US 4,999,095 A · Recovery of mixed acids from mixed salts

Abstract

A process for recovering concentrated mixed acids comprising HF from mixed salts at a high efficiency is disclosed. The process comprises the steps of providing an electrodialytic water splitter comprising at least one unit cell, each cell comprising a first compartment and a second compartment, feeding an aqueous solution comprising at least two salts formed from at least two different anions to the first compartment, one of said anions being fluoride, feeding a liquid comprising water to the second compartment, passing current through said electrodialytic water splitter to produce an aqueous product comprising mixed acids formed from the different anions in the second compartment, and an aqueous salt-containing product comprising a reduced concentration of said anions in the first compartment, and recovering aqueous products from the second compartment. The process is particularly useful in the production of concentrated HNO.sub.3 at unexpectedly high current efficiencies, and has particular utility in the area of regenerating stainless steel pickling acid mixtures comprising HF and HNO.sub.3.

Claims15

Dependent claims

A process for recovering a mixed acid solution comprising hydrofluoric acid from a solution comprising salts of the acids to be recovered comprising the steps of:

(a) providing an electrodialytic water splitter comprising at least two unit cells, each unit cell comprising a means for splitting water comprising a bipolar membrane or spaced apart anion and cation membranes, a first compartment and a second compartment, said electrodialytic water splitter additionally comprising a single pair of anode and cathode electrodes said at least two unit cells being between the anode electrode and the cathode electrode;
(b) feeding an aqueous solution comprising at least two salts formed from at least two different anions to the first compartment, one of said anions being fluoride anions;
(c) feeding a liquid comprising water to the second compartment;
(d) passing current through said electrodialytic water splitter to produce an aqueous product comprising mixed acids formed from the different anions in the second compartment, and an aqueous salt-containing product comprising a reduced concentration of said anions in the first compartment;
and
(e) recovering aqueous product comprising hydrofluoric acid from the second compartment.

3 more elements

Dependencies are inferred from the claim text.

Recovery of mixed acids from mixed salts

Life of this patent

Recovery of mixed acids from mixed salts

Life of this patent

Abstract

Claims15