College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, 730000, China.
College of Agronomy and Biotechnology, China Agricultural University, Beijing, 100094, China.
Environ Pollut. 2024 Oct 1;358:124537. doi: 10.1016/j.envpol.2024.124537. Epub 2024 Jul 11.
Microbially induced carbonate precipitation (MICP) is a promising technique for remediating heavy metal-contaminated soils. However, the effectiveness of MICP in immobilizing Cd in alkaline calcareous soils, especially when applied in agricultural soils, remains unclear. Biochar and magnesium oxide are two environmentally friendly passivating materials, and there are few reports on the combined application of MICP with passivating materials for remediating heavy metal-contaminated soils. Additionally, the number of treatments with MICP cement and the concentration of calcium chloride during the MICP process can both affect the effectiveness of heavy metal immobilization by MICP. Therefore, we conducted MICP and MICP-biochar-magnesium oxide treatments on agricultural soils collected from Baiyin, Gansu Province (pH = 8.62), and analyzed the effects of the number of treatments with cement and the concentration of calcium chloride on the immobilization of Cd by MICP and combined treatments. The results showed that early-stage MICP could immobilize exchangeable cadmium and increase the residual cadmium content, especially with high-concentration calcium chloride MICP treatment. However, in the later stage, soil nitrification and exchange processes led to the dissolution of carbonate-bound cadmium and cadmium activation. The fixing effect of MICP influence whether the MICP-MgO-biochar is superior to the MgO-biochar. Four treatments with cement were more effective than single treatment in MICP-biochar-magnesium oxide treatment, and the MICP-biochar-magnesium oxide treatment with four treatments was the most effective, with passivation rates of 40.7% and 46.6% for exchangeable cadmium and bioavailable cadmium, respectively. However, attention should be paid to the increase in soil salinity. The main mechanism of MICP-magnesium oxide-biochar treatment in immobilizing cadmium was the formation of Cd(OH), followed by the formation of cadmium carbonate.
微生物诱导碳酸钙沉淀（MICP）是修复重金属污染土壤的一种很有前途的技术。然而，MICP 在固定碱性钙质土壤中的 Cd 的效果，特别是在农业土壤中应用时，仍不清楚。生物炭和氧化镁是两种环保钝化材料，关于 MICP 与钝化材料联合应用修复重金属污染土壤的报道较少。此外，MICP 过程中使用的 MICP 水泥的处理次数和氯化钙的浓度都会影响 MICP 固定重金属的效果。因此，我们在甘肃省白银市采集的农业土壤上进行了 MICP 和 MICP-生物炭-氧化镁处理，并分析了水泥处理次数和氯化钙浓度对 MICP 及联合处理固定 Cd 的影响。结果表明，早期的 MICP 可以固定可交换态镉并增加残留镉含量，尤其是高浓度氯化钙 MICP 处理。然而，在后期，土壤硝化和交换过程导致碳酸盐结合态镉的溶解和镉的活化。MICP 的固定效果影响 MICP-MgO-生物炭是否优于 MgO-生物炭。在 MICP-生物炭-氧化镁处理中，4 次水泥处理比单次处理更有效，4 次水泥处理的 MICP-生物炭-氧化镁处理效果最好，对可交换态镉和生物有效态镉的钝化率分别为 40.7%和 46.6%。但是，应注意土壤盐度的增加。MICP-氧化镁-生物炭处理固定镉的主要机制是形成 Cd(OH)2，随后形成碳酸镉。
