Hydrofluoric acid treatment for improved performance of a nanofiltration membrane

A method is proposed to improve the performance of a commercial nanofiltration membrane by treatment of the membrane with a hydrofluoric (HF) solution. A DS5DL (Osmonics) membrane, immersed for 14 days in HF (1% w/v), showed better solution permeability without deterioration of its potential for rejection of impurities. Such a prepared membrane was used for the purification of industrial phosphoric acid (8 M), which is characterized by a relatively high content of ionic impurities. The second application was for removal of Na2SO4 from industrial wastewater. In both cases the treated membrane showed an increment in flux and improvement in rejection of impurities as compared to the untreated membrane. The additional advantage was reduced membrane fouling after modification with HF.