Study on the behavior of nanofiltration membranes using for chromium(III) recovery from salt mixture solution

Results of studies of the effects of concentrate salt solutions characterized by low pH, on the nanofiltration membrane surface properties used for the separation of chromium(III) have been presented in this paper. It was shown that the low pH of the concentrate salt solutions and cleaning bath with hydrochloric acid irreversibly altered the charge of tested membranes. As the consequence an instability of permeability and selectivity of the membrane during the process was noticed. The effect of alkaline bath used after cleaning with a solution of hydrochloric acid to regenerate the surface charge of tested membranes was also examined. The results showed that the use of bath in the form of sodium hydroxide leads to the partial recovery of a low surface charge of the membranes. In addition a significant improvement in the stability of the tested NF membranes used for the separation of chromium(III) from concentrate salt solutions at low pH was observed. Moreover, SEM images obtained for the tested membranes cleaned with solutions of HCl and NaOH indicated no mechanical defects in the structure of the examined membranes.

► Low pH and high salt concentration in chromium solution modified NF membrane surface
► Two washing procedures to reproduce the properties of NF membranes was analyzed
► Potential zeta, SEM and permeability of membranes was determined
► Membrane bathing with HCl reduced its scaling but not the surface charge reproduced
► Mixed HCl–NaOH bath leads both reduce of membrane scaling and recovery its charge