PROCESS FOR CAUSTICIZING GREEN LIQUOR IN CHEMICAL RECOVERY FROM BLACK LIQUOR IN ALKALINE PULPING

摘要

This invention provides an improved process for recovering chemicals fromblack liquor inalkaline pulping, which is achieved by introducing depuration treatments ofgreen liquor and limebefore causticization reaction and a two-step-causticization procedure in thecausticization procedureof the conventional chemical recovery process. The process of this inventionnot only avoids thegeneration of the waste residue (lime mud) from the beginning and saves therecovery and treatmentof lime mud, but also can directly produce a series of precipitated calciumcarbonate products withvarious particle sizes by regulating process conditions while the alkali isrecovered, said CaCO3products including a CaCO3 suitable for making coated paper, wherein =50% of the CaCO3 has aparticle size below 2µm; a CaCO3 suitable for making neutral sized paper,wherein = 90% of theCaCO3 have a particle size below 2µm; a superfine CaCO3 having an averageparticle size 1µm. Thepresent invention can be used for treatment of pollution of black liquor inthe alkaline pulping.