Synthesis of citric acid-modified resins and their adsorption properties towards metal ions.

Types of resins anchored on citric acid were synthesized and identified. The citric acid-modified resins PS-CA, PS-O-CA and PS-N-CA were synthesized by anchoring citric acid on PS-Cl, PS-OH and PS-NH2, respectively. The PS-CA, PS-O-CA and PS-N-CA were used to adsorb Fe3+, Al3+, Cu2+, Pb2+, Cd2+ and Hg2+. The influences of pH, adsorption time and metal ion concentration on the adsorption capacities of the resins were investigated. After optimization, PS-CA was a good adsorbent to Fe3+, Cu2+, Pb2+ and Cd2+ with qm values of 143.9 mg g-1, 77.4 mg g-1, 18.9 mg g-1 and 119.9 mg g-1, respectively. PS-N-CA was a good adsorbent to Al3+ and Hg2+ with qm values of 176.6 mg g-1 and 114.9 mg g-1, respectively. The adsorption kinetics and adsorption isotherm experiments indicated that the pseudo-first-order rate equation was more appropriate for characterizing the kinetic data and the Langmuir model was more suitable for fitting the equilibrium data. The reusability of the citric acid-modified resins was also evaluated and these resins exhibited considerable reusability.