Abstract: Ferrous sulfate(FeSO4) is used to stabilize chromium-contaminated soils. Leaching test, alkaline digestion test and sequential extractions test are conducted to investigate the variation of stabilize properties of FeSO4 treated chromium-contaminated soils along with particle size and pH. The results show that the leaching concentration(hexavalent chromium and total chromium), hexavalent chromium content of the soil are decreased significantly with particle size decreased. Sequential extractions test show that: with the decreased of particle size, the weak acid soluble fraction(F1) of chromium content decreased, while the reducible(F2) and oxidisable(F3) changed oppositely. The hexavalent chromium leaching concentration and hexavalent chromium content were decreased significantly with pH decreased; while the total chromium leaching concentration changed oppositely. There is a threshold value for pH in terms of its influence on chromium speciation. The weak acid soluble and oxidisable fraction of chromium content decreased with the pH decreased before its reached the threshold value; while the reducible changed oppositely. The weak acid soluble of chromium content increased with the pH decreased after its reached the threshold value; while the reducible and oxidisable fraction changed oppositely. The changing in stabilized 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