Nanoadsorbents for oilfield produced water treatment: synthesis of silica and magnetite nanoparticles for naphthenic acid removal

The treatment of produced water, generated in large volumes during oil and gas production, poses a significant environmental challenge faced by the petroleum industry, particularly due to the presence of dissolved organic contaminants such as naphthenic acids. This study reports the synthesis and characterization of nanoadsorbents based on silica and magnetic nanoparticles for application in the polishing stage of produced water treatment, specifically targeting the removal of naphthenic acids. Silica nanoparticles were synthesized using a modified Stöber method, while magnetic nanoparticles were obtained through a coprecipitation method. The surface properties of these nanoparticles were modified to enhance their interaction with naphthenic acids, as confirmed by changes in particle size, as well as their chemical and surface properties. In batch adsorption experiments using synthetic produced water, silica nanoparticles with hydrophobic surface groups exhibited the highest benzoic acid adsorption capacity, reaching 21.9 mg/g. These results highlight the potential of engineered nanomaterials as effective adsorbents, where hydrophobic interactions dominate the adsorption mechanism under the evaluated conditions. An inverse relationship between pH and removal efficiency was observed, and it was demonstrated that the removal efficiency remains consistent across the industrially relevant pH range of 5.5 to 8. Furthermore, the SiO₂ nanoadsorbent demonstrated a superior multicomponent adsorption capacity, validating the potential of these nanoadsorbents for the treatment of real oilfield produced water.