Removal of Residual Oil from Produced Water Using Magnetic Nanoparticles

Abstract

Summary Recent studies have shown encouraging results using amine-coated magnetite (Fe3O4) nanoparticles to remove residual oil from produced water using a magnetic field. However, the manufacturing of magnetite nanoparticles requires an expensive coating operation, which limits the application of this technology in large-scale treatment operations. The goal of this study is to develop a simple, efficient, and economically feasible method for removing oil from produced water using nanoparticles. Iron oxide nanoparticles are biocompatible and even safely used in medical applications. This study focuses on the removal of residual oil from produced water using uncoated, recyclable, and less expensive maghemite (γ-Fe2O3) nanoparticles. These particles have shown the potential for removing oil layers from the surface of water. However, they have not been tested for their capability of removing emulsified and dissolved oil from produced water. In this study, commercial and synthesized maghemite nanoparticles were used. The maghemite nanoparticles were synthesized using the coprecipitation process. Laboratory-synthesized produced water samples with high oil concentration (1,000 ppm) were prepared by mixing medium oil with brine [1,180 ppm sodium chloride (NaCl) solution]. The nanoparticles were dispersed in 3% NaCl brine (w/w) at varying concentrations (0.31 to 5 mg/cm3) to form different nanosuspensions. Subsequently, the nanosuspensions were mixed with synthesized produced water for 10 minutes. When a magnetic field was applied to the mixture, a clear separation of the nanoparticles was observed within seconds. Residual oil in the samples was measured using nondispersive infrared spectroscopy. Oil content analysis confirmed the successful (99.9%) removal of oil from laboratory-synthesized water samples. For the real produced water samples, results showed a reduction of oil content to an undetectable level (i.e., less than 0.1 ppm). The ease of nanoparticle collection and washing after subsequent water treatments further demonstrates the feasibility of magnetic nanoparticle (MNP)-based separations for large-scale use in produced water treatment operations. The unique finding of this study is the elimination of one additional step of synthesizing (amine coating) MNPs. Direct use of uncoated maghemite nanoparticles with high oil removal efficiency can reduce produced water treatment costs and promote this technology as an economically feasible option within the industry.