Flocculation of kaolin by waxy maize starch phosphates

Waxy maize starch phosphates were tested as flocculants in order to determine if they have the potential to replace petroleum-based polymer flocculants currently used commercially. Phosphorylation was carried out by dry heating of starches and sodium orthophosphates at 140 degrees C for 4 h. Native and phosphorylated waxy maize starches were ineffective as flocculants for kaolin in deionized water. However. in the presence of small amounts of Ca2+ (1-4 mM), starch phosphates were effective flocculants of kaolin at concentrations as low at 3-4 ppm. The optimal degree of substitution (DS) for flocculation was 0.024 but the effect of DS was rather small over the range DS 0.007-0.08. Although a common synthetic polymer flocculant (polyacrylamide-co-acrylic acid) was effective at I ppm, the lower cost of starches should make them economically competitive. Published by Elsevier Ltd.