Presentation on theme: "Principles of Metal Sulfide Formation"— Presentation transcript:
1 Principles of Metal Sulfide Formation Back to basics, alwaysPrinciples of Metal Sulfide Formation
2 Metal Sulfide in nature interaction between an appropriate metal ion and biogenicallyor abiogenically formed sulfide ion:M2+ + S2- →MSBiogenikAbiogenikbacterial sulfate reductionfrom bacterial mineralization of organic sulfur-containing compounds
3 Solubility Products for Some Metal Sulfides Because of their relative insolubility, themetal sulfides form readily at ambient temperatures and pressures.
4 case of amorphous iron sulfide (FeS) formation 1The ionization constant for FeS[Fe2+] = [H+]2/[H2S] x 10-19/10-21,96 = [H+]2/[H2S] x 1021,962[S2-]= 10-21,96 [H2S]/[H+]2The ionization constant for H2S3The constant for the dissociation of H2S into HS- and H+[HS-][H+]/[H2S]= 10-6,964The constant for the dissociation of HS- into S2- and H+[S2-][H+]/[HS-]= 10-15The following calculations will show that relatively low concentrations of metal ions, typical in some lakes, will form metal sulfi des by reacting with low concentrations of H2S. The ionic activities. in these calculations are taken as approximately equal to concentration because of the low concentrations involved. The following examines the case of amorphous iron sulfi de (FeS) formation.
5 LABORATORY EVIDENCE IN SUPPORT OF BIOGENESIS OF METAL SULFIDES
6 minimize metal toxicity for D. desulfuricans Batch Culturescobalt sulfide on addition of 2CoCO3 · 3Co(OH)2,nickel sulfide on addition of NiCO3 or Ni(OH)2bismuth sulfide ,on additionof (BiO2)2CO3 ·H2O,reported that sulfides of Sb, Bi, Co, Cd, Fe, Pb, Ni, and Zn wereformed in a lactate-containing broth culture of Desulfovibrio desulfuricans to which insoluble salts of selected metals had been added.Miller (1949,1950)minimize metal toxicity for D. desulfuricansMetal ion toxicity depends in part on the solubility ofthe metal compound from which the ion derivesFor instance, he found that bismuth sulfi de was formed on additionof (BiO2)2CO3 ·H2O, cobalt sulfi de on addition of 2CoCO3 · 3Co(OH)2, lead sulfi de on additionof 2PbCO3 · Pb(OH)2 or PbSO4, nickel sulfi de on addition of NiCO3 or Ni(OH)2, and zinc sulfi deon addition of 2ZnCO3 · 3Zn(OH)2. The metal salt reactants were added as insoluble compounds tominimize metal toxicity for D. desulfuricans. Metal ion toxicity depends in part on the solubility ofthe metal compound from which the ion derives. Obviously, for a metal sulfi de to be formed fromanother metal compound that is relatively insoluble, the metal sulfi de must be even more insolublethan the source compound of the metal. Miller was not able to demonstrate copper sulfi de formationfrom malachite [CuCO3 · Cu(OH)2], probably because malachite was too insoluble relative tocopper sulfi des in the medium. Miller (1949) also showed that with addition of Cd or Zn ions to theculture medium, the yield of total sulfi de produced from sulfate by the bacteria in batch culture wasgreater than in the absence of the added metal ions. This was because the uncombined sulfi de itselfbecomes toxic to sulfate-reducers at high enough concentration.
