Study On The Synergistic Solidification Of Manganese In Electrolytic Manganese Residue By Microorganisms And Red Mud

The rapid development of the electrolytic manganese industry makes the accumulation of electrolytic manganese residue(EMR)increase day by day,and the leaching of soluble manganese ions from EMR has caused damage to the local ecological environment.To reduce the leaching of manganese ions,it is imperative to find a suitable manganese ion curing method.In this paper,a typical manganese slag yard in Guangxi was taken as the research object,and the spatial distribution characteristics of heavy metal pollution and microorganisms in the site were investigated and analyzed.The optimum conditions and solidification mechanism of red mud-sulfate reducing bacteria(SRB)synergistic solidification of manganese in EMR were explored.The synergistic remediation effect was further verified by dynamic leaching column experiments,and high-throughput sequencing technology was used to analyze the differences in microbial community structure and changes in functional genes.The field repair work verified the actual effect of the bacterial liquid spray repair.The results of this study are as follows:The results of field investigation showed that only Mn in the leachate of the slag yard exceeded the limit of the Integrated Wastewater Discharge Standard(GB 8978-1996),and the maximum exceeding multiple was 2790 times.Other heavy metals did not exceed the standard.The contents of Cd,Pb,Fe,Mn,and As in EMR were positively correlated with the depth of the slag heap,and the physicochemical properties of leachate were also correlated with microorganisms.The contents of Mn2+,Mn3+,and Mn4+in EMR were 87.11%,8.14%,and 4.75%,respectively.The leaching toxicity of manganese was 1027.97 mg/L.The relative abundance of Desulfovibrio in SRB acclimated by Mn2+-rich medium was 11.8%.The optimum conditions of red mud-SRB synergistic remediation were determined by Taguchi experiment,that is,the addition amount of red mud was 20%,the inoculation amount of bacterial liquid was 15%,the temperature was 30℃,and the addition amount of yeast extract was 1.4 g/L.Under optimal conditions,the curing rate of manganese can reach 98.63%after 42 days of continuous repair.The synergistic solidification mechanism shows that the solidification mechanism of manganese by functional bacteria includes biotransformation,biomineralization and biosorption.Under the reductive remediation system,Mn3+ and Mn4+ in EMR were converted to Mn2+.Red mud provided cations such as Ca2+ and Mg2+ for the remediation system.Through biomineralization,the solidified products were manganese sulfide and ankerite((CaMg0.3Fe0.7Mn0.1)(CO3)2).The biosorption was manifested in the whole repair process,and the polysaccharides,phosphates,and peptides on the cell surface were involved in the adsorption of heavy metals.Under different leaching conditions,the leaching concentrations of Cu,Cd,Zn,As,and Pb in the solidified products were lower than those before remediation,which met the Surface Water Environment Quality Standard(GB 38382002)class V standards.The leaching concentration of manganese was 15.84 mg/L,and the synergistic remediation significantly reduced the leaching of manganese in the slag sample.The manganese concentration was 15.76 mg/L at 9 months after restoration,indicating that the solidified body had environmental stability and long-term effectiveness.The experiments in the leaching column showed that red mud-SRB synergistic remediation group(ECS)was more effective than the single SRB remediation group(ES).After 70 days of remediation,the manganese concentration in the leachate of ECS was 13.23 mg/L.Metagenomic analysis showed that the functional genes of microorganisms involved in metabolism,cellular processes,and signal transduction in the synergistic remediation system were improved,which was conducive to the establishment of microecology in the remediation system.The field demonstration project of SRB remediation of EMR showed that after 12 weeks of remediation,the solidification rate of Mn reached more than 99%,and the vegetation on the surface of the slag heap was restored.The average concentration of manganese in the leachate of the remediation area was 15.24 mg/L at 56 weeks after the start of remediation,and the manganese concentration in the remediation area showed a continuous decreasing trend.High-throughput sequencing results showed that microorganisms in the repair area promoted the circulation of N and S elements.