Solution crystallization process for the production of incongruently-soluble acid phosphates by incorporating phosphate salt solution wash

摘要

A novel method for producing incongruently-soluble alkali metal acid phosphates in a solution crystallization process by incorporating a phosphate wash solution. The phosphate wash solution improves product purity by removing entrained free acid from the surface of the incrongruently-soluble phosphate crystals. Thus, the wash improves the physical propterties of the crystals, such as the hygroscopicity and handling characteristics. The phosphate wash solution significantly reduces the amount of crystals dissolved during the washing step and therefore results in significantly higher product recoveries when compared to conventional crystal washing techniques. Additionally, a solution crystallization method is disclosed for producing mixed cation, incongruently-soluble phosphate crystals. The process utilizes a reaction mixture having an excess of the theoretical molar amount of phosphorus required for the incongruently soluble phosphate salt. The entrained free acid from the excess amount of phosphorous is then washed from the crystal surface utilizing a phosphate solution.