Abstract: Immobilization property of sodium diethyl dithiocarbamate (DDTCNa) on Cr³⁺ and Ni²⁺ in polluted soil was investigated by column leaching process. Experimental results indicated that good immobilization effect of heavy metals in polluted soil was obtained when DDTCNa was used. Especially， DDTCNa showed better immobilization effect on Cr³⁺. Immobilization rate of heavy metal increased with the increase of DDTCNa dosage. When DDTCNa dosage was 110g·kg^-1， more than 99% of Cr³⁺ and Ni²⁺ can be immobilized. Additionally， leaching pH had some effect on immobilization of Cr³⁺ and Ni²⁺. With the reducing of leaching pH， immobilization effect of Cr³⁺ and Ni²⁺ decreased. However， high immobilization rate of Cr³⁺ and Ni²⁺， which were more than 90%， could also be obtained. And immobilization rate of Cr³⁺， which was higher than 99.68%， decreased slightly with the reduction of leaching pH. The formation of metal sulfide chelating precipitates and the immobilization mechanism were systematically studied by XRD measurements and coordination chemistry analysis. The results showed that four-membered chelating precipitates with the coordination number of 4 and 6， respectively， which were Ni(DDTC)₂ and Cr(DDTC)₃， could be obtained when DDTCNa reacted with the heavy metals. Moreover， the stability of Cr(DDTC)₃ was much better than Ni(DDTC)₂， so better immobilization property of Cr³⁺ was obtained.

Key words: sodium diethyl dithiocarbamate (DDTCNa);heavy metals, immobilization, soil, chelating precipitates