天然沸石同步去除水中氨氮和磷酸盐

通过静态吸附实验考察了浙江缙云产天然沸石对溶液中氨氮和磷酸盐的同步去除能力及机制,结果表明,天然沸石对溶液中氨氮的吸附过程较好地满足拟二级动力学模型、Langmuir和Dubinin-Radushkevich等温吸附模型。天然沸石对磷酸盐的去除能力随溶液中初始氨氮浓度的增加而增加。当溶液pH由7.0增加到9.0时,天然沸石对氨氮的吸附能力随之增加,而当pH由9.0增加到10时,天然沸石对氨氮的吸附能力则下降。当溶液pH低于7.5时,天然沸石对溶液中的磷酸盐无去除能力,当溶液pH位于7.5～9.0时,天然沸石对磷酸盐的去除能力随pH的增加急剧增加,当溶液pH大于9.0时,天然沸石对磷酸盐的去除能力随pH的增加则呈下降趋势。天然沸石对溶液中氨氮和磷酸盐的同步去除过程是自发进行、吸热及熵增加的过程。天然沸石对溶液中氨氮的吸附机制为离子交换,对磷酸盐的去除机制则为化学沉淀作用。

Simultaneous removal of ammonium and phosphate from aqueous solution by natural zeolite

The simultaneous removal of ammonium and phosphate from aqueous solution by natural zeolite originated from Jinyun County,Zhejiang Province,China was investigated by using batch experiments.The adsorption kinetic data of ammonium onto the natural zeolite could be well described by a pseudo-second-order model.The adsorption equilibrium data of ammonium onto the natural zeolite fitted well to the Langmuir and Dubinin-Radushkevich isotherm models.The phosphate removal efficiency of natural zeolite increased with the initial concentration of ammonium in aqueous solution.The ammonium adsorption efficiency of natural zeolite increased with increasing solution pH from 7.0 to 9.0,but deceased with increasing solution pH from 9.0 to 10.0.The natural zeolite has no affinity to phosphate in aqueous solution at pH below 7.5.The phosphate removal efficiency of natural zeolite increased dramatically with increasing solution pH from 7.5 to 9.0,but decreased with increasing solution pH from 9.0 to 10.0.The calculated thermodynamic parameters such as Gibbs free energy(ΔG0),enthalpy(ΔH0) and entropy(ΔS0) changes showed that the simultaneous removal of ammonium and phosphate by the natural zeolite was spontaneous and endothermic process.The mechanism for the adsorption of ammonium onto the natural zeolite was ions exchange,and the mechanism for the removal of phosphate by the natural zeolite was chemical precipitation.