农田土壤重金属Cd的环保淋洗剂筛选研究

土壤淋洗是一种有效修复重金属污染土壤的方法,而淋洗剂的选择是淋洗过程的关键因素,直接影响淋洗效率。研究了4种淋洗剂(乙酸、柠檬酸、CaCl₂、FeCl₃)对Cd轻度污染的农田土壤淋洗性能及影响因素。结果表明:淋洗效果依次为FeCl₃＞柠檬酸＞乙酸＞CaCl₂;FeCl₃的淋洗机理是Fe³⁺与土壤中的Cd²⁺离子交换,其水解出的H⁺可促进碳酸盐结合态Cd溶出,Cl^-还可与Cd²⁺形成稳定的螯合物;经优化后的最佳的淋洗条件是固液比为1∶5,浸提时间为4 h,此时乙酸、柠檬酸、CaCl₂和FeCl₃的最大土壤Cd去除率分别为30.24%,24.62%,24.82%,81.90%;pH值对淋洗效果的影响较大,除CaCl₂外,3种淋洗剂的淋洗效果都随pH值的升高而降低(pH值在2.5～5.0范围内),FeCl₃的淋洗效果降低最为显著。研究成果可为Cd污染农田土壤修复提供技术支撑。

Selecting Ferric Chloride as an Environmental-friendly Washing Agent for Heavy Metal Cadmium in Farmland Soil

Soil washing is an effective approach for the remediation of heavy metal contaminated soil. Soil washing agent is a crucial factor which directly affects the efficiency of washing. We examined the performances of four washing agents, inclusive of acetic acid, citric acid, CaCl₂, and FeCl₃, in purifying farmland soil slightly contaminated by Cadmium (Cd) and the influential factors. We found that the effect of FeCl₃ is the optimum, followed by citric acid, acetic acid, and CaCl₂ in sequence.The H⁺ hydrolyzed from the exchange between Fe₃⁺ from FeCl₃ solution and Cd²⁺ from the soil stimulated the dissolution of carbonate bounded form of Cd; Cl^- together with Cd²⁺ could also form a stable chelate. In optimized operation condition (solid-liquid ratio at 1∶5, and washing for 4 hours), the maximum removal rate of Cd was 30.24%, 24.62%,24.82%, and 81.90% by acetic acid, citric acid, CaCl₂, and FeCl₃, respectively. The pH value of soil had large impact on the washing effect. Apart from CaCl₂,the washing effects of the other three washing agents all declined with the rising of pH value within 2.5-5.0, among which the washing effect of FeCl₃ underwent the most severe decline.