7 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 theinvestigators thought the reactions are likely to occur in nature.source of hydrogen for the bacterial reduction of sulfateThehydrogen resulted from corrosion of the steel wool by the spontaneous reaction,Fe0 + 2H2O → H2 + Fe(OH)2Baas Becking and Moore (1961)used by the sulfate-reducers in the formation of hydrogen sulfide.4H2 + SO H+ H2S + 4H2OThey succeeded in forming covellite from malachite where Miller (1950) failed, probably because they performedtheir experiment in a saline medium (3% NaCl) in which Cl− could complex Cu2+, therebyincreasing the solubility of Cu2+.The media were saline to simulate marine (near-shore and estuarine) conditions under which theinvestigators thought the reactions are likely to occur in nature. They formed ferrous sulfi de fromstrengite (FePO4) and from hematite (Fe2O3). They also formed covellite (CuS) from malachite[CuCO3· Cu(OH)2]; argentite (Ag2S) from silver chloride (Ag2Cl2) and from silver carbonate (AgCO3);galena (PbS) from lead carbonate (PbCO3) and from lead hydroxycarbonate [PbCO3·Pb(OH)2]; andsphalerite (ZnS) from smithsonite (ZnCO3). All mineral products were identifi ed by x-ray powderdiffraction studies. Baas Becking and Moore (1961) were unable to form cinnabar (HgS) from mercuriccarbonate (HgCO3), probably owing to the toxicity of the Hg2+ ion. They were also unable toform alabandite (MnS) from rhodochrosite (MnCO3), or bornite (Cu5FeS4) or chalcopyrite (CuFeS2)from a mixture of cuprous oxide (Cu2O) or malachite and hematite and lepidochrosite. They succeededin forming covellite from malachite where Miller (1950) failed, probably because they performedtheir experiment in a saline medium (3% NaCl) in which Cl− could complex Cu2+, therebyincreasing the solubility of Cu2+. The starting materials that were the source of metal were all relativelyinsoluble, as in Miller’s experiments. Baas Becking and Moore found that in the formation ofcovellite and argentite, native copper and silver were respective intermediates that disappeared withcontinued bacterial H2S production.Leleu et al. (1975) synthesized ZnS by passing H2S produced by unnamed strains of sulfatereducingbacteria through a solution of ZnSO4. In one experiment, biogenic H2S formation and ZnSprecipitation by the biogenic H2S occurred in separate vessels. In a second experiment, biogenesisof H2S and precipitation of ZnS occurred in the same vessel at an initial ZnSO4 concentration inthe culture medium of 10−2 M. The ZnS formed under either experimental condition was identifi edas a sphalerite–wurtzite mixture by powder x-ray diffraction. The presence of Zn directly in theculture medium caused a lag in H2S production, which was not observed when H2S was generatedin a separate vessel.ZnS from ZnCO3Covellite (CuS) from Malachite [CuCO3.Cu(OH)2]Galena (PbS) from PbCO3 and [PbCO3.Pb(OH)2]Ferrous sulfide from FePO4 and Fe2O3Argentite (Ag2S) from silver chloride (Ag2Cl2) and silver carbonate (AgCO3)ZnS unable to form alabandite (MnS) from MnCO3 or Cu5FeS4 or CuFeS2 from a mixture of Cu2O or malachite and hematite and lepidochrosite.unable to form cinnabar (HgS) from mercuric carbonate
8 COLUMN EXPERIMENT: MODEL FOR BIOGENESIS OF SEDIMENTARY METAL SULFIDES The relatively high toxicity of many of the heavy metals for sulfate-reducing bacteria has been usedas an argument that these organisms could not have been responsible for metal sulfi de precipitationin nature (Davidson, 1962a,b). However, in a sedimentary environment, metal ions will be mostlyadsorbed to sediment particles such as clays or complexed by organic matter (Hallberg, 1978), whichlessens their toxicity. Such adsorbed or complexed ions are still capable of reacting with sulfi de andprecipitating as metal sulfi des, as was shown experimentally by Temple and LeRoux (1964). Theyconstructed a column in which clay or ferric hydroxide slurry carrying adsorbed Cu2+, Pb2+, andZn2+ ions was separated by an agar plug from an underlying liquid culture of sulfate-reducersactively generating hydrogen sulfi de in saline medium. They also tested clay that was carrying Fe3+in this setup. They found that, in time, bands of precipitate formed in the agar plug separating theslurry of metal-carrying adsorbent from the culture of sulfate-reducing bacteria (Figure 20.1). Thebands formed as upward-diffusing sulfi de ion species and downward diffusing, desorbed metal ionspecies encountered each other in the agar. Differential desorption of metal ions from the adsorbentand differential diffusion in the agar accounted for the discrete banding of the various sulfi des.These results demonstrate that biogenesis of relatively large amounts of sulfi des in a sedimentaryenvironment is possible, even in the presence of relatively large amounts of metal ions. The mainrequirement is that the metal ions are in a nontoxic form (e.g., adsorbed or complexed) or combinedin the form of insoluble mineral oxide, carbonate, or sulfate. As Temple (1964) pointed out,syngenetic microbial production of metal sulfi de in nature is possible. Restrictions on the process,
