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192 8 Microbial Leaching of Metals, 1 Introduction trated form In gold mining operations biooxi. dation is used as a pretreatment process to,partly remove pyrite or arsenopyrite This. Future sustainable development requires process is also called biobeneficiation where. measures to reduce the dependence on non solid materials are refined and unwanted im. renewable raw materials and the demand for purities are removed GROUDEV 1999 STRAS. primary resources New resources for metals SER et al 1993 The terms biomining bio. must be developed with the aid of novel tech extraction or biorecovery are also applied. nologies in addition improvement of alredy to describe the mobilization of elements from. existing mining techniques can result in metal solid materials mediated by bacteria and fungi. recovery from sources that have not been of HOLMES 1991 MANDL et al 1996 RAWLINGS. economical interest until today Metal winning 1997 WOODS and RAWLINGS 1989 Biomin. processes based on the activity of microorgan ing concerns mostly applications of microbial. isms offer a possibility to obtain metals from metal mobilization processes in large scale. mineral resources not accessible by conven operations of mining industries for an eco. tional mining BOSECKER 1997 BRIERLEY nomical metal recovery. 1978 BRYNER et al 1954 TORMA and BAN The area of biohydrometallurgy covers. HEGYI 1984 Microbes such as bacteria and bioleaching or biomining processes ROSSI. fungi convert metal compounds into their 1990 Biohydrometallurgy represents an in. water soluble forms and are biocatalysts of terdisciplinary field where aspects of microbiol. these leaching processes Additionally apply ogy especially geomicrobiology geochemis. ing microbiological solubilization processes it try biotechnology hydrometallurgy mineralo. is possible to recover metal values from in gy geology chemical engineering and mining. dustrial wastes which can serve as secondary engineering are combined Hydrometallurgy. raw materials is defined as the treatment of metals and met. al containing materials by wet processes and,describes the extraction and recovery of met. als from their ores by processes in which aque, 2 Terminology ous solutions play a predominant role PARK. ER 1992 Rarely the term biogeotechnolo, In general bioleaching is a process de gy is also used instead of biohydrometallurgy. scribed as being the dissolution of metals FARBISZEWSKA et al 1994. from their mineral source by certain naturally,occurring microorganisms or the use of mi. croorganisms to transform elements so that,the elements can be extracted from a material. when water is filtered trough it ATLAS and 3 Historical Background. BARTHA 1997 PARKER 1992 Additionally, the term biooxidation is also used HANS One of the first reports where leaching. FORD and MILLER 1993 There are however might have been involved in the mobilization. some small differences by definition BRIER of metals is given by the Roman writer Gaius. LEY 1997 Usually bioleaching is referring Plinius Secundus 23 79 A D In his work on. to the conversion of solid metal values into natural sciences Plinius describes how copper. their water soluble forms using microorgan minerals are obtained using a leaching process. isms In the case of copper copper sulfide is K NIG 1989a b The translation reads ap. microbially oxidized to copper sulfate and proximately as follows Chrysocolla is a liquid. metal values are present in the aqueous phase in the before mentioned gold mines running. Remaining solids are discarded Biooxida from the gold vein In cold weather during the. tion describes the microbiological oxidation winter the sludge freezes to the hardness of. of host minerals which contain metal com pumice It is known from experience that the. pounds of interest As a result metal values re most wanted chrysocolla is formed in copper. main in the solid residues in a more concen mines the following in silver mines The liquid. 3 Historical Background 193, is also found in lead mines although it is of mi mine in Spain 10 years earlier SALKIELD. nor value In all these mines chrysocolla is also 1987 As a consequence to the ban of open air. artificially produced by slowly passing water ore roasting and its resulting atmospheric sul. through the mine during the winter until the fur emissions in 1878 in Portugal hydrometal. month of June subsequently the water is evap lurgical metal extraction has been taken into. orated in June and July It is clearly demon consideration in other countries more intense. strated that chrysocolla is nothing but a de ly In addition to the ban cost savings were an. composed vein other incentive for the development Heap. The German physician and mineralogist leaching techniques were assumed to reduce. Georgius Agricola 1494 1555 describes in transportation costs and to allow the employ. his work de re metallica also techniques for the ment of locomotives and wagons for other ser. recovery of copper that are based on the leach vices SALKIELD 1987 From 1900 on no open. ing of copper containing ores SCHIFFNER air roasting of low grade ore was conducted at. 1977 A woodcut from his book illustrates the Rio Tinto mines. the manual transport of metal containing Efforts to establish bioleaching at the Rio. leachates from mines and their evaporation in Tinto mines had been undertaken in the begin. the sunlight Fig 1 ning of the 1890s Heaps 