Performance of ceramic nanofiltration membrane for desalination of dye solutions containing NaCl and Na₂SO₄

Removing mixture salts from dye solutions using membrane technology still need to be improved for high dye rejection and low salt rejection. In this work, ceramic membrane with pore size of 1.5 nm presented a satisfactory desalination of dye solutions containing NaCl and Na₂SO₄ compared with two commercial organic nanofiltration membrane elements (DK and DL). Effect of salt content, salt type, molar ratio of NaCl and Na₂SO₄, dye concentration and pH on performance of ceramic membrane for desalination of Eriochrome black T (EBT) were investigated. The results showed that dye rejection decreased by increasing salt content, dye concentration and solution pH. Compared with dye-NaCl solutions, a relative high flux and low rejection of dye were observed when treating dye-Na₂SO₄ solutions. For the mixture salt-dye solutions, the flux, which was higher than that for the single salt-dye solutions, first increased then decreased with decreasing C_NaCl/C_Na2SO4 due to the change of structure of cake layer. Supper-molecule aggregates of EBT formed by hydrogen-bond is mainly responsible for the high rejection of EBT (> 99%) at acid conditions. The rejection of NaCl and Na₂SO₄ was below 20% and 40%, respectively. These promising results demonstrates that the new ceramic membrane has a potential application in dye purification.