Adsorption kinetics and solution chemistry governing organophosphorus herbicide removal from water by magnetic ion exchange resin

Glyphosate (GLY) and its main metabolite, aminomethylphosphonic acid (AMPA), are highly polar, anionic micropollutants frequently detected in surface and groundwater, posing threats to the environment and human health. This study investigates the removal of GLY and AMPA by a commercially available magnetic ion exchange resin (MIEX) and explains how adsorption kinetics and solution chemistry govern the process under environmentally relevant conditions. MIEX is compared with polymer-based spherical activated carbon (PBSAC), a high-capacity adsorbent with a fundamentally different removal mechanism. Batch experiments under varying MIEX doses, initial contaminant concentrations, pH, and ionic strengths provided insights into the removal of GLY and AMPA. A MIEX dose of 10 mL/L achieved removal of 91 ± 3% for GLY and 79 ± 5% for AMPA from an initial concentration of 1 μg/L. Although PBSAC exhibited higher equilibrium adsorption capacities, MIEX provided rapid uptake through readily accessible ion-exchange sites. Adsorption saturation was not approached within the investigated concentration range, and the adsorption isotherm showed near-linear behavior, indicating that adsorption capacity was not the limiting factor. Adsorption performance depended strongly on pH and ionic strength, with the highest removal at pH 4–10. Increasing ionic strength markedly reduced adsorption kinetics, particularly for GLY, supporting an electrostatically-controlled and reversible ion-exchange mechanism. The results demonstrate that, under environmentally relevant conditions, the performance of MIEX toward GLY and AMPA is governed more strongly by adsorption kinetics, solution chemistry, and the accessibility of ion-exchange sites than by equilibrium adsorption capacity and highlight the importance of kinetic considerations for short-contact water treatment.