Study On The Preparation Of Large Size Of Sodium Fluorosilicate Crystal

Sodium fluorosilicate is an important inorganic chemical product and widely used to agriculture and industry, such as insect pesticide, cement additives, wood antiseptic, etc.Sodium fluorosilicate is commonly prepared by the reaction of H₂SiF₆ with saturated NaCl solution at room temperature in batch-wise, and small crystal of Na₂SiF₆ with wide particle size distribution is obtained that it's difficulty to filtration, transportation, storage and application. Therefore, the manufacture of large size of sodium fluorosilicate crystal is quite necessary. So, systematic investigation on the crystallization process of sodium fluorosilicate is very important. The following aspects are studied in this paper.Firstly, the reaction condition of fluosilicic acid with sodium chloride is studied and optimal process conditions are obtained. The influence of crystallizer type on the crystallization of sodium fluorosilicate is also investigated. The experimental results show that the influences of feed concentration, feed position and crystallizer type on Crystal Size Distribution (CSD) of sodium fluorosilicate are great. The optimal concentration of H₂SiF₆ is 12%, quicksandy sodium fluorosilicate with good CSD is prepared by continuous crystallizer such as Oslo and DTB crystallizer. The excess of H₂SiF₆ in crystal growth section is good for crystal growth. And Oslo crystallizer has simple structure comparing with DTB crystallizer. It can be used in sodium fluorosilicate crystallization.Secondly, reaction crystallization kinetics of sodium fluorosilicate has been studied, and kinetic data is prepared for design of Oslo crystallizer. The solubility and metastable zone in sodium fluorosilicate solution has been measured. The nucleation rate, growth rate and average size of crystal are obtained in MSMPR crystallizer using the population balance technique. two kinetic equations are...