Calcium hydrogen phosphate, commonly known as precipitated calcium phosphate in industry, is abbreviated as precipitated calcium phosphate.
Calcium hydrogen phosphate is obtained by reacting a suspension of lime milk or limestone powder with phosphoric acid, and the precipitate is filtered, dried, and crushed. Its main component is calcium hydrogen phosphate dihydrate, with a molecular weight of 172.09. Calcium hydrogen phosphate is a dry, loose powder like crystal, with a neutral appearance and low moisture absorption. It is easy to transport, store, and apply. Products made from wet process phosphoric acid, due to impurities, are gray white or yellow in fertilizer grade, and white or gray white in feed grade.
Pure calcium hydrogen phosphate is an important feed additive. Mainly providing phosphorus and calcium, it is usually required to maintain a calcium phosphorus ratio of 1:1-2:1 in feed, and calcium hydrogen phosphate is the most suitable variety. Calcium hydrogen phosphate is a common component of nitrate phosphate fertilizer, ammonium superphosphate and their composite fertilizers. Due to high production costs, the promotion and application of calcium hydrogen phosphate in fertilizers are limited.
Calcium hydrogen phosphate consists of two types: calcium hydrogen phosphate dihydrate and anhydrous calcium hydrogen phosphate, commonly used as calcium hydrogen phosphate dihydrate. Dicalcium hydrogen phosphate dihydrate, a pure substance containing 41.25% phosphorus pentoxide, slightly soluble in water, easily soluble in acid, insoluble in ethanol, and soluble in ammonium citrate solution. Anhydrous calcium hydrogen phosphate, with a pure content of 52.17% phosphorus pentoxide, has a low solubility in citric acid solution.
Calcium hydrogen phosphate dihydrate is a thermosensitive substance, and crystalline water can be removed by heating. At higher temperatures, it not only dehydrates quickly but also completely. Dicalcium hydrogen phosphate dihydrate is a high concentration of soluble phosphate fertilizer suitable for use as a base fertilizer, suitable for various soils and crops. Its fertilizer efficiency is the same as that of ordinary superphosphate, and it has a significant effect on acidic soil.
Calcium hydrogen phosphate is produced by neutralization and precipitation of phosphoric acid and lime milk. The production of dicalcium phosphate consists of two steps: the preparation of phosphoric acid solution and the precipitation of dicalcium phosphate.
Fertilizer grade calcium hydrogen phosphate is generally produced by processing phosphate rock with inexpensive and easily available by-product hydrochloric acid, which is relatively economical and feasible. Feed grade products require high purity and are usually processed and produced using degummed bone residue, hot process phosphoric acid, or purified wet process phosphoric acid as raw materials.