10 m in height of. The Rio Tinto mines in south western Spain low grade ore containing 0 75 Cu were. are usually considered the cradle of biohydro built and left for one to three years for natu. metallurgy These mines have been exploited ral decomposition SALKIELD 1987 20 to. since pre Roman times for their copper gold 25 of the copper left in the heaps were re. and silver values However with respect to covered annually It was calculated that ap. commercial bioleaching operations on an in proximately 200 000 t of rough ore could be. dustrial scale biohydrometallurgical tech treated in 1896 Although industrial leaching. niques had been introduced to the Tharsis operations were conducted at the Rio Tinto. mines for several decades the contribution of,bacteria to metal solubilization was confirmed. only in 1961 when Thiobacillus ferrooxidans,was identified in the leachates. Early reports state that factors affecting bio,leaching operations were the height of the. heap particle size initial ore washing with,acid and temperature control to about 50 C. SALKIELD 1987 Another critical factor was,the supply of water for the leaching heaps Al. though usually acidic mine waters were used,for ore processing 4 billion liters of freshwater. were required annually SALKIELD 1987,Although metal leaching from mineral re. sources has a very long historical record EHR,LICH 1999 ROSSI 1990 and although the oxi. dation of reduced sulfur compounds and ele,mental sulfur resulting in the formation of sul. furic acid was demonstrated already in the,1880s WINOGRADSKY 1887 the oxidation of. metal sulfides was not described until 1922,when mobilization of zinc from zinc sulfide. Fig 1 Woodcut from the book de re metallica writ was investigated RUDOLFS 1922 RUDOLFS. ten by Georgius Agricola 1494 1555 illustrating and HELBRONNER 1922 It was found that the. the manual recovery of copper containing mine transformation of zinc sulfide to zinc sulfate. effluents which are collected in wooden basins and was microbially mediated Based on these re. concentrated in the sun sults the economic recovery of zinc from zinc. 194 8 Microbial Leaching of Metals, containing ores by biological methods was 4 2 Models of Leaching. proposed In 1947 Thiobacillus ferrooxidans, was identified as part of the microbial commu Mechanisms. nity found in acid mine drainage COLMER and, HINKLE 1947 A first patent was granted in Originally a model with two types of mech. 1958 ZIMMERLEY et al 1958 The patent de anisms which are involved in the microbial. scribes a cyclic process where a ferric sulfate mobilization of metals has been proposed. sulfuric acid lixiviant solution is used for metal EWART and HUGHES 1991 SILVERMAN and. extraction regenerated by aeration ferrous EHRLICH 1964 1 Microorganisms can oxi. iron oxidation by iron oxidizing organisms dize metal sulfides by a direct mechanism. and reused in a next leaching stage obtaining electrons directly from the reduced. minerals Cells have to be attached to the min,eral surface and a close contact is needed The. adsorption of cells to suspended mineral parti,cles takes place within minutes or hours This. has been demonstrated using either radioac, 4 Principles of Microbial tively labeled Thiobacillus ferrooxidans cells. Metal Leaching grown on NaH14CO3 or the oxidative capacity. of bacteria attached to the mineral surface,ESCOBAR et al 1996 Cells adhere selectively. 4 1 Leaching Mechanisms to mineral surfaces occupying preferentially ir. regularities of the surface structure EDWARDS, Mineralytic effects of bacteria and fungi on et al 1999 EWART and HUGHES 1991 In ad. minerals are based mainly on three principles dition a chemotactic behavior to copper iron. namely acidolysis complexolysis and redoxo or nickel ions has been demonstrated for Lep. lysis Microorganisms are able to mobilize met tospirillum ferrooxidans ACUNA et al 1992. als by 1 the formation of organic or inorgan Genes involved in the chemotaxis were also. ic acids protons 2 oxidation and reduction detected in Thiobacillus ferrooxidans and. reactions and 3 the excretion of complexing Thiobacillus thiooxidans ACUNA et al 1992. agents Sulfuric acid is the main inorganic acid 2 The oxidation of reduced metals through. found in leaching environments It is formed the indirect mechanism is mediated by ferric. by sulfur oxidizing microorganisms such as iron Fe3c originating from the microbial. thiobacilli A series of organic acids are formed oxidation of ferrous iron Fe2c compounds. by bacterial as well as fungal metabolism present in the minerals Ferric iron is an oxidiz. resulting in organic acidolysis complex and ing agent and can oxidize e g metal sulfides. chelate formation BERTHELIN 1983 A kinet and is chemically reduced to ferrous iron. ic model of the coordination chemistry of min which in turn can be microbially oxidized. eral solubilization has been developed which again EWART and HUGHES 1991 In this case. describes the dissolution of oxides by the pro iron has a role as electron carrier It was pro. tonation of the mineral surface as well as the posed that no direct physical contact is needed. surface concentration of suitable complex for the oxidation of iron. forming ligands such as oxalate malonate In many cases it was concluded that the di. citrate and succinate FURRER and STUMM rect mechanism dominates over the indi. 1986 Proton induced and ligand induced rect mostly due to the fact that direct