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Biogenesis and Biodegradation of Sulfide Minerals at Earth’s Surface Geomicrobiology of Sulfide Minerals
Aldyla Nisa Raditya 10407013 Astri Elia 10407015 Ariani Intan Utami 10407016 Venessa Alia 10407032 Vilandri Astarini 10407035 Annissa Kurnia Maulida 10407040 Zara Zentira 10607053 Group 4School of Life Sciences and TechnologyBandung Institute of Technology2010
Introduction Sulfide minerals at a glance
-2 Sulfide = S-2 -2 +6 0
€ $ Rp = Cu, Ni, Zn, Co Sulfate Metal ions + oxidized sulfides Some sedimentary environments • Soil • Sediments • Rock surfaces REDUCTION OXIDATION Other microbes Sulfate-reducing bacteria (SRB) Metal sulfides Sulfide minerals FeS (pyrite) Bioextraction (bioleaching) Metal industry utilization Biobeneficiation(microbial pretreatment to remove pyrite from gold ores)
Ore biogenesis Ore biomobilization Bioleaching
Where it comes Natural Origin of Metal Sulfides
Hydrothermal Origin (Abiotic) Current theory: The help of plate tectonics Most metal sulfides (including those of commercial interest) Formation Igneous origin A result of subduction of oceaniccrust, enriched in Cu with hydrothermal activity at mid-oceanspreading-centers Terrestrial deposit of porphyry copper ore
White smokers • Relatively more significant quantity of metal sulfides deposition occurs • The brine is cooler than that of black smoker’s Metal sulfide “smoke” (black mineral) Deposited as the vents (chalcopyrite CuFeS2, sphalerite ZnS) Cooling outside the oceanic crust White smoke is depleted in some base metals, but still contains major quantities of Fe, Mn, & H2S Metal sulfide (black mineral) presipitated inside the crust Seawater Magma heat Cooling in upper oceanic crust
Sedimentary Metal Sulfides of Biogenic Origin relatively rare most common Nonferrous sulfides Iron sulfides reducing zone in sedimentary deposits in estuarine environment (peat, salt marsh) Burried in formed sediment Hydrothermal or microbial origin Plentiful supply of sulfate Metal sulfides = metal compound + H2S IMPORTANT Bacterial reduction (anaerobic) Each >1% metal deposited needs 0.1% carbon (dry weight) and an enriched source of metals (e.g. hydrothermal solution) Metal sulfides = iron compound + H2S Iron pyrite (FeS2) Seasonalreoxidation as conditions in the environment change from reducing to oxidizing Not a permanent sink for iron
Back to basics, always Principles of Metal Sulfide Formation
Metal Sulfide in nature interaction between an appropriate metal ion and biogenically or abiogenically formed sulfide ion: M2+ + S2- →MS Biogenik Abiogenik bacterial sulfate reduction from bacterial mineralization of organicsulfur-containing compounds
Solubility Products for Some Metal Sulfides Because of their relative insolubility, the metal sulfides form readily at ambient temperatures and pressures.
[Fe2+][S2-]= 10-19 1 The ionization constant for FeS [Fe2+] = [H+]2/[H2S] x 10-19/10-21,96 = [H+]2/[H2S] x 1021,96 • case of amorphous iron sulfide (FeS) formation 2 [S2-]= 10-21,96 [H2S]/[H+]2 The ionization constant for H2S 3 The constant for the dissociation of H2S into HS- and H+ [HS-][H+]/[H2S]= 10-6,96 4 The constant for the dissociation of HS- into S2- and H+ [S2-][H+]/[HS-]= 10-15
Batch Cultures cobalt sulfide on addition of 2CoCO3 · 3Co(OH)2, nickel sulfide on addition of NiCO3 or Ni(OH)2 bismuth sulfide ,on addition of (BiO2)2CO3 ·H2O, reported that sulfides of Sb, Bi, Co, Cd, Fe, Pb, Ni, and Zn were formed in a lactate-containing broth culture of Desulfovibriodesulfuricansto which insoluble salts of selected metals had been added. Miller (1949,1950) minimize metal toxicity for D. desulfuricans Metal ion toxicity depends in part on the solubility of the metal compound from which the ion derives
Desulfovibriodesulfuricans and Desulfotomaculum sp. (Clostridium Desulfuricans). They grew them in lactate or acetate medium containing steel wool. The media were saline to simulate marine (near-shore and estuarine) conditions under which the investigators thought the reactions are likely to occur in nature. source of hydrogen for the bacterial reduction of sulfate The hydrogen resulted from corrosion of the steel wool by the spontaneous reaction, Fe0 + 2H2O → H2 + Fe(OH)2 Baas Becking and Moore (1961) used by the sulfate-reducers in the formation of hydrogen sulfide. 4H2 + SO42- + 2H+ H2S + 4H2O They succeeded in forming covellite from malachite where Miller (1950) failed, probably because they performed their experiment in a saline medium (3% NaCl) in which Cl− could complex Cu2+, thereby increasing the solubility of Cu2+. Ferrous sulfide from FePO4 and Fe2O3 Covellite (CuS) from Malachite [CuCO3.Cu(OH)2] Argentite (Ag2S) from silver chloride (Ag2Cl2) and silver carbonate (AgCO3) Galena (PbS) from PbCO3 and [PbCO3.Pb(OH)2] ZnS from ZnCO3 unable to form cinnabar (HgS) from mercuric carbonate ZnS unable to form alabandite (MnS) from MnCO3 or Cu5FeS4 or CuFeS2 from a mixture of Cu2O or malachite and hematite and lepidochrosite.
