Research on Efficient Method for Removing Fluorine from Fluorine-bearing Minerals in Pyrrhotite

Pyrrhotite is a key raw material for sulfuric acid production, and its product quality involves technical indicators for elements such as fluorine, arsenic, lead, zinc, and carbon, among which fluorine content is subject to the most stringent limits. Fine-grained fluorine-bearing minerals intercalated in pyrrhotite, or fluorine-bearing minerals intergrown with pyrrhotite, are difficult to completely separate through conventional beneficiation methods, thus preventing the production of high-quality pyrrhotite products. In this study, an automated mineral liberation analysis system (BPMA) was used to investigate the mineral composition of pyrrhotite, the particle size of fluorine-bearing minerals, and their liberation and intergrowth characteristics. The results show that fluorine in pyrrhotite mainly occurs in fine-grained fluorite (CaF₂, accounting for 91.97% of the total fluorine) and fluorine-bearing silicate minerals. The fluorite particles mostly below 10 μm, with 96% existing as fully liberated particles or with the proportion of partially liberated grain. Based on this analysis, an acid leaching process for fluorine removal pretreatment of pyrrhotite concentrate was proposed. The optimal treatment conditions were determined at room temperature, with a L/S of 3∶1, stirring speed of 300 r/min. Utilized HCl to adjust and maintain the reaction system pH at 1.5–2, and a leaching time of 1 h. This process effectively removes fluorite, carbonate minerals, and some fluorine-bearing silicate minerals. After treatment, the sulfur grade has increased from 34.41% to 36.0%, and the fluorine content decreased to below 0.01%, achieving the technical requirements for first-grade pyrrhotite. This method is suitable for the efficient removal of fluorine-bearing minerals such as fluorite, apatite, and epidote from pyrrhotite. However, its effectiveness may be limited for fluorine-bearing minerals occurring as grossular or completely encapsulated by quartz, necessitating further exploration of alternative removal methods.