低分子有机酸去除土壤中重金属条件的研究

采用化学萃取实验,以湖南郴州柿竹园和湖南衡阳水口山矿区的重金属污染农田土壤为研究对象,采用柠檬酸、草酸、酒石酸作为低分子有机酸萃取剂,在一定的条件下对污染土壤中重金属进行萃取实验,确定各个单因素的适宜条件。结果表明,对于湖南郴州和衡阳两个污染地区土壤运用化学萃取技术萃取重金属来进行土壤修复是实际可行的;柠檬酸、酒石酸、草酸对各种土壤中的重金属都表现出了良好的萃取能力,是高效的土壤重金属萃取剂;单因素的适宜萃取条件为100mmol·L^-1有机酸溶液,固液比1∶5,恒定温度35℃,pH为3,反应时间24h,且萃取率随着电解质浓度的增大而提高;土壤中重金属存在形态与萃取效果有一定的相关性,稳定态（残渣态、硫化物和有机结合态、铁-锰氧化物结合态）金属含量高,表现为较低的萃取率;反之,萃取率高;柠檬酸、草酸、酒石酸3种萃取剂均能有效地降低衡阳污染土壤中的重金属浓度,3种萃取剂的萃取效率依次为酒石酸〉草酸〉柠檬酸。

Extraction Condition for Heavy Metals from Contaminated Soil by Using Low Molecular Organic Acids

Chemical extraction experiments were conducted to study the effects of three low molecular organic acids,including citric acid,oxalic acid and tartaric acid,on extraction efficiency of heavy metals from polluted soils at various conditions. The contaminated soils were collected from two red paddy soils from Chenzhou and Hengyang in Hunan Province. The goals of this study were making sure the best extraction conditions for rehabilitation of polluted soils. The results were summarized as follows：It was practical and viable to rehabilitate the soils polluted by heavy metals in Chenzhou and Hengyang through chemical extraction using low molecular organic acids. Citric acid,tartaric acid,and oxalic acid were effective in heavy metal extraction from the soils. For the polluted soils,the suitable extraction conditions for single-factor experiment were：concentration of organic acids 100 mmol·L^-1,solid-to-liquid ratio 1∶5,temperature 35 ℃,pH3,and contact time 24 h. Extraction efficiencies of organic acids removing soil heavy metals increased with concentrations of supporting electrolyte. Some kind of relativity existed between speciation of soil heavy metals and extraction efficiency of organic acids. The higher the contents of stable heavy metals（residual,sulfuration and organic bound,and iron-manganese oxide bound）,the lower the extraction efficiency. For Hengyang soil,three organic acids were all effective to remove heavy metals,but the sequence of extraction efficiency was tartaric acid oxalic acid citric acid.