Batch washing of cadmium from soil and sludge by a mixture of Na2S2O5 and Na2EDTA

Washing of cadmium contaminated soil and sludge using a mixture of 0.1 M Na2S2O5 and 0.01 M Na2EDTA was investigated in the batch mode. Initial Cd concentration in samples was 500 mg kg−1. The sequential extraction was conducted to study of what form that Cd was removed. SPSS program version 9.01 was performed to determine what soil parameter had the greatest influence on the washing. The organic matter in soil was found to be the main factor for the washing. Soil with low organic matter would have high percentage of removing Cd. When adding more washing solution, the Cd removal efficiency was lower. The highest removal efficiency was between 67.83% and 97.3% when using a 1 g:2.5 ml soil to washing solution ratio. The predominant form of the removed Cd was exchangeable form. By contrast for the sludge, the highest Cd removal efficiency was 17.13% when using sludge in washing solution at the ratio of 1 g:7.5 ml. Most of washed Cd was in reducible form.