A simple and green preparation of red mud-coated membrane for efficient separation of oil-in-water emulsions

Abstract

This study presented a novel, low-cost and environmentally-friendly underwater superoleophobic membrane for influential separation of oil-in-water emulsions. The membrane was prepared by single-step deposition of waste red mud with sodium alginate on the nitrocellulose support through a vacuum pumping. The red mud-coated membrane had a superamphiphilic characteristic in air, whereas it demonstrated an underwater superoleophobic feature with contact angle values above 159( ± 2)°. The prepared membranes with different amount of red mud showed effective separation performance having rejection and flux values greater than (98.5% and 945 L/m2 h; 99.1% and 1033 L/m2 h; 93.7% and 1186 L/m2 h; 99.8% and 1224 L/m2 h; 99.9% and 1028 L/m2 h) for emulsions of various oils and solvents (diesel, mineral oil, toluene, kerosene and petroleum ether)-in-water, respectively. The oil rejection and permeate flux remained stable at the end of 5 cycles of the emulsion separation and also in the corrosive solutions, including NaOH, HCl and NaCl at 0.5 M of each one. Consequently, the usage of waste red mud in the preparation of underwater superoleophobic membrane through the suggested way can be offered as economical, practical and environmentally benign option for both implementing the efficient separation of oil-in-water emulsions and reuse of the industrial by-products.