Kinetics study of leaching calcium fluoride with sodium phosphate and sodium hydroxide

Since the disadvantages of the current prevailing method that sodium hydroxide and sodium carbonate have been used to leach low-grade scheelite with a large amount of leaching agent and low leaching rate, a new process for synergistically efficiently leaching low-grade scheelite with sodium phosphate-sodium hydroxide-calcium fluoride is proposed. During the leaching process, calcium fluoride used as a solid source of fluorine, first dissolves and releases free fluoride ions, and then participates in the leaching reaction of scheelite to generate calcium fluorophosphate precipitation. Therefore, its dissolution rate has a greater influence on the leaching rate of scheelite. In this paper, the kinetics of calcium fluoride leaching by sodium phosphate sodium hydroxide was studied by the method of equal leaching rate. The effects of leaching temperature and sodium phosphate concentration on the leaching rate of calcium fluoride were investigated. The results showed that the leaching rate of calcium fluoride was greatly affected by leaching temperature, but less affected by the concentration of sodium phosphate. The apparent activation energy of leaching reaction was 134.57 kJ/mol with the apparent reaction order 0.92. The leaching process of calcium fluoride was controlled by chemical reaction. This study has a theoretical guidance for strengthening the leaching process of low-grade scheelite.