Analysis of attachment process of bubbles to high-density oil: Influence of bubble size and water chemistry

The interaction studies between high-density oil and bubbles were investigated to understand the bubble attachment behaviour on oil with respect to bubble size, pH and temperature. An increase in the bubble size from 350 µm (microbubbles) to 1000 µm (macrobubbles) demonstrated a decrease in the attachment force due to the reduction in contact angle by 7%. The results were in good agreement with the bubble-strength visualization tests, as the retraction of microbubble attached onto oil demonstrated a significant change in shape from concave to convex, as opposed to constant shape of macrobubble attachment-retraction from the oil layer. This was attributed to a higher cross sectional area to volume ratio (IA:V) of 12.3 for oil-microbubble attachment compared to IA:V of 4.9 for oil-macrobubble attachment. Due to the higher IA:V, microbubble is more firmly attached onto the oil layer compared to macrobubbles. Therefore, microbubbles could help to enhance the flotation process as it would preferentially attach to the oil contaminant as opposed to macrobubbles. The results also indicate that increase in pH is detrimental for oil-bubble attachment due to the production of natural surfactants, while the increase in temperature does not appear to affect the bubble attachment on the oil layer.