Effect Of Manganese Oxides On Arsenic Bearing Soil And Its Influencing Factors And Mechanisms

Arsenic?As?is a highly toxic metal,which can cause skin cancer,bladder cancer and other diseases.Soil is seriously polluted due to the extensive use of sewage irrigation,industrial sludge and arsenic-containing pesticides in agricultural production.Arsenic pollution in soil has become one of the increasingly serious environmental problems.The remediation effects of commercial manganese oxides and Biological Manganese Oxides on arsenic-contaminated soil were studied.The main research contents are as follows:1)The effects of two kinds of manganese oxides on arsenic remediation were studied by leaching experiments?water extraction and TCLP extraction?,and the effects of manganese oxides type,dosage,incubation time,coexisting ions and other factors on arsenic remediation were studied;2)The morphological changes of arsenic in soil before and after manganite remediation were analyzed by continuous leaching method;3)The potential toxicity of manganese oxides after remediation was studied through plant germination experiments.4)Analysis of microbial structure and biodiversity changes before and after manganese oxide remediation based on 16S RNA high throughput sequencing.5)Through the results of XPS before and after soil remediation,the remediation mechanism of manganese oxides on arsenic bearing soil was analyzed.The main conclusions are as follows:1)The remediation effects of four commercial manganese oxides?micron manganese dioxide,nano manganese dioxide,nano manganese trioxide and nano manganese tetroxide?on arsenic contaminated soil were studied.The results showed that:When the dosage of four manganese oxides was 1%,5%and 10%respectively,the leaching amount of water-soluble arsenic and TCLP arsenic in soil could be effectively reduced by the four commercial manganese oxides.With the increase of the dosage of manganese oxides,the leaching amount of arsenic gradually decreased.Compared with the four kinds of manganese oxides,the effect of nano manganese oxide is slightly better than that of micron manganese dioxide.Tessier continuous leaching results showed that the proportion of exchangeable arsenic decreased and that of organic bound arsenic increased after adding manganese oxide.The results of plant toxicity test showed that the seed germination rate,relative root length and seed germination index were increased after adding four commercial manganese oxides,indicating that the toxicity of arsenic in soil was reduced.The results of XPS before and after soil remediation showed that As?III?in soil was transformed into As?V?.2)The effect of manganese oxide produced by Manganese Oxidizing Bacteria on the remediation of arsenic in soil was studied.The results show that:Compared with the four commercial manganese oxides,the dosage of Biological Manganese Oxides in arsenic remediation was significantly reduced,and the effect of unit dosage on arsenic remediation was higher.With the prolongation of the repair time?15,30,45 and 60days?,there was no significant change in the repair effect of arsenic.When the repair time was 15 days,the repair of arsenic was stable.Adding 1%,2%and 3%inorganic salts?such as FeCl₃,CaCl₂ and NaCl?to the soil can significantly reduce the arsenic leaching from the soil by Biological Manganese Oxides and improve the arsenic recovery efficiency by Biological Manganese oxides.FeCl₃ is the best,while adding Na₂HPO₄ can significantly inhibit the arsenic recovery efficiency by Biological Manganese oxides.Tessier continuous leaching results showed that the proportion of exchangeable arsenic decreased with the addition of Biological Manganese oxides,while the proportion of residual arsenic increased,which was basically consistent with commercial manganese oxides.The results of high-throughput sequencing showed that after 30 days of bio-manganese oxide remediation,the biodiversity of soil was significantly improved,and the bacterial structure was significantly changed at phylum,class and genus levels.The higher the dosage of manganese oxide,the more obvious the change of bacterial community.