Varying Pyrite Feed Grade on Flotation Performance in Degrading Water Quality: Effects on Froth Stability and Gangue Management

• Varying pyrite feed grade and water quality studied simultaneously in flotation. • Higher feed grade and ionic strength of process water increased froth stability. • Depressant dosage improved pyrite grades by reducing non-floating gangue recovery. • No clear effect of feed grade or water quality on Fe recovery. • Developed relationships linking feed grade, water quality, and flotation performance. Flotation systems are complex, multifaceted and water intensive. Process operators are becoming increasingly aware that detrimental process water quality and variations in ore mineralogy can affect the overall process efficiency. The depletion of ore feed grades with respect to valuable minerals further complicates the concentration of ores through froth flotation. Although evidently critical, ore feed grade and water quality are in most cases not controlled, thereby rarely investigated together as varying parameters. This study seeks to develop an understanding into the effects of varying ore feed grade on gangue recoveries, froth stability and flotation performance under different water qualities. Batch flotation results showed solids and water recovered increased with feed grade all depressant dosages and ionic strength of plant water. Higher feed grades and ionic strengths generally resulted in the most stable froth as indicated by solids and water recoveries. The Fe recoveries were within a similar range of ∼80 to 94 % for all feed grades suggesting that there was not much influence on Fe recoveries either the feed grade, ionic strength of plant water or depressant dosage was varied. Increasing the feed grade led to an increase in Fe grades at all depressant dosages and synthetic plant water types. The highest Fe grade was about ∼27 % for 3 % pyrite feed < 34 % for 6 % pyrite feed grade < 35 % for 12 % pyrite feed. Furthermore, this increase was not directly proportional to the hydrophobic component. Finally, Fe grades increased in conjunction with depressant dosage at each pyrite feed grade for all synthetic plant water types, owing to the reduction in NFG reporting to the concentrate, which dilutes the grade. Overall, flotation performance was enhanced as measured by the solids and water recoveries, froth stability and grade.