The Selection Of Washing Reagents For Soils Polluted By Cadmium And Chromium

This paper summarized remediation technologies for soils polluted by heavy metals and the research progress of washing reagents.The status quo of the soils polluted by cadmium and chromium was briefly discussed. Based on the consultation of papers, three organic acids, two chelating agents and one biosurfactant were chosen as the washing reagents for this study. Laboratory investigation was promoted to compare the effects of various washing reagents and the influence of concentration and time towards washing efficiency. The results are as follows:(1) Citric acid and tartaric acid have a remarkable effect towards cadmium in soils, after8hours citric acid and tartaric acid can remove59.50%and58.75%of Cd respectively at the concentration of0.6mol/L Oxalate acid is less efficient than citric acid and tartaric acid. EDTA can remove38.00%of Cd, MGDA can remove Cd to some extent, while it is not as efficient as EDTA. Saponin can hardly remove Cd from contaminated soils.(2) Citric acid, tartaric acid and oxalate acid can effectively remove Cr from contaminated soil. Their efficiency is in the following order oxalate acid>citric acid>tartaric acid. At the concentration of0.6mol/L citric acid, tartaric acid, oxalate acid can reach the removal rate of39.52%、30.44%and43.11%after12hours。EDTA has a comparatively low efficiency, and can only remove9.66%of Cr at the concentration of0.1mol/L, MGDA and saponin can hardly remove Cr from soil.(3) The BCR sequential extraction procedure indicates that the content of acid extractable, reducible, oxidizable and residual fraction of Cd-contaminated arid soil are:23.60%、37.20%、21.00%、18.20%, as to Cd-contaminated paddy soil, the number is:41.82%、24.00%、13.36%、20.82%. The fraction of heavy metal plays an important role in washing effectiveness of reagents. For example, the saponin can only remove7.5%of the total Cd from Cd-contaminated acid soil at the concentration of4%, while it can remove41.59%of Cd from Cd-contaminated paddy soil.The results indicate that organic acids are promising agents for soil washing processing, and the removal efficiency of heavy metals depends on the concentration of washing agents, reaction time, the fraction distribution of heavy metals in soils.