9 Bioextraction of Metal Sulfide Ores by Complexation
10 acidophilic iron-oxidizing bacteria oxidized byMetal sulfide oresacidophilic iron-oxidizing bacteriaan amount of acid-consuming constituents in the host rockextracted by :Penicillium sp.mine-tailings pond of the White Pine Copper Co. in MichiganAspergillus sp.complexing agentsunidentified metabolitesmobilization of copper in an oxidized mining residue by A. niger in a sucrose–mineral salts medium.mobilize copper from sedimentary ores Czapek’s brothcontain : sucrose, NaNO3, cysteine, methionine, or glutamic acidThe chief mobilizing agentsact as acidulants as well as ligands of metal ionsgluconic and citric acids
11 Wenberg et al. (1971)grew fungus in the presence of copper ore (sulfide or native copper minerals with basic gangue constituents)addition of citratelowered the toxicity of the extracted copperwhen the fungus was grown in the presence of the ore
12 obtained better results grew the fungus in the absence of the oretreated the ore with the spent medium from the fungus cultureby forming complexesThe organisms forms ligandsextracted the metals from the oresmore stable than the original insoluble form of the metals in the ores
13 MA : metal salt (mineral) MA+ HCh → MCh + H+ + A−MA : metal salt (mineral)HCh : ligand (chelating agent)MCh : the resultant metal chelateA− : the counter ion of the original metal salt (S2−)The S2− may undergo chemical or bacterial oxidation(Chemical Processing, 1965)
15 Air, bacteria and moisture during mining Acid Mine DrainageYellow boy in a stream receiving aciddrainage from surface coal mining.An Enviromental problem in coal-Mining regionDegrades water quality > Mixing of acid mine water into natural in riverPolluted water for human consumption and industrial useAir, bacteria and moisture during miningPyritePyrite OxidationPropagation cycleInitiator reactionFormation of AMD
16 The breakdown of pyrite Leads to the formation of sulfuric acid and ferrous ironpH values ranging from 2 to 4.5Sulfate ion concentrations ranging from 1,000 to 20,000 mg L−1 but a nondetectable ferrous iron concentrationThe acid formed attack other minerals associated with the coal and pyrite, causing breakdown of rock fabricAlumunium : Highly toxic
17 Pyrit Oxidation : Ferric ion oxidation In AMD will be detectable some of acidophilic iron oxidizing thiobacilli. Acidithiobacillus ferrooxidans is involved, pyrite biooxidation proceedsPyrit Oxidation :Ferric ion oxidationAcidithiobacillus thiooxidans : Oxidized elemental sulfur (S0) and other partially reduced sulfur species : Intermediates in pyrite oxidation to sulfuric acidMetallogenium-like organism that they isolated from AMD ( Walsh and Mitchell (1972) ) - pH drops below 3.5.
18 An early study by Harrison (1978) Artificial coal spoilDeposit into mound d= 50 cm l= 25cm on plastic trayand migrated upwardAbsorbedSamplingInoculated : 20 L of an emulsion of acid soil, drainage water, and mud from a spoil from an old coal stripmineMicrobial successionin coal spoilunder laboratory conditions
19 Initial samples : The base of the mound Heterotrophic bacteria.2 weeks : The population density of ∼107 cells g−1After 8 weeks : heterotrophs were still dominantBetween 12 and 20 weeks : The population decreasedNear the summit of the mound,First 15 weeks : Heterotrophs predominatedAcidithiobacillus thiooxidans and Acidithiobacillus ferrooxidansHigher pH valuesProtozoans, algae, and arthropodMetallogenium was not seenpH 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 from the oxidation of pyrite by ferric sulfate:FeS2 + Fe2(SO4)3 → 3FeSO4 + 2S0After 8 weeks : heterotrophs were still dominantBetween 12 and 20 weeks : The population decreasedResult...
20 NEW DISCOVERIES RELATING TO ACID MINE DRAINAGE A fairly recent study of abandoned mines at Iron Mountain, California.The ore body at Iron Mountainvarious 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 comingThe distribution of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans from a pyrite depositin the Richmond Mine, seepage from a tailings pile and AMD storage tanks outside this mine
21 Acidithiobacillus ferrooxidans Occurred in slime-based communities at pH >1.3 at temperatures below 30°CAffect precipitation of ferric iron but seemed to havea minor role in acid generationactive role in generating ferric iron as an oxidizing agentL. ferrooxidansAbundant 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
22 The Richmond Mine revealed the presence of Archaea in summer and fall months: Archaea represented ∼50% of the total populationcorrelated these population fluctuations with rainfall and conductivity, (dissolved solids), pH, and temperature of the mine waterFerroplasma acidarmanus, grew in slime streamers on the pyrite surfaces.extremely acid-tolerant : pH optimum at 1.2Its cells lack a wallArchaean order Thermoplasmales