Sulfate removal from concentrated sodium chloride brines for chloralkali industry with nanofiltration membranes

Abstract

Nanofiltration membrane elements have been employed for the treatment of solutions containing raw brine generated by chloralkali industry. This study focused on the selection of appropriate nanofiltration membrane element and the assessment of their performance for the removal of sulfate and the retention of chloride from feed solutions. The influence of membrane type, temperature, pressure and sodium sulfate concentration on the selective removal of sulfate from concentrated sodium chloride brines were investigated. A high passage of sodium chloride and rejection of sodium sulfate were achieved with two different commercial nanofiltration membrane elements, DL2540 produced by GE Osmonics and NF270-2540 manufactured by FilmTec (Dow), suggesting that both membranes can be employed in sulfate removal from sodium chloride brines for chloralkali industry. Operating pressure and temperature showed no significant effects on sulfate rejection under the tested conditions. However permeate flux increased with both temperature and pressure in the tested ranges. The influence of temperature on permeate flux was due to the dependency of the viscosity of salt solution, which follows the Arrhenius model. Sodium concentration in feed had significant effects on permeate flux, sulfate rejection, and sulfate concentration at membrane interface and in permeate. Sulfate rejection and permeate flux reduced sharply with the increase of sulfate concentration in feed.