碱性条件下胡敏酸吸附镉的特征研究

为了探讨胡敏酸在碱性条件下的吸附镉机理，了解碱性盐化土壤中镉污染机理和生态环境之间的关系，实验研究了胡敏酸在碱性条件吸附镉的特征。采用批吸附试验方法，研究不同Cd初始浓度、反应时间、不同pH和离子强度对胡敏酸吸附镉的影响，结果表明：胡敏酸具有较强吸附镉的能力，可以用Langmuir吸附模型和Temkin吸附模型很好地拟合其等温吸附过程（r分别为0.9809和0.9816）；在60 min内的快速反应阶段和60 min至6 h间的慢速反应阶段，胡敏酸对镉的吸附量分别为2.895 mg·g-1和3.342 mg·g-1，吸附反应平衡前6 h的动力学过程可以用Elovich方程进行很好的拟合（r为0.9285）；随着pH增加，吸附率表现出逐步增加趋势，并以pH为4.5和8.5为界，呈现两端增加速度快，中间增加慢的规律性；在较低浓度离子强度下，离子强度的增加促进胡敏酸吸附镉；而在高离子强度下，表现出相反的规律性；在相同的条件下，不同离子强度对胡敏酸吸附镉的影响大小为：氯化钙〉氯化镁〉氯化钾〉氯化钠。土壤在盐化的过程中，由于无机盐浓度的增加，增加了重金属离子的生物可利用性，加大了重金属离子的生态风险。

Adsorption Features of Cadmium by Humic Acid in Alkaline Conditions

In order to investigate the adsorption mechanism of cadmium on humic acid in alkaline condition and understand cadmium contamination mechanisms and its relationship with the ecological environment in alkaline saline soil, the adsorptions of cadmium on humic acid were studied by experiment in alkaline conditions. The different effect of initial concentration, reaction time, different pH and ionic strength on the adsorption of cadmium by humic acid were investigated though batch adsorption test methods. The results indicated that, humic acid had strong cadmiumadsorption ability. Langmuir and Temkin adsorption models were well fitted isotherm adsorption process （r are 0.9809 and 0.9816）. The adsorption capacities at the rapid response period within 60 minutes and the slow reaction within 60minutes to 6 hours, are 2.895 mg·g-1 and 3.342 mg·g-1, respectively. The process before the adsorption reaction reached equilibrium state can be well described by the Elovich equation （r = 0.9285）. As the pH increased, the adsorption rate showed a gradual increasing trend, and had two boundaries at pH 4.5 and 8.5, respectively. In low ionic concentration, ionic strength can be increased to promote cadmium adsorption on humic acid. However, the opposite regularity was represented in high ionic concentration. Under the same test conditions, the different ionic strengths affect the abilities of humic acid adsorption of cadmium as follow： calcium chloride〉magnesium chloride〉potassium chloride〉 sodium chloride. The bioavailability and the ecological risk of heavy metals are increased during the soil salinization process, due to the increase in salt concentration.