Recycle of synthetic calcium fluoride and waste sulfuric acid to produce electronic grade hydrofluoric acid.

An innovative method for utilizing synthetic calcium fluoride (CaF), recovered from fluoride-containing semiconductor wastewater, and waste sulfuric acid (HSO) to produce hydrofluoric acid (HF) was investigated. The research was set to study the low-temperature production of HF via reaction of synthetic CaF and waste HSO. The impact of four factors, including HSO concentration, total volume (HSO + HO)/CaF ratio, drying temperature of synthetic CaF, and reaction carried out under different temperature, on HF productivity was investigated in this study. HF yield increased with increasing HSO concentration and total volume/CaF ratio under room temperature. Generally, reactions carried out under low-temperature (< 100 °C) had a positive impact on HF yield. The higher temperature led to an increase in absorbed-HF but a decrease in total-HF. The reaction of commercial CaF and 70% HSO had a higher absorbed-HF yield of 61.7% than synthetic CaF and 70% waste HSO, which had a yield of 36%. This was due to the higher purity of the commercial CaF and fewer interference ions in HSO. HF productivity was lowered by CaSO, which hindered the reaction of reactants and also the generation of fluorosulfuric acid.