Efficient separation of emulsified oily wastewater using chitosan-based hydrophobic magnetic flocculant

Emulsified oily wastewater is a type of refractory and harmful wastewater with high environmental risk. Flocculation is a widely used chemical method for the pretreatment of oily wastewater. Natural flocculants are not only abundant and cost-effective but also exhibit excellent biodegradability and avoid secondary pollution. Chitosan was used as the raw material in this study. The Stöber method was employed to coat SiO2 onto the surface of Fe3O4, through which a dense SiO2 shell with a thickness of approximately 20 nm was formed by controlled hydrolysis-condensation of tetraethyl orthosilicate (TEOS). This process was specifically conducted in an ammonia-catalyzed ethanol/water co-solvent system maintained at pH 10.5, where the reaction conditions were systematically optimized to 25°C, 350 rpm stirring speed, and 5-hour duration, ultimately enhancing the composite's mechanical strength and resistance to both acidic and alkaline environments. Additionally, a magnetic flocculant, FDY (functionalized dodecyl modified composite material) was prepared by loading n-dodecyl mercaptan, which contains hydrophobic functional groups, onto its surface. Chitosan was grafted onto the surface via thermal initiation. The magnetic flocculant FDY-CS (Functionalized dodecyl modified and chitosan supported composites) was characterized using infrared spectroscopy and scanning electron microscopy. Building on this, a magnetic flocculant was combined with polyacrylonitrile to treat emulsified oily wastewater. The emulsification and de-oiling performances were investigated under varying conditions, including different dosages, pH levels, and kaolin content. These results demonstrate that conventional PAC (Polyaluminium chloride) flocculants produce small, loose flocs when treating emulsified oily wastewater. In contrast, the flocs formed by the magnetic flocculant FDY-CS combined with PAC were larger, denser, and more easily settled. The zeta potential and FTIR spectra of the flocs confirmed that the primary mechanisms for emulsification and deoiling were electric neutralization and hydrophobicity of FDY-CS. • Magnetic flocculant FDY-CS was prepared by grafting polymerization method using chitosan and nano Fe 3 O 4 as raw materials. • Chitosan based hydrophobic modified magnetic flocculant can make the oil droplet coagulate better. • The electric neutralization and hydrophobicity of magnetic flocculant FDY-CS are the main demulsification and flocculation mechanism.