A study on the low-temperature wet synthesis of hydrofluoric acid from synthetic calcium fluoride and waste sulfuric acid

Abstract

An innovative method for utilizing synthetic calcium fluoride (CaF2), recovered from fluoride-containing semiconductor wastewater, and waste sulfuric acid (H2SO4) to produce hydrofluoric acid (HF) was investigated. The research was set to study the low-temperature production of HF via the reaction of synthetic CaF2 and waste H2SO4. The impact of H2SO4 concentration and total volume (H2SO4 + H2O)/CaF2 ratio, drying temperature of synthetic CaF2 on HF productivity were investigated in this study. HF yield increased with increasing H2SO4 concentration and total volume/CaF2 ratio under room temperature. In addition, the HF produced in the reactions involving the 105 oC-dried synthetic CaF2 were higher than the 600 oC-dried synthetic CaF2 ones. The study will not only find uses for this semiconductor wastes but also provide a greener alternative to the current commercial production of HF.