微生物诱导碳酸盐沉淀及其在固定重金属领域的应用进展

生物矿化已受到化学、物理、生物、材料、医学、生命及环境等多学科的广泛关注，其中，以尿素为底物的MICP（微生物诱导碳酸盐沉淀）技术是生物矿化领域的研究热点之一.在分析MICP过程中的酶解机理和生物大分子在微生物矿化过程中的作用基础上，通过对重金属离子的矿化产物和碳酸盐矿化菌的成矿因素分析，揭示MICP矿化产物的特征及形成条件.碳酸盐矿化菌主要产生脲酶分解尿素，增加土壤CO₃2-饱和度，其代谢产生的胞外聚合物具有多种功能团组合和键能连接，起着调控生物矿化的作用.MICP技术可用于固定土壤和水体中的Cu、Pb、Zn、Cd、Cr、As等重金属，重金属主要以共沉淀的形式被固定，阴阳离子型重金属以类质同象置换方式分别占据方解石中的CO₃2-位和Ca2+位，从而促使污染土壤中的可交换态重金属向碳酸盐结合态转移.但是，MICP技术主要针对减少重金属的生物可利用性，不能满足以全量来计算的现行土壤环境质量标准，且MICP技术在长期有效性、生物安全性和土壤理化性质等方面存在诸多隐患.因此，由试验条件转向实际应用具有一定挑战.建议寻找更稳定的方法以阻止碳酸盐矿物中的重金属溶出，且有必要将开发高效的土著微生物复合菌剂作为未来MICP研究的方向之一. 

Microbial Induced Carbonate Precipitation and Its Application for Immobilization of Heavy Metals: a Review

Biomineralization has attracted much attention from chemistry, physics, biology, material, medicine, life and environment sciences. Microbial induced carbonate precipitation (MICP) using urea as the substrate is one of the hot topics. Herein, we reviewed the enzymatic mechanism of MICP and the function of biomacromolecule in the progress of biomineralization. Previous studies showed that the concentration of soil carbonate increases due to the decomposition of urea which can be enhanced in the presence of urease produced by ureolytic bacteria. Meanwhile, the extracellular polymer substance (EPS) secreted by the bacteria, possessing varied functional groups and chemical bonding, can regulate the biomineralization. The results demonstrated that MICP can remediate heavy metals pollution, such as Cu, Pb, Zn, Cd, Cr and As both in soil and solution. Co-precipitation is the dominant mechanism for the heavy metals immobilization, via cation → Ca2+/anion → CO₃2- substitution, resulting in carbonate-bound heavy metals. Therefore, MICP is useful to reduce the bioavailability of heavy metals. However, it does not change the soil quality according to the current standards which base on the total concentration of heavy metals. Furthermore, there are potential risks on several topics, such as long-term validity, biological safety and change of physical or chemical properties, which challenge the application of MICP to immobilize heavy metals in soil. The technique should be further developed to re-immobilize the released heavy metals due to the dissolution of carbonate minerals. Meanwhile, multiple native microbial communities should be developed to insure the effectiveness of MICP in varied environments.