The role of hydrolyzed metal cations in the liquid-liquid extraction of ultrafine silica with dodecyl sulfate

As part of a fundamental study on the recovery of fine particles, ultrafine silica was liquid-liquid extracted with the anionic collector sodium dodecyl sulfate (SDS). Isooctane and water were used as the two liquid phases. The pH dependence of the recovery level of the silica was determined in the absence and presence of metal salts, such as Fe(III), Al(III) and La(III), for physicochemical interpretation on the role of the hydrolyzed metal species during the anionic liquid-liquid extraction of the silica fines. The results showed that the silica could not be recovered without the metal salts, while the addition of the metal salt led to a significant increase in recovery in a certain pH range. Comparison of these results and the distribution diagrams of the metal species indicated that the increase in recovery is in line with the formation of metal hydroxides, hydroxo complexes and precipitates. Also, the minimum extraction edges of the silica in terms of pH were correlated to the residual concentration of the respective metal species in the water phase; the hydroxo complexes that form prior to the precipitation pH were the species responsible for the silica activation as well.