The dynamic contact angle of a bubble with an immersed-in-water particle and its implications for bubble–particle detachment

• Static contact angle of a 3 mm stainless steel particle was measured at 72°.
• Advancing and receding contact angles were measured at 106° and 45°.
• Dynamic contact angle varied in bubble–particle detachment process.
• Advancing contact angle should be reached to start the detachment.

The contact angle is of great importance in measuring the wetting characteristics of mineral particles. The dynamic contact angle is more relevant to flotation than the static contact angle, as the flotation environment is generally in a turbulent regime. Therefore, the dynamic contact angle should be used in the calculation of the capillary force which stabilizes bubble–particle aggregates in a turbulent field. In this paper, the static contact angle and the dynamic contact angle of a bubble detaching from a 3 mm stainless steel particle were measured using a high speed camera. The static contact angle calculated from the force balance analysis on the bubble was consistent with the angles measured optically (71.3°), which is in line with the published value (72°). Using the sphere tensiometry method, the advancing and receding contact angles were measured to be 106° and 45°, respectively. The detachment process was captured using a high speed camera operated at 1000 frames per second. The three phase contact on the left side of the bubble retracted as the contact angle in the upstream reached the advancing contact angle. However, the three phase contact on the right side of the bubble pinned on the surface of the particle as the contact angle in the downstream did not reach the receding contact angle. The dynamic contact angle of a bubble detaching from a particle was measured and it became asymmetric along the three phase contact line under the influence of a turbulent flow.

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