Use of silica sol in selective sulphide mineral flotation

Micro- and batch flotation tests were conducted to explore the use of silica sol to control metal ions to reduce accidental activation and misplacement of minerals. As a comparison other 'metal control reagents', ethylenediaminetetraacetic acid (EDTA) and polyphosphate were also tested. X-ray photoelectron spectroscopy (XPS) was used to probe the silica sol-mineral interaction mechanism.Micro flotation was performed on single mineral samples over a pH range 7 to 11. It was found that silica sol depressed all Cu minerals, Cu and Pb activated pyrite and Pb activated sphalerite but did not depress Cu activated sphalerite. XPS analysis revealed that silica sol adsorbed on all Cu minerals and Cu and Pb activated pyrite. Silica sol partially removed Pb from Pb activated sphalerite and had no apparent interaction with Cu activated sphalerite. The depressant action, therefore, appeared to be primarily adsorption of silica sol to form hydrophilic sites.In the batch tests, generally, silica sol, polyphosphate and EDTA increased the rate of flotation in the Cu stage and in the Zn stage. This is attributed to removal of hydrophilic metal hydroxy species, i.e., surface 'cleaning'. Polyphosphate, and to a lesser extent EDTA, improved selectivity in the Zn stage for Les Mines Selbaie and Mine Louvicourt and arguably for Hudson Bay Mining and Smelting. This selectivity was not identified in the trials at Brunswick Mine directly on Zn stage flotation feed. The varying effect of polyphosphate on selectivity is attributed to the level of 'excess Cu' used in Zn activation: the higher the excess, the greater the effect of polyphosphate. In conclusion, silica sol has some metal ion control capability but seems less attractive in this role than say polyphosphate