Preparation of polyvinylidene fluoride membranes with enhanced hydrophobicity and its applications in chromium recovery using supported liquid membranes in practical scale

This study focuses on the development of polyvinylidene fluoride (PDVF) membranes with enhanced hydrophobicity and their application for supported liquid membrane (SLM)-based solvent extraction. Flat sheet membranes were prepared via vapor-induced phase separation (VIPS), followed by non-solvent-induced phase separation (NIPS). PVDF flat sheet membrane was prepared with different solvents, namely N-methylpyrrolidone, dimethylformamide (DMF), dimethylacetamide, and dimethylsulfoxide, and at different VIPS times. The effect of different solvents and VIPS time on the membrane characteristics and performance was studied. PVDF membrane prepared with DMF solvent with VIPS time of 7.5 min gave optimum results in terms of membrane characteristics and performance with a water contact angle of 95.5 degrees. The optimized PVDF flat sheet membrane was used as support in a SLM setup for the extraction and recovery of chromium from a simulated aqueous feed solution similar to tannery effluent with concentrations ranging from 5 to 75 ppm. Dodecane, modified with 1-dodecanol and decalin, was used as an organic solvent with tri-caprylmethylammonium chloride (Aliquat 336) as an extractant. NaNO3 solution was used as a stripping solution. The processes of extraction and stripping were carried out simultaneously in a single-step operation to recover chromium. The extraction of chromium achieved in 3 h using an in-house-prepared hydrophobic PVDF membrane as support for the liquid membrane varies from 63.08% for feed containing 5 ppm chromium to 50.59% for feed containing 75 ppm chromium, with a maximum extraction of 70.92% for feed with 50 ppm chromium.