Effect of feed preparation on copper activation in flotation of Mt Keith pentlandite

Abstract

In this work, the effect of copper sulphate on the flotation of Mt Keith pentlandite ores was studied. As Mt Keith operates separate size flotation circuits, e.g. slime (−8 μm), fine (−25 μm) and coarse (−160 μm) circuits, tests were conducted on streams of different particle size distributions prepared with the use of cyclones. The flotation response with and without the addition of copper sulphate was examined, first, on feed streams prepared by a laboratory grinding mill and cyclone and, second, on streams collected directly from the plant. It was found that copper sulphate had an adverse effect on flotation performance when the flotation feeds were prepared in the laboratory. In the flotation of slime-fine fractions that combined slime and fine particles, the addition of copper sulphate depressed nickel flotation while increasing gangue entrainment. In the flotation of coarse fractions, the addition of copper sulphate depressed nickel flotation without affecting gangue entrainment. However, when samples were collected directly from the plant streams and floated in a laboratory flotation cell, the addition of copper sulphate increased nickel recovery without affecting gangue entrainment in the flotation of slime, fine and coarse fractions. To explain this discrepancy, pulp chemistries in the two different types of tests were compared. It was found that the plant mills at Mt Keith produced a much more reducing grinding environment than the laboratory mill. This might contribute to the completely different behaviour which copper sulphate exhibited on flotation performance. This study also demonstrates the importance in considering plant pulp chemistry during research development in a laboratory.