Kinetics And Characteristics Of Secondary Minerals In Nitrate Reduction Coupling To Fe (?) Oxidation By Microorganism

Microbial-mediated iron redox process is an important way and pathway of iron circulation in the earth's crust,especially in the anaerobic water environment or the nitrate reduction process of ferrous iron in sediments,and the participation of microorganisms plays an important role.In the nitrate-reducing Fe(II)oxidation process,there are two processes that simultaneously oxidize ferrous iron.One is the direct oxidation of microorganisms,and the other is the indirect chemical oxidation by the product of nitrate reduction(nitrite).The oxidation and mineralization of ferrous iron in this process will lead to the production of trivalent iron(hydrogen)oxide lepidocrocite and goethite.These secondary iron minerals will cause the cell encrustation.The existence of these secondary iron minerals has an extremely important impact and significance on the migration and transformation of other pollutants in the environment,and the acid,reducing conditions and iron-reducing microorganisms in the environment will all affect the stability of the secondary minerals.Many factors of the natural environment in the process of microbial-mediated nitrate reduction and ferrous oxidation may affect the formation and mineralogical characteristics of secondary minerals,but the process and the solubility of secondary minerals is still unclear.So the experiment purposes are(1)To study the influence of the change of bacterial concentration and the change of ferrous concentration on secondary minerals in the process of nitrate reduction and ferrous oxidation;(2)To explore the microbial-mediated oxidation and mineralization processes of ferrous iron under the nitrate/nitrite system;(3)Explore the effects of iron-reducing bacteria,reducing agents,HCl on the stability of secondary minerals.The conclusions of this experiment are as follows:(1)In the nitrate system,high bacterial concentration promotes nitrate reduction and ferrous oxidation,while the higher the ferrous concentration,the lower the reaction rate and the lower the degree under the conditions of low bacterial concentration;The higher the concentration of ferrous iron,the better the crystallization of secondary minerals,and it has a certain inhibitory effect on nitrate reduction.Both the bacterial concentration and the ferrous concentration will promote the reduction of nitrite,but the secondary minerals formed by ferrous oxidation will have a strong inhibitory effect on the reduction of microorganisms.The types and crystallinity of the secondary minerals are still mainly affected by the concentration of ferrous iron.(2)In the process of nitrate reduction and oxidation of ferrous iron,the nitrate system mainly produces goethite,and the nitrite system mainly produces lepidocrocite.In the nitrate system,the oxidation of ferrous iron and the formation of secondary minerals are mainly affected by biological and chemical denitrification.But the main denitrification under the nitrite system is chemical denitrification.(3)In the process of nitrate reduction and oxidation of ferrous iron,the nitrate system mainly produces goethite,and the nitrite system mainly produces lepidocrocite.In the early stage of mineralization,the oxidation rate of ferrous iron in the nitrite system is faster than the nitrate system,which leads to a difference in the mineralization phase.The faster ferrous iron is oxidized to form lepidocrocite,and the slower to form goethite.(4)The results of using different concentrations of hydrochloric acid to dissolve secondary minerals.Goethite(biological action)has strong stability to low concentration hydrochloric acid,but have limited tolerance to high concentration hydrochloric acid.But the stability of lepidocrocite(chemical action)is very weak for different concentrations of hydrochloric acid.The secondary minerals generated by the nitrate system under acidic conditions are more stable and have more potential in the treatment of heavy metals.(5)The iron-reducing bacteria MR-1 has a certain reduction effect on biogenic iron minerals,while its reduction effect on chemical iron minerals is weak.This is mainly due to the competition between the presence of nitrite and iron reduction.The strong reducing agent sodium dithionite has a significant dissolution effect on both minerals,and the dissolution effects increases in the increase in the concentration of sodium dithionite,and the biogenic iron mineral has a more stable mineral structure,so it dissolves more slowly.