Micro Analysis of Lead Immobilization Mode of Microbial Induced Calcium Carbonate Precipitation

Microbial-induced carbonate precipitation (MICP) is an effective technology for repairing heavy metal-contaminated soil and groundwater. Previous studies have shown that MICP is capable of immobilizing various heavy metals including lead (Pb) and revealed immobilization mechanisms include abiotic precipitation, biotic precipitation and bio-sorption. However, the difference in curing modes under different bacterial solution concentration and lead ion concentration has not been systematically studied. This study: (1) the curing efficiency under different bacterial solution concentration, different cementing solution concentration and different lead ion concentration was studied; and (2) identifies controlling biotic and abiotic factors of the Pb immobilization model by MICP. Under different cement solution concentrations, with the increase of cement solution concentration, the precipitation quality first increases and then decreases. The cement solution concentration of 0.75 mol/L and Pb2+ concentration of 600 mg/L have the highest yield of calcium carbonate. The cement solution concentration is roughly negatively correlated with the removal rate of lead ions; In the test tube test with different bacterial solution concentration, the bacterial solution concentration was positively correlated with the yield of calcium carbonate. Through a series of micro tests, it can be seen that when the bacterial solution concentration is low, the calcium carbonate is mainly massive and spherical crystal, and when the bacterial solution concentration is high, the calcium carbonate crystal is scaly. When the concentration of bacterial solution is low, the solidification mode of lead is mainly calcium carbonate wrapping and surface adsorption. When the concentration of bacterial solution is high, the solidification mode of lead is mainly coprecipitation. The biological mechanism mainly occurs in a period of time before precipitation.