两性膨润土增强不同层次紫色土吸附Cu2+的研究

为了证实两性粘土对不同层次紫色土吸附Cu~(2+)的促进作用,以不同比例(25%、50%和100%)十四烷基二甲基甜菜碱(BS-14)修饰膨润土作为两性基质,将其分别以5%的比例(质量比)添加至表层和粘化层紫色土中,采用批处理法研究不同两性基质添加比例对表层紫色土(ZS)和粘化层紫色土(ZA)吸附Cu~(2+)的等温吸附特征,并对比温度、p H值和离子强度对Cu~(2+)吸附效果的影响。结果表明:(1)表层紫色土添加BS膨润土(ZS-BS)和粘化层紫色土添加BS膨润土(ZA-BS)对Cu~(2+)的吸附量均随着BS膨润土中BS-14修饰比例的增大而增加,且相同BS-14修饰比例下ZA-BS对Cu~(2+)的吸附量高于ZS-BS。(2)p H值在3~5范围内,表层和粘化层紫色土对Cu~(2+)的吸附量均随p H值的升高而增大。温度从20℃增加到40℃时,两层次土样对Cu~(2+)的吸附量均随温度的升高而增加。土样对Cu~(2+)的吸附量在离子强度I=0.1 mol/L时最大,在I=0.01 mol/L时最小。(3)热力学参数结果表明添加BS膨润土后,不同层次紫色土吸附Cu~(2+)是一个自发、吸热和熵增的过程。

Study on the Enhanced Adsorption of Cu2+ in Different Purple Soil Layers by Amphoteric Bentonite

In order to confirm the adsorption effects of amphoteric clay on heavy metal ions (Cu²⁺) in different purple soil layers, tetradecyl dimethyl betaine(BS-14) modified bentonite with different proportion(25%, 50% and 100%)were chosen as an amphoteric matrix; the proportions of 5% (mass ratio) of those matrix were respectively added to surface layer and clay layer of purple soil, and the batch method was used to study the isothermal adsorption of Cu²⁺ with different matrix proportions and soil layers. The effect of temperature, pH values and ionic strength was also studied. Results show that: (1)The adsorption capacity of Cu²⁺ in ZS-BS(surface purple soil added with BS bentonite) and ZA-BS(clay purple soil added with BS bentonite) increase with increasing BS modified proportion in BS bentonite, and that of ZA-BS is higher than ZS-BS under the same BS modified proportion. (2) When the pH value is 3-5, the adsorption capacity of Cu²⁺ in surface layer and argillic layer of purple soil added with the pH value increase, showing the same trend under the influence of temperature.The maximum adsorption capacity of Cu²⁺ in two layer soil samples appears as the ionic strength is 0.1 mol/L, with the minimum of 0.01 mol/L. The thermodynamic parameters indicate that adding amphoteric bentonite on the Cu²⁺ adsorption in different purple soil layers is a spontaneous, endothermic and entropy increase process.