Electrodialytic purification process

Claim 2

In an electrodialysis process of passing an electric current through an electrodialysis cell comprising (a) a catholytic compartment containing a cathode and a catholyte, (b) an anolyte compartment containing an anode and an anolyte comprising an acidic aqueous solution containing dissolved multivalent metal cations and selected from (1) aqueous electroplating-type acids, (2) aqueous salt of a cation and an anion containing a multivalent metal ion, (3) aqueous salt of a multivalent metal cation and an anion of an acid containing sulfur, phosphorus, halogen or carbon, and (4) mixtures thereof, (c) the anolyte and catholyte compartments being separated by a cation-permeable membrane, the improvement comprising employing as the catholyte an aqueous solution of an inorganic carbonate, bicarbonate or hydroxide or mixtures thereof which form carbon dioxide and/or water upon contact with said acidic anolyte, whereby the electrodialysis can be carried out at high efficiency and high capacity without adversely affecting the capacity of the electrodialysis cell by precipitation of salts in the separating membrane and the quality of the anolyte by reverse migration of anions from the catholyte to the anolyte.

Claim 3

The process of claim 1 wherein said catholyte comprises a water soluble inorganic hydroxide and the concentration of said hydroxide is maintained at less than that which under the operating conditions causes formation of significant amounts of insoluble multivalent metal cation hydroxides in said membrane.

Claim 4

In the electrolytic purification of an aqueous solution of electroplating-type acids containing a multivalent metal ion in the anion portion of said acid, which solution is contaminated with dissolved multivalent metallic cations by passing electric current through an electrodialysis cell comprising (a) a catholyte compartment containing a cathode and a catholyte and (b) an anolyte compartment containing an anode and an anolyte comprising said contaminated acid solution, the anolyte and catholyte compartments being separated by a cation-permeable membrane, the improvement comprising employing as the catholyte an aqueous solution of a water-soluble inorganic carbonate, bicarbonate, hydroxide and/or mixtures thereof which forms carbon dioxide and/or water on contact with the anolyte, and transporting said multivalent metal cation contaminants from the anolyte through said membrane into said catholyte for reaction therein with the carbonate, bicarbonate and/or hydroxide and wherein the concentration of said hydroxide is maintained at sufficiently less than 5 wt. percent to minimize formation of insoluble hydroxides in said membrane whereby a high-capacity, efficient electrodialytic purification can be carried out without adversely affecting the oxidation state of the metal ions in the anolyte.

Claim 5

In the electrolytic purification of an aqueous solution of electroplating-type acids containing a multivalent metal ion in the anion portion of said acid, which solution is contaminated with dissolved multivalent metallic cations by passing electric current through an electrodialysis cell comprising (a) a catholyte compartment containing a cathode and a catholyte and (b) an anolyte compartment containing an anode and an anolyte comprising said contaminated acid solution, the anolyte and catholyte compartments being separated by a cation-permeable membrane, the improvement comprising employing as the catholyte an aqueous solution of a water-soluble inorganic carbonate, bicarbonate, hydroxide and/or mixtures thereof which forms carbon dioxide and/or water on contact with the anolyte, and transporting said multivalent metal cation contaminants from the anolyte through said membrane into said catholyte for reaction therein with the carbonate, bicarbonate and/or hydroxide and wherein the concentration of said hydroxide is maintained at sufficiently less than 5 wt. percent to minimize formation of insoluble hydroxides in said membrane whereby a high-capacity, efficient electrodialytic purification can be carried out without adversely affecting the oxidation state of the metal ions in the anolyte.

Claim 6

The purification according to claim 3 wherein the inorganic carbonate or bicarbonate is an alkali metal carbonate, an alkali metal bicarbonate, ammonium carbonate, or ammonium bicarbonate.

Claim 7

The purification according to claim 4 wherein the inorganic carbonate or bicarbonate is sodium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, or ammonium bicarbonate.

Claim 8

The purification according to claim 3 wherein said catholyte is a water-soluble inorganic hydroxide in admixture with water-soluble inorganic carbonate or bicarbonate.

Claim 9

The purification according to claim 3 wherein said anolyte acid solution comprises chromic acid, molybdic acid, tungstic acid or mixtures thereof.

Claim 10

The purification according to claim 3 wherein said catholyte contains a water-soluble inorganic hydroxide and the concentration of said hydroxide is maintained at less than that which under the operating conditions causes formation of significant amounts of insoluble multivalent metal cation hydroxides in said membrane.

