烟气脱硫石膏对滩涂围垦土壤重金属解吸及残留形态的影响

滩涂围垦土壤是重金属等难降解污染物的主要最终归宿场所之一,其重金属的解吸将影响重金属的迁移性、生物有效性和潜在毒性,研究重金属的解吸对土壤污染评价、修复及环境容量预测至关重要.研究了烟气脱硫石膏对广州市南沙滩涂围垦土壤重金属的解吸效果,并分析了烟气脱硫石膏对重金属形态的影响.在离心管中称取20.0 g过0.25mm筛土样,加入20 mL水和不同量的烟气脱硫石膏,在室温下于恒温振荡器振荡,风干研碎后用原子吸收分光光度法测定重金属全量,并用Tessier连续提取法研究了处理前后重金属形态变化.研究结果表明,随着脱硫石膏施用量的增加,经过振荡离心后的滩涂围垦土壤中重金属质量分数先急剧下降,之后变化趋于平缓.与原土相比各重金属最大解吸率分别为:Cd 30.38%,Cu17.73%,Ni 15.00%,Zn 14.19%,Pb 9.46%,Cr 8.89%.比较处理前后重金属的形态变化,发现各重金属的可交换态解吸率均达50%以上,并且重金属碳酸盐结合态质量分数也有减少.说明烟气脱硫石膏能降低土壤对重金属的吸附,经振荡离心后能降低土壤中重金属的毒性和生物可利用性.

Effects of desulfurized gypsum on heavy metal desorption and speciations in tidal flat reclaimed soil

Tidal flat reclaimed soil is one of the ultimate sink of heavy metals. The mobility, bioavailability and toxicity of heavy metals in soil are most likely controlled by their desorption properties. A better understanding of the desorption is crucial for assessment and remediation of heavy metal polluted soils, and for prediction of the metal sorption capacity of soils. The effects of desulfurized gypsum on desorption of Pb, Zn, Cu, Ni, Cr and Cd in tidal flat reclaimed soil were studied. The changes of heavy metal speciations in soil treated with desulfurized gypsum were analyzed. 20 gram of soil samples, 20 milliliters of deioned water and different amount of desulfurized gypsum were filled in centrifugal tubes. Then the soil samples were shaked automatically at room temperature, centrifuged and air dried. The total heavy metal content of soil was determined by HC1- HNO3- HF- HClO4 extraction. The chemical fractions of heavy metals in soil were determined using Tessier sequential extraction procedure. The concentrations of Cd, Zn, Pb, Cu, Cr and Ni in each solution were determined by atomic adsorption spectrometry. Results showed that the heavy metal content in soil decreased after treatment with desulfurized gypsum. The maximum desorption efficiency was 30.38% for Cd, 17.73% for Cu, 15.00% for Ni, 14.19% for Zn, 9.46% for Pb, 8.89% for Cr. Sequential fractionations of treated and untreated soil samples showed that desulfurized gypsum was effective in desorbing the exchangeable and carbonate forms of Cd, Cu, Ni, Zn, Pb and Cr.