Integrated micro-macrobubbles flotation technology for the recovery of high density oil from contaminated sands

2017-02-26T23:24:33Z (GMT) by Lim, Mee Wei
The devastating impact of marine oil spillage on shoreline highlights the urgency for remediation methods that could remove the oil contaminant. Flotation technology was utilized as a method for the separation of oil from sand via gas-liquid-solid system. The success of flotation depends on three phenomena; oil liberation, bubble-particle attachment and bubble-particle flotation. Therefore, this research aims to examine the fundamental parameters and mechanisms that could influence the integrated microbubble (≈90 μm) - macrobubble (≈1.0 mm) flotation efficiency for the removal of bunker oil from beach sands. The study on the liberation of oil from sand was conducted through interaction studies between solid-liquid phase. It was found that an increase in temperature, pH, sand particle size and wettability led to an increase in sand detachment efficiencies due to the decrease in attachment forces between sand and oil. These results were confirmed via zeta potential data and DLVO theory. The interaction studies between liquid and gas phases were also investigated to further understand the parameters that would affect the attachment between oil and bubbles. The contact angle of bubble-oil experiment and bubble attachment visualization test demonstrated that the usage of microbubbles provided a stronger bubble-oil attachment as compared to macrobubbles. This indicates that microbubbles would preferentially attach to the oil contaminant as opposed to macrobubbles. However, while the usage of smaller bubbles would lead to better attachment on oil, the lack of lifting force limits the flotation efficiency. Therefore, the usage of an integrated micro-macrobubble system was subsequently introduced in a single flotation cell to further improve the flotation efficiency of oil contaminant. The presence of microbubbles is beneficial to enhance the macrobubble attachment process onto oil phases during the flotation process. Hence, the interaction studies between gas-gas phases were conducted by analyzing the static and dynamic bubble attachment to understand the symbiotic relationship between bubbles, as microbubbles could increase the probability of bubble-particle attachment, while macrobubbles could provide the sufficient lifting force to aid flotation. The results showed that the probability of bubble-bubble attachment was greater compared to bubble-oil attachment. This is advantageous for the application of integrated bubble flotation as the interaction between microbubbles and macrobubbles could provide a better bubble attachment with sufficient lifting force. Laboratory-scaled flotation experiments were subsequently carried out to investigate the efficiency of integrated bubble flotation as compared to single micro or macrobubble flotation. At the optimized parameter of 40 Celcius, pH 12.5, and duration of 30 minutes, the maximum oil removal efficiency from the integrated micro-macrobubble flotation was found to be 68.6% for oil-wet sands, while almost all of the oil contaminants were removed from the water-wet sands. In addition, the micro-macrobubble flotation showed an increase of approximately 10% for both oil-wet and water-wet conditions compared to the single bubble flotation. The results from the flotation studies were in good agreement with the former interaction studies. Therefore, this indicates that the integrated micro-macrobubble flotation method is a promising, simple and low energy method for the removal of bunker oil from contaminated sand.