Removal of heavy metal ions from water by cross-linked carboxymethyl corn starch

Corn starch after cross-linking with POCl₃ (1%, v/w, starch db) was carboxymethylated with sodium chloroacetate (5-20%, v/w, starch db) to examine the metal removal activity of the starch from water. The cross-linked carboxymethyl starch [degree of substitution (DS) 0.02-0.08] was dispersed (0.5-3.0%) in aqueous solutions of divalent metal ions (Cu, Pb, Cd and Hg, approximately 200 ppm), and the starch-metal complex was filtered. Removal efficiency of the metal ions from their aqueous solutions increased proportionally with the DS of the carboxymethyl group and the starch content in the solution. Ionization of the carboxymethyl groups in starch was necessary for the effective metal removal. When the starch pH was adjusted below 4.0 after carboxymethylation, the starch was no longer an effective metal binder. The metal ions interacted with starch, 10 min after the starch was added. Lead, cadmium, and mercury ions in water were almost completely removed when 1% starch (DS 0.081, pH 6.0) was used. Under the same conditions, copper concentration was reduced from 203 to 71 ppm. Starch could be recovered by washing the metal ions from the complex with weak acid (pH 2.0) although the metal-binding activity of the starch was slightly reduced by this process.