铵离子在蒙脱石表面吸附特征及机理

Adsorption Characteristics and Mechanism of Ammonium Ions on Montmorillonite Surface

采用自然沉降法从膨润土中提纯出蒙脱石,考察了NH^+4初始浓度、固液比、pH、离子强度及共存稀土La^3+等因素对NH^+4在蒙脱石上吸附的影响规律,并进行了吸附动力学和热力学模型分析。结果表明,固液比增大使蒙脱石对NH^+4的吸附率增大而NH^+4初始浓度的增大使吸附率减小;溶液pH的增大会促进NH^+4在蒙脱石上的吸附,但当pH大于8以后吸附率迅速降低;水溶液中La^3+比NH^+4具有更大的竞争吸附能力,La^3+的存在会极大地降低NH^+4在蒙脱石上的吸附效果;NH^+4能在蒙脱石上的吸附过程符合伪二级动力学方程,在1.5 min后可以快速达到吸附平衡。NH^+4在蒙脱石上的最大吸附量Qm在0.23 mmol/g,吸附反应较好地符合Freundlich等温吸附模型,且由热力学参数吸附焓ΔH(-65.6 kJ/mol),提高温度会抑制NH^+4的吸附。

The montmorillonite was purified from bentonite by natural sedimentation method.The effects of NH^+4 initial concentration,solid-liquid ratio,pH,ionic strength and coexisting rare earth La^3+on the adsorption of NH^+4 on montmorillonite were investigated.The adsorption dynamic and thermodynamic models were analyzed.The results showed that the increase of solid-liquid ratio increases the adsorption rate of NH^+4 on montmorillonite while the increase of NH^+4 initial concentration decreases the adsorption rate;the increase of solution pH will promote the adsorption of NH^+4 on montmorillonite,but when the pH reaches 8,the adsorption rate decreases rapidly.La^3+in aqueous solution has greater competitive adsorption capacity than NH^+4.The presence of La^3+will greatly reduce the adsorption effect of NH^+4 on montmorillonite.The adsorption process of NH^+4 on montmorillonite accords with pseudo-second-order kinetic equation.The adsorption equilibrium can be reached quickly after 1.5 min.The adsorption reaction of NH^+4 on montmorillonite is in good agreement with the Freundlich isotherm adsorption model with the maximum adsorption amount Qm of 0.23 mmol/g.According to the thermodynamic parameters adsorb entropyΔH(-65.6 kJ/mol),increasing the temperature will inhibit the adsorption of NH^+4.