Process for removing fluoride from a wastewater and producing hydrofluoric acid therefrom

Abstract

A process for producing hydrofluoric acid from SiF.sub.6.sup.2- in a wastewater is disclosed. The process is carried out by (i) combining (NH.sub.4).sub.2 SO.sub.4, at a pH high enough such that the sulfate is in its divalent state, with SiF.sub.6.sup.2- from said wastewater in an amount in excess of that stoichiometrically required to form (NH.sub.4).sub.2 SiF.sub.6 as follows: (NH.sub.4).sub.2 SO.sub.4 +SiF.sub.6.sup.2- .fwdarw.(NH.sub.4).sub.2 SiF.sub.6 +SO.sub.4.sup.2- (ii) concentrating a solution including (NH.sub.4).sub.2 SiF.sub.6 and excess (NH.sub.4).sub.2 SO.sub.4 to precipitate and separate (NH.sub.4).sub.2 SiF.sub.6 of high purity therefrom; (iii) re-solubilizing the (NH.sub.4).sub.2 SiF.sub.6 for reaction with NH.sub.4 OH to form NH.sub.4 F liquor and precipitated Si(OH).sub.4 ; (iv) separating the NH.sub.4 F liquor from the precipitated Si(OH).sub.4 ; (v) reacting the NH.sub.4 F with water to form precipitated NH.sub.4 F.multidot.HF and ammonia gas; (vi) reacting NH.sub.4 F.multidot.HF with NaF to yield precipitated NaF.multidot.HF and NH.sub.4 F liquor; and (vii) heating and decomposing the NaF.multidot.HF into HF and NaF.

Dependencies are inferred from the claim text.