Process for causticizing green liquor in chemical recovery from black liquor in alkaline pulping

摘要

The improved process is achieved by introducing depuration of green liquor and lime before causticization and two special causticization steps in causticization procedure of conventional chemical recovery processes. It not only avoids the generation of waste residue (lime mud) from the beginning and saves the re-burning and filling land of lime mud, but also can directly produce a series of precipitated calcium carbonate products with various particle sizes by regulating process conditions while alkali is recovered. The CaCO₃ products include CaCO₃ wherein >=50% of CaCO₃ has a particle size below 2 mum, CaCO₃ wherein >=90% of CaCO₃ have a particle size below 2 mum, and a superfine CaCO₃ having an average particle size <1 mum. The CaCO₃ obtained by this process can be directly used for papermaking and other industrial applications.