was. mineral solubilization occurs simultaneously equated with direct physical contact This. in the presence of ligands under acidic condi domination has been observed for the oxida. tions tion of covellite or pyrite in studies employing. mesophilic T ferrooxidans and thermophilic,Acidianus brierleyi in bioreactors which con. sisted of chambers separated with dialysis,membranes to avoid physical contact LARS. SON et al 1993 POGLIANI et al 1990 How,4 Principles of Microbial Metal Leaching 195. ever the attachment of microorganisms on around cells of T ferrooxidans during growth. surfaces is not an indication per se for the exis on synthetic pyrite films ROJAS et al 1995. tence of a direct mechanism EDWARDS et al Footprints of organic films containing col. 1999 The term contact leaching has been loidal sulfur granules are left on the mineral. introduced to indicate the importance of bac surface upon detachment of the bacteria. terial attachment to mineral surfaces TRI From the existing data two indirect leach. BUTSCH 1999 ing mechanisms have been proposed whereas. The following equations describe the di no evidence for a direct enzymatically medi. rect and indirect mechanism for the oxida ated process has been found SAND et al. tion of pyrite MURR 1980 SAND et al 1999 1999 The mineral structure is the determining. factor for the prevailing type of leaching,direct mechanism In the thiosulfate mechanism. thiobacilli,thiosulfate is the main intermediate resulting. 2 FeS2c7 O2c2 H2O 2 FeSO4 from the oxidation of pyrite molybdenite or. c2 H2SO4 1 tungstenite Polysulfide and elemental sulfur. are the main intermediates in the polysulfide,indirect mechanism during the oxidation of galena. sphalerite chalcopyrite hauerite orpiment or,4 FeSO4cO2 T ferrooxidans L ferrooxidans. realgar The presence of iron III at the begin, c2 H2SO4 ning of mineral degradation is an important. 2 Fe2 SO4 3c2 H2O 2 prerequisite SAND et al 1999,chemical oxidation. The following equations summarize the oxi, FeS2cFe2 SO4 3 3 FeSO4 dation mechanisms SAND et al 1999. T thiooxidans,Thiosulfate mechanism found for FeS2 MoS2. 2 Sc3 O2cH2O 2 H2SO4 4 WS2, However the model of direct and indirect FeS2c6 Fe3cc3 H2O S2O2c. metal leaching is still under discussion Re c6 H c. cently this model has been revised and re, placed by another one which is not dependent S2O2P. c5 H2O 2 SO2P, on the differentiation between a direct and c10 H c. an indirect leaching mechanisms SAND et, al 1995 1999 All facts have been combined Polysulfide mechanism found for PbS CuFeS2. and a mechanism has been developed which is ZnS MnS2 As2S3 As3S4. characterized by the following features 1, cells have to be attached to the minerals and in 2 MSc2 Fe3cc2 Hc 2 M2ccH2Sn. physical contact with the surface 2 cells form c2 Fe2c 7. and excrete exopolymers 3 these exopoly, meric cell envelopes contain ferric iron com H2Snc2 Fe3c 0 25 S8c2 Fe2cc2 Hc 8. pounds which are complexed to glucuronic, acid residues These are part of the primary at 0 25 S8c3 O2c2 H2O 2 SO2P. tack mechanism 4 thiosulfate is formed as, intermediate during the oxidation of sulfur Several biomolecules are involved in the. compounds 5 sulfur or polythionate gran aerobic respiration on reduced sulfur and iron. ules are formed in the periplasmatic space or compounds It has been found that up to 5 of. in the cell envelope soluble proteins of T ferrooxidans is made of. Thiosulfate and traces of sulfite have been an acid stable blue copper protein called rus. found as intermediates during the oxidation of ticyanin BLAKE et al 1993 Additionally the. sulfur SHRIHARI et al 1993 Sulfur granules iron II respiratory system contains a puta. colloidal sulfur have been identified as ener tive green copper protein two types of cyto. gy reserves in the exopolymeric capsule chrome c one or more types of cytochrome a. 196 8 Microbial Leaching of Metals, a porin and an iron II sulfate chelate BLAKE was autoclaved to obtain a sterile leaching so. et al 1993 The acid stability of rusticyanin lution without enzymatic activities and to eval. suggests that it is located in the periplasmic uate the leaching ability of acid formed 4. space Figure 2 shows a scheme of the model Leaching by fresh medium Fresh non inocul. which combines the electron transport se ated and sterile medium was added to the fly. quence proposed earlier with concepts stem ash suspension and used as control 5 Chem. ming from the debate on direct indirect ical leaching due to the preparation of the ash. leaching mechanisms BLAKE and SHUTE suspension acidification to pH 5 4 Certain. 1994 BLAKE et al 1993 HAZRA et al 1992 elements such as e g Cd or Zn might be chem. SAND et al 1995 ically mobilized already during acidification. Some details of the metal mobilization MWI fly ash contains reduced copper spe. mechanism the importance of the presence cies chalcocite Cu2S or cuprite Cu2O. and attachment of microorganisms and their whereas zinc and others are present in their. active contribution have been demonstrated fully oxidized forms BROMBACHER et al. for the leaching of fly ash from municipal 1998 Therefore copper release from fly ash is. waste incineration MWI BROMBACHER et directly affected and enhanced by T ferrooxi. al 1998 Generally several mechanisms of dans whereas Zn as well as Al Cd Cr and Ni. metal mobilization can be distinguished 1 are released primarily due to the acidic envi. Contact leaching effect on the release of met