Enhanced removal of nano-oil droplets utilizing polysilicate aluminum ferric (PSAF): Leveraging bridging and non-polar surface advantages.

Hydraulic oil leaks during mechanical maintenance, resulting in flushing wastewater contaminated with dispersed nano-oil droplets. In this study, 75 mg L-1 of polysilicate aluminum ferric (PSAF) was stirred at 350 rpm and the optimal chemical oxygen demand (COD) removal was 71%. The increase of PSAF led to more hydrolysis of Fe, and 1,175 cm-1 hydroxyl bridged with negative oil droplets. At the same molar concentration, PSAF hydrolyzes cationic metals more rapidly than polymeric aluminum chloride (PAC). PSAF forms flocs of smaller complex structures with greater bridging. The Al-O and Si-O peaks occurred at 611 and 1,138 cm-1, indicating the formation of Si-O-Fe and Si-O-Al bonds on the flocs surface. Higher stirring speeds did not change the free energy of the flocs surface γTot, mainly because the decrease in the van der Waals force (γLW) offset the increase of Lewis acid-base force (γAB). Preserving the non-polar surface, in summary, owing to its bridging abilities and affinity for non-polar surfaces, PSAF demonstrates superior efficiency over PAC in capturing and removing oil droplets.

Treating mechanical washing wastewater with iron-in-oil characteristics by changing the fate of iron.

The mechanical washing wastewater contained a large amount of oil, and the iron wrapped in the oil was slowly released into water. This caused the effluent quality to fluctuate, causing common polymeric aluminum chloride (PAC) to ineffectively remove the water-in-oil. The method uses Ca2+ to demulsify and ClOx- to destroy the water-in-oil structure, which releases Fe from the oil droplets. The active oxygen produced by NaClOx further converts Fe2+ into Fe3+ and then combines with NaOH to form Fe(OH)3-flocs core, which improves the flocculation efficiency of PAC. The optimal ratio was approximately 400 µL of NaClOx, 200 µL of 1 mol L-1 CaO, and 12 mL of 12.8 g L-1 PAC. The oil removal rate reached 99.88% and the residue density was 178.42 mg L-1. The maximum Fe and chemical oxygen demand (COD) removal rates were close to 49.2 and 99.89%, respectively. In field applications, wastewater should be acidified first, and acidification oxidation is more effective than direct oxidation. In short, a novel way for treating mechanically washed wastewater with iron-in-oil characteristics by changing the environmental fate of iron is provided.