GB814638A - Process for the manufacture of solid metal fluoborates containing water of crystallisation - Google Patents

Abstract

Metal fluoborates and particularly those of copper, cadmium, zinc and nickel, containing water of crystallization, are prepared by reacting with the metal itself or with a compound thereof such as the carbonate, oxide or hydroxide, a highly concentrated fluoboric acid (or hydronium tetrafluoborate) of which the water content is such that together with any water produced in the reaction it corresponds with the water of crystallization of the fluoborate desired. The concentrated fluoboric acid may be obtained by reacting boric anhydride with liquid hydrogen fluoride or concentrated aqueous solutions thereof in a proportion of 1 mol. of B2O3 to 8 mols. of HF whilst maintaining the reaction between - 40 DEG C. and + 20 DEG C. Such a reaction is preferably effected in a polythene vessel containing concentrated fluoboric acid from a previous operation. Alternatively hydronium tetrafluoborate reactant may be prepared by reacting boron trifluoride hydrate with anhydrous hydrofluoric acid in a mol. ratio of 1:1 to obtain HBF4.H2O with a melting point of 50 DEG C. The fluoboric acid or the hydronium tetrafluoborate thus produced may be reacted to form solid metal fluoborates. Aqueous 1.35 mol. solutions of the fluoborates produced have a pH of 1 to 1.7 and the pH may be raised by the addition of the corresponding metal borate to the solution of the fluoborate or alternatively, by selecting a suitable mol. ratio of the initial reactants, a crystalline metal fluoborate containing by-product hydroxy fluoborate and borates may be produced having a higher pH. According to a typical example, concentrated tetrafluoboric acid was placed in a cooled vessel and boric anhydride and hydrofluoric acid were introduced alternately in small quantities whilst maintaining the temperature at 40 DEG to 70 DEG C. The concentrated fluoboric acid so produced was reacted with zinc carbonate; on cooling to room temperature the mass solidified to crystalline zinc fluoborate hexahydrate. Zinc oxide might be similarly employed. The zinc fluoborate contained zinc hydroxy fluoborate and zinc borate so that a 1.35 mol. aqueous solution thereof had a pH of 3. Further examples relate to cadmium, nickel and copper fluoborate production, and to the production of the fluoboric acid reactant by treating BF3.H2O with gaseous or aqueous hydrogen fluoride.