| The utilization of chemical eluant agents could activate and complex soil heavy metals, which achieve the goal of reducing soil heavy metal pollution. In order to evaluate the restoring efficiency of soil cadmium pollution, this study discussed the washing efficiencies of cadmium and distribution characteristics of cadmium as well as the changing of soil properties after washing by simulation in laboratory. The main results showed as follows:The leaching efficiency raised as the ascending concentrations of three kinds of organic acid, the cadmium leaching rate of citric was significantly higher than that for oxalic acid and tartaric acid (P<0.05). Under different pH status, cadmium leaching rate of citric acid of increased with the increasing of the pH. On the contrary, the cadmium leaching rates of oxalic acid and tartaric acid decreased when the pH increased. In addition, cadmium leaching rates of citric acid were 8 and 9 times of those for oxalic acid and tartaric acid when pH was 7.0. After washing, the residue states of cadmium increased by 30-40%(P<0.05).Among them, when the pH beyond 7.0, the residue states of cadmium was over 50% after washing by oxalic acid and tartaric acid. Furthermore, not obviously differences of soil organic matter were found after washing by low molecular organic acid, but with the increasing of pH, soil organic matter content showed a trend of decrease in general. When compared with before leaching, the concentrations of soil total nitrogen and total phosphorus significantly decreased by different concentrations of low molecular organic acid. Moreover, the concentrations of total nitrogen and total phosphorus decreased by 42% and 75% after washing by tartaric acid at 1%, but the total potassium increased generally. The concentrations of soil total nitrogen significantly reduced after washing by low molecular organic acid in different pH, but with the increase of pH, the concentrations of soil total nitrogen increased significantly. However, no apparently differences of soil total phosphorus were found after washing by citric acid in different pH conditions.Humic acid with low concentration on the removal of the soil cadmium pollution has a prominent effect when the pH status is 5.0. In addition, the combination of fulvic acid and potassium chloride on soil cadmium leaching efficiency appeared to increase and then decrease with the duration time. When the concentration of fulvic acid was 0.05%, the leaching time was 2 hours, leaching rate reached to 98.2%. The residue states of cadmium occupied more than 50% of total cadmium after washing with humic acid in each concentration. However, in acidic conditions the exchangeable states of cadmium was dominant speciation. When the duration time was 4 hours by the combination of fulvic acid and potassium chloride, the residue speciation of cadmium was 1.07-1.43 times compared with before washing. The concentrations of soil organic matter increased after washing by humic acid. In addition, with the increasing pH of humic acid, the concentrations of soil organic matter showed a trend of increase then decrease after washing. Moreover, the concentrations of soil total nitrogen and total phosphorus reduced significantly by washing with humic acid. While no significant decreased of soil total potassium was found after washing, which were in line with the variations of soil total nitrogen, phosphorus and potassium after washing by humic acid in different pH conditions.The remediation experiment of mine soil indicated that humic acid and the combination of fulvic acid and potassium chloride appeared more effective in removing of cadmium for mine soil. Besides, the residue speciation of cadmium was more than 50% after washing by each agent. In conclusion, humic acid and the combination of fulvic acid and potassium chloride were promising in remediation of cadmium through soil washing process for mine soil. |
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