Breakthrough and Elution Curves for Adsorption of Phosphates on an OH-Type Strongly Basic Ion Exchanger

Abstract

The breakthrough and elution curves for adsorption of H3PO4, H2PO4- and HPO42-, PO43- ions on an OH-type strongly basic ion exchanger were investigated in a packed-bed column. The results appeared to be technically feasible. In all phosphate systems, sharp breakthrough curves were obtained, and they were affected by inlet concentrations. The breakthrough times decreased with an increase in the inlet concentration. The ion-exchange capacities of phosphates in the column decreased in the following order: H3PO4 aqueous solution > NaH2PO4 aqueous solution > Na2HPO4 aqueous solution > Na3PO4 aqueous solution. The values of the ratio between the ion-exchange capacity and the total ion-exchange capacity of the resin were in the range of 100−30%. The experimental breakthrough data were correlated by neglecting the effect of axial dispersion and by using a linear driving force assumption in the intraparticle diffusion. At a separation factor of R ≥ 0.0594, the theoretical breakthrough lines were calculated numerically for the Langmuir isotherm, while at 0.000 42 ≤ R ≥ 0.035 27, the theoretical breakthrough lines were all calculated using an analytical solution for the rectangular isotherm. The values of the intraparticle effective diffusivity increased with an increase in the influent concentration. In H3PO4 and NaH2PO4 systems, the contribution of surface and pore diffusions was significant, while in Na2HPO4 and Na3PO4 systems, the contribution of the pore diffusion was significant. The phosphate ions adsorbed in the column bed were completely eluted by using a NaOH aqueous solution.