The production method used is mainly the neutralization method, that is, after phosphoric acid is reacted with potassium hydroxide or potassium bicarbonate, and potassium carbonate, the end point of the reaction is controlled, and the neutralization solution is concentrated to remove insolubles, and then After cooling, it is crystallized, centrifuged and dried to obtain a product. However, because phosphoric acid is divided into thermal process phosphoric acid and wet process phosphoric acid, wet process phosphoric acid is mainly carried out by using phosphate rock and inorganic acid to produce weak acid according to the principle of strong acid. The root and other elements, such as calcium, form calcium sulfate insoluble matter, which is obtained by filtration.
However, because the quality of phosphate rock will affect the quality of wet-process phosphoric acid, the quality of phosphoric acid products prepared from wet-process phosphoric acid is not stable. At the same time, it also makes the obtained phosphoric acid have a higher impurity content and lower purity, so that When using phosphoric acid prepared from wet-process phosphoric acid to produce potassium phosphate products, it will not only make potassium phosphate low in purity and unstable quality, but will also cause added potassium hydroxide or potassium carbonate, Potassium ions in potassium bicarbonate interact with other impurity elements to form insolubles, which in turn causes a waste of potassium ions, resulting in an increase in the amount of potassium hydroxide, potassium carbonate or potassium bicarbonate added, resulting in higher preparation costs and higher resource consumption .
Based on the existing preparation technology of tripotassium phosphate, we provide a method for preparing tripotassium phosphate from wet-process phosphoric acid, which includes the following steps:
(1) Take wet-process phosphoric acid with a phosphorus pentoxide concentration of 15%, analyze the content of sulfate radicals in it, and add phosphate rock powder to it. The amount of phosphate rock powder added is the mass ratio of the sulfate radical content. 1:1, after 30 minutes of reaction, add ammonia water or pass in ammonia gas, adjust the pH to 3, and filter to obtain slurry and filter residue;
(2) Take potassium hydroxide, add potassium hydroxide to the slurry, and control the molar ratio of the amount of potassium hydroxide to the amount of phosphorus pentoxide in the wet-process phosphoric acid to be 6:1. After the feeding is completed, The negative pressure is controlled to 0MPa, and the temperature is 85°C for evaporation and crystallization. When a large number of crystals appear in the solution, stop evaporation, cool to room temperature, and filter to obtain the mother liquor and the primary product; the primary product is washed to obtain tripotassium phosphate.
The purity of the said tripotassium phosphate is 98.1%. In the washing, the washing liquid produced by washing is returned to step 1 and mixed with wet-process phosphoric acid. In the evaporative crystallization, the gas generated in the crystallization process is absorbed by dilute phosphoric acid, and then returned to be mixed with the wet-process phosphoric acid in step 1. The concentration of the dilute phosphoric acid is 15%. The mother liquor is sent to the compound fertilizer production line; the filter residue is sent to the compound fertilizer production line. The potassium hydroxide is a solid added to the slurry. The content of phosphorus pentoxide of the phosphate rock powder is not less than 7%. The said phosphate rock powder has a particle size of 40 mesh.
