Purification Of KH₂PO₄ As A Phosphate Glass Material

Metaphosphate is an essential component to prepare phosphate glass. The glass made from metaphosphate, in which the total content of transition metal ions as impurity is less than 5 ppm, can be used to produce glass of high-power laser due to its excellent optical transmission. It can also be used as lens of missile. So the related preparation technique of the metaphosphate with high purity is important for military industry.In general, KPO3,Which is one of the basic materials for making phosphate glass, can be obtained by heating KH2PO4. In this work, a phosphate glass material, KH2PO4, in which the total content of Fe3+, Co2+, and Ni2+ as impurity is less than 5 ppm has been prepared by ion exchange method. Four types of ion exchange resins, including two weakly basic anion exchange resins 701 and 703, and two chelating resins D751 and D402 were chosen to adsorb the transition metal ions Fe3+, Co2+, and Ni2+ as impurity. The results showed that chelating resins D751 and D402 possess higher sorption capabilities and good regeneration capability.Furthermore, the factors such as pH, concentration of solution, reaction time, temperature, and flow rate that can exert effects on the exchange properties of the D751 and D402 were investigated. The results indicated that Fe3+ can easily be adsorbed by the chelating resin D402, but the content of Ni2+ in KH2PO4 can not be reduced to≤3 ppm by the resin. Compared to D402, the chelating resin D751 is better. The optimum conditions for the purification of KH2PO4 with D751 are pH 4.0-5.0, temperature of 20-30℃, and flow rate of 1mL/min. Under the optimum conditions, the total impurity content in the KH2PO4 was reduced with the D751 from 23 ppm to≤3 ppm. This work provides parameters for large-scale preparation of KH2PO4 with high purity.