Claim 11

A process for the electrolytic preparation of substantially pure acids containing a multivalent metal ion in the anion portion of the acid from an aqueous solution of a salt of a cation and an anion containing a multivalent metal ion by passing electric current through a dialysis cell comprising: (a) a catholyte compartment containing a cathode and a catholyte comprising an aqueous solution of an inorganic carbonate, bicarbonate, hydroxide, or mixtures thereof, wherein said hydroxide concentration at sufficiently less than 5 wt. percent to minimize formation of insoluble hydroxides in said membrane, (b) an anolyte compartment containing an anode and an anolyte comprising an aqueous solution of a salt of a cation and an anion containing a multivalent metal ion, and dissolved multivalent metal cation contaminants and (c) a cation permeable membrane separating said anolyte compartment from said catholyte compartment, whereby said desired acid containing a multivalent anion is obtained substantially free of anion and cation impurities, whereby said multivalent metal cation contaminants are transported from said anolyte through said membrane into said catholyte for reaction with said carbonate, bicarbonate and/or hydroxide.

Claim 12

A process for the electrolytic preparation of substantially pure acids containing a multivalent metal ion in the anion portion of the acid from an aqueous solution of a salt of a cation and an anion containing a multivalent metal ion by passing electric current through a dialysis cell comprising: (a) a catholyte compartment containing a cathode and a catholyte comprising an aqueous solution of an inorganic carbonate, bicarbonate, hydroxide, or mixtures thereof, wherein said hydroxide concentration at sufficiently less than 5 wt. percent to minimize formation of insoluble hydroxides in said membrane, (b) an anolyte compartment containing an anode and an anolyte comprising an aqueous solution of a salt of a cation and an anion containing a multivalent metal ion, and dissolved multivalent metal cation contaminants and (c) a cation permeable membrane separating said anolyte compartment from said catholyte compartment, whereby said desired acid containing a multivalent anion is obtained substantially free of anion and cation impurities, whereby said multivalent metal cation contaminants are transported from said anolyte through said membrane into said catholyte for reaction with said carbonate, bicarbonate and/or hydroxide.

Claim 13

The process of claim 9 wherein said cation is selected from alkali metals and ammonium.

Claim 14

The process of claim 9 wherein said salt cation is a monovalent inorganic metal.

Claim 15

The process of claim 9 wherein said salt anion is selected from chromate, molybdate, tungstate and mixtures thereof.

Claim 16

The process of claim 12 wherein said anolyte comprises said salt substantially free of sulfate and chloride ions, whereby said desired acid is obtained substantially free of said sulfate and chloride ions.

Claim 17

An electrolytic process for the separation of a salt of a multivalent metal cation and an anion of an acid containing sulfur, phosphorus, halogen or carbon by converting said salt into the hydroxide, carbonate or bicarbonate salt of said multivalent metal cation and the acid of said anion by passing electric current through an electrodialysis cell comprising (a) a catholytic compartment containing a cathode and a catholyte of an aqueous solution of water-soluble inorganic carbonate, bicarbonate, hydroxide or mixtures thereof, wherein the concentration of said water-soluble hydroxide is maintained at less than about 5 weight percent, and (b) an anolyte compartment containing an anode and an acidic anolyte comprising an aqueous solution of said salt of a multivalent metal cation, said catholyte and anolyte compartments being separated by a cation-permeable membrane.

Claim 18

An electrolytic process for the separation of a salt of a multivalent metal cation and an anion of an acid containing sulfur, phosphorus, halogen or carbon by converting said salt into the hydroxide, carbonate or bicarbonate salt of said multivalent metal cation and the acid of said anion by passing electric current through an electrodialysis cell comprising (a) a catholytic compartment containing a cathode and a catholyte of an aqueous solution of water-soluble inorganic carbonate, bicarbonate, hydroxide or mixtures thereof, wherein the concentration of said water-soluble hydroxide is maintained at less than about 5 weight percent, and (b) an anolyte compartment containing an anode and an acidic anolyte comprising an aqueous solution of said salt of a multivalent metal cation, said catholyte and anolyte compartments being separated by a cation-permeable membrane.

Claim 19

The separation according to claim 14 wherein said cation is selected from nickel, copper, zinc, aluminum, cadmium, tin, antimony, bismuth, chromium and mixtures thereof.

Claim 20

The separation according to claim 14 wherein said anion is selected from sulfate, chloride, phosphate, carboxylate, and mixtures thereof.

Claim 21

The separation according to claim 14 wherein said catholyte contains an alkali metal carbonate, alkali metal bicarbonate, ammonium carbonate, ammonium bicarbonate and/or mixtures thereof.