Zeolite/calcium carbonate composite for a synergistic adsorption of cadmium in aqueous solution
Daniela O. Profeta, Marcella A. da Silva, Diêgo N. Faria, Daniel F. Cipriano, Jair C. C. Freitas, Fabiana Soares dos Santos, Thiago M. Lima, Sancler C. Vasconcelos, Mendelssolm Kister de Pietre
Abstract
The present work describes the production of synthetic FAU-type zeolites, obtained from different silicon sources, and impregnated with CaCO 3 . The results showed that the dispersion of CaCO 3 particles over the zeolite surface combined with its adsorption sites improved the performance of the adsorbents for Cd 2 + removal in aqueous solution when compared to pristine zeolites. The commercial beta zeolite sample, used as a reference, revealed unsatisfactory performance on Cd 2+ uptake since both the Al and Ca contents were lower than those found in the synthetic FAU-type zeolites. Adsorption tests, associated with kinetic studies and adsorption isotherms, revealed that chemisorption, especially ion exchange, with monolayer formation at the zeolite surface, was the main mechanism involved in the Cd 2+ uptake process. These results showed then that it is necessary to impregnate the samples with CaCO 3 , since the Cd 2+ removal efficiency is raised for all samples, possibly due to the synergistic contribution of the adsorption sites present in both the zeolite and the CaCO 3 particles. Furthermore, the FAU-type zeolite sample with a larger crystal size or larger particle aggregate showed greater capacity to disperse the CaCO 3 on its surface, enhancing the Cd 2+ uptake.