Positively and negatively charged additives modulate microbial-induced carbonate precipitation (MICP) for lead-contaminated loess remediation

leaching to seventy to eighty milligrams per liter after cycling, consistent with uniform carbonate precipitation observed in SEM. In contrast, CS induced more negative potentials, about minus sixteen point two millivolts, but suppressed microbial activity, leading to patchy precipitation and higher leaching levels of ninety to ninety-five milligrams per liter. Collectively, the findings demonstrate that additive regulation of diffuse double layer characteristics and precipitation pathways governs both mechanical durability and heavy metal stabilization. GO provided the most favorable balance between strength and Pb immobilization, followed by Ca-Ls, while CS showed limited benefits. This study provides new insights into additive-assisted MICP as a practical and sustainable strategy for improving the environmental safety and engineering reliability of Pb-contaminated loess under freeze-thaw conditions.