Purification of emulsified oily polluted waters with modified melamine foams

Abstract

Oil and gas industry operations produce tremendous amounts of wastewater (produced water; PW). Tertiary treatment of the PW in the final treatment stage is challenging due to the presence of colloids with sizes < 500 nm and a low concentration target for the effluent of <10 mg/L. This study was focused on the purification of colloidal PW with modified melamine foams (MFs) and ferric chloride. The modified MFs exhibited superhydrophobic and superoleophilic character due to increasing roughness and complexation of Fe3＋ ions within the MF structure. The modified MF showed separation efficiencies up to 86 ± 3% for emulsions containing 120 ppm carbon. The Fe3＋ cations changed the hydrophilicities of the foams and made them highly hydrophobic, and they also contributed significantly to the adsorption of negatively charged species, such as crude oil droplets modified with an anionic surfactant (sodium dodecyl sulfate). The demulsification mechanism involved multiple diffusion processes run over different time scales, including diffusion of an emulsion into the foam and diffusion of the oil droplets within the foam, combined with parallel adsorption of the oil droplets onto the solid skeleton of the foam. The adsorption capacity of the MFs increased linearly with increasing initial concentration of crude oil content in the PW. The MFs were reusable for six consecutive cycles.