Abstract: Chemical remediation of hexavalent chromium Cr(VI) contamination in soil involves two processes of reduction and stabilization. The aim of this study was to reduce the highly hazardous and highly mobile Cr(VI) in soil to the low hazardous and easily adsorbed trivalent chromium Cr(III), and further achieve stabilization. Chromium-contaminated soil from an industrial site in Ningbo, Zhejiang province, was selected for remediation. The effectiveness of different ratios of reducing agents, including oxalic acid, ferrous sulfate, urea, attapulgite clay, and zero-valent iron, was compared by measuring the Cr(VI) content in the soil. Based on reduction effectiveness and raw material costs, four different ratios of reducing agents were determined, namely 1% zero-valent iron, 1% ferrous sulfate, 0.5% attapulgite soil, and 3% ferrous sulfate. These four reducing agents were combined in pairs and added to the soil to compare their reduction effects. Four stabilizing agents, included biochar, quicklime, calcium-magnesium phosphate fertilizer and water-soluble silicon fertilizer were added to the reductant reduced soil with a mass ratio of 2%, and the Cr(VI) content in the soil was measured to evaluate the stabilizing effects. The results showed that the combination of 1% zero-valent iron and 1% ferrous sulfate achieved a reduction rate as high as 70.2%, demonstrated better reduction effects and lower costs compared to other treatments, so this combination was identified as the optimal reducing agent combination. The stabilization effect of 2% biochar was the best, and it was finally determined to be the stabilizer. In summary, the compound formulation of 1% zero-valent iron +1% ferrous sulfate and 2% biochar has the best reduction and stabilization effect on Cr(VI) which could be further verified in actual operation.

Key words: soil contamination, hexavalent chromium, chemical remediation, reducing agents, stabilizing agents