Pre-wetting of sand for high speed oil-water separation

The search for a simple, affordable, and rapid separation method for oil-water mixtures is one of the most serious challenges that the world is facing today. Superhydrophobic, or superoleophilic, materials and surfaces are promising choices for these types of separations. In the present study, a high speed gravity-driven oil–water separation method has been realized by using pre-wetting of river sand, sea sand, and desert sand. The superoleophobicity properties of these pre-wetted sand materials have been found to be good, with a maximum oil contact angle of about 141.1° for desert sand and a minimum oil contact angel of 113.8° for sea sand. Also, the relationship between the porosity of the respective sand type and the water phase separation rate was, for the first time, obtained by using the LBM Shan-Chen model and micro-CT characterization. As a result of a simple particle size screening, the highest kerosene-water separation rate for sea sand was 24.3 ± 2.4 mm/s. In fact, this is the highest oil-water separation rate that has ever been achieved for a sand material. In addition to the effect of sand particle size, other factors affecting the rate of oil-water separation (such as number of separation cycles, thickness of sand layer, temperature, pH value, salt concentration, and different oil-water mixtures) have also been investigated.