Electrochemically Assisted Deposition of Calcite for Application in Surfactant Adsorption Studies

The ability to study the adsorption behavior of surfactant species is of interest in the field of enhanced oil recovery (EOR), especially pertaining to alkaline surfactant flooding. In this work, a calcite model mineral surface was obtained by electrochemically assisted deposition. This was achieved via the nitrate and/or oxygen electroreduction reactions in the presence of bicarbonate and calcium ions, by which controlled deposition of calcium carbonate was effected on a quartz crystal microbalance sensor covered with an electroactive gold layer. In addition, the effect of pH and Ca ²⁺ concentration on the effective surface charge of the deposited calcite particles was mapped. Calcite-modified sensors were used in conjunction with a quartz crystal microbalance with dissipation monitoring to study the effect of Na ⁺ and Ca ²⁺ concentration on the adsorption behavior of an anionic alcohol alkoxy sulfate (AAS) surfactant. Adsorption of the surfactant remained indifferent to ionic concentrations around the isoelectric point of calcite. Still, electrostatics play an important role in this regard, and it is essential to decrease the Ca ²⁺ concentration sufficiently to minimize AAS adsorption. The results from this study show that a relatively simple method allows for the controlled deposition of a model rock surface, and there is ample opportunity to extend the work to other metal oxide surface types, including complex mixtures as can be obtained by co-deposition. Furthermore, the findings from these adsorption studies aid in the determination of optimal flooding parameters, with the aim to increase the efficiency and efficacy of EOR.