Kinetics and Equilibria of Cd(II) Adsorption onto a Chemically Modified Lawny Grass with H[BTMPP

Abstract

Removing Cd(II) by a modified lawny grass adsorbent (RG) containing H[BTMPP] (Cyanex272) has been investigated in this paper. The grass sorbents were characterized by SEM, FTIR, and elemental analysis, confirming that carboxylic groups were introduced onto the grass by chemical modification (citric acid (1CG)) and H[BTMPP] was successfully immobilized onto the grass (H-RG and H-1CG). H[BTMPP] played an important role in improving the maximum adsorption capacities to 133.2 mg·g−1 from 89.26 mg·g−1 and shortened the equilibration time from (40 to 20) min. From the batch experiments, the optimum pH is in the range of 5.5−6.0 for all adsorbents. H-1CG always had a higher ability to adsorb cadmium ions and the removal rate could be up to 99.54%. The kinetic equilibria could be explained as pseudosecond-order. Column experiments showed that breakthrough began at 160 bed volumes (BV) with H-1CG. A selection of 0.1 mol·L−1 HCl was used as the optimum desorption agent and elution is completed within 25 BV. Thermodynamic results indicated the adsorption of Cd(II) is spontaneous and endothermic. An ion exchange mechanism is involved in the adsorption process. This modified method can be regarded as an efficient strategy to improve the adsorption of cadmium from aqueous solution.