Study On Application And Ion Exchange Of Cd～(2+) In Synthesized Analcime

Zeolites have particular crystal structures, in which reversible cation exchanges could take place. These exchanges could improve their absorption abilities and catalysis capacities, which applied in environment restoration, purification and replacement etc. Analcime is one of the zeolite minerals and have been interested both domestic and abroad in recent years. The ion exchange capability and application of analcime and Cd²⁺ were investigated which offer directive theory for exploitation and utilize of analcime.The analcime used in our experiments, synthesized from diatomite, has fine crystallization and purification. Its Si/Al is near 2, and the main cation is Na⁺. The water saturated adsorption capacity in static state is 3.64%, and the exchange capacities are 0.625mmol/g and 0.313mmol/g for univalent and bivalent cations respectively.In this paper we have discussed different influences to the ion exchanges by different conditions such as temperatures, initial Cd²⁺ concentrations, pH values and coexistence of cations etc. When the pH value of the solution contained in Cd²⁺ is near 5, the amount of Cd²⁺ exchange in analcime reaches to a summit; when the temperature increases, the amount of Cd²⁺ exchange in unit mass analcime also increases; when initial Cd²⁺ concentration decreases, the remove rate of Cd²⁺ increases while the amount of Cd²⁺ exchange in unit mass analcime also decreases; when other cations coexist in solution, there must be some influences to the Cd²⁺ exchange in analcime. Cations in solution may result in ion exchange competition, and for the capacity of ion exchange competition, Pb²⁺ is the strongest, then the Cd²⁺.The isotherms of Cd²⁺ exchange in analcime under different temperatures such as 20℃, 40℃, 60℃ and 80℃ have been described and their thermodynamics features have been discussed. In the same initial Cd²⁺ concentration, the amount of Cd²⁺ exchange in analcime increases with the rise of temperature. Under the same temperature the amount of Cd²⁺ exchange in analcime also increases as the initial Cd²⁺ concentration increases.In 20℃ and 40℃, the selectivity of Cd²⁺ to analcime is less than that of Na⁺ to analcime; in 60²⁺ and 80℃,the selectivity of Cd²⁺ to analcime is more than that of Na⁺ to analcime.The maximum ion exchange degree of Cd²⁺ to analcime is 0.669. This ion exchange process, Δ_rH_m^θ>0 ,is an endothermic reaction. As the tempetature becomes higher, the Δ_rG_m^θ gets lower.The Cd²⁺ exchange in analcime is enhanced as the temperature increases.At different temperatures, the entropy of the ion exchange of Cd²⁺ to analcime is increasing.