用淋洗法修复张士灌区Cd Pb污染沉积物的研究

Remediation of Sediment Contaminated by Cd and Pb in Zhangshi Irrigation AreaUsing a Washing Technology

采用淋洗法,以组成为0.5m ol·L-1C aC l2和0.1m ol·L-1H C l的复合药剂作为淋洗剂处理沈阳张士灌区C d、Pb污染沉积物(C d39m g·kg-1,Pb1250m g·kg-1),在pH=1.0、反应时间30m in、淋洗剂液固比3∶1、搅拌速度500r·m in-1、温度25℃的条件下,复合淋洗剂对C d和Pb的去除率分别达到70.8%和29.3%。粒级分析表明,沉积物中C d和Pb主要存在于细粒部分,因此,分级处理能够减少处理量,降低成本。一定酸度下C l-的络合作用可能是复合淋洗剂的主要强化淋洗机制。

A washing technology was applied to treat the sediment contaminatedby Cd and Pb in Shenyang Zhangshi irrigation area (Cd 39 mg·kg-1, Pb 1 250 mg·kg-1) using a solution containing 0.5 mol·L-1 CaCl2 and 0.1mol·L-1 HCl. The optimized prescription was obtained through systemic washing experiments in this study. Several related factors were optimized in the experiment, including reaction temperature, washing time and shaking rate in our laboratory. The results indicated that the suitable ratio of liquid and solid was 3∶1, the removal rates of Cd and Pb in the contaminated sediment were 70.8%and 29.3%,under the condition of pH=1.0, reaction time with 30 min, shaking rate at 500 r·min-1 and temperature at 25℃, respectively. The sediment granularity analysis showed that the heavy metals of Cd and Pb mainly existed in fine particles,therefore, classification pretreatment may reduce the treating load and decreased the cost greatly. In addition, the heavy metal contents in the leaching liquor were detected and a method of lime treatment was carried out to purify the leaching liquor to be regenerated easily. Meanwhile, the heavy metal contents, 0.1 mg·kg-1 of Cd and 0.51 mg·kg-1 of Pb, respectively, in the washed sediment were found to be in accordance with the standard of waste solid lixiviating liquid. The results indicated that the concentrations of Pb and Cd in the washed sediment were in allowable range. The main washing mechanism of CaCl2 and HCl solution might be the complex function of Cl-ion under 0.1 mol·L-1 H+ionconcentration, which was testified by the experiments through adding extra NaCland Ca(NO3)2, respectively. As a conclusion, this kind of washing technology may be practiced in situ remediation of heavy metal contaminated sediment.