushed and agglomerated low grade chalcopyrite ore. The relative distribution of the microorganisms in the flowing leachate solution (‘PLS’), the stagnant interstitial liquid and weakly and strongly attached to the mineral surfaces was determined at various time points during the leach. There was a distinct difference in population dynamics in each of these discrete phases. The microbial cells present in the interstitial phase dominated the microbial population in the ore bed. Particularly, the microbial concentration in the free flowing PLS was found to be a poor representation of the ore-associated microbial population. The calculated growth rate of At. ferrooxidans in the PLS was unreasonably high when modelled as a continuous system, indicating that change in cell concentration in the PLS was dominated by transfer from the mineral ore associated population. However, the transfer rate was not correlated directly to changes in either the interstitial or attached population sizes. Therefore, unless transfer rates can be accounted for, PLS population dynamics do not accurately represent those in the column as a whole. Growth rates of microorganisms in the interstitial, weakly mineral-attached and strongly mineral-attached phases better predicted growth of At. ferrooxidans on the whole ore system owing to the dominance of the microbial location in these phases.     

金精矿生物氧化过程中菌体吸附的重要性研究

利用改进装置探索了无菌以及嗜酸性氧化亚铁硫杆菌分别吸附于矿石表面、游离于培养基中等条件下,矿石氧化过程的基本工程学特征。结果表明,菌体吸附氧化时,溶液中的Eh值和矿石的氧化率高于游离菌氧化和无菌氧化;电镜观察可见矿石表面菌体吸附留下的蚀坑;A.ferrooxidans游离氧化时的矿石氧化率大于无菌氧化过程。六偏磷酸钠的加入能改变矿石表面的电性,提高菌体在矿石表面的吸附率。     

Geochemical and Mineralogical Characterization of a Pyritic Waste Pile at the Anjir Tangeh Coal Washing Plant, Zirab, Northern Iran

Coal washing at the Anjir Tangeh plant, in Zirab, northern Iran, has produced more than 1.5 Mt of coal wastes. These waste materials were geochemically and mineralogically characterised to guide development of an appropriate remediation scheme. Three vertical trenches up to 4 m deep were excavated from the coal waste pile surface and 25 solid samples were collected at 0.5 m intervals. The samples were analysed for total concentrations of 54 elements, paste pH, SO ₄ ^?2 , CO ₃ ^?2 , and HCO₃ ^?. The lowest pH values were measured at a depth of 0.3 m. The upper portion (1 m) of one profile was moderately oxidised, while oxidation in the other two profiles did not extend more than 0.8 and 0.5 m beneath the pile surface. The waste piles have low acid-producing potential (15–21.87 kg CaCO₃/t) and high values of acid-neutralizing potential (0.06–96.2 kg CaCO₃/t). Fe, Al, S, Na, Mn, Pb, Zn, Cd, and Ag increased with increasing depth, while Mo, Sr, Zr, and Ni decreased with increasing depth. The results show pyrite oxidation at depth and subsequent leaching of the oxidation products. Mn, Zn, Cu, Pb, Ag, and Cd are the most important contaminants of concern at this site.     

Substrate utilisation by Acidianus brierleyi,Metallosphaera hakonensis and Sulfolobus metallicus in mixed ferrous ion and tetrathionate growth media

When presented with ferrous ions and tetrathionate in growth media, individual archaeal species, Acidianus brierleyi, Metallosphaera hakonensis and Sulfolobus metallicus, exhibited different patterns of substrate utilisation and cell growth. Total cell numbers for A. brierleyi were about 60% of those for M. hakonensis and S. metallicus after complete substrate utilisation, and specific growth rates were affected by substrate concentration and cell growth history. High iron(II) concentrations inhibited S. metallicus growth. In relation to mixed microbial communities in high-temperature bioleaching reactors, the results are consistent with the hypothesis that specific growth rates of different species grown on different substrates strongly influence community structure. The combination of T-RFLP with substrate analysis and cell counts is a valuable analytical tool for the discrimination and semi-quantitative estimation of species in mixed cultures that can be used to gain better understanding of community structures and population dynamics in complex bioleaching systems.     

