Recycle of synthetic calcium fluoride and waste sulfuric acid to produce electronic grade hydrofluoric acid
2021
Lin, Min-Fa | Wu, Jhong-Lin | Chang, Ken-Lin | Lee, Wen-Jhy | Chang, Chih-Ping | Lin, Yung-Chang | Chen, Po-Han
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 reaction of synthetic CaF₂ and waste H₂SO₄. The impact of four factors, including H₂SO₄ concentration, total volume (H₂SO₄ + H₂O)/CaF₂ ratio, drying temperature of synthetic CaF₂, and reaction carried out under different temperature, on HF productivity was investigated in this study. HF yield increased with increasing H₂SO₄ concentration and total volume/CaF₂ 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 CaF₂ and 70% H₂SO₄ had a higher absorbed-HF yield of 61.7% than synthetic CaF₂ and 70% waste H₂SO₄, which had a yield of 36%. This was due to the higher purity of the commercial CaF₂ and fewer interference ions in H₂SO₄. HF productivity was lowered by CaSO₄, which hindered the reaction of reactants and also the generation of fluorosulfuric acid.
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