有机酸和FeCl3复合浸提修复Cd、Pb污染农田土壤的研究

采用振荡浸提方法,研究了有机酸(柠檬酸、酒石酸)与Fe Cl3复合浸提对Cd、Pb污染农田土壤重金属的去除效果和影响因素,测定了浸提前后土壤中重金属形态和浸提液中常量元素含量。结果表明,柠檬酸(100 mmol·L-1)和Fe Cl3(20 mmol·L-1)复合浸提,对土壤中Cd、Pb的去除效率分别达到了40.7%和20.9%,酒石酸(100 mmol·L-1)和Fe Cl3(20 mmol·L-1)复合浸提,对Cd、Pb的去除效率分别达到了42.6%和16.5%,均高于相同浓度有机酸、Fe Cl3单独浸提的去除效率。有机酸-Fe Cl3对重金属的去除率随p H值升高而减少。液固质量比为5∶1、浸提时间为24 h、浸提3次比较适宜;有机酸-Fe Cl3对Cd的去除主要是交换态(77.3%~79.8%)和铁锰氧化态(86.7%~87.0%),有机结合态几乎没有变化;对Pb的去除主要是铁锰氧化态(70.0%~70.8%)和有机结合态(58.8%~66.0%),交换态显著增加至24.2%~24.5%,Cd、Pb碳酸盐结合态几乎消失,残渣态无变化。污染土壤中的Pb经过多次浸提,去除率可显著提高,连续3次浸提达到47.0%~48.2%。

Remediation of Cadmium and Lead Contaminated Farmland Soil by Washing with Combined Organic Acids and FeCl3

Soil washing is one option to remediate heavy metal contaminated soils. The present study examined the removal efficiency of cadmium(Cd) and lead(Pb) from a farmland soil by batch extraction with mixture of organic acid(citric acid or tartaric acid) and FeCl₃. Metal fractions before and after soil washing were also determined. The Cd and Pb removal efficiency from the soil was up to 40.7% and 20.9% for mixture of citric acid(100 mmol·L^-1) and FeCl₃(20 mmol·L^-1), and up to 42.6% and 16.5% for mixture of tartaric acid(100 mmol·L^-1) and FeCl₃(20 mmol·L^-1), respectively. The metal removal efficiency was higher for mixed reagents than single reagent. Increasing pH of washing solution decreased the removal efficiency of heavy metals. The optimum washing conditions were liquid to solid ratio of 5:1, washing time of 24 h and washing cycles of 3. Metal fractionation showed that the removed Cd by organic acids combined with FeCl₃ was mainly from exchangeable(77.3%~79.8% decline) and Fe-Mn oxides forms(86.7%~87.0% reduction), while the organic matter bound metals were almost unchanged. The removed Pb came from Fe-Mn oxides(70.0%~70.8% decrease) and organic matter form(58.8%~66.0% drop). After soil washing, however, the exchangeable Pb significantly increased to 24.2%~24.5%, but Cd and Pb in carbonates almost disappeared with residual metal form unchanged. The removal efficiency of Pb in soil could be significantly increased by repeated washing, and up to 47.0%~48.2% of Pb could be extracted after 3 washing cycles.