Ion exchange in zeolites. Part 2.—Hydrolysis and dissolution of zeolites NaX and NaY

Abstract

Hydrolysis of zeolites NaX and NaY through H₃O⁺ exchange has been studied in deionised water and NaNO₃ solutions. Hydrolysis was found to enhance the dissolution of silicon and aluminium from the zeolites. Equations based on the thermodynamic mass-action law were derived for the prediction of hydrolysis equilibria (Na⁺ concentration and pH) over a range of different initial conditions. The agreement between predictions and observations was generally good in moderate Na⁺ concentrations. At low Na⁺ concentrations, however, predictions failed owing to the strong decrease of the zeolite selectivities for H₃O⁺ ions with decreasing Na⁺ concentration in solution. Predictions were also affected, to a small extent, by the silicate and carbonate ions present in the solutions. The carbonate ions resulted from CO₂ that had been preabsorbed by the zeolites from air. Dissolution of silicon and aluminium from the zeolites was very slow, so no equilibrium parameters for this process could be established.