Abstract: Ferrous sulfate (FeSO4) was used to stabilize chromium-contaminated soils. Leaching test, alkaline digestion test and sequential extraction test were conducted to investigate the effects of particle size and organic dosage on the stability properties and risk assessment of FeSO4-treated chromium-contaminated soils, respectively. Results showed that the leaching concentration (hexavalent chromium and total chromium) and hexavalent chromium content decreased significantly with the decrease of particle size, but decreased with the increase of organic dosage. When Fe(II)/Cr(VI) molar ratio was three, the Cr(VI) and total Cr leaching concentrations were about 4.68 mg/L and 8.9 mg/L, respectively, which were lower than the Identification standards for hazardous wastes: identification for extraction toxicity (GB/T5085.3－2007) of China. Furthermore, when Fe(Ⅱ)/Cr(VI) molar ratio was three and organic dosage was 5%, the amount of Cr(VI) in the soil was 28.3 mg/kg, lower than the threshold allowed by Environmental quality standards for soils (GB15618－2008) for industrial and commercial reuse of China (Cr(VI)<30 mg/kg). However, the residential land reuse (Cr(VI)<5 mg/kg) was only achieved by adding the organic dosage of 10%. Sequential extraction test showed that with the decrease of particle size, the weak acid-soluble fraction of Cr content decreased, the Cr content in the reducible state increased, while the Cr content in the oxidisable state was slightly affected. In addition, organic matter transformed Cr from weak acid-soluble fraction and reducible fraction to oxidisable fraction. The changing in the stability properties and risk assessment of stabilized soil can be attributed to the change of chromium speciation.

Key words: chromium-contaminated soil, stabilization, leaching properties, speciation evolution, risk assessment