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 aqu eous pH in the absence and presence of trivalent metal ions such as al uminum (III) and chromium (III) ions. The results of the extraction ar e correlated with the corresponding electrokinetic measurements. In th e system including no metal ions, the recovery of silica fines is poss ible around pH 3.3. This pH value exists between the two isoelectric p oints of silica and isooctane, where the two carry different charges. Heterocoagulation theory is closely related to the recovery peak in th is pH range. When a metal nitrate salt is added in the system, several peaks appear in the pH-recovery curve. The electrokinetic measurement s show that at these pH values the zeta potential of silica and isooct ane are considerably decreased due partly to the presence of metal hyd roxide species, complexes or precipitates, so that no electrostatic re pulsion between fines and oil droplets could take place; the fines can concentrate at the oil-water interface through attraction due to disp ersive forces.