Causticizing method and process device for preparing precipitated calcium carbonate by recycling papermaking alkali

Abstract

The invention provides a causticizing method and a process device for preparing precipitated calcium carbonate by recycling papermaking alkali. The causticizing method comprises the following steps: a) mixing Ca(OH)2-containing digestive liquid and NaOH-containing solution with an aragonite type calcium carbonate seed crystal, sequentially feeding the mixed solution to multiple causticizing tanks for performing causticizing reaction, and respectively feeding Na2CO3-containing green liquor to each causticizing tank; b) precipitating and separating the reaction solution in the last causticizing tank to obtain a first coated slurry and a primary white liquor; and c) further causticizing the first coated slurry and Na2CO3-containing solution, completely reacting the incompletely reacted Ca(OH)2, and separating a second coated slurry and a secondary white liquor. According to the causticizing method, a multistage countercurrent causticizing technology is employed, not only is the alkali recycled, but also the aragonite type crystal structure-based precipitated calcium carbonate with high whiteness and fine granularity can be obtained, wherein the precipitated calcium carbonate can be directly used to fill the paper and can replace the commercial precipitated calcium carbonate; in addition, the causticizing method dispenses with customizing special reaction equipment for the existing alkali recovery process, and is easy to implement.

Description

technical field [0001] The invention relates to the field of papermaking, in particular to a causticizing method for recovering papermaking alkali to prepare precipitated calcium carbonate, and a causticizing process device for recovering papermaking alkali to prepare precipitated calcium carbonate. Background technique [0002] Alkaline pulping is a process widely used in most pulp and paper mills (especially straw pulp and paper mills). In the causticizing process of alkaline pulping and papermaking, a large amount of precipitated calcium carbonate (white mud) will be produced. Causticization is the removal of Na in the green liquor produced by alkaline pulping and papermaking 2 CO 3 with Ca(OH) 2 The causticization reaction occurs to produce NaOH-containing white liquor and precipitated CaCO 3 The reaction process of white clay. [0003] At the same time, calcium carbonate is increasingly used as a filler and coating pigment in industries such as papermaking. With t...

AI Technical Summary

Problems solved by technology

However, the lime mud produced by the traditional causticizing process has the problems of low whiteness and poor shape uniformity, which cannot meet the needs

In the existing papermaking technology, commercial calcium carbonate is generally used as filler, but there are few reports on the technical scheme of directly causticizing to produce precipitated calcium carbonate without carbonization after causticizing

Images