Effect of membrane properties on chromium(III) recirculation from concentrate salt mixture solution by nanofiltration

This paper presents results concerning the influence of membrane properties on effective recirculation of chromium(III) from tannery wastewater by nanofiltration process. DK, HL, DL “thin film” membranes and asymmetric CK membrane were tested for theirs permeability and selectivity on model chromium solution contained 2 gCr3+/dm3, 10 gCl−/dm3 and 10 gSO42−/dm3. Presented results allowed to conclude that both the high permeability and selectivity of NF membranes used for chromium recirculation from low pH, concentrate salt mixture solution are dependent on the membrane surface charge phenomenon. The retaining of the high permeate flux of chromium tannery wastewater at pH below 4, required the use of membranes with their IP as low as possible to assured the negative NF membrane surface charge and low chloride ions retention equal to 7–11%. As a consequence the polarization effect was reduced and the increase of permeate flux was observed. The use of such membranes guarantees obtaining of both a high permeate flux and a concentrated solution of chromium(III) as retentate which is suitable for recirculation. Due to the fouling and aggressive conditions characterized the tanning wastewater the polyamide/polysulfone membranes are suggested. The cellulose acetate membranes do not ensure satisfied results during treatment of tannery wastewater.

Research highlights
► Recirculation of Cr(III) from model tannery solution by NF was studied.
► Effect of properties of NF membranes on process was analyzed.
► High permeability of membranes is obtained for negative membrane charge.
► Low pH and high salt concentration in tannery solution modified membrane charge.
► Membranes with low IP allows obtaining a concentrate of Cr(III) under TMP of 14 bar.