Study of STAB- and DDAB-modified sepiolite tructures and their adsorption performance for emulsified oil in produced water

Electrostatic adsorption and hydrophobicity constitute the main functions of effective removal of emulsified oils (EOs) in produced water. Here, sepiolite (Sep) is modified with single-chain and double-chain organic cation surfactants, stearyl trimethyl ammonium bromide (STAB) and dimethyl dioctadecyl ammonium bromide (DDAB). Analyses of SEM, CA and zeta-potential indicated that individually-dispersed Sep fibers modified to form Sep fibrous aggregates with a more hydrophobic and electropositive surface, which greatly improved EOs adsorption and oil-water separation efficiency, and EOs removal efficiency exceeded 99%. The maximum adsorption capacities were 957.0 mg/g for STAB-Sep and 1031.5 mg/g for DDAB-Sep, suggesting that modified Sep with double chains exhibited a high affinity for EOs. Both the Langmuir and the Freundlich isotherms could be used to explain the adsorption process. Thermodynamic parameters proved that the adsorption process was a spontaneous endothermic physical process. This study provides a theoretical foundation for the design of high-efficiency and low-cost organoclay adsorbents.