Experimental Study on Stabilization of Heavy Metal-Contaminated Soil by Biochar–MICP–Electrokinetics Combined Technology

Soil heavy metal pollution is becoming increasingly severe, while traditional remediation methods are inefficient and lack long-term stability. This study innovatively combines electrokinetic remediation (EK), microbial-induced calcium carbonate precipitation (MICP), and biochar for synergistic stabilization of contaminated soil. It evaluates the combined technology by comparing it with individual EK and MICP treatments through chemical speciation analysis and the Toxicity Characteristic Leaching Procedure (TCLP). The concentration of 1 mol/L urea–CaCl2 was identified as optimal for microbial activity, achieving a microbial cell density (OD600) of 1.0, a urease activity of 12 U/g, and a soil pH maintained within the range of 7.8–8.2. Corn stover biochar significantly enhanced urease activity—being 49.4% higher than that in the coconut shell biochar group and 25% higher than that in the bamboo biochar group—and increased the microbial survival rate by 25.4%. Group D1, which adopted the sequence of “EK treatment first, followed by biochar-synergized MICP treatment,” exhibited the best performance. It achieved stabilization efficiency of 51.90%, 73.40%, and 36.26% for bioavailable Cu, Cd, and Pb, respectively—all higher than those of individual EK and MICP treatments. Additionally, the residual fractions of heavy metals increased significantly, the leaching concentration of Cd in the anode region was below 1 mg/L, and energy consumption was 12.16% lower than that of the EK group. Microstructural analysis confirmed that the combined method promoted the formation of stable calcite, thereby improving soil aggregation and alleviating soil compaction. These findings collectively validate the proposed technology as a highly effective and sustainable strategy for stabilizing heavy metal-contaminated soil.