Hexavalent Chromium Reduction In The Complicated System Of Clay Mineral-Dissolved Iron-Microorganism And Its Possible Reaction Mechanisms

In the natural environment,Cr(?)is widely concerned because it has strong fluidity and is toxic to organisms.However,Cr(?)is slightly toxic and insoluble,and is often adsorbed or precipitated on the surface of soil or minerals as chromium hydroxide,so it converts Cr(?)into Cr(?)is an important means of controlling chromium pollution.At present,there are many studies on the migration and transformation of chromium pollution by single factor(such as dissolved Fe(?),organic acid,etc.),but the actual chromium contaminated sites are often complex systems with multiple environmental factors coexisting.Therefore,the study of the migration and transformation of chromium by complex systems with multiple environmental factors is of great significance to the actual environmental treatment project.By simulating the groundwater environment,this paper combines multiple single factors(dissolved Fe(?),clay minerals,lactic acid and microorganisms)that is common in natural environments into one complex multi-environmental factor to explore the impact of structure Fe(?)in clay mineral nontronite and composite Fe(?)system that include clay mineral and dissolved Fe(?)on the effect of Cr(?)reduction in a neutral anaerobic environment firstly.It was found that(1)the rate of reduction of Cr(?)by the structure Fe(?)in nontronite is slower than that of composite Fe(?),and sodium lactate can participate in the reduction of Cr(?)as an additional electron donor during the reaction.(2)The chromium oxide or hydroxide formed by the reaction of the composite Fe(?)system with Cr(?)has an adsorption effect on Cr(?),indicating that in the composite Fe(?)system,the removal of Cr(?)is the result of a combination of reduction and adsorption reactions.Then,we investigated the effect of different forms of Fe(?)-microbe coexistence system on Cr(?)reduction by adding dissimilatory iron reduction model MR-1 to the above system.By product analysis and mineral characterization of the reaction products,the results show :(1)In different forms of Fe(?)-microbial system,the reduction rate and reduction of Cr(?)are mainly affected by the form and content of Fe(?)and the activity of bacteria.Clay minerals can adsorbe or immobilize the reduction products of Cr(?),which can reduce their direct contact with microorganisms.It has a certain protective effect on microorganisms,thereby increasing the activity of microorganisms.The Fe(?)formed by microbial reduction of Fe(?)indirectly promotes the reduction of Cr(?).(3)By studying the complex system of clay mineral-dissolved iron-microorganism,it is found that the rate and reduction amount of Fe(?)in the microbial reduction system is proportional to the iron content of clay minerals.In this paper,by studying the process of reduction reaction of Cr(?)in coexisting multi-factor complex system which include caly mineral,dissolved iron,microorganisms and organic acid,find that the system of iron-rich clay mineraldissolved Fe(?)system-microbial MR-1 can increase the rate of reduction and reduction of Cr(?)to the greatest extent.It has important implications for the treatment of chromium pollution in a complex environment like groundwater.