微生物固化和稳定化铅污染粉土的强度与污染物浸出特性

Strength and pollutant leaching characteristics of microbial solidified and stabilized lead-contaminated silt

微生物矿化修复重金属污染土场地可同步实现控制污染物与提高土体强度的双重目标。采用巴氏芽孢杆菌对铅污染粉土进行注浆固化和稳定化试验,以胶结液浓度、铅污染浓度为影响变量,分析污染粉土的固化强度特性,以及铅污染物的稳定化形态与浸出特性。结果表明:微生物固化500 mg/kg铅污染粉土的强度能够达到793 kPa,可交换态铅含量降至94.8 mg/kg;浓度为0.50~0.75 mol/L胶结液比更高浓度的胶结液有利于控制顶出液中铅污染物的流失;微生物固化和稳定化粉土中可交换态铅和碳酸盐结合态铅含量呈负相关关系。对于铅污染浓度低于500 mg/kg的粉土,在酸性浸提液下的毒性淋滤试验(TCLP)铅离子浸出浓度能够降至5 mg/L的限值内。方解石和铅-钙碳酸盐共沉淀形成的无定形团聚体是固化铅污染粉土的主要胶结物,铅污染物通过碳酸盐共沉淀、直接吸附、碳酸钙包裹等形式实现稳定化。物理破碎能够使部分包裹稳定化的铅污染物二次释放。微生物注浆处理能够有效提高铅污染粉土的强度,大幅降低污染粉土中可交换态铅的占比,对铅污染物有良好的稳定效果。

Bioremediation of heavy metal contaminated soil sites by microbial mineralization can simultaneously achieve the dual goals of controlling pollutants and improving soil strength.The solidification and stabilization tests of lead-contaminated silt were carried out by using Bacillus pasteurii.In the tests,the control variables were concentrations of cementing solution and lead-contaminated concentrations of silt.The solidifying strength,the stabilization form and leaching characteristics of lead-contaminated silt were analyzed.The applicability,microbial solidification mechanism and lead-contaminated silt stabilization were discussed based on the microscopic morphology of microbial-induced mineral deposition products.The results show that the strength of 500 mg/kg lead-contaminated silt solidified by microorganism reachs 793 kPa,and the exchangeable lead content is reduced to 94.8 mg/kg.The cementing solution with a concentration of 1.00 mol/L can achieve higher strength and lead stability for lead-contaminated silt than other cementing solution.The cementing solution with the concentration of 0.50-0.75 mol/L is better than that with high concentration to control the loss of lead pollutants in the push-out liquid.For 1000 mg/kg lead-contaminated silt,the lead ion loss rate in push-out liquid is reduced to 1.21%.When the cementing solution concentration is 1.00 mol/L,the carbonate production is the highest one,but too high cementing solution concentration is not conducive to carbonate precipitation.There is a negative cor-relation between exchangeable lead and carbonate bound lead in microbial solidified and stabilized silt.The proportion of exchangeable lead in contaminated silt is greatly reduced by bio-grouting.Bio-grouting treatment reduces the exchangeable lead content of 500 mg/kg contaminated silt to less than 26.7%.Using 1.00 mol/L cement solution,the exchangeable lead contents in silt contaminated with 100,300,500 and 1000 mg/kg are reduced to 14.6,43.7,94.8 and 269.2 mg/kg,respectively.For silt contaminated with lead concentration less than 500 mg/kg,even under acidic leaching conditions,the lead leaching concentration by TCLP is reduced to less than the limited value of 5 mg/L.The amorphous aggregates formed by co-precipitation of calcite and lead-calcium carbonate are the main cementations for solidifying lead-contaminated silt.Lead pollutants are stabilized by carbonate co-precipitation,direct adsorption and calcium carbonate encapsulation.Physical crushing make partial package stabilized lead pollutants release again.Bio-grouting treatment can effectively improve the strength of lead-contaminated silt,and greatly reduce the proportion of exchangeable lead in the contaminated silt,and has a good stabilization effect on lead pollutants.