Development of manufacturing process for high quality calcium carbonate by causticizing process in a kraft pulp mill - Part 2: Controlling factors for precipitation of aragonite -

Precipitated calcium carbonate is produced as a by-product in the causticization step of the kraft pulping process. There are many advantages to use this by-product, causticizing calcium carbonate (CCC), as filler and coating pigment in paper. By using this CCC for paper materials, lime-kiln operation can be shortened or stopped, resulting in the reduction of fuel oil for calcination of calcium carbonate. Furthermore, accumulated impurities in the lime cycle can be removed constantly. In our previous reports, we showed that aragonite crystal with high quality performance was obtained in the causticizing reaction. However, it is not clear the reason why high quality aragonite crystal could be obtained by the causticizing reaction. In this paper, the effect of reaction conditions on the precipitation of aragonite was precisely investigated. The results showed that aragonite crystal could be obtained under the conditions at optimum temperatures with relatively low CO3 2- concentration. In addition, the presence of NaOH in the mother liquor accelerated the precipitation of aragonite crystal. These favorable conditions to precipitate aragonite crystal can be easily formed in the causticizing reaction ; therefore, causticizing reaction is suitable to produce aragonite crystal.