In situ investigation and visualisation of microbial attachment and colonisation in a heap bioleach environment: The novel biofilm reactor

In this paper, the development of a novel means of investigating the attachment and subsequent biofilm formation of mineral bioleaching micro-organisms to mineral surfaces in situ is described. The protocol was developed to investigate the interactions of micro-organisms with sulfide minerals and low-grade chalcopyrite ore under conditions resemblant of a bioheap environment. The method makes use of a biofilm reactor in which thin sections of mineral ore are mounted. The reactor is operated as a continuous flow-through system. Attachment of pure and mixed cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum is assessed. The technique allows for the investigation of microbial ecology with special regard to microbe–mineral attachment, site and mineral specific associations of micro-organisms and spatial organisation of microbial communities present through the use of fluorescent microscopy techniques. Preliminary fluorescent in situ hybridisation (FISH) analysis of the attachment of L. ferriphilum and A. ferrooxidans to massive chalcopyrite sections, as well as to low-grade chalcopyrite containing ore sections is presented. In the case of both low-grade and massive sulfide mineral samples, attachment of mixed micro-colonies was observed in regions where surface defects were prevalent. In low-grade samples, preferential attachment was observed in regions where sulfide minerals were present. The density of the attached micro-colonies increased with an increase in contacting time (from 20, 72 and 96 h) and was indicative of an actively growing mono-layered biofilm.     

Stability of As(V)-sorbed schwertmannite under porphyry copper mine conditions

Arsenic (As), a very poisonous inorganic pollutant is a major toxicant in tailings of porphyry copper deposits. Retention of As by Schwertmannite (a ferric-oxyhydroxysulfate mineral) has attracted much attention in recent years due to its strong binding affinity to toxic As species. The stability of As(V)-sorbed schwertmannite under copper mine waste conditions is not fully understood. The present study investigates the effect of Cu²⁺, Fe²⁺, pH, and ageing time on the stability of As(V)-sorbed schwertmannite (Sch-As). The results indicate that Cu²⁺ has no significant effect on the stability of Sch-As and that the As(V) incorporated in schwertmannite can retard or significantly inhibit Fe²⁺-catalyzed transformation of schwertmannite to goethite under acidic conditions (pH 3–4). The Sch-As aged at different pHs from 3 to 11 at 25 °C exhibits no mineralogical phase changes even after ageing for 120-days; however the concentration of As released from the solid phase appears to be strongly pH-dependent even after ageing for only 24 h. The release of As was negligible at pHs from 2 to 7, and there was considerable release of As at extremely acidic and alkaline conditions. This indicates that the release of As from Sch-As was controlled by environmental factors such as pH, Cu²⁺, and Fe²⁺ rather than time.     

Oxidation of isochemical FeS2 (marcasite–pyrite) by Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans

A research-grade mineral sample that contained marcasite and pyrite (FeS₂) was subjected to the oxidation by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Oxidation of FeS₂ by A. ferrooxidans produced acid, and the redox potential increased with sulfide dissolution and the oxidation of Fe²⁺. Jarosite was detected in solids from spent cultures. Preferential oxidation of either mineral was not consistently observed across all treatments. Neither iron sulfide was oxidized by A. thiooxidans.     

Investigation of the attachment of Thiobacillus ferrooxidans to mineral sulfides using scanning electron microscopy analysis

Thiobacillus ferrooxidans is a facultatively aerobic bacteria which catalyses the oxidation of inorganic substrates; in particular mineral sulfides.The mechanism(s) for the oxidation of mineral sulfides is not completely understood. The direct oxidation mechanism involves the attachment of bacteria to the mineral surface. Scanning Electron Microscopy (SEM) was used to investigate the surface erosion of three mineral sulfide samples by the attachment of Thiobacillus ferrooxidans (DSM 583). The mineral samples; Pyrite, a chalcopyrite concentrate ('termed Chalconc) and a sample containing arsenopyrite and loellingite (FeAs₂) (termed Arsenoconc) were all mounted in resin blocks and following the addition of T.ferrooxidans the particles exhibited varying degrees of surface erosion. Erosion patterns on the surface of minerals from the chalconc and arsenoconc samples appeared to follow the crystallographic structure of the mineral species. However, no apparent erosion patterns were observed on the pyrite sample. In addition, elemental sulfur was found deposited on the surfaces of each mineral sample. Chalopyrite in the Chalconc sample exhibited preferential erosion compared with the pyrite and indicated the electrochemical nobility of pyrite. In addition, during the oxidation of the Arsenoconc sample, loellingite was seen to be have been significantly more oxidised than the arsenopyrite.The observations from the SEM suggested a greater involvement of the indirect oxidation mechanism which utilises the oxidant ferric iron than direct bacterial attachment.     

