天然沸石对海水中氨氮的吸附特性

Adsorption properties of ammonium nitrogen in seawater by natural zeolite

以天然沸石为吸附剂进行吸附海水中氨氮实验研究,考察了沸石粒径、反应液pH值和盐度对吸附效果的影响,对吸附动力学和热力学特性进行了探讨。实验结果表明,天然沸石粒径越小,越有利于其对海水中氨氮的吸附,反应液pH值对氨氮吸附影响较小,但在碱性条件下NH+4能够与海水中的Mg2+、PO3-4反应生成Mg NH4PO4·6H2O沉淀,导致反应液氨氮平衡浓度降低。随着海水盐度梯度增加,天然沸石对氨氮的吸附量呈显著下降趋势。天然沸石对海水中氨氮的吸附是快速吸附、缓慢平衡的过程,吸附过程较好地满足准二级动力学模型。吸附等温线更好地符合Langmuir等温吸附方程,通过热力学计算发现,△G0为负值,而△H0和△S0均为正值,说明天然沸石对海水中氨氮的吸附是吸热易发过程。

The natural zeolite was employed as adsorbent for removing ammonia nitrogen from seawater. A series of experiments were conducted to investigate the effects of zeolite particle size,solution pH and salinity on amount of NH＋4 adsorbed. The kinetic and thermodynamic models of ammonia adsorption by natural zeolite were also analyzed. The experimental results indicated that the decrease of the zeolite particle size has a clear benefit on ammonia adsorption in seawater. The solution pH had little effect on ammonia adsorption,but ammonium ions could combine with magnesium and phosphate ions in seawater to from magnesium ammonium phosphate（Mg NH4PO4·6H2O） precipitation under alkaline conditions,which result in a decrease in equilibrium concentration of ammonium nitrogen. The ammonia adsorption process by natural zeolite could be divided into the initial fast adsorption stage and the slow equilibrium stage,and the experimental data properly correlated with the pseudo-second-order kinetic model. The isotherms adsorption data was best represented by the Langmuir model.Thermodynamic parameters analysis showed that value of △G0was negative,while values of △H0and △S0were positive. These results indicated that the adsorption of ammonium ion by natural zeolite was a spontaneously endothermic process.