• Remediated soil treated by thermal curing exhibited strong inherent resistance to acidic attack with the formation of ZnCr₂O₄ spinel.

The centralized utilization of heavy-metal-contaminated soil has become the main strategy to remediate brownfield-site pollution. However, few studies have evaluated the ecological and human health risks of reusing these remediated soils. Considering Zn as the target metal, systematic pH-dependent leaching and the Community Bureau of Reference (BCR) extraction were conducted at six pH values (pH= 2, 4, 6, 8, 10, 12) for the remediated soil treated through thermal curing. The pH-dependent leaching results showed that with the formation of ZnCr₂O₄ spinel phases, the remediated soil exhibited strong inherent resistance to acidic attack over longer leaching periods. Furthermore, the BCR extraction results showed that the leaching agent pH value mainly affected the acid-soluble fraction content. Moreover, a strong complementary relationship was noted between the leaching and acid-soluble fraction contents, indicating that the sum of these two parameters is representative of the remediated soil risk value. Therefore, we proposed a two-step calculation method to determine the sum of the two heavy metal parameters as the risk value of remediated soil. In contrast to the traditional one-step calculation method, which only uses the leaching content as the risk value, this two-step calculation method can effectively avoid underestimating the risk of remediated soil.