Optimization of novel composite membranes for water and mineral recovery by vacuum membrane distillation

In mining industries, the process combining ultrafiltration (UF) and reverse osmosis (RO) is often used for wastewater treatment, but RO brine discharge is a big issue. Membrane distillation (MD) has been proposed to solve this problem by significantly increasing the water recovery ratio, and recovering minerals. However, membranes with high hydrophobicity targeting for MD, particularly for vacuum membrane distillation (VMD) are still scarce. Hyflon AD is a novel candidate for fabricating membranes for MD. In this paper, the effects of membrane fabrication parameters, such as coating time, heat treatment and pre-filling were investigated and optimized. Membrane morphology, mechanical properties and VMD performance of the composite membranes were tested. The results showed that the hydrophobicity and elongation at break of the membrane were significantly improved after coating. The coating polymer concentration, coating time, heat treatment temperature and heat treatment time for the membrane coated by Hyflon AD40L and Hyflon AD40H, respectively were optimized. Monovalent alcohols can be excellent pre-filling agents to improve membrane performance. Separation performance of the membrane coated by Hyflon AD40H was better than that of the one coated by Hyflon AD40L.