Method for preparing potassium dihydrogen phosphate from wet phosphoric acid

Abstract

The invention relates to the technical field of potassium dihydrogen phosphate preparation, and especially relates to a method for preparing potassium dihydrogen phosphate from wet phosphoric acid. The method is characterized in that a two-step reaction of wet phosphoric acid is carried out to prepare potassium dihydrogen phosphate, and the method comprises the following steps: reacting wet phosphoric acid with ammonia water, adjusting the pH value of the above obtained slurry to 3.0-7.0 to remove Fe, Al and other cations and F, Si and other anion impurities from the wet phosphoric acid in order to purify wet phosphoric acid, reacting the purified ammonium dihydrogen phosphate slip with potassium hydroxide or potash or potassium bicarbonate, and carrying out evaporation crystallization under a vacuum degree of 0-0.01MPa at a temperature of 85-95DEG C to prepare high-quality potassium dihydrogen phosphate with the purity of 98.3-98.8%.

Description

technical field [0001] The invention relates to the technical field of potassium dihydrogen phosphate production, in particular to a method for preparing potassium dihydrogen phosphate from wet-process phosphoric acid. Background technique [0002] Potassium dihydrogen phosphate is a fine product of phosphate, which can be widely used in chemical, pharmaceutical, food, agriculture, animal husbandry, petroleum, paper, detergent and other industries, and occupies an important position in the fine phosphate product series. At present, the production of fine potassium dihydrogen phosphate in China mostly adopts phosphoric acid prepared by thermal phosphoric acid or wet process phosphoric acid to carry out purification treatment, and the purified phosphoric acid obtained after neutralization reaction with the corresponding potassium raw material is prepared, but due to the production of purified phosphoric acid raw material The cost is high and the purification is difficult, resu...

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Problems solved by technology

However, the ion exchange resin itself has the disadvantage of small exchange capacity, and the concentration of the exchange solution is low, which causes great pressure on the subsequent evaporation, and at the same time, the equipment and cost investment are large.

[0005] The double decomposition method is the chemical reaction between potassium chloride and phosphoric acid or its acid salt to produce potassium dihydrogen phosphate. In this method, the replacement of potassium dihydrogen phosphate with cheap potassium chloride can reduce the cost. The reaction conditions are mild, the production equipment is relatively simple, and the operation is convenient. , no discharge of three wastes, stable quality, and lower cost compared with the neutralization method; but the resulting product KH 2 PO 4 The quality of the neutralization method is not as good as that of the neutralization method, and it can basically only be used in the agricultural field, and this method consumes a lot of energy and severely corrodes the equipment. The resulting product contains chlorides, and the added value of the by-product hydrochloric acid or chloride salt is low.

[0006] From the above prior art, it has become a trend to use wet-process phosphoric acid as a raw material to directly prepare potassium dihydrogen phosphate to become a trend in this industry, but the method in the prior art uses wet-process phosphoric acid as a raw material to directly prepare dihydrogen phosphate There are still many problems in the process route of potassium, which makes it difficult to guarantee the energy saving and emission reduction of the process route of the prepared potassium dihydrogen phosphate and the purity of potassium dihydrogen phosphate, which leads to the direct preparation of dihydrogen phosphate by wet-process phosphoric acid The cost of potassium is relatively high, and the energy consumption is large; at the same time, my country's phosphate rock resources are abundant, but most of them are of medium and low grade, which makes the content of phosphorus pentoxide in wet-process phosphoric acid low, and the impurity content is high, and each impurity The specificity is strong, and the purification is difficult, which makes it difficult to directly prepare potassium dihydrogen phosphate products from phosphoric acid prepared by wet-process phosphoric acid process, and the product has low purity and poor quality.