Adsorption of Cr(III) by IRA-900 Resin in Sodium Phosphite and Sulfuric Acid System

Abstract

Chromium (Cr), a toxic heavy metal, poses significant environmental and health risks when industrial effluents containing Cr are discharged untreated. Addressing this challenge, this study developed a selective chromium removal strategy using IRA-900 resin in a sulfuric acid system with sodium phosphite (NaH2PO3) as a complexing agent. In the NaH2PO3-H2SO4 system, IRA-900 resin exhibited exceptional selectivity for Cr3+ with minimal co-adsorption of competing ions. The adsorption process followed the Langmuir isotherm model (R2 > 0.99), indicating monolayer chemisorption dominated by homogeneous active sites, and achieved a maximum capacity of 103.56 mg·g−1. Characterization via XPS, FT-IR, and SEM-EDS revealed a two-step mechanism: Cr3+ reacts with H2PO3− to form an anionic complex, and then the complex undergoes electrostatic interaction and ion exchange with chloride ions (Cl−) on the quaternary ammonium groups of the resin. The chromium-loaded resin demonstrated remarkable structural stability, resisting Cr3+ desorption under conventional elution conditions. This property provides a novel pathway for chromium solidification in industrial wastewater, effectively minimizing secondary pollution risks. This work advances the design of ligand-assisted ion-exchange systems for targeted heavy metal removal, offering both high selectivity and environmental compatibility in wastewater treatment.