Kinetics of cadmium(II) sorption by an iminodiacetic ion exchanger in the presence of a nonionic surfactant

The kinetics of cadmium(II) sorption from separate solutions and from the mixtures with nonionic surfactant Lutensol AO-10 (oxyethylated alkohols) in hydrogen form of chelating iminodiacetic ion exchanger Purolite S-930 has been investigated: kinetic curves and breakthrough curves have been obtained, determining the concentration of nonionic surfactant spectrophotometrically, and that of cadmium(II) complexometrically. The kinetic coefficients (B-l), the coefficients of the intraparticle diffusion (D, m(2)s(-1)), the effective kinetic coefficients of the external mass transfer (beta, s(-1)), the overall rate constants (k(0), s(-1)) and the distribution coefficients (K-d) have been calculated. Cadmium(II) sorption from the separate solutions and from the mixtures with AO-10 is controlled by the intraparticle diffusion at pH 5 and pH 7.6. Reducing the initial solution acidity from pH 5 to pH 7.6, the coefficients of intraparticle diffusion (D) for cadmium(II) increase, although they decrease as the cation exchanger saturation increases. The equilibrium sorption of cadmium(II) is slightly higher at pH 7.6 than at pH 5 both without and with the surfactant. The performance of Purolite S-930 packed column with respect to cadmium(II) is better in the absence than in the presence of the surfactant: the action of AO-10 interferes with the removal of cadmium(II). The sorption of AO-10 is negligible both in the absence and in the presence of cadmium(II). Regeneration of Purolite S-930 using 0.7 M HCl for both the removal of-cadmium(II) and the conversion into hydrogen form enables the 100% recovery of the sorptive capacity. The rate of the cadmium(II) intraparticle diffusion, its negligible concentration at the breakthrough, sufficiently high equilibrium, sorption and the ability to restore the sorptive capacity refer to the possibility of the hydrogen form of Purolite S-930 practical use, including the purification of plating rinse water for its recycling, preventing the environmental contamination with cadmium(II).