ronment Acidification of the fly ash pulp. als Stock cultures of Thiobacillus ferrooxidans chemical mobilization led already to consid. and Thiobacillus thiooxidans were added to erable extraction yields for Cd Ni and Zn and. ash suspensions and cells were in direct con could slightly be increased using non inoculat. tact with the fly ash Growth of thiobacilli ed sterile medium as lixiviant Fig 3 By com. might be stimulated by increased energy avail paring leached amounts of copper by filtered. ability from oxidation of reduced solid parti cell free spent medium with autoclaved sterile. cles 2 Metal solubilization by metabolically spent medium it was concluded that signifi. active enzymatic compounds in the absence cant amounts of copper were mobilized in. of bacterial cells Stock cultures were filtered contrast to other elements by metabolic. to obtain the cell free spent medium This me products of T ferrooxidans Leaching with cell. dium was used for leaching 3 Metal solubil free spent medium indicating a solubilizing. ization by non enzymatic extracellular meta mechanism due to extracellular components. bolic products Cell free spent medium see 2 was significantly more effective than a leach. Fig 2 Schematic mechanistic bio,leaching model after HAZRA et. al 1992 SAND et al 1995 1999,SCHIPPERS et al 1996 RAWLINGS. 1999 C cytoplasm CM cell,membrane PS periplasmatic. space OM outer membrane,EP exopolymers Cyt cyto,chrome RC rusticyanin. MeS metal sulfide,4 Principles of Microbial Metal Leaching 197. Fig 3 Solubilized metals from fly ash,originating from municipal waste incinera. tion in suspensions of 40 g LP1 in percent,of the metal amount present with different. lixiviants within 8 d All samples were,incubated in triplicate The release of me. tals due to acidification of the fly ash pulp,is indicated as chemical mobilization see. text for explanation, ing with autoclaved spent medium where ex ing in g LP1 NH4 2SO4 3 0 K2HPO4 0 5. creted enzymes had been inactivated It is MgSO4 7 H2O 0 5 KCl 1 0 Ca NO3 2. known that several components involved in 4 H2O 0 01 FeSO4 7 H2O 44 22 and 1 mL. the electron transport chain of Thiobacillus 10 N sulfuric acid SILVERMAN and LUNDGREN. rusticyanin cytochromes iron sulfur pro 1959 Cells are harvested diluted and added. teins are located in the periplasmic space to pyrite suspensions with a pulp density of. BLAKE and SHUTE 1994 SAND et al 1995 20 g LP1 Total soluble iron as well as sulfate. and might therefore also be present in the cell formed during oxidation is periodically deter. free spent medium catalyzing oxidation of re mined. duced metal compounds Metal bioleaching in acidic environments. In many leaching environments conditions is influenced by a series of different factors. especially iron II and iron III concentra Tab 1 Physicochemical as well as microbio. tions vary with the duration of the leaching logical factors of the leaching environment are. This makes it difficult to assess the importance affecting rates and efficiencies In addition. and the effect of the presence of bacteria Us properties of the solids to be leached are of. ing an experimental setup to maintain con major importance ACEVEDO and GENTINA. stant concentrations of ferrous and ferric iron 1989 BRIERLEY 1978 DAS et al 1999 MURR. it was possible to show that in the presence of 1980 As examples pulp density pH and par. T ferrooxidans rates of pyrite or zinc sulfide ticle size were identified as major factors for. leaching are increased HOLMES et al 1999 pyrite bioleaching by Sulfolobus acidocalda. FOWLER and CRUNDWELL 1999 FOWLER et al rius LINDSTROM et al 1993 Optimal condi. 1999 tions were 60 g LP1 1 5 and 20 m respec,tively The influence of different parameters. such as activities of the bacteria itself source, 4 3 Factors Influencing Bioleaching energy mineralogical composition pulp den. sity temperature and particle size was studied, Standard test methods have been developed for the oxidation of sphalerite by T ferrooxi. to determine leaching rates of iron from dans BALLESTER et al 1989 Best zinc dis. pyrite mediated by Thiobacillus ferrooxidans solution was obtained at low pulp densities. ASTM 1991 An active culture of T ferro 50 g LP1 small particle sizes and tempera. oxidans is grown in a defined medium contain tures of approximately 35 C. 198 8 Microbial Leaching of Metals, Tab 1 Factors and Parameters Influencing Bacterial Mineral Oxidation and Metal Mobilization. Factor Parameter, Physicochemical parameters of a bioleaching environment temperature. redox potential,water potential,oxygen content and availability. carbon dioxide content,mass transfer,nutrient availability. iron III concentration,surface tension,presence of inhibitors. Microbiological parameters of a bioleaching environment microbial diversity. population density,microbial activities,spatial distribution of microorganisms. metal tolerance,adaptation abilities of microorganisms. Properties of the minerals to be leached mineral type. mineral composition,mineral dissemination,grain size. surface area,hydrophobicity,galvanic interactions,formation of secondary minerals. Processing leaching mode in situ heap dump or tank. pulp density,stirring rate in case of tank leaching opera. heap geometry in case of heap leaching, Metal oxidation mediated by acidophilic mi enced iron II oxidation by T ferrooxidans. croorganisms can be inhibited by a variety of with uranium and thorium showing