Presentation on theme: "PRINCIPLES OF METAL SULFIDE FORMATION Back to basics, always."— Presentation transcript:
PRINCIPLES OF METAL SULFIDE FORMATION Back to basics, always
Metal Sulfide in nature M 2+ + S 2- MS interaction between an appropriate metal ion and biogenically or abiogenically formed sulfide ion: BiogenikAbiogenik bacterial sulfate reduction from bacterial mineralization of organic sulfur-containing compounds
Solubility Products for Some Metal Sulfides Because of their relative insolubility, the metal sulfides form readily at ambient temperatures and pressures.
case of amorphous iron sulfide (FeS) formation The ionization constant for FeS [Fe 2+ ][S 2- ]= The ionization constant for H 2 S [S 2- ]= ,96 [H 2 S]/[H + ] 2 2 The constant for the dissociation of H 2 S into HS - and H + [HS - ][H + ]/[H 2 S]= 10 -6,96 3 The constant for the dissociation of HS - into S 2- and H + [S 2- ][H + ]/[HS - ]= [Fe 2+ ] = [H + ] 2 /[H 2 S] x /10 -21,96 = [H + ] 2 /[H 2 S] x 10 21,96
LABORATORY EVIDENCE IN SUPPORT OF BIOGENESIS OF METAL SULFIDES
Batch Cultures Miller (1949,1950) reported that sulfides of Sb, Bi, Co, Cd, Fe, Pb, Ni, and Zn were formed in a lactate-containing broth culture of Desulfovibrio desulfuricans to which insoluble salts of selected metals had been added. bismuth sulfide,on addition of (BiO 2 ) 2 CO 3 ·H 2 O, cobalt sulfide on addition of 2CoCO 3 · 3Co(OH) 2, nickel sulfide on addition of NiCO 3 or Ni(OH) 2 minimize metal toxicity for D. desulfuricans Metal ion toxicity depends in part on the solubility of the metal compound from which the ion derives
Baas Becking and Moore (1961) Desulfovibrio desulfuricans 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, Fe 0 + 2H 2 O H 2 + Fe(OH) 2 used by the sulfate- reducers in the formation of hydrogen sulfide. 4H 2 + SO H + H 2 S + 4H 2 O Ferrous sulfide from FePO 4 and Fe 2 O 3 Covellite (CuS) from Malachite [CuCO 3.Cu(OH) 2 ] Argentite (Ag 2 S) from silver chloride (Ag 2 Cl 2 ) and silver carbonate (AgCO 3 ) Galena (PbS) from PbCO 3 and [PbCO 3.Pb(OH) 2 ] ZnS from ZnCO 3 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. 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+.
COLUMN EXPERIMENT: MODEL FOR BIOGENESIS OF SEDIMENTARY METAL SULFIDES
BIOEXTRACTION OF METAL SULFIDE ORES BY COMPLEXATION
acidophilic iron-oxidizing bacteria Metal sulfide ores oxidized by 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. unidentified metabolites mobilize copper from sedimentary ores Czapeks broth contain : sucrose, NaNO3, cysteine, methionine, or glutamic acid complexing agents mobilization of copper in an oxidized mining residue by A. niger in a sucrose– mineral salts medium. The chief mobilizing agents gluconic and citric acids act as acidulants as well as ligands of metal ions
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
obtained better results grew the fungus in the absence of the ore treated the ore with the spent medium from the fungus culture The organisms forms ligands extracted the metals from the ores by forming complexes more stable than the original insoluble form of the metals in the ores
MA : metal salt (mineral) HCh : ligand (chelating agent) MCh : the resultant metal chelate A : the counter ion of the original metal salt (S 2 ) The S 2 may undergo chemical or bacterial oxidation (Chemical Processing, 1965) MA+ HCh MCh + H + + A
FORMATION OF ACID COAL MINE DRAINAGE
Acid Mine Drainage 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 Air, bacteria and moisture during mining Pyrite Oxidation Formation of AMD Initiator reaction Propagation cycle
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 L1 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
In AMD will be detectable some of acidophilic iron oxidizing thiobacilli. Acidithiobacillus ferrooxidans is involved, pyrite biooxidation proceeds Pyrit Oxidation : Ferric ion oxidation Acidithiobacillus thiooxidans : 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.
An early study by Harrison (1978) Artificial coal spoil Deposit into mound d= 50 cm l= 25cm on plastic tray Absorbed and migrated upward Sampling 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
Result... 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 g1. The sulfur-oxidizing bacteria were assumed to be making use of elemental sulfur resulting from the oxidation of pyrite by ferric sulfate: FeS2 + Fe2(SO4)3 3FeSO4 + 2S0 Initial samples : The base of the mound Heterotrophic bacteria. 2 weeks : The population density of 107 cells g1 After 8 weeks : heterotrophs were still dominant Between 12 and 20 weeks : The population decreased Near the summit of the mound, First 15 weeks : Heterotrophs predominated Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans Higher pH values Protozoans, algae, and arthropod Metallogenium was not seen Between 12 and 20 weeks : The population decreased After 8 weeks : heterotrophs were still dominant
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 of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans from a pyrite deposit – in the Richmond Mine, seepage from a tailings pile and AMD storage tanks outside this mine
Occurred in slime-based communities at pH >1.3 at temperatures below 30°C Affect precipitation of ferric iron but seemed to have a minor role in acid generation active role in generating ferric iron as an oxidizing agent Acidithiobacillus ferrooxidans Abundant in subsurface slime-based communities. Occurred in planktonic form at pH values in the range of 0.3–0.7 between 30 and 50°C active role in generating ferric iron as an oxidizing agent L. ferrooxidans
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 Ferroplasma acidarmanus, grew in slime streamers on the pyrite surfaces. extremely acid-tolerant : pH optimum at 1.2 Its cells lack a wall Archaean order Thermoplasmales