Preparation Of Potassium Dihydrogen Phosphate By Liquid-Lquid Inhomogeneous Double Decomposition Method

Preparation of potassium dihydrogen phosphate (KDP) by liquid-liquid inhomogeneous double decomposition method was studied in this paper. An extractant with low water solubility, high extract-efficiency and good selectivity for hydrochloric acid extraction was employed. Equilibrium relationship of phosphoric acid abstraction and double decomposition was studied. Optimal process route was acquired by studying the influences of extraction temperature, extraction time, amount-of-substance ratio of extractant to phosphoric acid, amount-of-substance ratio of phosphoric acid to potassium chloride, and addition amount of diluting agent on the extraction rate, etc. As a result, we extracted the wet-process phosphoric acid at 30℃for 20 min with the molar concentration ratio and the phase ratio of extractant versus phosphoric acid was 1:1.7 and 2:1 respectively; Double decomposition was carried at 30℃. The molar concentration ratio and phase ratio of the phosphoric acid in extractant and potassium chloride solution was 1:4 and 4:1 respectively. Under these conditions, purity of potassium dihydrogen phosphate was more than 99.6%and mass fraction of chlorine ion was less than 0.2%, mass fraction of potassium oxide and phosphoric pentoxide was more than 34.4%and 51.94%respectively. The product could meet the requirement of the first-class of the industrial product of KDP.Production cost was reduced by substituting potassium hydroxide with potassium chloride and substituting hot-process phosphoric acid with wet-process phosphoric acid. The adoption of the extractant made the process with low energy consumption, simple flow and high purity product.