Adsorption Stability And Improvement Of Heavy Metals In Soil By Biochar-zeolite Combined With MICP

The pollution caused by heavy metals has always been the focus of environmental protection,especially the soil pollution caused by heavy metals,which poses a great threat to human health.Microbial-induced calcium carbonate precipitation(MICP)has been widely used in remediation of soil pollution,but a large amount of ammonia is produced in this process,which is easily released into the environment and causes secondary pollution.In recent years,biochar-zeolite composites have been applied in soil remediation and improvement,and have good adsorption effect on ammonia.Therefore,this study investigated the modification and improvement effect of biochar-zeolite composites combined with MICP on soil.Firstly,biochar and zeolite composites were prepared by ball milling method,and characterized.The results showed that biochar and zeolite were combined evenly and the composite effect was good.The toxicity of biochar-zeolite composite material on urease producing bacteria was investigated.The results showed that under the dosage of biochar-zeolite composite material selected in this experiment,it had no inhibition on microbial growth,and it could be used to strengthen MICP remediation of heavy metal contaminated soil.Secondly,the stabilization effects of composite materials on heavy metals and ammonia nitrogen in water and soil were studied.The results show that the dosage is 10g/L,water temperature is 30℃,p H is 7-8,reaction time is 120 min,ammonia nitrogen concentration,cadmium ion concentration is 50 mg/L,lead ion concentration is 200 mg/L:The removal rates of ammonia nitrogen,Cd and Pb are 50.79%,99.15% and 99.21%,and the adsorption capacities are 2.54 mg/g,4.96 mg/g and 19.84 mg/g,respectively.When the ratio is 1:1 and the milling time is 6 h,the removal rates of Pb and Cd in the composite with MICP(MM5)are 97.82% and 96.94%,respectively.Compared with the composite material with ratio 1:1 and ball milling time 6 h(BM5)The increase was 20.97% and17.53%,respectively.In the soil remediation experiment,the effective state,leaching and speciation of heavy metals were determined.The results showed that cac L2-diethyltriamine pentaacetic acid(DTPA)content of Pb and Cd decreased by45.73%～57.88% and 62.5%～67.24%,respectively,compared with CK,after biochar-zeolite combined MICP treatment.Compared with CK,the carbonate binding state of Pb increased by 5.4%～6.4%,and the exchangeable state content of Cd decreased by5.7%～6.5%,indicating that composite materials combined with MICP technology can enhance the stability of heavy metals in soil.Finally,the effects of composite materials combined with MICP technology on the physical and chemical properties of heavy metal contaminated soil and plant growth were investigated.The results showed that after MM treatment,soil organic matter content increased by 9.54～40.37 mg/kg compared with CK,and plant fresh and dry weight increased by 0.8%～72.68% and 6.1%～108.16% compared with CK,respectively.Compared with CK,the root length of plants increased by 88.89%-111.11%,and the plant height increased by 61.43%-82.85%.It can be concluded that composite materials combined with MICP can improve soil physical and chemical properties,increase soil nutrients,promote plant growth,and reduce the threat of heavy metals to plant growth.In conclusion,the results of this study have certain theoretical significance and practical application value for the fixation of heavy metals in soil.