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Principles of Metal Sulfide Formation

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:. M 2+ + S 2- →MS. Biogenik. Abiogenik. bacterial sulfate reduction.

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Principles of Metal Sulfide Formation

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  1. Back to basics, always Principles of Metal Sulfide Formation

  2. 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

  3. Solubility Products for Some Metal Sulfides Because of their relative insolubility, the metal sulfides form readily at ambient temperatures and pressures.

  4. [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

  5. LABORATORY EVIDENCE IN SUPPORT OF BIOGENESISOF METAL SULFIDES

  6. 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

  7. 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.

  8. COLUMN EXPERIMENT: MODEL FOR BIOGENESIS OF SEDIMENTARY METAL SULFIDES

  9. Bioextraction of Metal Sulfide Ores by Complexation

  10. oxidized by Metal sulfide ores an amount of acid-consuming constituents in the host rock extracted by : • Penicillium sp. • mine-tailings pond of the White Pine Copper Co. in Michigan • Aspergillus sp. complexing agents unidentified metabolites mobilization of copper in an oxidized mining residue by A. nigerin a sucrose–mineral salts medium. mobilize copper from sedimentary ores Czapek’s broth contain : sucrose, NaNO3, cysteine, methionine, or glutamic acid The chief mobilizing agents act as acidulants as well as ligands of metal ions gluconic and citric acids acidophilic iron-oxidizing bacteria

  11. Wenberg et al. (1971) grew fungus in the presence of copper ore (sulfide or native copper minerals with basic gangue constituents) addition of citrate lowered the toxicity of the extracted copper when the fungus was grown in the presence of the ore

  12. obtained better results grew the fungus in the absence of the ore treated the ore with the spent medium from the fungus culture by forming complexes The organisms forms ligands extracted the metals from the ores more stable than the original insoluble form of the metals in the ores

  13. MA+ HCh → MCh + H+ + A− MA : metal salt (mineral) HCh : ligand (chelating agent) MCh : the resultant metal chelate A−: the counter ion of the original metal salt (S2−) The S2− may undergo chemical or bacterial oxidation (Chemical Processing, 1965)

  14. Formation of Acid Coal Mine Drainage

  15. Acid Mine Drainage Air, bacteria and moisture during mining Pyrite • Yellow boy in a stream receiving acid drainage from surface coal mining. An Enviromental problem in coal-Mining region Degrades water quality > Mixing of acid mine water into natural in river Polluted water for human consumption and industrial use Pyrite Oxidation Propagation cycle Initiator reaction Formation of AMD

  16. The breakdown of pyrite • Leads to the formation of sulfuric acid and ferrous iron • pH values ranging from 2 to 4.5 • Sulfate ion concentrations ranging from 1,000 to 20,000 mg L−1 but a nondetectable ferrous iron concentration • The acid formed attack other minerals associated with the coal and pyrite, causing breakdown of rock fabric • Alumunium : Highly toxic

  17. In AMD will be detectable some of acidophilic iron oxidizing thiobacilli. Acidithiobacillus ferrooxidans is involved, pyrite biooxidation proceeds • Pyrit Oxidation : • Ferric ion oxidation • Acidithiobacillusthiooxidans : Oxidized elemental sulfur (S0) and other partially reduced sulfur species : Intermediates in pyrite oxidation to sulfuric acid • Metallogenium-like organism that they isolated from AMD ( Walsh and Mitchell (1972) ) - pH drops below 3.5.

  18. An early study by Harrison (1978) Inoculated : 20 L of an emulsion of acid soil, drainage water, and mud from a spoil from an old coal strip mine Microbial succession in coal spoil under laboratory conditions

  19. Result... After 8 weeks : heterotrophs were still dominant • pH had dropped from 7 to 5. • pH to just below 5 >> caused by a burst of growth by sulfur-oxidizing bacteria, >> then died off progressively. • The heterotrophic population increased again to just below 107 g−1. • The sulfur-oxidizing bacteria were assumed to be making use of elemental sulfur resulting fromthe oxidation of pyrite by ferric sulfate: FeS2 + Fe2(SO4)3 → 3FeSO4 + 2S0 Between 12 and 20 weeks : The population decreased

  20. NEW DISCOVERIES RELATING TO ACID MINE DRAINAGE • A fairly recent study of abandoned mines at Iron Mountain, California. • The ore body at Iron Mountain • various metal sulfides and was a source of Fe, Cu, Ag, and Au. • A signifi cant part of the iron was in the form of pyrite. The drainage currently coming • The distribution ofAcidithiobacillus ferrooxidans andLeptospirillum ferrooxidansfrom a pyrite deposit • in the Richmond Mine, seepage from a tailings pileand AMD storage tanks outside this mine

  21. The Richmond Mine revealed the presence of Archaea • in summer and fall months: Archaea represented ∼50% of the total population • correlated these population fluctuations with rainfall and conductivity, (dissolved solids), pH, and temperature of the mine water • Ferroplasmaacidarmanus, grew in slime streamers on the pyrite surfaces. • extremely acid-tolerant : pH optimum at 1.2 • Its cells lack a wall • Archaeanorder Thermoplasmales

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