RECOVERY OF WATER AND INORGANIC CHEMICALS FROM KRAFT BLACK LIQUOR USING MEMBRANE SEPARATION PROCESSES

Recovery of water with inorganic compounds in kraft black liquor was s tudied by pressure carbonation followed by different combinations of m embrane separation processes. Experiments were carried out to observe the effect of carbonation on black liquor, in terms of conversion of l ignin-bound alkali compounds into carbonate salts. Further, the reacti on rate during carbonation was studied and a correlation for decrease of active alkali with time is presented, which is equivalent to a firs t order rate equation. different combinations of membrane processes us ed were (a) ultrafiltration of the carbonated liquor followed by nanof iltration, (b) nanofiltration of the carbonated liquor, and (c) direct nanofiltration of untreated black liquor. comparisons were made in te rms of recovery of the inorganics, quality of the permeate, and permea te flux. Of the three combinations, the first scheme yields higher rej ection and better recovery as well as reasonable permeate flux. Recove ry was higher for higher feed concentrations.