Effect of physico-chemical and operating conditions on the growth and activity of Acidithiobacillus ferrooxidans in a simulated heap bioleaching environment

Recent understanding of microbial retention within heap bioleaching systems has highlighted the importance of quantifying microbial growth and activity in both the bulk flowing solution and in the ore-associated phases. Typically, industrial heap bioleaching operations report variations in process conditions such as inoculum preparation and concentration and elevated copper concentrations in the recycled irrigation solution. In this paper, a mini-column reactor system containing pre-constructed and agglomerated, low-grade ore samples representing grab samples from a larger heap, were used to investigate the effect of a selection of physico-chemical and operating conditions on microbial growth, colonisation and substrate utilisation kinetics, considering both the planktonic and sessile populations of Acidithiobacillus ferrooxidans. The factors studied included inoculum size, inoculum cultivation conditions, availability of ferrous iron in the bulk flowing solution and copper concentration in the bulk flowing solution. The microbial population in the interstitial phase, i.e. associated with, but not bound to, the ore, remained the most abundant within the heap under all physico-chemical conditions considered. A comparison of the tests with different inoculum sizes found that a smaller inoculum size resulted in an increased delay in microbial growth and ferrous iron oxidation, but similar apparent maximum specific growth rates and iron oxidation rates. In contrast to the microbial culture grown on pyrite, a delay in microbial activity was observed for the culture grown on ferrous iron. However, greater microbial cell densities were reached, in the interstitial and attached phases compared with the pyrite-grown culture. The introduction of 6 g L⁻¹ cupric ions into the feed solution containing 0.2 g L⁻¹ ferric iron resulted in decreased microbial growth rate in the interstitial phase but not in the attached phase. Where the pyrite culture was pre-exposed to cupric ion, the microbial growth rate in the interstitial and attached phases was significantly enhanced. Nevertheless, the presence of cupric ion in the irrigation solution resulted in a decrease in microbial ferrous iron oxidation rate, irrespective of pre-culture conditioning. This study emphasises the important role played by the stagnant interstitial phase during the colonisation of a low-grade heap, particularly under adverse conditions for microbial growth and activity. It also highlights the role of inoculum culture conditions on the potential trade-off between increased heap colonisation and increased lag periods in microbial activity during heap start-up.     

Two-step oxidation of a refractory gold-bearing sulfidic concentrate and the effect of organic nutrients on its biooxidation

Methods for improving the treatment efficiency of a refractory gold-bearing sulfidic concentrate are proposed. These methods consist of the oxidation of the concentrate during a two-step process, which includes a high temperature ferric leaching step and a subsequent biooxidation step, and the use of organic nutrients during the biooxidation step. The concentrate contained 34.7% pyrite and 7.9% arsenopyrite. The biooxidation of the concentrate (for a one-step process) was conducted at 45 °C in two bioreactors that were connected in series under continuous conditions. The pyrite and arsenopyrite oxidation levels after 240 h were 60.2% and 92.0%, and the gold recovery level by carbon-in-pulp cyanidation was 65.7%. The two-step process included the leaching of the concentrate by a biologically generated Fe³⁺-containing solution and the subsequent biooxidation of the leach residue. In this case, the pyrite and arsenopyrite oxidation levels after 240 h of biooxidation were 65.7% and 94.1%, and the gold recovery level was 71.7%.The effect of an organic nutrient (yeast extract) on biooxidation during the two-step process was studied. The pyrite and arsenopyrite oxidation levels after 240 h of biooxidation under mixotrophic conditions were 73.5% and 95.1%, and the gold recovery level was 77.9%. The effect of the organic nutrient on the microbial population was determined. Sulfobacillus thermosulfidooxidans and Acidithiobacillus caldus were the predominant microorganisms studied under both autotrophic and mixotrophic conditions. Archaeon Acidiplasma sp. MBA-1 was a minor component of the microbial community under autotrophic conditions but was one of the predominant microorganisms studied under mixotrophic conditions. These results suggest that the organic nutrient changed the composition and increased the activity of the microbial population.Thus, a two-step process with organic nutrients added during biooxidation may be considered as an effective strategy for treating refractory pyrite–arsenopyrite concentrates.     

