Collectorless liquid-liquid extraction of silica fines in trivalent metal salts solutions

The recovery level of silica fines by liquid-liquid extraction without the use of a collector has been investigated as a function of the aqueous pH in the absence and presence of trivalent metal ions such as aluminum (III) and chromium (III) ions. The results of the extraction are correlated with the corresponding electrokinetic measurements. In the system including no metal ions, the recovery of silica fines is possible around pH 3.3. This pH value exists between the two isoelectric points of silica and isooctane, where the two carry different charges. Heterocoagulation theory is closely related to the recovery peak in this pH range. When a metal nitrate salt is added in the system, several peaks appear in the pH-recovery curve. The electrokinetic measurements show that at these pH values the zeta potential of silica and isooctane are considerably decreased due partly to the presence of metal hydroxide species, complexes or precipitates, so that no electrostatic repulsion between fines and oil droplets could take place; the fines can concentrate at the oil-water interface through attraction due to dispersive forces.