Process For Preparation Of High Purity Ammonium Phosphate Of With Coupling Of Extractive Purification And Stagewise Reaction

Solvent extraction is the main method of purification of wet phosphoric acid, its costs are lower than thermal phosphoric acid, but its impurities level is higher, so wet phosphoric acid is required to be purified by solvent extraction or other methods in the preparation for the high purity grade phosphate products. Present solvent extraction process typically includes: concentration, extraction, scrubbing, back-extraction and so on, the back-extracted phosphoric acid is then used as the starting materials for preparation of phosphates. From the theoretical analysis, phosphoric acid in organic phase can directly react to prepare for phosphates, which can eliminate back-extracting operation. Through controling the neitralisation reaction degree of phosphoric acid, different purity level phosphates may be got by crystallisation from extract phase.With ammonium phosphates as end products, a coupling process of extractive purification and stagewise reaction has been experimentally studied. The processes include: concentration, multi-stage extraction, multi-stage scrubbing and stagewise reaction, while methyl isobutyl ketone is used as extractant, through this process we can obtain different grades of ammonium phosphates (one part is high purity ammonium phosphates).In order to establish the method for preparation of high purity ammonium phosphates through stagewise reaction, thermodynamic properties of end products and impurities salts were firstly researched. The solid liquid equilibrium properties of monoammonium phosphate, diammonium phosphate, ferric phosphate and ammonium sulphate in methyl isobutyl ketone were studied. Known from researching result, when temperature was ranged from 25℃to 35℃, the sequence of solubilities in water-saturated methyl isobutyl ketone is listed as follows:monoammonium phosphate<ammonium sulphate<ironic phosphate<diammonium phosphate, and it will be more conductive to grading salt reaction at temperature of 35℃.On this basis, initial process of preparation of ammonium phosphate through grading reaction was proposed, and corresponding technological study was conducted. Studies indicated that the optimal conditions for extracting purification:acid concentration is from 75% to 79%, mass ratio between organic solvent and concentrated phosphoric acid is 1.2:1, the temperature is 30℃; the optimal conditions for scrubbing purification:the concentration of scrubbing acid is from 53% to 54%. mass ratio between organic extraction phase and scrubbing acid phase is 1:0.4. the temperature is 30℃.Based on the above research, the extractive purified wet phosphoric acid is used for production of ammonium phosphate by stagewise reactive crystallizaion, by controlling the reaction degree industrial grade, food grade and high purity grade phosphates can be obtained in the reacting process. Reaction products can be crystallized directly from the extract phase, so the traditional process of evaporating water to get phosphate products can be eliminated.