Chromium and cadmium adsorption on radiation-grafted polypropylene copolymers: regeneration, kinetics, and continuous fixed bed column studies

Metal ion adsorbents bearing amino and iminodiacetic groups were synthesized via radiation-induced graft polymerization of emulsified glycidyl methacrylate monomer from polypropylene non-woven fabric followed by subsequent reaction of the epoxide functional groups with ethylenediamine or iminodiacetic acid. The resulting amino- and iminodiacetic-type adsorbents exhibited excellent Cr(VI) and Cd(II) adsorption performance, respectively, based on the results of batch and column adsorption experiments. The Cr(VI) ions bound on the amino-type adsorbent were desorbed with 2M NaOH solution, while the bound Cd(II) ions were effectively stripped off from the iminodiacetic-type adsorbent by using organic acids, such as citric, acetic and oxalic acid. Both adsorbents showed more than 94% adsorption efficiency after five consecutive adsorption–desorption cycles. The adsorption dynamics of the metal ions to the synthesized grafted adsorbents obeys pseudo-second order kinetics. The radiation-grafted adsorbents exhibited comparable, if not better performance than commercially available ion-exchange resins. Continuous fixed bed column adsorption was performed, and the breakthrough curves were plotted at varying feed solution flow rate. The column-packed amino-type adsorbent can treat more than 4000 BV (> 1500 mL) of 3 ppm Cr(VI) solution at 155 BV hr−1 flow rate before the breakthrough. Lastly, the amino-type adsorbent was successfully applied in the treatment of actual tannery wastewater, with the resulting effluents meeting the national standards.