Valdivino Francisco dos Santos Borges

Controlling or reducing the adsorption of surfactants on reservoir rock surfaces has been a challenging task in enhanced oil recovery (EOR) methods, as it directly affects the cost-effectiveness of the projects. The adsorption of surfactants on rock surfaces can modify their hydrophobicity, surface charge, and other important parameters that govern EOR processes, such as reducing the interfacial tension between water and oil and increasing permeability. Therefore, understanding the adsorption mechanism on rocks is essential for developing alternatives that improve the effectiveness of these processes. In this work, the adsorption of surfactants on carbonate materials was evaluated considering variations in temperature, contact time, and surfactant concentration. The surfactants used were derived from vegetable oils, aiming for a sustainable approach: saponified coconut oil (SCO), saponified babassu coconut oil (SBCO), and saponified castor oil (SMO). The finite bath method was used, resulting in adsorption efficiencies of 85.74%, 82.52%, and 45.30% for SCO, SBCO, and SMO, respectively. The Sips isotherm and the pseudo-second-order model were found to be suitable for characterizing these systems. The simulation of SCO adsorption isotherms on limestone by the Langmuir model was more accurate than that using the Freundlich model. The limestone showed a negative surface charge of approximately −35.0 mV at pH 6.5; this negative charge varied over a wide pH range. These zeta potential data for the samples confirmed that hydrophobic interactions played an important role in the adsorption of the surfactants. Thermodynamic evaluation indicated spontaneous and endothermic adsorption of SCO on limestone. The systems were also characterized by FTIR, TG/DTG, XRD, XRF, SEM, and zeta potential.

The aquatic environments can be contaminated by various metal ions, including Fe³⁺, Pb²⁺, Cr⁶⁺. In order to capture these ions the industry commonly uses different natural adsorbents or chemically treated. Based on this approach, this work aimed to treat diatomite with a micelle solution and microemulsion systems, formulated with UNITOL L-90, n-butanol, kerosene and distilled water. The diatomite treated with micelle solution did not provide a significant improvement in removal efficiency, reaching 62% for Fe³⁺, 58% for Pb²⁺ and 47% for Cr⁶⁺. While the diatomite treated with microemulsion had a substantial increase in the capture percentage reaching 99% of Fe³⁺, 65% for Pb²⁺ and 66% for Cr⁶⁺. Therefore, based on the results it is clear that surfactant is incorporated to diatomite when a microemulsion system is applied, enhancing the use of this systems in water treatment process. The ethoxylate groups present in the diatomite modified with the microemulsion were fundamental to improve the adsorption capacity of the Fe³⁺, Pb²⁺ and Cr⁶⁺ ions.