Acidified water glass in the selective flotation of scheelite from calcite, Part I: performance and impact of the acid type

To improve the performance of sodium silicate in scheelite flotation and allow the selective separation of scheelite from other semi-soluble salt-type minerals such as calcite, three acids, sulfuric, oxalic and for the first time hydrochloric are used to acidify sodium silicate (also called water glass). A literature review of previous usage of acidified water glass shows that no comparison between acids was made before, that comparisons with alkaline water glass were limited and that the idea that acidified water glass is more efficient at lower dosages has not been proven in scheelite flotation. As a consequence, the impact of the acid type, the ratio between acid and sodium silicate and acid dosage is tested in single mineral flotation and batch flotation experiments. All three acids allow a higher performance of acidified water glass compared to alkaline water glass at lower dosages and with little addition of acid: the tungsten recovery and grade are improved while silicates and to a lesser extent calcium-bearing minerals float less. The dosage of acid is less determining than the mass ratio of the acid to sodium silicate, except in the case of hydrochloric acid. Overall, the acid type does not matter as all three acids perform well in flotation, whereby oxalic and hydrochloric acid are better.