Pretreatment of Saline Oilfield Wastewater Using Magnesium-Silica-Rich Clay

Abstract This study explores the potential of locally sourced clays from Qatar for treating industrial wastewater characterized by high salinity and complex contamination. The adsorbent materials were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Brunauer–Emmett–Teller (BET) surface area analysis, and Fourier transform infrared (FTIR) spectroscopy. The local clays were then evaluated and compared with commercial clay and organoclays for their ability to remove chemical oxygen demand (COD), total organic carbon (TOC), and conductivity. Based on the combined characterization and screening results, a shale rock (SR) with a high surface area (185.7 m 2 /g) and palygorskite content exhibited the best performance, achieving up to 21% COD removal at a 100 g/L dosage. Further investigation of SR examined the effects of contact time, dosage, particle size, pH, temperature, and regeneration. Post-treatment analysis revealed substantial reductions in ammonia (from 31.02 to 3.7 mg/L), diesel-range organics (DRO) (from 3.39 to 0.0064 mg/L), oil content, PAHs, and metals, including As, Ba, Cr, and Zn. Mechanistic insights were obtained through post-adsorption FTIR, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), indicating that contaminants removal involved hydrophobic interactions, electrostatic attraction, ion exchange, hydrogen bonding, and surface complexation. Overall, these findings highlight the potential of processed local clays as low-cost and effective materials for the pretreatment of complex industrial wastewater.