RECOVERY OF ACIDS FROM MATERIALS COMPRISING ACID AND SALT

We have discovered an improved, energy efficient method for recovering and regenerating acid from a solution comprising acid and salt. The process comprises of the steps of supplying a solution comprising salt and a first concentration of acid to a first compartment (D) of an electrodialysis apparatus (2) comprising a first compartment and a second compartment (C), supplying a liquid comprising water to the second compartment, applying a direct current to the electrodialysis apparent to form, in the first compartment, a first product comprising salt and a second concentration of acid, the second concentration of acid being less than the first concentration of acid, and, in the second compartment, a second product comprising water and enriched in acid by a proportionite amount, recovering the first product, recovering the second product, recovering acid from the first product using electrodialytic water splitting (11) to convert at least a portion of the salt to a third product comprising acid, and recovering the third product. The process has particular utility for the recovery and regeneration of mixed acids from spent pickle liquors containing free nitric acid and salts of an anion other than nitrate anion.