Studies on process development for the separation of sodium chloride from residue after evaporation of reverse osmosis reject solution

The membrane reject streams generated in industrial waste stream are evaporated in solar evaporation pan/multiple effect evaporator. The residue after evaporation (RAE) from reverse osmosis reject streams lacks reusable characteristics, due to a high contamination of inorganic and organic salts. In this investigation, a process was developed to separate sodium chloride from the RAE by selective ion precipitation using hydrogen chloride gas. The possible ways of hydrogen chloride gas was evaluated and used for the precipitation of sodium chloride. The optimized process parameters for the separation of sodium chloride were as follows: hydrogen chloride gas purging time, 3 min; pH, 8.0; temperature, 30 °C; concentration of RAE, 60% (w/v) and H/D ratio, 2.23 for the 100 mL working volume. The RAE and the recovered sodium chloride were characterised, for SEM, XRD and Cyclic voltametry to identify the structural and composition of the material. The results confirmed that the recovered salt is NaCl. The cost toward the disposal of this RAE was also analyzed against present process.