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-NH, respectively. The PS-CA, PS-O-CA and PS-N-CA were used to adsorb Fe, Al, Cu, Pb, Cd and Hg. 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 Fe, Cu, Pb and Cd with values of 143.9 mg g, 77.4 mg g, 18.9 mg g and 119.9 mg g, respectively. PS-N-CA was a good adsorbent to Al and Hg with values of 176.6 mg g and 114.9 mg g, 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.