Improvement of the binding capacity of metal cations by sugar-beet pulp. 1. Impact of cross-linking treatments on composition, hydration and binding properties

Saponification and cross-linking by formaldehyde and epichlorohydrin were performed on beet pulp in order to improve its potentialities as an ion-exchanger, either by increasing its cation-exchange capacity and/or by decreasing its hydration capacities. Effects of the treatments on sugar composition, on swelling and water-retention capacities, and on the binding of two metal cations (Zn2+ and Pb2+) are reported. Saponification doubled the cation-exchange capacity without modifying the sugar composition or decreasing the hydration properties. The swelling capacity was thus identical to that of the initial pulp (similar to 32 ml g(-1) at pH similar to 7 in water). Treatment with formaldehyde had little effects on the hydration properties. The best results in terms of hydration properties were obtained with epichlorohydrin, which lowered the swelling and water-retention capacities to 7 ml g(-1) and 2 g g(-1), respectively, independently of pH and ionic strength. Binding properties were not altered by this treatment. However, the conditions used led to major changes in sugar composition, with severe loss of pectins at the lower epichlorohydrin levels. This loss was reduced at higher levels of epichlorohydrin, suggesting that pectins were involved in the crosslinking. Binding properties were not altered by such a treatment. (C) 1998 Published by Elsevier Science Limited. All rights reserved.