Elimination of AsF3 from anhydrous HF using AgFAsF6 as a mediator

Elimination of the arsenic (III) impurity AsF3 from anhydrous hydrogen fluoride has been demonstrated using a bench-scale apparatus (∼500 mL of HF), with a Ag(II) salt AgFAsF6 as a mediator. In this process, AsF3 is oxidized by AgFAsF6 to AsF5. In the next step, AsF5 is eliminated from HF by reaction with NaF. The oxidizer, AgFAsF6, is reduced to AgAsF6 which is regenerated to AgFAsF6 by F2 in HF at room temperature. This method can reduce the arsenic content in HF from a few hundred ppm to the industrially required level (<3 ppm). The results for three other methods (distillation, oxidation by F2 gas, and oxidation by K2NiF6) are reported and compared with the AgFAsF6 method in a preliminary examination (using ∼4 mL of HF).