Transformation Process Of Schwertmannite And Environmental Behavior Of As Mediated By Sulfate Reducing Bacteria

Schwertmannite widely exist in the environment of low pH and rich in sulfate and iron.Because of their large specific surface area and isomorphism,they are easily loaded by arsenic(As).However,when the environmental conditions change,the mineral phase of schwertmannite change,and the Asoriginally loaded in mineral is likely to be re-released into the environment,which brings risks to the surrounding environment.In order to understand the phase transition process of the mineral and the environmental behavior of Asin the process,schwertmannite and Asbearing schwertmannite was synthesized by chemical rapid method.The anoxic reduction of minerals by a sulfate reducing bacteria(Desulfosporosinus meridiei sp.nov.)and the effect of 9,10-anthraquinone-2,6-disulfonic acid(AQDS)on the process were investigated in the presence of AQDS and Desulfosporosinus meridiei sp.nov.(DSM).(1)Objective to explore the effect of AQDS on DSM mediated phase transformation of schwertmannite.AQDS,pure schwertmannite,and DSM were co-cultured in one system,and the control group was the system without AQDS.The culture period was 18 days.The sampling process was carried out in the anaerobic operation platform.Through the analysis of the physical and chemical properties of the solution,we can see that the addition of AQDS accelerates the time for the system to reach the restore environment,Fe²⁺is detected before S^2-,and more S^2-can be detected in the solution.Scanning electron microscope(SEM)analysis showed that the appearance of minerals in the two systems changed from spherical to scaly.The XRD analysis of the minerals after 18 days shows that the newly formed minerals in the two systems include vivianite,FeS and S⁰.Furthermore,Mossbauer spectrum analysis of minerals after 18 days showed that complete phase transformation occurred in the system with AQDS,while there were 50%of schwertmannite without AQDS.The results show that AQDS can change the electron transfer mode in the system and promote the complete phase transformation of schwertmannite.(2)To explore the effect of different SO₄^2-concentration on DSM mediated phase transformation of Asbearing schwertmannite(As-Sch)and environmental behavior of As.Different concentrations of soluble SO₄^2-,As-Sch and DSM were co cultured in one system.The control group was the system without DSM inoculation.The culture period was 70 days.The sampling process was carried out in the anaerobic operation platform.Through the analysis of the physical and chemical properties of the solution,it can be seen that DSM takes lactic acid as the electron donor,SO₄^2-as the electron acceptor,and reduces SO₄^2-to S^2-.The concentration of SO₄^2-,Fe²⁺and As(?)in the solution increases after S^2-reductive dissolution of As-Sch,and the released As(?)is further reduced to As(?)by microorganisms,thus increasing the toxicity,migration and bioavailability of As.In addition,the formation of S⁰,FeS and As₂S₃ was induced by the sulfidation of DSM to As-Sch.The released Fe²⁺in turn catalyzes the mineral phase transformation of As-Sch,such as Fe²⁺,PO₄^3-,AsO₄^3-,leading to the formation of vivianite and parasymplesite,respectively.With the formation of secondary minerals,most of Ascan be re-fixed in solid phase,Co-precipitated with newly formed minerals or adsorbed on new minerals.Compared with As-Sch,the content of amorphous iron oxide bound Asin minerals decreased,while the content of surface bound Asin iron oxide compounds increased,and the mobility of Asincreased.The addition of SO₄^2-can strengthen this result.(3)Objective to explore the effect of AQDS on DSM mediated phase transformation of As-Sch and environmental behavior of As.AQDS,As-Sch,and DSM were co-cultured in one system,and the control group was the system without AQDS.The culture period was 18 days.The sampling process was carried out in the anaerobic operation platform.Through the analysis of the physical and chemical properties of the solution,it can be seen that after 18 days of reaction,the system with AQDS released 70?M Asmore than the system without AQDS;The Mossbauer spectrum analysis of the minerals after 18 days showed that As-Sch in the system with AQDS had complete phase transformation,while there were 24%schwertmannite in the system without AQDS.Through the continuous extraction of minerals after 18 days of reaction,it can be seen that DSM mediated dissolution and reduction of As-Sch,the vast majority of Astransformed to a more unstable state,and the Asoriginally loaded on the minerals was released into the aqueous solution.A small part of Astransforms to a more stable state,and it is difficult to release residual Asinto the environment.The addition of AQDS enhances this result.The results show that AQDS can accelerate the reduction of Fe³⁺on As-Sch,promote the dissolution of minerals,cause the collapse of minerals,complete phase transformation of As-Sch,and basically release all Asoriginally loaded on minerals into aqueous solution.The formation of new minerals(such as vivianite,S⁰,and FeS)can only make a small amount of Asre-fixed on the minerals,and most of Asremains in the liquid phase,which greatly increases the mobility of As.