Abstract
The potential of employing nanofiltration for the removal of sulfate from concentrated chlor-alkali brine has been investigated. Polybenzimidazole (PBI) was chosen to fabricate nanofiltration hollow-fiber membranes through the dry-jet wet phase-inversion technique because of its robust mechanical strength and excellent chemical stability. The feed solution was a concentrated brine consisting of 253.3 g L-1 NaCl, 9.7 g L-1 Na2SO4, and 9.5 g L-1 Na2CrO4 with a pH value greater than 12.65. The PBI membranes showed high sulfate rejection (up to 98.4% at pH 13.25 and 25 bar) and low chloride rejection (less than 4.0%), thus simultaneously obtaining an extremely high di-/monovalent anion selectivity. In addition, the sulfate and chromate rejections increased with increasing solution pH and/or operating pressure. The impressive separation performance can be attributed to the unique pore and charge characteristics and superior chemical stability of PBI NF membranes. It was found that the mean effective pore size ...
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