Study On Multi-Component Ion Exchange Equilibra Of Modified Zeolite

The technology of extracting potassium from seawater by zeolite is a new method for development and utilization of the abundant potassium resource in seawater. There are ion exchange equilibria between zeolite and Na⁺,K⁺,NH₄⁺,Ca²⁺ in this technology. It has great significance to find out multi-component ion exchange equilibria for guiding the preparation of high efficient exchanger and the optimization of ion exchange technology and parameters. In this paper, the ion exchange equilibria between the clinoptilolite and the solutions systems of K⁺-Na⁺-NH₄⁺ and K⁺-Na⁺-Ca²⁺ were investigated to lay a foundation for further studies of this technology.The ion exchange equilibria between the clinoptilolite and the solution system of Na⁺-Ca²⁺ were investigated. The ion exchange equilibrium data were mensurated at the temperature of 25℃, 50℃and 75℃and the corresponding isotherms were constructed. Diagram of Kielland was constructes and thermodynamic functions of ion exchange process were calculated. The results show that ion exchange between the clinoptilolite and the solution systems of Na⁺-Ca²⁺ is incomplete exchange; lower temperature is propitious to the adsorption of Na⁺, by contraries higher temperature is in favor of the selectivity of zeolite to Ca²⁺.The ion exchange equilibria between the clinoptilolite and the ternary solution systems of K⁺-Na⁺-NH₄⁺ and K⁺-Na⁺-Ca²⁺ were investigated. The ion exchange equilibrium data of above systems were mensurated at the temperature of 0℃, 25℃, 50℃and 75℃and the corresponding isotherms were constructed. Based on the experimental results, the ternary separation factors of above ions were calculated. The results show that in the K⁺-Na⁺-NH₄⁺ system, the values of the KNH 4,Naαare more than 3, the values of 4,NHαKNa from 1 to 3 and the values ofαKN a,NH4 below 1. Therefore ion exchange selective sequence of clinoptilolite is K⁺>NH₄⁺>Na⁺; lower temperature is propitious to the adsorption of zeolite to K⁺, by contraries higher temperature is in favor of the selectivity of zeolite to NH₄⁺. It is also found that in the K⁺-Na⁺-Ca²⁺ system, the values of the KαCa,Naare more than 8, the values ofαKCa,Nanearby 1 and the values ofαKNa,Ca below 1, so ion selectivity sequence of clinoptilolite is K⁺>Na⁺>Ca²⁺, thereinto the Ca²⁺ belongs to partial exchange and has little influence on the selectivity of zeolite to K⁺; lower temperature is propitious to the selectivity of zeolite to K⁺, and higher temperature has the adsorption of zeolite to Na⁺ enhanced.