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Diesel Oil Removal by Froth Flotation Under Low Interfacial Tension Conditions I: Foam Characteristics, and Equilibration Time

Abstract Froth flotation is a surfactant‐based separation process which is suitable for treating dilute wastewaters. To achieve high performance for the froth flotation operation, the combination of an ultra‐low interfacial tension (IFT) between excess oil and excess water phases, high foam production rates, and high stability of the foam produced, must be attained. To obtain the ultra‐low interfacial tensions, a Winsor Type III or middle phase microemulsion has to be formed. In this study, branched alcohol propoxylate sulfate sodium salt with 14–15 carbon number and 4 PO groups (Alfoterra 145–4PO) was used to form microemulsions with diesel oil. From the results of this work, an increase in surfactant concentration decreased the IFT, and increased foam stability. To obtain the minimum IFT in the region of a Winsor Type III microemulsion, the addition of 5 wt.% NaCl was needed. However, this optimum salinity does not result in effective froth flotation due to poor foam characteristics. The results indicate that both the IFT and the foam characteristics should be optimized to achieve high efficiency of oil removal in a froth flotation operation. Unlike the previously‐studied ethylbenzene system, agitation of the solution before introduction into the flotation column yielded the lowest diesel oil removal efficiency because of the poor foam characteristics compared to either unagitated systems or systems allowed to equilibrate for one month.