Investigating immobilization efficiency of Pb in solution and loess soil using bio-inspired carbonate precipitation

Abstract

Lead (Pb) metal accumulation in surrounding environments can cause serious threats to human health, causing liver and kidney function damage. This work explored the potential of applying the MICP technology to remediate Pb-rich water bodies and Pb-contaminated loess soil sites. In the test tube experiments, the Pb immobilization efficiency of above 85% is attained through PbCO3 and Pb(CO3)2(OH)2 precipitation. Notwithstanding that, in the loess soil column tests, the Pb immobilization efficiency decreases with the increase in depth and could be as low as approximately 40% in the deep ground. PbCO3 and Pb(CO3)2(OH)2 precipitation has not been detected as the majority of Pb2+ combines with –OH (hydroxyl group) when subjected to 500 mg/kg Pb2+. The alkaline front promotes the chemisorption of Pb2+ with CO32− reducing the depletion of quartz mineral close to the surface. However, OH− is in shortage in the deep ground retarding the Pb immobilization. The Pb immobilization efficiency thus decreases with the increase in depth. Quartz and albite minerals, when subjected to 16,000 mg/kg Pb2+, appear not to intervene in the chemisorption with Pb2+ where the chemisorption of Pb2+ with CO32− plays a major role in the Pb immobilization. Compared to the nanoscale urease applied to the enzyme-induced carbonate precipitation (EICP) technology, the micrometer scale ureolytic bacteria penetrate into the deep ground with difficulty. The ‘size’ issue remains to be addressed in near future.