Controlled assembly of nanoscale building units to form special micro-/nanostructures is of interest for achieving desired properties in many practical applications. The raspberry- or strawberry-like hierarchical structure with multi-level dimensions is one example of special surface wettability design. In this work, a series of coatings with hierarchical nanostructure and dual roughness are constructed on sintered stainless steel mesh and stainless steel fiber felt via layer-by-layer self-assembly of SiO₂ nanoparticles having different sizes. The surface is then chemically treated to obtain the wetting properties needed for intended separation of oil from water. The surface morphology of the coatings is observed using scanning electron microscopy and atomic force microscopy. The surface wetting properties are investigated by measuring the coatings' water and oil contact angle in air and under water. The results show that the stainless steel mesh with such coatings has superhydrophobicity, and thus can efficiently separate regular oil–water mixtures. Furthermore, the stainless steel fiber felt treated with similar coatings can also separate oil-in-water emulsions through the non-sieving coalescence mechanism, achieving an oil–water separation efficiency as high as 99.4%.

A new bubbling organic liquid membrane extraction using primary amine N1923 at large aqueous-to-oil phase ratios was suggested to extract and enrich extremely low concentration rare earths from the acidic sulfate leach solutions of ion-absorbing type rare-earth ores. It was revealed that bubbling organic liquid membrane extraction was in fact an interfacial chemical reaction of organic extractant molecules absorbing at the surface of the organic liquid membrane supported by gas bubbles with the target metal ions in the aqueous solutions. Rare earths with a concentration about 100 mg/L can be extracted selectively and enriched efficiently into the organic extractant liquid membrane layer covered on the surface of dispersed gas bubbles. However, Al in leach solutions was not extractable and remained in the raffinates, due to a kinetic nonequilibrium separation behavior of rare earths and Al on the surface of the organic liquid membrane. It was the differences in reaction rate of rare earths and Al with primary amine N1923 that intensified their separation. The separation coefficient of rare earths to Al could reach 44.89. The extraction raffinate, flowing-out from the extraction tower after large-phase-ratio extraction, contains aluminum sulfate and can be returned back to displace traditional ammonium sulfate for performing in situ leaching of rare earths from the ion-adsorption ores. The leaching percentage of rare earths was high up to 84.4%. The present work highlights an environmentally friendly and green sustainable new approach to treat ion-adsorbing type rare-earth ores by combining leaching and solvent extraction processes together to solve the problems from ammonia and nitrogen pollution during traditional processes using ammonium sulfate to leach rare-earth ores and ammonium bicarbonate to precipitate rare earths.