A First Report on the Selective Precipitation of Sodium Chloride from the Evaporated Residue of Reverse Osmosis Reject Salt Generated from the Leather Industry

The reverse osmosis process has been actively implemented in the leather sector for the recovery of water from secondary biologically treated wastewater. The membrane reject stream is evaporated in solar evaporation pan/multiple effect evaporator. The evaporated residue (ER) of the reject stream from reverse osmosis lacks reusable characteristics, owing to a high contamination of inorganic and organic salts. In this investigation, an attempt was made to separate sodium chloride from the saturated solution of ER by the common ion effect in the presence of other inorganic and organic contaminants, using hydrogen chloride gas. The optimized process parameters for the selective precipitation of sodium chloride were as follows: time, 3 min; pH, 8.0; temperature, 40 degrees C; and concentration of ER, 60% (w/v). The ER and the recovered salts were characterized, using SEM-EDX and XRD. This is probably the first report on the precipitation of sodium chloride from the ER. The cost toward the disposal of this ER was also analyzed.