Kinetic and isotherm studies on perchlorate sorption by ion-exchange resins in drinking water treatment

The ion exchange capacity of five cationic resins (A532E, A520E, A400E, PWA-5, PSR-2) with regard to perchlorate ion was examined in batch kinetics and isotherms. The specificity of each resin was calculated from batch kinetic tests and results confirmed that the A532E and PSR-2 resins are more specific than the others for perchlorate removal. Furthermore, these results show PSR-2 and PWA-5 resins follow a pseudo-first order relation whereas exchanges are better described by pseudo-second order relations. The rate limiting step of ion exchange process was identified, for A400E, A520E and A532E as being the intraparticular diffusion, while PSR-2 and PWA-5 resins have an ion exchange rate limited by the external diffusion. Finally, the isotherm experiments show that the ion exchange equilibrium for perchlorate can be modelled by Langmuir relation for all resins and confirm that perchlorate ions are fixed forming a monolayer without interaction between molecules. The Langmuir model results indicate the maximal exchange capacities for perchlorates are of the same order of magnitude for all resins (from 183 mg g−1 for A400E to 115 mg g−1 for A532E). However for the removal of traces of perchlorates in drinking water, the experimental results confirm the benefit of perchlorate specific resins A532E and PSR-2.