Purification Of Ammonium Dihydrogen Phosphate

Phosphate optical glass material with good processing of optical and mechanical properties, high purity metaphoshate, in which the total content of transition metal ions as impurity is less than 5 ppm, is the main material to prepare the high-performance phosphate laser glasses. Due to the presence of transition metal ions, it can have strong absorption near ultraviolet to the infrared region for the metaphoshate glass. Thus, the preparation of high purity metaphoshate is the key to manufacturing of high-performance laser glass.Ion exchange is widely used to purify substances, since ion exchange resin can be used repeatedly through the exchange and regeneration, with the lower costs. Because the high-purity alkaline metal or alkaline earth metal metaphoshate can be produced by the reaction of high purity ammonium dihydrogen phosphate and alkaline metal or alkaline earth metal chlorides, high purity ammonium dihydrogen phosphate is the premise for preparation of high-purity metaphoshate.Ammonium dihydrogen phosphate was purified by ion exchange method. Three types of ion exchange resin were chosen to remove the transition metal ions, including Fe³⁺, Co²⁺, Ni²⁺and Cu²⁺. The obtained results showed that chelating resin D401 possesses the highest sorption capacities for the transition metal ions compared to other resins. The factors, such as pH and temperature that can exert effects on the properties of D401, were systematically investigated. The optimum conditions for purification of NH₄H₂PO₄ are pH 4.0～4.5, 30～40oC. Under these conditions, the total content of the transition metal ions can be reduced to 2.3 ppm in the salt. This work provides parameters for large-scale preparation of NH₄H₂PO₄ with high purity.