In the textile industry, high salinity waste streams are a challenge urging for the recovery and
purification of dyes and salts (e.g., NaCl), requiring a treatment going beyond the classical filtration by
e.g., reverse osmosis to produce pure water. In this work, two commercial loose nanofiltration (NF)
membranes (Sepro NF 6 and NF 2A, Ultura) are proposed to fractionate dye/salt aqueous mixtures. It was
observed that both NF membranes have a salt rejection o33.3% in solutions with 0.1–40.0 g L1 of NaCl
at 6 bar. Furthermore, both membranes have 499.6% retention of direct dyes (direct red 80, direct red
23, and congo red), even though 40.0 g L1 NaCl is present, indicating salt addition has no obvious
impact on the dye retention. The combination of a low salt rejection and a high dye rejection indicates
the feasibility for the reuse of salt from fractionation in forward osmosis and bipolar membrane
electrodialysis. Application of diafiltration for an aqueous mixture containing direct red 80 (1000 ppm)
and NaCl (20 g L1) by both membranes demonstrates that above 95% of NaCl is removed from
aqueous mixture, and o0.9 g L1 NaCl remains after the addition of pure water with a volume factor of
4.0 in the feed solution. At the premise of excellent diafiltration performance, concentration as the posttreatment
for dye recovery expectedly indicates direct red 80 is concentrated by a factor of 4.0 for both
membranes while keeping the salt concentration with a very slight increase. Over 99.9% dye retention in
both diafiltration and concentration procedures yields a very high recovery since o0.045% of dye is
permeated. These results indicate that loose nanofiltration membranes have potential for dye/salt
fractionation.