Ion exchange of zeolite Na-P-c with Pb2+, Zn2+, and Ni2+ ions

This paper examines the ion-exchange properties of synthetic zeolite Na-P-c ,, which was produced from perlite-waste fines and has a SiO2:Al2O3 ratio o f 4.45:1 and a cation-exchange capacity (CEC) of 3.95 meg g(-1). Although e quilibrium is attained rapidly for all three metals, exchange is incomplete , with A(c)(max) (maximum equilibrium fraction of the metal in the zeolite) being 0.95 for Pb, 0.76 for Zn, and 0.27 for Ni. In both Na --> 1/2Pb and Na --> 1/2Zn exchange, the normalized selectivity coefficient is virtually constant for (N)A(c) (normalized equilibrium fraction of the metal in the z eolite) values of less than or equal to0.6, suggesting a pronounced homogen eity of the available exchange sites. The Gibbs standard free energy, Delta G(degrees), of the Na --> 1/2Pb exchange calculated from the normalized sel ectivity coefficient is -3.11 kJ eq(-1) and, for the Na --> 1/2Zn exchange, it is 2.75 kJ eq(-1). Examination of the solid exchange products with X-ray diffraction (XRD) rev ealed a possible decrease in crystallinity of zeolite Pb-P-c as suggested b y the significant broadening and disappearance of diffraction lines. This d ecrease is associated with a reduction of pore opening, as indicated from F ourier-transform infrared analysis (FTIR), which in turn results in a decre ase of the amount of zeolitic water. Thermogravimetric-differential thermog ravimetric (TG-DTG) analysis showed that water loss occurs in three steps, the relative significance of which depends on the type of exchangeable cati on and subsequently on the type of complex formed with the cation and/or th e zeolite channels. Zeolite Na-P-c might be utilized in environmental appli cations, such as the treatment of acid-mine drainage and electroplating eff luents.