Mechanism of Preparing Hydrofluoric Acid from Low-grade Associated Fluorite

ObjectiveSingle type fluorite is currently the primary raw material for hydrofluoric acid production. However, its reserves are insufficient, with a guarantee life of around ten years. The reserve of associated fluorite is approximately twice that of single type fluorite. Nevertheless, the lack of research on the associated fluorite as a raw material for hydrofluoric acid production impedes its high-value utilization. MethodIn this article, high grade single type fluorite with a grade of 99.1% and low-grade associated type fluorite with a purity of 85.2% were studied. The reaction processes of high purity fluorite and low purity associated fluorite with concentrated sulfuric acid at varying conditions of temperature, time, and molar ratios of liquid to solid were investigated. ResultAt a temperature of 200 ℃ for 4 h, the optimal molar ratio of liquid to solid for single fluorite was 1.25∶1, with a conversion rate of HF up to 98.1%. When producing acid from associated fluorite, the dosage of concentrated sulfuric acid was higher at an optimal molar ratio of liquid to solid of 1.5∶1 and a conversion rate of HF up to 82.1%. The gypsum crystal produced by single fluorite had a large particle size, good crystallinity and a dense surface. However, the gypsum crystals produced by associated fluorite were small in particle size, irregular in shape and closely packed. ConclusionTherefore, distinct spiral patterns were evident in the gypsum particles produced by associated fluorite, and the agglomeration phenomenon of gypsum produced by associated fluorite was more serious than that of single fluorite, which hindered the efficient acid production reaction.