Equilibrium and dynamic ion exchange studies of Cr3+ on zeolites

ABSTRACT. In this paper, the chromium uptake in zeolites NaA and NaX was investigated in equilibrium condition and in dynamic systems at 30oC. The separation factors, obtained from the equilibrium data, were very similar to the isotherms Cr-NaA e Cr-NaX, which indicates that, in equilibrium conditions both zeolites remove similar quantities of chromium ions. For the dynamic runs, it was observed that the large size of hydrated chromium ion inhibited its exchange in all zeolite sites causing huge differences in the breakthrough curves. The dynamic data were used to estimate some mass transfer parameters such as the length of unused bed, operational ratio and dimensionless variance for various flow rates. Based on the breakthrough results, the optimal condition for column operation was 11 mL/min for zeolite NaA and 9 mL/min for zeolite NaX. Moreover, through the dynamic capacity of the column, it was concluded that the zeolite NaX has been more efficient for dynamic chromium uptake due to the larger aperture of its cages. Key words: chromium ion-exchange, fixed-bed, zeolite, isotherm, breakthrough curve. RESUMO. Troca iônica em equilíbrio e dinâmica de Cr3+ em zeólitas NaA e NaX. Neste trabalho foi investigada a remoção de íons Cr3+ pelas zeólitas NaA e NaX, e