碳酸镁与镉离子的吸附和沉淀作用研究

Sorption and Precipitation of Cadmium on Magnesium Carbonate

以碳酸镁为吸附剂,在镉离子初始浓度为0~6 mmol/L,初始pH值为4和7的条件下,研究了碳酸镁与镉离子的吸附与沉淀作用。结果表明,由于碳酸镁的溶解及与体系中氢离子的中和,碳酸镁—镉体系的最终pH值为10.4左右;体系的平衡pH值随着镉离子初始浓度的增加而减小;体系中镉的平衡浓度随着初始镉离子浓度的增加缓慢上升;碳酸镁对镉的吸附等温线为折线型,不符合Freundlich和Langmuir模型,符合伪二阶吸附动力学模型。结合碳酸镁吸附镉前后固相表征的结果,说明碳酸镁与镉离子的作用机制随着镉离子浓度的增加,从离子交换发展为离子交换和表面配位反应并存,最后表现为表面沉淀。

The sorption and precipitation between cadmium and magnesium carbonate was studied in condition that initial pH = 4,7 and initial cadmium concentration 0-6 mmol/L. The result showed that the final pH value maintained 10. 4 or so because of the dissolution of magnesium carbonate and the neutralization of hydrogen ions. The equilibrium pH decreased with the increase of the initial cadmium concentration. The cadmium equilibrium concentration increased slowly with the increase of initial concentration. Adsorption isotherms of magnesium carbonate on cadmium showed folding line,inconsistent with the Langmuir model and the Freundlich model,followed pseudo second-order kinetics model. Considering the results of solid phase characterization before and after the sorption of magnesium carbonate on cadmium,it was shown that,with the increase of cadmium,the correlation between magnesium carbonate and cadmium developed from ion exchange to coexistence of ion exchange and surface reaction and finally to surface precipitation.