Influence of Admixture Impurities on the Crystal Quality of Inorganic Phosphorus Compound

抄録

In the crystallization process, it is known that impurities in the mother liquor inhibit the crystal growth or decrease the crystal purity. It is important to investigate the influence of impurities on the crystal growth and crystal purity in the presence of admixture impurities considering application to a real industrial process. In this study, the influence of impurities on the crystal growth and the crystal purity has been simultaneously evaluated for the growth of the crystalline particles under the real industrial process solution where admixture impurities exist. The operation method was proposed in order to increase the productivity, at the same time, maintaining the certain crystal purity. The crystal growth rate is increased by masking Ca²⁺, an impurity which inhibits the crystal growth, with the addition of EDTA in the real industrial process solution where admixture impurities exist. It means that an initial supersaturation σ_i which is necessary to achieve a certain crystal growth rate can be lowered. Moreover, when the same crystal growth rate was established in two systems, the crystal purity also became almost similar. It is found that Ca²⁺ had no influence on the crystal purity though Ca²⁺ inhibited the crystal growth rate. It is clear from this study that the driving force of crystal growth, maintaining the certain crystal purity, can be lowered by preventing the influence of impurities that inhibit the crystal growth. Therefore, the operation method can be proposed in order to improve the productivity, maintaining the crystal purity, in the production of the crystal in the presence of admixture impurities.