The relationship among contact angle, induction time and flotation recovery of coal

Flotation is used to separate valuable minerals from gangue minerals based on the differences in their natural or induced hydrophobicity. Flotation recovery is a direct indicator of flotation performance. Similarly, induction time and contact angle are often used to characterize floatability. In order to measure the correlation of these indicators, contact angle measurements, induction time measurements and flotation tests were performed. The bubble-particle induction time measurements were performed with a homemade induction timer. Fourier translation infrared spectroscopy analysis was used to characterize the surface functional groups of different coals. The results showed that shorter induction times and greater contact angles resulted in higher flotation recoveries. However, induction time measurements can reveal the floatability of individual particle size fractions, which cannot be realized in traditional contact angle measurements. Moreover, the contact angle is measured in an equilibrium system while the induction time represents a dynamic measurement. For a dynamic flotation system, it would be more appropriate to describe floatability of coal particles by induction time rather than traditional contact angle.