Removal of Oil from a Crude Oil-in-Water Emulsion by a Magnetically Recyclable Diatomite Demulsifier

Diatomite (DM) has superior adsorption performance for heavy metal ions in wastewater. However, the application of DM as a demulsifier in the treatment of a crude oil-in-water (O/W) emulsion has not yet been reported in the literature. In this work, a novel amphipathic and magnetically recyclable DM (M-DM) was synthesized by compounding with Fe3O4 nanoparticles and surface modifications. M-DM presented favorable demulsification performance under broad pH levels of the crude O/W emulsion. The demulsification efficiency (DE) reached a maximum when the M-DM dosage was increased to 450 mg/L. Moreover, M-DM could be recovered using its magnetism and still retained superior DE for 4 cycles. As a result of the strong interfacial activity, M-DM can reach the oil-water interface and interact with interfacial films. It was believed that the synergistic effect of electrostatic attraction and hydrogen bond interaction between M-DM and asphaltenes (main component of the interfacial film) promoted the rupture of the interfacial film and accelerated the coalescence of oil droplets to realize the oil-water separation of the O/W emulsion. This work provides a prospective novel demulsifier with cost-efficient, environmentally friendly, and universal application for the treatment of crude O/W emulsions.