Mesophile Bacteria • F. acidarmanusgrow best in a pH range of ∼1.5–2.5. F. acidarmanus, a recent discovery, grows at a pH as low as 0 (optimum pH 1.2) at a temperature of ∼40°C. • F. acidiphilumgrows in a pH range of 1.3–2.2 (optimum pH 1.7) in a temperature range of 15–45°C • AcidithiobacillusferrooxidanssecretedEPS formation. The EPSs enable attachment to sulfide mineral surfaces.
Acidimicrobium ferrooxidans • L. ferrooxidans(Mesophile)andAcidimicrobiumferrooxidans(Moderate thermophile)can promote metal sulfide oxidation only by generating Fe3+ from dissolved Fe2+ which then oxidizes metal sulfide abiotically
Extreme Thermophile • Acidianusbrierleyiand Sulfolobus sp. can oxidize a variety of metal sulfides including pyrite, marcasite, arsenopyrite, chalcopyrite, NiS, and probably CoS. • A. brierleyican oxidize molybdenite in the absence of added iron • molybdate ion is less toxic to Acidianusbrierleyi Acidianus brierleyi Sulfolobus sp
Direct oxidation • microbes have to be in intimate contact with the mineral they attack (enzymatic oxidation) • Bacterial attachment to mineral sulfide surfaces at specific sites • Some evidence suggests that direct microbial attack is initiated at sites of crystal imperfections • a collective model is that bacterial cells possessing this ability act as catalytic conductors
in transferring electrons from cathodic areas on crystal surfaces of a metal sulfide via an electron transport system in the cell envelope to oxygen • In this model : cell attached to the surface of a Cu2S particle (acts as a conductor) electrons it removes in the oxidation of Cu(I) of Cu2S and transfers to oxygen.
the outer membrane of Acidithiobacillusferrooxidanscontains a high-molecular weight c-type cytochrome Cyc2 that has the capacity to promote the oxidation of Fe2+ to Fe3+ at the outer surface of the outer membrane. (Yarzabal et al., 2002)
Biooxidation of Sulfide Minerals Indirect Oxidation
Indirect Oxidation It may be generated initially from dissolved ferrous iron (Fe2+) at: • pH 3.5 – 5 in a mesophilic temperature range by Metallogenium • pH <3.5 in a mesophilic temperature by Acidithiobacillusferrooxidansand Leptospirillumferrooxidans • thermophilic temperature by Sulfolobusspp, Acidianusbrierleyiand Alicyclobacillustolerans
Indirect Oxidation Ferric iron in acid solution acts as an oxidant of the metal sulfides in indirect attack: * A central role of Acidithiobacillusferrooxidansin an indirect oxidation process is to regenerate Fe3 + from the Fe2+ formed MS + 2Fe3+ → M2+ + S0 + 2Fe2+
Pyrite Oxidation Elemental sulfurmay form a film on the surface of metal sulfide crystals in chemical oxidation and interfere with further chemical oxidation of the residual metal sulfide The chemical oxidation of metal sulfides must occur in acid solution below pH 5 to keep enough ferric iron in solution.
Biooxidation of Sulfide Minerals Pyrite Oxidation
Pyrite Oxidation Acidithiobacillusferrooxidansrepresents a special case in which direct and indirect oxidation of the mineral CANNOT BE READILY SEPARATED because ferric iron is ALWAYS a product. Experimentally, there ara4 phases in the leaching of pyrite by Acidithiobacillusferrooxidansin a stirred reactor.
Pyrite Oxidation • The first phase (5 days): • unattached bacteria (planctonic) decerase • small amount of dissolved ferric iron added with the inoculum reacted with some of the pyrite. • The second phase (5 days): • - Start of pyrite dissolution with oxidation of its iron and sulfur • - Planktonic bacteria multiexponentially and the pH began to drop
Pyrite Oxidation • The third phase (10 days) : • Significant increase in dissolved ferric iron, the ferrous iron concentration remaining low • Planktonic bacteria continued to increase exponentially, pH continued to drop • The fourth phase (25 days) : • The dissolved Fe(III)/Fe(II) ratio decreased, iron and sulfur strongly oxidized, and the planktonic bacteria reached a stationary phase • - The surface of the pyrite particles now showed easily recognizable square or hexagonal corrosion pits.
METAL SULFIDE ORES • Low-grade sulfide ores generally contain metal values at concentrations below 0.5% (w/w). • Bioleaching was used commercially only with low-grade portions of an ore and with ore tailings→ it is now also used in treating high-grade ore and ore concentrates. • Ore heaps may consist of high grade ore.
The lixiviant • As a fine spray onto ore heaps and dumps → avoids waterlogging • makes possible the growth and multiplication of appropriate acidophilic iron-oxidizers and the oxidation of pyrite, chalcopyrite, and nonferrous metal sulfides in the ore.
as microbial and chemical activities continue → the solution in the heaps/dumps becomes charged with dissolved metal values → after issuing from the heaps/dumps it is collected as pregnant solution Copper Separation: treatment of pregnant solution with sponge iron (Fe0) • The sponge iron precipitated the copper by cementation in a process Cu2+ + Fe0 → Cu0 + Fe2+ (The copper metal: very impure and required further refinement by smelting)
Barren solution that entered the heaps/dumps caused; High acidity of the lixiviant may also play an important role in preventing metal ions formed during leaching from being adsorbed by the host rock(Ehrlich, 1977; Ehrlich and Fox, 1967).