Concentration of Sodium Sulfate from Pickle Liquor of Tannery Effluent by Electrodialysis

An electrodialysis technique using indigeneously prepared interpolymer membranes and a laboratory-scale electrodialysis unit having an effective area of 25 cm x 12 cm with 20 pairs of ion-exchange membranes was used for the concentration of sodium sulfate of pickle liquor by the recycling method. In the first stage the sodium sulfate in the effluent was concentrated three and half times with respect to the original effluents, thereby rendering the concentrate usable in the tannery process. The diluate of first stage solution was further subjected to electrodialysis in a once through pass system, and the total dissolved solids content of the second stage diluation was brought down to less than 1000 ppm. This process offers the possibility of either reusing the water or safely discharging it. The parameters voltage, flow rate, and change of concentration with fresh effluent were investigated. The energy requirement and current efficiency were also calculated.