METHOD FOR LIGNIN SEPARATION FROM BLACK LIQUOR COMPRISING REMOVAL OF SULPHUR COMPOUNDS FROM FORMED WATER EFFLUENT

摘要

The method is for separation of lignin from original black liquor (BLIN) having a first precipitation phase (PR1/PR2) for precipitation of lignin by a first acidification using acidifier, CO2, at alkaline conditions, then separating a lignin cake with subsequent suspension of the lignin cake in a strong acid to leach our metals from the lignin followed by dewatering and obtaining a clean lignin product LP. The acidic liquid phase (FL1) subjected to a sulphur removal process wherein a calcium containing compound is added to the acidic liquid phase, whereby sulphur in the acidic liquid phase is reacting with the calcium compound forming solid gypsum which could be separated and bled off from the process. The remaining acidic liquid could then be returned to the recovery process without negatively affecting the sulphur balance of the mill.