Method for preparing spherical calcium carbonate by causticizing paper making green liquor

Abstract

The invention discloses a method to causticize and produce spherical calcium carbonate with papermaking green liquor and comprises the steps that: attapulgite is added in clear papermaking green liquor, green mature mud of which is removed, then is centrifugally separated to get purified green liquor, ZnSO4 solution is added drop by drop and is reacted to get solution containing ZnS crystal seed; the crystal seed is added to the purified green liquor, then Ca(OH)2 slurry is added drop by drop, reacted, filtered to get white mud calcium carbonate and white liquor; white mud calcium carbonate is cleaned to get purified white mud filter cake. The method of the invention well solves the secondary pollution problem of white mud, the treatment process is simple and quick, whiteness of the white mud CaCO3 obtained is high and the invention partly replaces American porcelain clay and calcined kaolin; besides, smoothness of paper pattern, glossiness of coating paper, surface strength, ink absorption and other differences are not large.

Description

technical field [0001] The invention relates to a method for purifying green liquor in the pulp and paper industry. Background technique [0002] Alkaline chemical pulp black liquor is extracted, evaporated and concentrated, and the melt obtained after burning is dissolved in dilute white liquor or water to form green liquor, the main component of which is sodium carbonate. In the process of causticization, lime is added to the green liquor, so that the sodium carbonate in the green liquor is converted into sodium hydroxide to form white liquor, and at the same time, the precipitated white mud is obtained. [0003] At present, lime mud produced by alkali pulping plants using wood as raw material is generally recovered by calcined lime method. However, a large amount of heavy oil and other fuels are generally used in the process of calcining recycled lime in lime mud, and the calcination process is relatively complicated, which makes The overall cost of lime obtained after c...

AI Technical Summary

Problems solved by technology

The main components of these solid particles are hydroxides or sulfides of Fe, Mn, Al, Mg, and silicon compounds. The compounds of Fe and Mn are colored impurities. If they are not separated, they will be entrained to white during the causticizing reaction. In the mud, the whiteness of the white mud is reduced; and if the silicon compound is not separated, CaSiO will be generated during the causticization reaction. 3 Entrained into the lime mud, it makes it difficult to filter and wash the white mud, and it also causes serious wear and tear on the papermaking equipment when the white mud is used as a paper-making filler and a pigment for paper coating.

In addition, the solid particles in the green liquor will be used as white mud (CaCO 3 ) seed crystals during formation, so that the generated white mud CaCO 3 Irregular particle shape, uneven particle distribution

White mud CaCO 3 The irregular shape of the particles will also lead to increased wear on the papermaking equipment; while the lime mud CaCO 3 In addition to being related to the impurity content, the whiteness is also related to the white mud CaCO 3 Particle shape is related to particle distribution, white mud CaCO 3 Irregular particle shape and uneven particle distribution can also lead to white mud CaCO 3 decrease in whiteness

[0006] In the Chinese patent CN1264752C, the green liquor is used for causticizing reaction without further purification treatment, and the whiteness of the obtained lime mud is not high, and its use in papermaking will cause great wear and tear on papermaking equipment

A small amount of Ca(OH) is used in Chinese patents CN1239166A, CN1546789, and CN1436894 2 Pretreatment of green liquor, but this treatment method does not completely remove impurities

In Chinese patent CN1641100A, although sodium polyacrylate or water-soluble starch is used to purify green liquor, this sodium polyacrylate or water-soluble starch is not a flocculant, and this treatment method can only remove a small amount of positively or negatively charged Particles with larger particle size are flocculated, and it is quite difficult to separate sodium polyacrylate or water-soluble starch from the green liquor. It is difficult to separate them by sedimentation. Non-toxic starch clogs the pores of the filter cloth and makes the filtration process quite slow

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