Abstract: 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 ?m, CaCO3 wherein ?90% of CaCO3 have a particle size below 2 ?m, and a superfine CaCO3 having an average particle size <1 ?m. The CaCO3 obtained by this process can be directly used for papermaking and other industrial applications.

Abstract: This invention provides an improved process for recovering chemicals from black liquor in alkaline pulping, which is achieved by introducing depuration treatments of green liquor and lime before causticization reaction and a two-step-causticization procedure in the causticization procedure of the conventional chemical recovery process. The process of this invention not only avoids the generation of the waste residue (lime mud) from the beginning and saves the recovery and treatment of lime mud, but also can directly produce a series of precipitated calcium carbonate products with various particle sizes by regulating process conditions while the alkali is recovered, said CaCO3 products including a CaCO3 suitable for making coated paper, wherein ?50% of the CaCO3 has a particle size below 2 ?m; a CaCO3 suitable for making neutral sized paper, wherein ?90% of the CaCO3 have a particle size below 2 ?m; a superfine CaCO3 having an average particle size <1 ?m.