Constraint Of Mineral Solubility On The Microbial Reductive Decomposition Of Sulfate Minerals And Iron Oxides

Sulfate reducing bacteria（SRB）is important functional bacteria in the terrestrial environment,wherethey play important roles in elementalcycles,the earth’s ecology and environmentaltreatments.Using sodium lactate as carbon source,this study designed experiments to investigate the effect of mineralogical properties on SRB-mediated decomposition of minerals.Three experiments were carried out:（1）the decomposition of gypsum and anhydritewith and without goethite;（2）the decomposition of anglesite with and without goethite;（3）the decomposition of porous nanomagnetite and nanomaghemite.During the experiments,theparametersof pH,ORP,protein,sulfur ions,sulfate,magnetic susceptibilitywere monitored.Before and after the experiments,physical and chemical properties of thesolid matters weredeterminedThrough analyzing these results,the mechanisms of mineral solubility on their reductive decomposition by the mediation of SRB wereobtained.The main results are as follows:In the gypsum and anhydrite experiments,atthe end of the experiments S^2-and protein concentrationsincreased with an order ofsodium sulfate>gypsum>anhydrite,suggestingthat the growth ofSRB is controlledby thedissolution rate of sulfate minerals.Both the growth of SRB and the decomposition of sulfate minerals werepromoted at the addition of goethite.The promotion mechanism can be related to the detoxication of S^2-through forming iron sulfides.In the SRB-PbSO₄ system,pH and redox potential decreased gradually through the batch experiments.Aqueous SO₄^2-increased in the first 40 h when SRB growth was in the static state,and kept stable during the following logarithmic and steady growth periods.Protein and acid volatile sulfur increased with the growth of SRB.When the experiment was terminated,it was found that anglesite had been transformed to cerussite（PbCO₃）and Pb S.In goethite added experiment,a portion of S^2-produced by SRB reacted with goethite to form iron sulfes.The decomposition process for anglesite can be described as: Pb released from anglesite is retained by CO₃^2-to form cerussite（PbCO₃）,while that of SO₄^2-is reduced to S^2-by SRB.S^2-then reacts with Pb that is released either from anglesite or cerussite to form galena（PbS）.Goethite promoted the decomposition of anglesite.There are two possible mechanisms for this promotion: Fe²⁺ that was released from goethite promotedthe biological activity of SRB,and Fe²⁺relieved thebiological toxicity of S^2-through forming iron sulfides.The magnetic susceptiblity of both magnetite and maghemite changed regularly at the inoculation of SRB.For magnetite,it increased during the first 25 days,and kept stable thereafter.For maghemite,it increased during the first 20 days,and decreased slowly thereafter.The results show that: SRB can decompose magnetic iron oxides directly;structural Fe²⁺ in magnetite canreact with S^2-to form iron sulfides,which then encapulate magnetite and make it inactive.;magnetic susceptibility can be used as indirect indexfor characterizating the decompositionof nano magnetic iron oxides.