higher tox. factors such as e g organic compounds sur icities than copper and nickel LEDUC et al. face active agents solvents or specific metals 1997 Silver mercury ruthenium and molyb. The presence of organic compounds yeast ex denum reduced the growth of Sulfolobus. tract inhibited pyrite oxidation of T ferrooxi grown on a copper concentrate MIER et al. dans BACELAR NICOLAU and JOHNSON 1999 1996 Industrial biocides such as tetra n bu. Certain metals present in bioleaching environ tyltin isothiazolinones N dimethyl Nb phe. ments can inhibit microbial growth therefore nyl Nb fluorodichloro methylthio sulfamide. reducing leaching efficiencies For instance ar or 2 2b dihydroxy 5 5b dichlorophenylmethane. senic added to cultures inhibited Sulfolobus dichlorophen reduced the leaching of man. acidocaldarius grown on pyrite and T ferro ganese oxides by heterotrophic microorgan. oxidans grown on arsenopyrite HALLBERG et isms ARIEF and MADGWICK 1992 Biocides. al 1996 LAN et al 1994 Additions of copper were externally added as selective inhibitors to. nickel uranium or thorium adversely influ suppress unwanted organisms and to improve. 4 Principles of Microbial Metal Leaching 199, manganese leaching efficiencies At low con It has been demonstrated recently that the. centrations of 5 mg LP1 however mangan addition of small amounts of amino acids cys. ese mobilization was increased by 20 BOUS teine in this case resulted in an increased. SIOS and MADGWICK 1994 pyrite corrosion by T ferrooxidans as com. Also gaseous compounds can show inhibito pared to controls without additions ROJAS. ry effects on metal leaching Aqueous phase CHAPANA and TRIBUTSCH 2000 It is suggest. carbon dioxide at concentration 10 mg LP1 ed that the microorganisms may profit from. was inhibiting growth of T ferrooxidans on weakening and break up of chemical bonds. pyrite arsenopyrite pyrrothite ore NAGPAL mediated by the formation of the cysteine py. et al 1993 Optimal concentrations of carbon rite complex This might also be the case under. dioxide were found to be in the range of 3 to natural conditions by the excretion of cys. 7 mg LP1 There are reports on the stimulation teine containing metabolites An inexpensive. of bacterial leaching and the increase of leach alternative to increase metal recovery from. ing rates by supplementing leaching fluids with ore heaps by the addition of sulfur containing. carbon dioxide ACEVEDO et al 1998 BRIER amino acids such as cysteine has been suggest. LEY 1978 TORMA et al 1972 Concentrations ed TRIBUTSCH and ROJAS CHAPANA 1999. of 4 v v carbon dioxide in the inlet gas of a Other metabolites excreted by Thiobacillus. fermenter showed maximum growth rates of might also enhance metal leaching efficiencies. T ferrooxidans maximum iron II copper Wetting agents such as mixtures of phospho. and arsenic oxidation ACEVEDO et al 1998 lipids and neutral lipids are formed by Thioba. Pulp densities of 20 g LP1 delayed the onset cillus thiooxidans BEEBE and UMBREIT 1971. of bioleaching of pyrite derived from coal As a consequence growth of T thiooxidans on. BALDI et al 1992 Increasing pulp densities sulfur particles is supported by the excretion. from 30 to 100 g LP1 decreased rates of pyrite of metabolites acting as biosurfactants which. oxidation in Sulfolobus cultures NGUBANE facilitate the oxidation of elemental sulfur It. and BAECKER 1990 For fungi such as Asper was also hypothesized that Thiobacillus caldus. gillus niger optimal pulp densities for maxi is stimulating the growth of heterotrophic or. mum metal leaching efficiencies were found to ganisms in leaching environments by the ex. be in the range of 30 to 40 g LP1 BOSSHARD cretion of organic compounds and is support. et al 1996 Quartz particles at pulp densities ing the solubilization of solid sulfur by the for. of 80 g LP1 almost completely inhibited the mation of surface active agents DOPSON and. oxidation of covellite by T ferrooxidans espe LINDSTROM 1999 Metal solubilization might. cially in the absence of iron II CURUTCHET also be facilitated by microbial metabolites ex. et al 1990 creted by organisms other than Thiobacillus. During bioleaching processes coprecipita which are part of microbial consortia found in. tion of metals with mineral phases such as ja bioleaching operations Microbial surfactants. rosites can reduce leaching efficiencies HI which show large differences in their chemical. ROYOSHI et al 1999 In addition the precipita nature are formed by a wide variety of micro. tion of compounds present in the leachates on organisms In the presence of biosurfactants. the minerals to be leached can make the solid which lead to changes in the surface tension. material inaccessible for bacterial leaching metal desorption from solids might be en. Organic solvents such as flotation or solvent hanced resulting in an increased metal mobil. extraction agents which are added for the ity in porous media It has been suggested that. downstream processing of leachates from bio this metabolic potential can be practically used. leaching might also lead to inhibition prob in the bioremediation of metal contaminated. lems ACEVEDO and GENTINA 1989 Isopro soils MILLER 1995 However there is some. pylxanthate and LIX 984 used as flotation evidence that surface active compounds as. agent and solvent extraction agent respective well as organic solvents are inhibitory to bio. ly prevented the oxidation of pyrite and chal leaching reactions and prevent bacterial at. copyrite by T ferrooxidans HUERTA et al tachment MURR 1980 The external addition. 