Microbial-induced carbonate precipitation prevents Cd²⁺ migration through the soil profile

Cadmium (Cd)-containing wastewater has been used to irrigate agricultural land. However, long term usage has resulted in the accumulation of Cd in the soil systems, which can eventually leach into the aquifer, contaminating groundwater. Microbial-induced carbonate precipitation (MICP), an economical and effective method, was used to block the in situ migration of Cd²⁺ in the soil profile. The results of the laboratory experiments showed that the maximum Cd²⁺ adsorption capacity of the soil exposed to MICP (8.92 mg/g) was higher than that of soil without MICP (7.12 mg/g). The Thomas model provided a good fit for the Cd²⁺ migration process in soil exposed to MICP (R² > 0.96), and Cd²⁺ was trapped more effectively by soil exposed to MICP than by soil alone. Further testing showed that the Cd²⁺ retention time in the MICP soil column increased with increasing soil urea content and pH but decreased with increasing flow rate. Soil physico-chemical properties showed that the MICP process increased the soil particle size and Cd capacity and decreased the proportion of exchangeable Cd in the soil. Scanning electron microscopy and X-ray diffraction analyses confirmed the generation of CdCO₃ in the MICP soil column. The findings of this study indicate that MICP can be effectively used to immobilize Cd²⁺ and prevent its migration in the soil profile.