Nanoparticle depressants - The effect of colloidal silica in the froth flotation of calcium minerals

Colloidal silica is investigated as a potential selective nanoparticle depressant in the flotation process of calcium minerals. The micro particle separation of calcium minerals by selective froth flotation is a challenging task. The difficulty arises from the similar surface properties of the minerals and thus similar responses to different known families of flotation collectors (selectively adsorbing surfactants). The effect of colloidal silica and its interactions with the reagent system were investigated by varying its modification and specific surface area/particle size. Microflotation of scheelite (calcium tungstate), fluorite (calcium fluoride), calcite (calcium carbonate) and apatite (calcium fluorophosphate) was used to investigate whether colloidal silica has an effect on the minerals. Initial results show that colloidal silica prevents calcite from floating, while scheelite, fluorite and apatite are not affected by the presence of the reagent, regardless of the dosage. Moreover, batch flotation tests have shown significant differences between the three modifications (Sodium stabilized colloidal silica, sodium stabilized modified with aluminate and sodium stabilized modified with silane) in terms of the significant effect on the selectivity. Fundamental investigations have been carried out to figure out how the different modifications perform and at which phase of the flotation process. The upscaling of the technology was then investigated on a pilot and industrial scale.