1995 This fact is of special importance when of Tween reduced the oxidation of chalcopyr. spent leaching liquors are recycled for a reuse ite by T ferrooxidans TORMA et al 1976 It. 200 8 Microbial Leaching of Metals, was concluded that the need of the microor 5 Microbial Diversity in. ganisms for surfactants is met by their own for, mation In contrast it was reported that the ad Bioleaching Environments. dition of Tween 80 increased the attachment of,T ferrooxidans on molybdenite and the oxida. tion of molybdenum in the absence of iron II A variety of microorganisms is found in. PISTACCIO et al 1994 leaching environments and has been isolated. from leachates and acidic mine drainage Al,though environmental conditions are usually. 4 4 Bacterial Attachment on described from an anthropocentric view as. Mineral Surfaces being extreme and harsh due to pH values as. low as P3 6 NORDSTROM et al 2000 and high, It is known that the formation of extracellu metal concentrations as high as 200 g LP1. lar polymeric substances plays an important NORDSTROM et al 2000 these systems can. role in the attachment of thiobacilli to mineral show high levels of microbial biodiversity in. surfaces such as e g sulfur pyrite or covellite cluding bacteria fungi and algae LOPEZ AR. Extraction or loss of these exopolymers pre CHILLA et al 1993 It has long been known. vent cell attachment resulting in decreased that bacteria Thiobacillus sp yeasts Rho. metal leaching efficiencies ESCOBAR et al dotorula sp Trichosporon sp flagellates Eu. 1997 GEHRKE et al 1998 POGLIANI and DO trepia sp amoebes and protozoa are part of. NATI 1992 It was concluded that a direct con the microbial biocenosis found in acidic waters. tact between bacterial cells and solid surfaces of a copper mine EHRLICH 1963 Recent de. is needed and represents an important prere tailed investigations based on molecular meth. quisite for an effective metal mobilization ods such as DNA DNA hybridization 16S. OSTROWSKI and SKLODOWSKA 1993 Interac rRNA sequencing RCR based methods with. tions between microorganisms and the miner primers derived from rRNA sequencing fluor. al surface occur on two levels BARRETT et al escence in situ hybridization FISH or im. 1993 The first level is a physical sorption be munological techniques revealed that micro. cause of electrostatic forces Due to the low bial bioleaching communities are composed of. pH usually occurring in leaching environ a vast variety of microorganisms resulting in. ments microbial cell envelopes are positively complex microbial interactions and nutrient. charged leading to electrostatic interactions flows such as synergism mutualism competi. with the mineral phase The second level is tion predation AMARO et al 1992 DE. characterized by chemical sorption where WULF DURAND et al 1997 EHRLICH 1997. chemical bonds between cells and minerals JOHNSON 1998 EDWARDS et al 1999 Selected. might be established e g disulfide bridges organisms of these communities are given in. In addition extracellular metabolites are Table 2 The composition of these communities. formed and excreted during this phase in the is usually subjected to seasonal fluctuations. near vicinity of the attachment site EWART and may vary between different mining loca. and HUGHES 1991 Low molecular weight tions EDWARDS et al 1999 GROUDEV and. metabolites excreted by sulfur oxidizers in GROUDEVA 1993 In addition organisms are. clude acids originating from the TCA cycle not homogeneously distributed over the whole. amino acids or ethanolamine whereas com leaching environment CERD et al 1993. pounds with relatively high molecular weights The organism studied most is Thiobacillus. include lipids and phospholipids BARRETT et ferrooxidans Although this is the best known. al 1993 In the presence of elemental sulfur organism from acidic habitats one may not. sulfur oxidizing microorganisms from sewage conclude that this organism is dominant in. sludge form a filamentous matrix similar to a these ecosystems It has been found that under. bacterial glycocalyx suggesting the relative im specific environmental conditions Leptospiril. portance of these extracellular substances in lum sp is even more abundant than T ferro. the colonization of solid particles BLAIS et al oxidans suggesting an important ecological. 1994 role in the microbial community structure of, 5 Microbial Diversity in Bioleaching Environments 201. bioleaching habitats SAND 1992 SCHRENK et extraction from mine tailings is more efficient. al 1998 Thiobacilli are members of the divi using thermophilic instead of mesophilic or. sion of Proteobacteria close to the junction ganisms extremely thermophilic microorgan. between the and subdivision whereas isms show a higher sensitivity to copper and to. leptospirilli are placed in the Nitrospira divi high pulp densities in agitated systems limit. sion RAWLINGS 1999 Genetic studies re ing therefore some practical applications. vealed that the role of T ferrooxidans in leach DUARTE et al 1993 NORRIS and OWEN. ing operations has probably been overestimat 1993, ed Excellent reviews on the genetics of Thio Although environmental conditions in. bacilli and leptospirilli have been published leaching operations favor the growth and de. recently RAWLINGS 1999 RAWLINGS and KU velopment of mesophilic moderately thermo. SANO 