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 °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 1 ppm, the lower cost of starches should make them economically competitive.