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 apparatus 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.

Recovery of acids from materials comprising acid and salt

Electrical energy is generated from acid-base neutralization reactions in electrodialytic cells. Permselective bipolar membranes in these cells are contacted on their cation selective faces by aqueous acid streams and on their anion-selective faces by aqueous base streams. Spontaneous neutralization reactions between the basic anions and acidic cations through the bipolar membranes produce electrical potential differences between the acid and base streams. These potential differences are transmitted to electrodes to produce electrical energy which is withdrawn from the cell.

Process for production of electrical energy from the neutralization of acid and base in a bipolar membrane cell

An improved process is described for recovering TiO 2 , useful as a white pigment, from ilmenite-type ores, including the steps of digesting the ore with aqueous hydrofluroic acid, separating out iron impurities from the resulting solution, precipitating hydrated titanium dioxide from the iron-free solution with ammonium hydroxide, and calcining the precipitate to obtain pigmentary TiO 2 , wherein the improvement comprises subjecting aqueous solutions of by-product ammonium fluoride, formed in the process, to electrodialytic water-splitting to form an aqueous solution of ammonium hydroxide and an aqueous solution of hydrogen fluoride and recycling said aqueous ammonium hydroxide to the precipitation step and said aqueous hydrogen fluoride to the digestion step.

Recovery of TiO2 from ilmenite-type ore by a membrane based electrodialysis process

A process for the treatment of an aqueous stream containing an acid or base and typically a precipitatable material such as a metal ion comprises: (a) subjecting the aqueous stream to (i) a treatment to produce a relatively pure stream of water and a concentrated aqueous stream, and (ii) water splitting to produce a stream of base, a stream of acid and a dilute aqueous stream of a concentration lower than the concentrated aqueous stream, the treatments (i) and (ii) being effected in either order, (b) recycling at least part of the pure water stream produced in (a)(i) to an earlier stream either in the production leading to said aqueous stream or to step (i) or (ii), (c) recycling at least part of the acid and/or base streams produced in (a)(ii) to an earlier stream either in the production leading to said aqueous stream or to an earlier step in the process, and (d) recycling at least part of the lower concentration stream produced in (a)(ii) to either (a)(i) or to another step in the process, whereby, when present, only the precipitatable material is removed from the aqueous stream, thereby obviating toxic waste disposal problems.

Membrane processes for metal recovery and pollution control in metal process industries

An electrodialytic distillative process for recovery of anhydrous hydrogen fluoride from an aqueous solution of fluosilicic acid and hydrogen fluoride wherein the concentration of hydrogen fluoride in said solution is such that hydrogen fluoride cannot be recovered therefrom by distillation, which comprises subjecting the solution to electrodialysis thereby increasing the total acids concentration in said solution to equal to or greater than about 46 weight percent, and thereafter recovering anhydrous hydrogen fluoride by distillation.

Process for the recovery of anhydrous hydrogen fluoride from aqueous solutions of fluosilicic acid and hydrogen fluoride

Fluorine values are recovered from fluosilicic acid aqueous streams by electrodialytic water-splitting of fluoride salt to hydrofluoric acid and hydroxide base and further optionally concentration of the hydrofluoric acid via membrane electro-dialysis, to produce anhydrous HF.

Chlanda Frederick Paul

Papers

Production of hf from fluorine by-products

Verfahren zur herstellung von fluorwasserstoff aus fluornebenprodukten