Removal of Cd(II) from Phosphoric Acid Solution by Adsorbents: Equilibrium and Kinetic Studies

Abstract

The phosphoric acid obtained by wet-process is rich in impurities including heavy metals like cadmium. This work deals with the cadmium elimination from acid, by its adsorption on natural or modified clays and activated carbon, to improve its quality. The clays used in this study were effective for cadmium trapping from wet-phosphoric acid since it was reduced to approximately 80%. Moreover, our study shows that the fixation of cadmium is proportional to the temperature which however cannot exceed 313 K. On the other hand, the kinetic data, at the equilibrium, indicated that cadmium is more fixed on the inserted EDTA in the K10 montmorillonite (M). The kinetics of adsorption could be described by two models: pseudo-first-order and pseudo-second-order, which depend on temperature and the nature of adsorbent. At different temperatures used and with various adsorbents viz., K10 Montmorillonite (M), Gross kaolinite (K), Activated carbon (C), EDTA inserted in K10 montmorillonite (MD), iron oxide inserted in K10 montmorillonite (MF) and Posidonia oceanica impregnated on kaolinite (KP), the pseudo second order model was the most reliable to determine the order of kinetics of adsorption of cadmium, which is also reflected a good correlation coefficient (above 0.97). The experimental equilibrium adsorption data of Cd(II) onto different adsorbents were in agreement with the Freundlich isotherm model.