1994 philic and extremely thermophilic microbial. Thiobacillus ferrooxidans belongs to the communities metal leaching at low tempera. group of chemolithotrophic organisms The or tures has also been observed Copper and. ganism is rod shaped usually single or in nickel were leached from pyritic ore samples. pairs non spore forming gram negative mo in significant amounts at 4 C AHONEN and. tile and single pole flagellated HORAN 1999 TUOVINEN 1992 However leaching rates. KELLY and HARRISON 1984 LEDUC and FER were lower by a factor of 30 to 50 as compared. RONI 1994 MURR 1980 As carbon source to experiments conducted at 37 C T ferrooxi. carbon dioxide is utilized Ferrous iron is oxi dans recovered from mine waters was able to. dized Ammonium is used as nitrogen source grow at 2 C with a generation time of approx. Although T ferrooxidans has been character imately 250 h suggesting a psychrotrophic na. ized as being a strictly aerobic organism it can ture of the organism FERRONI et al 1986. also grow on elemental sulfur or metal sulfides Bacterial iron mobilization has also been ob. under anoxic conditions using ferric iron as served at 0 C in ore samples obtained from. electron acceptor DONATI et al 1997 PRONK Greenland LANGDAHL and INGVORSEN 1997. et al 1992 Solubilization rates at these low temperatures. The genus Thiobacillus represents a versa were still approximately 25 to 30 of the max. tile group of chemolithoautotrophic organ imum values observed at 21 C All these find. isms Optimum pH values for growth vary ings may have a potential for practical applica. between 2 and 8 Fig 4 It has been demon tions in geographical areas where field opera. strated that sulfur oxidizing bacteria are ca tions are subjected to low temperature regimes. pable of reducing the pH of highly alkaline fly A series of heterotrophic microorganisms. ash suspensions amended with elemental sul bacteria fungi is also part of microbial bio. fur from approximately 9 to 0 5 KREBS et al leaching communities Tab 2 This group of. 1999 Fig 5 It is likely that thiobacilli con organisms uses extracellular metabolites and. tribute to increasing acidification of leaching cell lysates from autotrophs as carbon source. ecosystems in a successive mode In the initial resulting in the removal of an inhibitory excess. stages the growth of less acidophilic strains of carbon and stimulating therefore growth. e g Thiobacillus thioparus is stimulated and iron oxidation of thiobacilli BUTLER and. whereas during prolonged leaching the pH de KEMPTON 1987 FOURNIER et al 1998 In ad. creases gradually supporting growth of more dition several heterotrophs can also con. acidophilic strains This has already been ob tribute to metal solubilization by the excretion. served in metal leaching from wastewater sew of organic acids such as citrate gluconate oxa. age sludge BLAIS et al 1993 late or succinate,A variety of thermophilic microorganisms. especially Sulfolobus species has been en,riched and isolated from bioleaching environ. ments BRIERLEY 1990 NEMATI et al 2000,NORRIS and OWEN 1993 Temperature optima. for growth and metal leaching were in the,range between 65 and 85 C Although copper. Tab 2 Microbial Diversity of Acidic Bioleaching Environments and Acidic Mine Drainage Selection of Microorganisms known to Mediate Metal Bio. leaching Reactions from Ores and Minerals or known to be Part of the Microbial Consortia Found in Bioleaching Habitats. Domain Organism Nutrition Type Main pH Range pH Temperature Reference. 8 Microbial Leaching of Metals,Leaching Opt C, Archaea Acidianus ambivalens facult heterotrophic sulfuric acid JOHNSON 1998. Acidianus brierleyi facult heterotrophic sulfuric acid acidophilic 1 5 3 0 45 75 MU OZ et al 1995. Acidianus infernus facult heterotrophic sulfuric acid JOHNSON 1998. Ferroplasma acidiphilum chemolithoautotrophic ferric iron 1 3 2 2 1 7 15 45 GOLYSHINA et al 2000. Metallosphaera prunae chemolithoautotrophic ferric iron JOHNSON 1998. sulfuric acid, Metallosphaera sedula chemolithoautotrophic ferric iron acidophilic extr JOHNSON 1998. sulfuric acid thermophilic,Picrophilus oshimae JOHNSON 1998. Picrophilus torridus JOHNSON 1998, Sulfolobus acidocaldarius chemolithoautotrophic ferric iron 0 9 5 8 2 0 3 0 55 85 AMARO et al 1992. sulfuric acid, Sulfolobus ambivalens chemolithoautotrophic ferric iron extr ROSSI 1990. sulfuric acid thermophilic, Sulfolobus brierleyi chemolithoautotrophic ferric iron extr BRIERLEY 1977. sulfuric acid thermophilic, Sulfolobus hakonensis chemolithoautotrophic ROSSI 1990. Sulfolobus metallicus chemolithoautotrophic ROSSI 1990. Sulfolobus solfataricus chemolithoautotrophic ferric iron extr JOHNSON 1998. sulfuric acid thermophilic, Sulfolobus thermosulfidooxidans chemolithoautotrophic ferric iron extr JOHNSON 1998. sulfuric acid thermophilic, Sulfolobus yellowstonii chemolithoautotrophic ferric iron extr JOHNSON 1998. sulfuric acid thermophilic, Sulfurococcus mirabilis mixotrophic ferric iron acidophilic extr BARRETT et al 1993. sulfuric acid thermophilic JOHNSON 1998, Sulfurococcus yellowstonii mixotrophic ferric iron JOHNSON 1998. sulfuric acid,Thermoplasma acidophilum JOHNSON 1998. Thermoplasma volcanicum JOHNSON 1998, Bacteria Acetobacter methanolicus heterotrophic gluconate acidophilic GLOMBITZA et al 1988. Acidimicrobium ferrooxidans JOHNSON 1998,EDWARDS et al 1999. Tab 2 Continued, Domain Organism Nutrition Type Main pH Range pH Temperature Reference. Leaching