Chromium speciation and leaching behaviors of hexavalent chromium contaminated soil stabilized by FeSO4

Ferrous sulfate(FeSO4)was used to stabilize chromium-contaminated soils. Leaching test, alkaline digestion test and sequential extractions test were conducted to investigate the variation of chromium speciation and leaching properties of FeSO4 treated chromium-contaminated soils along with Fe(II)/Cr(VI) molar ratio and curing time. Results showed that the leaching concentration(hexavalent chromium and total chromium) and hexavalent chromium content of the soil were decreased significantly with Fe(II)/Cr(VI) molar ratio and curing time. When Fe(II)/Cr(VI) molar ratio was 3, the Cr(VI) and total Cr leaching concentrations 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 10, the amount of Cr(VI) in soil was below the threshold allowed by Environmental quality standards for soils(GB15618-2008) for industrial and commercial reuse of China (Cr(VI)<30 mg/kg). And the civil reuse of soil (Cr(VI)<5 mg/kg) was only achieved with Fe(II)/Cr(VI) molar ratio of 20. Sequential extraction procedures revealed that majority of acid soluble fraction of chromium was converted to reducible fraction with FeSO4 stabilized. The leaching concentration of Cr(VI) increased as exponential function with the amount of Cr(VI) increases in soil. The leaching test (TCLP, SPLP) could not reliably evaluate the stability effect of chromium.