Preparation of some starch-based neutral chelating agents

Various neutral starch derivatives have been prepared by reacting maize starch with mono- and dimethylol resins based on urea, thiourea, and melamine. The factors affecting these reactions were studied. These factors include curing duration, catalyst, and resin concentrations. The starch derivatives so prepared were used in heavy-metal removal from solutions. The sorption ability of those derivatives depends on resin type and metal ions. The sorption values of different starch derivatives follow the order (a) monomethylol resin-starch > dimethylol resin-starch; (b) thiourea resin-starch > urea resin-starch > melamine resin-starch. The sorption efficiency (%) of starch derivatives increases with increasing nitrogen content, reaching a maximum value and then decreasing. The sorption values of Hg2+ (mmol/mol resin) of different starch-monomethylol derivatives at the maximum values were 1135, 2624, and 2538 for urea, thiourea, and melamine derivatives, respectively. This indicates that urea derivatives act as bidentate ligands, while thiourea and melamine act as tridentate ligands. (C) 2000 Elsevier Science Ltd. All rights reserved.