Study Of The Preparation Of Potassium Dihydrogen Phosphate By Liquid-Liquid Ion Exchange

With organic solvent, a new ion exchange method of manufacturing potassium dihydrogen phosphate (KDP) from wet process phosphoric acid and potassium chloride has been developed. Firstly, wet process phosphoric acid is extracted by the mixing organic solvents of tri-n-octylamine(TOA), n-octanol and kerosene; then the organic solvent loaded with phosphoric acid reacts with potassium chloride solution; then KDP product can be produced by cooling crystallization of the aqueous phase of the ion exchange reaction. The effect of mixing volume ratio of the organic solvents and phase ratio on the phosphoric acid extraction, the relationship between relating factors such as phosphoric acid concentration in the organic phase, the potassium chloride concentration in the aqueous phase, temperature, phase ratio and so on and the equilibrium concentration change in both phases, and the recycling effect of the organic solvents are investigated. By using Pitzer electrolyte solution theory, thermodynamic constants, such as equilibrium constant Ka,△Hm, AGm and△Sm during the H2PO4-CI- exchange process are calculated, and it is concluded that the ion exchange is an exothermic process. Optimum process conditions are selected, and the produced KDP product has met the standard of the first-class of the industrial product of KDP.Additionally, the continuous operation of the ion exchange process has been investigated with the reciprocating sieve column. The process incorporates both the characteristics of organic solvent extraction and ion exchange and has made all the extraction, back-extraction and chemical reaction in the phosphate preparing processes integrated with the great merits of shorter process flow, simpler operation, less energy consumption and higher purity of the KDP product.