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(2), respectively. The PS-CA, PS-O-CA and PS-N-CA were used to adsorb Fe(3+), Al(3+), Cu(2+), Pb(2+), Cd(2+) and Hg(2+). 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(3+), Cu(2+), Pb(2+) and Cd(2+) with q(m) 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 Al(3+) and Hg(2+) with q(m) 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.