日本矿产资源经略强国战略分析

日本得益于强大的全球矿产资源经略能力,作为世界上矿产资源最贫乏的国家之一,也是全球为数不多的矿产资源强国之一。系统研究日本的全球矿产资源经略战略,对于我国矿产资源战略调整具有较强的借鉴意义。研究发现:(1)日本形成了以JOGMEC为核心的系统高效的矿产资源管理机构,为其境外开发提供了强有力的保障;(2)日本分别就能源、战略性金属矿产制订了以有效保障本国资源安全为核心的目标明确、可操作性的矿产资源战略;(3)通过财团运作,日本在全球资源市场获取了规模可观的市场份额,打造了多艘国际矿业航母;(4)通过资本运作,与美国金融财团形成利益共同体,获得了进入西方世界的入场券,在世界矿业市场上具有重要地位。     

Visualization of initial attachment of bioleaching bacteria using combined atomic force and epifluorescence microscopy

Bioleaching is the dissolution of metal sulfides, such as pyrite and chalcopyrite, by bacterial oxidation processes. It has been found that attachment of leaching bacteria to the mineral surface enhances the metal sulfide dissolution. The interaction of mixed cultures with respect to initial attachment processes has not been investigated. Therefore in this study we quantified and visualized initial colonization on pyrite by pure and mixed cultures. Strains of the genera Acidithiobacillus and Leptospirillum were tested. Sessile and planktonic cells were visualized by fluorescence microscopy using DAPI, FISH, Syto? 9, lectin- and calcofluor-staining. Additionally, atomic force microscopy (AFM) was used for the investigations on cell morphology, spatial arrangement of cells on pyrite and mineral surface topography. The morphology of planktonic and sessile cells is different. Moreover, planktonic cells show differences in morphology due to the use of different substrata. By using different visualization methods it could be proven that colonization and biofilm formation on pyrite in mixed cultures is mostly dominated by Leptospirillum spp. Interactions of different species resulted in increased production of extracellular polymeric substances (EPS) or caused bacteria showing little tendency to attach when in monoculture to be incorporated into a biofilm by those that attach preferentially. Consequently, biofilm formation and metabolic diversity were furthered. One of the most important results is the finding that not all bioleaching bacteria are involved to the same extent in biofilm formation. Thus, further work shall allow us elucidate the important bacteria for biotechnological use, thereby leaching processes can be faster, more efficient and costs can be reduced.     

微生物技术在矿物选冶过程中的研究进展

由于矿物逐渐被开采,优质矿物资源日益短缺,“贫、细、杂” 矿物的选别回收亟待解决,人们对选矿技术的要求越来越高。一些特殊的微生物本身或者其代谢物可以将矿物中的离子溶解出来,或者改变矿物的表面性质,并且,与传统选矿药剂和浸出剂相比,微生物具有成本较低,对后续环境污染小的优势,因此,微生物浮选和微生物冶金技术得到了快速的发展。本文介绍了国内外对微生物浸出、氧化、分解和微生物在矿物表面的吸附、化学反应及微生物细胞表面化学等方面的研究进展。      

Molecular characterisation of the microbial community of a full-scale bioreactor treating Bayer liquor organic waste

Sodium oxalate is an organic impurity produced during the Bayer refining of bauxite as a result of the degradation of humic materials associated with the ore. Physico-chemical oxalate destruction techniques, such as combustion, are often expensive and often pose greater environmental risk than the storage of solid oxalate waste. Biodegradation is a more economical and environmentally friendly way to degrade oxalate, but the microbial communities responsible for oxalate degradation have remained largely uncharacterised. In the present work, the microbial community of a full-scale bioreactor achieving complete degradation of oxalate was characterised using 16S rRNA gene clone libraries followed by phylogenetic analysis of the cloned near full-length 16S rRNA sequences. The community was dominated by species belonging to the α-, β- and γ-Proteobacteria groups. Novel oxalate-degrading bacteria belonging to the genus Halomonas and the β-Proteobacteria group were isolated from the microbial community and are currently being characterised.