Patent GB-234852-A (GB)
Title: Improvements in the manufacture of hydrofluoric acid
IPC: C01B7/19
Filed: 1925-06-02
Abstract: Pure hydrofluoric acid is obtained from substances containing silica as well as fluorine such as impure fluorspar by converting the mixture of hydrofluoric and hydrofluosilicic acids obtained by decomposing the fluorspar &c. with sulphuric or other acid wholly into hydrofluosilicic acid by means of silicon fluoride and treating the hydrofluosilicic acid so obtained with sodium, potassium, barium, or other metallic fluoride in order to produce pure hydrofluoric acid and a silico-fluoride which, on heating, yields a metallic fluoride and silicon-fluoride available for re-use.  Besides impure fluorspar, metallurgical slags containing fluorine and silicon and minerals such as apatite, sellaite, nocerite, and cryolite when associated with silica may also be used as raw material in the process.  In a modification the mixture of hydrofluoric and hydrofluosilicic acids produced in the first step of the process is used to decompose a metallic fluoride directly.  The Specification as open to inspection under Sect. 91 (3) (a) comprises also the addition of another non-metallic fluoride such as boron fluoride during the decomposition of the impure fluorspar &c. or to the resulting mix of hydrofluoric and hydrofluosilicic acids, when the mixture of complex fluorine acids is used to decompose a metallic fluoride to give pure hydrofluoric acid and a mixture of silico fluoride with another complex fluoride which yields, on heating, the non-metallic fluorides for re-use.  This subject-matter does not appear in the Specification as accepted.ALSO:Pure hydrofluoric acid is obtained from substances containing silica as well as fluorine such as impure fluorspar by converting the mixture of hydrofluoric and hydrofluosilicic acids obtained by decomposing the fluorspar with sulphuric or other acid wholly into hydrofluosilicic acid by means of silicon fluoride and treating the hydrofluosilicic acid so obtained with sodium potassium, barium, or other metallic fluoride in order to produce pure hydrofluoric acid and a silicofluoride which, on heating, yields a metallic fluoride and silicon fluoride available for re-use.  Besides impure fluorspar, metallurgical slags containing fluorine and silicon and minerals such as apatite, sellaite, nocerite, and cryolite when associated with silica may also be used as raw material in the process.  Any excess of silicon fluoride may be converted into sodium silicofluoride by treating it in aqueous solution with sodium chloride and fluorspar in the presence of a small quantity of acid. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the addition of another non-metallic fluoride such as boron fluoride during the decomposition of the impure fluorspar or to the resulting mixture of hydrofluoric and hydrofluosilicic acids, when the mixture of complex fluorine acids is used to decompose a metallic fluoride to give pure hydrofluoric acid and a mixture of silico fluoride with another complex fluoride which yields, on heating, the non-metallic fluorides for re-use.  This subject-matter does not appear in the Specification as accepted.