Identification of the sorption mechanism in zeolite NaY and silica gel

ABSTRACT

The study of the sorption mechanism and the initial pH of the solution influence in solid materials is necessary, because the simple fact of changing the pH of the solution can modify the sorption capacity of an adsorbate. It was evaluated the sorption of ions Ca²⁺ and Mg²⁺ at three pH values depending on the point of zero charge (pH_PZC) on NaY zeolite or silica gel (pH < pH_PZC; pH = pH_PZC; pH > pH_PZC). The sorption kinetics was obtained and adjusted by models of pseudo-first-order, pseudo-second-order and intraparticle diffusion of ions in the two studyied materials. In NaY zeolite adsorbent, the pH value had a higher sorption capacity was 4.3 (pH < pH_PZC) and pseudo-second-order model showed a better fit to the experimental data. In this material the adsorbed amount is small when compared to ion exchange. While in the silica gel, the highest sorption capacity occurred at pH 6.7 (pH > pH_PZC) and the model that best fit the data experimental was also the pseudo-second-order, concluding that the adsorption is main sorption mechanism.

Keywords:
Sorption mechanism; Silica gel; NaY zeolite; Point of zero chance