Effective removal of emulsified oil from oily wastewater using surfactant-modified sepiolite

Abstract In this study, tetradecyl trimethylammonium bromide (TTAB), cetyl trimethylammonium bromide (CTAB), and octadecyl trimethylammonium bromide (OTAB) were used to modify natural sepiolite via an ion exchange reaction to form organic sepiolite (organo-Sep) hybrids. This modification is particularly critical in order to obtain good affinity between organo-Sep hybrids and emulsified oil droplets (EOs). The loading surfactants changed the surface wettability from highly hydrophilic to increasingly hydrophobic, and a charge inversion from negative to positive occurred. Organo-Sep hybrids were investigated as adsorbents for removing emulsified oil from simulated oily wastewater. The morphology, texture, and surface properties of Sep and organo-Sep hybrids were characterized by various characteristic techniques, including SEM, XRD, FT-IR, contact angle analyzer, surface area analyzer, and ζ-potential analyzer. After modification, the BET surface area of Sep significantly increased from 297.8 to 698.6 m2/g, while the total pore volume of Sep raised from 0.840 to 3.080 cm3/g with an increase in alkyl chain length of surfactants. Experimental data showed that initial pH and temperature were two key factors affecting adsorption efficiency. It was observed that 98–99% of EOs was successfully removed by organo-Sep hybrids at 60 °C. The maximum adsorption capacities of TTAB-Sep, CTAB-Sep, and OTAB-Sep for EOs were determined from Langmuir isotherm at pH 6 and 60 °C as 434.7, 448.3 and 454.9 mg/g, respectively, along with good recyclability of more than 5 cycles. Thermodynamic data suggested that the adsorption process was physical, spontaneous, and endothermic in nature. Results showed that the organo-Sep hybrids were promising adsorbent materials for the preconcentration and separation of EOs from oily wastewater.