Radiation-Modified Carboxymethyl Starch Derivative as Metal Scavenger in Aqueous Solutions

Corn starch was chemically modified using sodium chloroacetate to yield carboxymethyl starch (CMS). The aqueous solutions of CMS at 15 and 50% (w/w) concentration were then irradiated by electron beam (EB) at various dosages (1, 2, 3, 5, 10, 20, and 50 kGy), resulting in a cross-linked carboxymethyl starch (CCMS). The maximum gel fraction, i.e. the highest degree of cross-linking, was achieved with a 50% (w/w) aqueous CMS solution irradiated at 2 kGy EB dosage. Metal removal efficiency of the CCMS was then evaluated for the extraction of copper (Cu) and cadmium (Cd) ions from aqueous solutions. Our results showed that the metal adsorption is pH dependent and the adsorption increases with increase of the pH of the metal solution from acidic towards neutral. The adsorption efficiency also showed the maximum value at the highest gel content, demonstrating the enhancement of adsorption by the physical entrapment of the ions in the CCMS network in addition to the primary chemical adsorption.