Opt C,Acidiphilium angustum EDWARDS et al 1999. Acidiphilium cryptum heterotrophic organic acids 2 0 6 0 mesophilic GOEBEL and. STACKEBRANDT 1994, Acidiphilium symbioticum heterotrophic organic acids 3 0 mesophilic BHATTACHARYYA et al. Acidobacterium capsulatum chemoorganotrophic 3 0 6 0 mesophilic KISHIMOTO et al 1991. Acidocella sp JOHNSON 1998,Acidomonas methanolica heterotrophic JOHNSON 1998. Arthrobacter sp heterotrophic BOSECKER 1993, Aureobacterium liquifaciens heterotrophic EDWARDS et al 1999. Bacillus sp heterotrophic CERD et al 1993,GROUDEV and. 5 Microbial Diversity in Bioleaching Environments,GROUDEVA 1993. Bacillus coagulans heterotrophic 5 4 6 0 22 BAGLIN et al 1992. Bacillus licheniformis heterotrophic 37 MOHANTY and MISHRA. Bacillus megaterium heterotrophic citrate KREBS et al 1997. Bacillus polymyxa heterotrophic, Chromobacterium violaceum heterotrophic cyanide LAWSON et al 1999. Comamonas testosteroni heterotrophic EDWARDS et al 1999. Crenothrix sp facult autotrophic ferric iron 5 5 6 2 18 24 ROSSI 1990. Enterobacter agglomerans heterotrophic 5 4 6 0 22 BAGLIN et al 1992. Enterobacter cloacae heterotrophic 22 BAGLIN et al 1992. Gallionella sp autotrophic ferric iron 6 4 6 8 6 25 ROSSI 1990. Kingella kingae EDWARDS et al 1999, Lactobacillus acidophilus heterotrophic 37 ACHARYA et al 1998. Leptospirillum ferrooxidans chemolithoautotrophic ferric iron 2 5 3 0 30 SAND 1992. RAWLINGS et al 1999, Leptospirillum thermoferrooxidans chemolithoautotrophic ferric iron 1 7 1 9 45 50 BARRETT et al 1993. Leptothrix discophora facult autotrophic ferric iron 5 8 7 8 5 40 EDWARDS et al 1999. sulfuric acid, Metallogenium sp heterotrophic ferric iron 3 5 6 8 4 1 ROSSI 1990. Ochrobacterium anthropi heterotrophic EDWARDS et al 1999. Propionibacterium acnes heterotrophic 37 ACHARYA et al 1998. Pseudomonas cepacia heterotrophic 5 4 6 0 22 BAGLIN et al 1992. Tab 2 Continued, Domain Organism Nutrition Type Main pH Range pH Temperature Reference. Leaching Opt C,8 Microbial Leaching of Metals, Pseudomonas putida heterotrophic citrate KREBS et al 1997. Psychrobacter glacincola heterotrophic EDWARDS et al 1999. Serratia ficaria heterotrophic EDWARDS et al 1999, Siderocapsa sp heterotrophic ferric iron ROSSI 1990. Staphylococcus lactis heterotrophic 37 ACHARYA et al 1998. Stenotrophomonas maltophila heterotrophic EDWARDS et al 1999. Sulfobacillus thermosulfidooxidans chemolithoautotrophic ferric iron extr 50 JOHNSON 1998. sulfuric acid acidoph, Thermothrix thiopara chemolithoautotrophic sulfuric acid neutral 60 75 BRIERLEY 1977. Thiobacillus acidophilus mixotrophic sulfuric acid 1 5 6 0 3 0 25 30 CERD et al 1993. JOHNSON 1998, Thiobacillus albertis chemolithoautotrophic sulfuric acid 2 0 4 5 3 5 4 0 28 30 JOHNSON 1998. Thiobacillus caldus chemolithoautotrophic sulfuric acid 45 AMARO et al 1992. DOPSON and LINDSTROM, Thiobacillus capsulatus chemolithoautotrophic sulfuric acid EWART and HUGHES. Thiobacillus concretivorus chemolithoautotrophic sulfuric acid 0 5 6 0 ROSSI 1990. Thiobacillus delicatus mixotrophic sulfuric acid 5 0 7 0 25 30 ROSSI 1990. Thiobacillus denitrificans chemolithoautotrophic sulfuric acid 5 0 7 0 30 GROUDEV and. GROUDEVA 1993, Thiobacillus ferrooxidans chemolithoautotrophic ferric iron 1 4 6 0 2 4 28 35 SAND 1992. sulfuric acid, Thiobacillus intermedius facult heterotrophic sulfuric acid 1 9 7 0 6 8 30 ROSSI 1990. Thiobacillus kabobis mixotrophic sulfuric acid 1 8 6 0 3 0 28 ROSSI 1990. Thiobacillus neapolitanus chemolithoautotrophic sulfuric acid 3 0 8 5 6 2 7 0 28 GROUDEV and. GROUDEVA 1993, Thiobacillus novellus chemolithoautotrophic sulfuric acid 5 0 9 0 7 8 9 0 30 ROSSI 1990. Thiobacillus organoparus mixotrophic sulfuric acid 1 5 5 0 2 5 3 0 27 30 ROSSI 1990. Thiobacillus perometabolis chemolithoheterotrophic sulfuric acid 2 6 6 8 6 9 30 ROSSI 1990. Thiobacillus prosperus chemolithoautotrophic sulfuric acid 1 0 4 5 23 41 HUBER and STETTER. Thiobacillus pumbophilus chemolithoautotrophic sulfuric acid 4 0 6 5 27 DROBNER et al 1992. Thiobacillus rubellus chemolithoautotrophic sulfuric acid 5 0 7 0 25 30 BARRETT et al 1993. Tab 2 Continued, Domain Organism Nutrition Type Main pH Range pH Temperature Reference. Leaching Opt C, Thiobacillus tepidarius chemolithoautotrophic sulfuric acid HUGHES and POOLE. Thiobacillus thiooxidans chemolithoautotrophic sulfuric acid 0 5 6 0 2 0 3 5 10 37 SAND 1992. Thiobacillus thioparus chemolithoautotrophic sulfuric acid 4 5 10 0 6 6 7 2 11 25 BLOWES et al 1998. Thiobacillus versutus chemolithoautotrophic sulfuric acid 8 0 9 0 ROSSI 1990. Thiomonas cuprinus facult heterotrophic sulfuric acid 3 0 4 0 30 36 HUBER and STETTER. Eukarya Actinomucor sp heterotrophic succinate 27 M LLER and F RSTER. Fungi Alternaria sp heterotrophic citrate 32 KOVALENKO and. 5 Microbial Diversity in Bioleaching Environments,oxalate MALAKHOVA 1990. Aspergillus awamori heterotrophic 28 OGURTSOVA et al 1989. Aspergillus fumigatus heterotrophic BOSECKER 1989, Aspergillus niger heterotrophic oxalate 30 DAVE et al 1981. citrate BOSECKER 1987, Aspergillus ochraceus heterotrophic citrate 28 OGURTSOVA et al 1989. Aspergillus sp heterotrophic citrate 30 TZEFERIS 1994. Cladosporium resinae heterotrophic 28 OGURTSOVA et al 1989. Cladosporium sp heterotrophic KOVALENKO and,MALAKHOVA 1990. Coriolus versicolor heterotrophic oxalate SAYER et al 1999. Fusarium sp heterotrophic oxalate BOSECKER 1989,oxalacetate.
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