Phosphate Adsorptions by a Copper Modified Weak Anion Exchange Resin

A weak anion exchange resin (WAER) modified with Cu 2+ ions was prepared and its adsorption behavior for phosphate species in batch and column systems were examined. While pristine WAER adsorbed phosphate species by Bronsted acid-base interaction, the Cu-WAER captured phosphate species mainly via loaded Cu 2+ ions through Lewis acid-base interaction. The Cu loading greatly improved phosphate adsorption of the WAER from 16.84 to 31.94 mg-P/g. Moreover, it maintained 53-92% phosphate adsorptions against competing anions (SO 4 2- , NO 3 - , and Cl - ) even the competitors were 17-33 times higher in the concentration than the phosphate species. The Cu-WAER followed Langmuir isotherm and pseudo-second order kinetics to absorb phosphate species. While the adsorption capacity increased from 31.94 to 61.03 mg-P/g as the temperature increased from 298 to 323 K, the adsorption rate constant decreased from 1.1×10 -3 to 0.4×10 -3 g/mg-min. The adsorption underwent endothermic intraparticle diffusion and dissociation of OH - /Cl - from the loaded Cu 2+ ions followed by exothermic phosphate complexation. The corresponding energies included ΔH ads 0 =22.65 kJ/mol, ΔS 0 =132.47 J/mol-K, and ΔG 0 = -16.83~-20.14 kJ/mol, and E d = 44.3 kJ/mol. Optimal pH for the highest adsorption was 3.42-5.20. The adsorption ability of used Cu-WAER beads could be regenerated by 0.1 N NaOH solution, and 96.23% of initial performance was still preserved even after 5 times of regeneration. In the column study, it reached 0.14-0.31 of batch adsorption capacity at 10-40 mg-P/L of phosphate concentration and 1.0-4.0 min of empty-bed-contact-time. Moreover, 99.05% of column performance was able to be recovered by a 0.1 N NaOH flow at 11 bed volume