皂角苷络合洗脱污灌土壤中重金属的研究

Study on desorption of heavy metal in sewage-irrigated soil by complexing with saponin

选择白银污灌土样为供试样品,采用振荡离心法研究了生物表面活性剂皂角苷(saponin)在不同浓度、pH值和离子强度条件下对供试土样中重金属的解吸影响,并采用Tessier法对解吸前后土样中的重金属形态进行了测定.结果显示,随皂角苷浓度增加,重金属解吸率随之增加,在皂角苷浓度为3%时,Cu、Cd、Pb、Zn解吸率分别达到43.87%、95.11%、83.54%和20.34%,而水及合成表面活性剂单独冲洗对重金属解吸率最大不超过5%;并且发现随土壤pH值增加,重金属解吸率逐渐减小;离子强度对Pb、Zn影响不大,而Cu、Cd随离子强度增大解吸率减小.比较冲洗前后重金属形态的变化,发现Cu、Cd、Pb、Zn元素的可溶态、碳酸盐结合态减少均达50%以上,Pb残渣态也减少60%左右,并且重金属氧化物结合态和有机态含量也有减少.说明皂角苷与重金属形成稳定的可溶性络合物,大大降低了土壤对重金属的吸附,从而降低了土壤中重金属的毒性和生物可利用性,表明皂角苷对污灌土样中重金属具有较好的淋洗去除效果.

In this paper,a plant-based biosurfactant saponin was selected to wash up the heavy metals, such as Cu, Cd,Pb and Zn, from the sewage irrigated soil with a series of batch-washing experiments. The results showed that desorption efficiency of heavy metals could be enhanced with the increase of the added saponin concentrations, and could finally reach 43.87 %, 95.11% , 83.54% and 20.34% for Cu, Cd,Pb, and Zn, respectively, by adding 3.0% of Saponin while desorption efficiency by water flushing alone was less than 5%. It was also found that the desorbed amount gradually decreased with the increase of pH values of the soil, which indicated that the high removal only took place in the week acidic environment. The ionic strength slightly had a negative influence on the desorption of Cd ,Cu, but no efforts on Pb,Zn. Comparing the spices transformation of heavy metals before and after desorption in the soil matrix by Tessier method, it was evident that soluble species and carbonated fractions of Cu ,Cd ,Pb ,Zn adsorbed on the soil surfaces were tremendously washed away. As a result, the toxicity and bio-reusability of the heavy metals in soil were significantly decreased.