Tailings Pond Surfactant Analogues: Effects on Toluene-Diluted Bitumen Drops in NaHCO3/K2CO3 Solution. Part 1: Dynamic Interfacial Tension

The interfacial properties and stability of the bitumen as films over free water or as droplets in process water require attention to aid the design of bitumen recovery methods that foster environmental sustainability. This paper addresses the nature and consequences of surfactant interactions with toluene-diluted bitumen (AOSB) in simulated tailings water. The interactions were monitored as functions of time (t) through measurements of dynamic interfacial tension σ(t). We compared the effects of adsorption of two simple surfactants, hexanoic acid (C5H11COOH or HAA), and the other having 3-cyclopentylpropionic acid (C5H9CH2CH2COOH or CPPA), with complex sodium naphthenates (SNs). The surfactants were adsorbed at the toluene/water interface as a control, and the Gibbs surface excess, the area per molecule, and critical breakpoint concentrations were determined. These data were used to select both surfactant concentrations for adsorption at the diluted bitumen/water interface and pH. σ(t) versus (t) was measured for the AOSB/water interface at pH near that of the surfactant solutions. Next, σ(t) versus (t) was measured for an AOSB/water system at three concentrations of each surfactant: trace, saturated, and near the critical breakpoint concentration (CMC). Depending upon the concentration and pH, each surfactant affected the interfaces differently depending upon concentration and pH. SN was the most effective for lowering σ(t) versus (t) synergistically at all concentrations. At low surfactant concentrations, HAA and CPPA inhibited the interfacial activity of AOSB/water unlike SN. At saturated concentrations, HAA and CPPA did not affect the interfacial activity of AOSB/water, while SN produced a synergistic effect. At CMC concentrations, HAA was more effective than CPPA but SN was exceptional in enhancing surface activity. Even if SN is removed from bitumen and is quite soluble in water, it re-adsorbs effectively with significantly reduced interfacial tensions.