| At present, the pollution of rivers and lakes in China is very serious, and the environmental dredging projects are increasing,producing a lot of pollution. The reduction and harmless treatment of dredging sediment is the key to the utilization of the resources,the emoval of heavy metals from sediments is the most important one. If not handled properly, not only environmental pollution would be caused, but it is also a wastage of precious metal resources. Electrokinetic remediation is a technique of using low voltage DC,which is applied at two ends, to remove heavy metal from polluted sediment by electric potential. Most of the heavy metals in the sediment can be removed by utilizing this electric repair technology,which is a high efficiency and fast technique. In this paper,laboratory-developed device of electrokinetic remediation was designed to remove the cadmium (Cd) for rapid-dehydrated sediment. The author explores the effect of voltage,reinforcing agent,electrode materials,processing time and different concentration of Cd on the removal rate of Cd, and by using metal chelating to recycle Cd from the water, the optimum process conditions was obtained. The experimental results show that:(1) In identical initial conditions, when the test voltage is 10 V, the removal rate of Cd was 54.78%, when the voltage rise to 30 V, the removal rate of cadmium reached 70.60%,the water content of sediment decline from 75% to 47.5%. Therefore, the increase of voltage is conducive to the removal of heavy metals and moisture.(2) Pretreating the sediment with cationic polyacrylamide (CPAM) and citric acid (CA)respectively, and experiments were carried out. It found that as sediment was pretreated by CPAM, the removal rate of Cd is 83.42%; the removal rate of it is 79.82% with the pretreatment by CA, which are higher than the contral group. Experiment also shows that CPAM can promote the dehydration and reduce the turbidity of water,so it is a good agent enhanced electrokinetic remediation.(3) In the case of the same initial conditions, the removal efficiency of Cd was compared with using different types of electrodes for electrokinetic remediation, the results showed that the removal efficiency high-to-low sequence was: porous carbon, graphite plate and stainless steel plate.(4) In the early stage of electrokinetic remediation, the removal rate of Cd increased fast, and the later growth slowed down, from 5 h to 6 h, the removal rate of Cd only increased by 0.024%, the water content of sediment does not change basically after 5 h.(5) Experiment under different concentrations of Cd, founding that the removal rate is about 80% when the concentration at 0.5 g/g-2.0 g/g of Cd, repairing effect is better, with the concentration increased, the removal efficiency decreased.The voltage was 30V, adding the enhancement agent CPAM, using porous carbon as electrode, processing 6 h, the removal rate of Cd was the highest, which was 91.12%.(6) Compared with the commercially available DTC organic sulfur, the laboratory-made metal trapping agent LH-07 is less used and the removal rate is higher. When the ratio of LH-07 to the residual water volume was 0.09:1, the removal rate of Cd2+ was the highest,which was 95.06%. The maximum removal rate of Cd2+ was 93.96% with the DTC organic sulfur when the volume ratio was 0.4:1. |
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