Equilibrium and kinetics of silver uptake by multinuclear alginate microcapsules comprising an ion exchanger matrix and cyanex 302 organophosphinic acid extractant

Uptake characteristics of alginate microcapsules containing bis(2,4,4-trimethylpentyl)monothiophosphinic acid for adsorption of Ag(I) ions were examined using batch methods. Under a definite initial Ag⁺ concentration (C_b), at equilibrium, all the Ag(I) ions are adsorbed by extractant, while above C_b, ion exchange by the alginate matrix becomes the dominating mechanism. The kinetic mechanism varies depending on the presence of coexisting ions (CI). If the concentration of CI is low, the kinetics is controlled by a combination of slow adsorption of Ag(I) ions by Cyanex 302 (HA) microdroplets and shielding of inner microdroplets by the outer reacting ones (physical-chemical shielding mechanism). At higher concentrations of CI, intrapore diffusion controls, the kinetics. Different types of the shrinking core model remarkably fitted the kinetics experiments. The microcapsules were able to selectively adsorbed 90% of the Ag(I) ions from a 10 ppm Ag(I) + 3 mol·dm^-3 Na⁺ solution. In addition, the uptake percentage was constantly high in wide range of pH values and Ag ⁺ concentrations.