污染土壤胶体释放特征及其对锌运移的作用

污染土壤样品采自辽宁省某炼锌企业周边农田。通过室内土柱淋溶实验,研究不同pH和离子强度下土壤胶体的释放特征以及对重金属Zn在土壤中运移的作用。结果表明,土壤胶体的释放均呈现先逐渐增强而后渐弱,并趋于稳定。pH和离子强度对土壤胶体的释放有明显的影响,弱酸(pH=6)条件最有利土壤中胶体的释放,其次是中性(pH=7)和碱性(pH=9)条件,在强酸(pH=4)条件下最弱。随离子强度增加,土壤中胶体的释放能力逐渐减弱。淋出液中胶体结合态Zn浓度均超过总Zn浓度的50%,且淋出液中的总Zn浓度与胶体的浓度相关性显著。经SPSS分析,pH=4、6、7和9时,该线性相关系数r分别为0.749、0.948、0.966和0.927,呈极显著相关关系。钙离子强度为0.001、0.01、0.1和0.5 mmol/L时,相关系数r分别为0.921、0.895、0.947和0.907,也呈现极显著相关关系。说明土壤地下水中Zn的运移主要受胶体释放的控制。

Releasing characteristics of colloids from contaminated-soil and their effect on transportation of zinc

Heavy metal contaminated soil sample was collected from farmland surrounding a zinc refinery plant in Liaoning province. In order to investigate the releasing characteristics of colloids from the soil and their effect on transportation of zinc in soil, leaching experiments in soil column were conducted under the condition of different environmental factors (pH, ionic strengths). Results indicated that the release value of colloids from soil tended to increase in the early of the leaching experiments and reached a peak, then lowered gradually, and kept a stable value at last. pH and ionic strength had a strong effect on the release of colloids. Under the condition of weak acidic solution (pH = 6), the release of colloids from the soil was the most heavily. The release was weakest in leaching solution with strong acidic condition (pH = 4). When pH = 7 or pH = 9, the release value was between the two values above. The releasing capacity of soil colloids decreased with the increase of the ionic strength. The concentration of colloid-binded zinc accounted to more than 50 % of total zinc content in the leachates, which suggested that the transportation of zinc in soil was significant correlation with the release of colloids from soil. Correlation coefficient r between the concentration of colloids and total zinc in leachates was calculated by SPSS software. Results showed that when the pH values were 4, 6, 7 and 9, r values were 0.749, 0.948, 0.966 and 0.927, respectively, which suggested that both had a highly significant correlation. When ionic strength in leaching solution were 0.001 mmol/L, 0.01 mmol/L, 0.1 mmol/L, and 0.5 mmol/L, r values were 0.921, 0.895, 0.947 and 0.907, respectively, which also suggested that both had a highly significant correlation. All these showed that the transportation of zinc in soil was mainly dominated by the release of the colloids.