In China, thousands of tons of highly toxic hexavalent Cr slags are produced annually. The existing remediation technologies face challenges due to the facile oxidation, “re-yellowing” effects, and contamination from iron additives, hindering the achievement of sustained governance and resource recycling for Cr pollution. This study conducted microbial mineralization experiments on soil at actual Cr-contaminated sites, delving into the stability, recyclability, and reaction mechanisms of mineralization products. The results indicate that this method can efficiently reduce Cr6+ and Fe3+ in Cr slag to form precipitates. After 60 d extensive air exposure, the mineralized products exhibited little reoxidation or re-decomposition, and demonstrated weak magnetism, indicating a potential for recovery by magnetic separation. This paper was to investigate a low-cost, efficient in-situ, and long-term governance solution for treatment of Cr pollution on-site and facilitation of the recovery and reuse of Cr resources.