Dissolution of starch and its role in the flotation separation of quartz from hematite

Abstract

Corn starches are cheap and eco-friendly flotation depressants for iron oxides, but their solubilities in water at ambient temperature are low. Starches are often treated by alkali or thermal gelatinization to enhance their dissolution before being used in iron ore flotation. Despite its importance, little is known about the fundamentals of starch dissolution and its role in iron ore flotation. In this paper, four corn starches (waxy, normal, G50 and G80) differing in the mass ratio of amylopectin to amylose were used to investigate the starch solubility as a function of solution preparation temperature and pH. It was found that the starch solubility increased with increasing the solution preparation temperature, pH, or the mass ratio of amylopectin to amylose. Three stages of starch dissolution (swelling – rupturing – releasing starch molecules/ghost) were observed, and the tendency for the rupturing followed the order of waxy starch>normal starch>G50>G80, indicating that a starch with higher amylopectin content could be more readily dissolved. Micro-flotation tests were carried out for pure hematite and quartz and their mixture with these four starches dissolved at different temperatures and pHs. The results suggest that there is a strong correlation between starch solubility and the depressing ability. Among these starches tested, waxy starch and normal starch, which have relatively high amylopectin contents, are preferred for being used in the flotation separation of quartz from hematite as depressant after proper solution preparation.