Study on Controlling the Dissolution of Calcium Dihydrogen Phosphate Using Ternary Phase Diagrams to Improve the Production Process of Phosphoric Acid

Phosphogypsum is a solid byproduct in the production of phosphoric acid in the traditional sulfuric acid process, and its output has caused a huge economic and environmental burden. In order to avoid the production of phosphogypsum and efficiently produce phosphoric acid, a novel study on the decomposition of phosphate ore by phosphoric acid was carried out. The influence of parameters on the decomposition efficiency of phosphate ore were explored systemically using response surface methodology (RSM). The concentration of phosphoric acid was the most important factor affecting the decomposition efficiency of phosphate ore in the phosphoric acid process, followed by reaction temperature and reaction time. The dissolution behavior of Ca(H2PO4)2 was studied using phase diagrams of ternary systems of P2O5-CaO-H2O. When the ratio of the practical doses of phosphoric acid to the theoretical/ stoichiometric doses of phosphoric acid (RatioP/T) was 3.3 and the phosphoric acid concentration (calculated as P2O5) was 35%, the decomposition efficiency of phosphate ore reached 98.34%, and the proportion of Ca(H2PO4)2 dissolved in the leach liquor reached 98.54%. A high proportion of dissolved Ca(H2PO4)2 reduced the loss of phosphorus, and the generation of clean gypsum was obtained under these experimental conditions. Clean gypsum produced by the phosphoric acid process is regular long columnar crystal and has few impurities. This study provides an efficient strategy for the production of phosphoric acid by controlling the dissolution of Ca(H2PO4)2, while avoiding the generation of phosphogypsum.