Electrodialytic conversion of complexes and salts of metal cations

• US 5,264,097 A
• Filed: 03/29/1991
• Issued: 11/23/1993
• Est. Priority Date: 03/29/1991
• Status: Expired due to Fees

• Current Assignee: Daniel J. Vaughan
• Original Assignee: Daniel J. Vaughan
• Inventors: Vaughan, Daniel J.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): Phasge, Arun S.
• Application Number:
  US07/677,525
• Time in Patent Office: 970 Days
• Field of Search: 204/151, 204/182.4, 204/301, 204/96, 204/DIG. 13
• US Class Current: 205/770
• CPC Class Codes: B01D 61/44 Ion-selective electrodialysis
• CPC Class Codes: C01B 7/0706 of hydrogen chloride
• CPC Class Codes: C01B 7/195 Separation; Purification
• CPC Class Codes: C23G 1/36 Regeneration of waste pickling liquors
• CPC Class Codes: C25F 7/02 Regeneration of process liquids

Abstract

Complexes and salts of metal cations in aqueous solutions are electrodialytically converted into a solution of acids substantially free of metal cations and insoluble metal hydroxides. Metal cations are insolubilized by hydroxyl ions formed in a catholyte while anions are electrotransported from the catholyte and converted into a solution of acids by hydrogen ions formed in an anolyte of an electrodialytic process. The conversion process is carried out electrically without the electrotransport of metal cations and is especially useful for reforming solutions of acids that form complexes when etching and finishing metal surfaces.

Claims

1. A process for the electrodialytic conversion in an electrodialytic cell comprising a catholyte and an anolyte separated by an anion permeable membrane of salts and complexes of metal cations and anions in an aqueous solution into an insoluble hydroxide of said metal cations and into acids or halogen of said salt or complex anions, said aqueous solution being selected from solutions of said salts or solutions of said complexes and solutions comprising mixtures of said salts and said complexes which comprises:

including at least one salt of an alkali cation in said aqueous solution (a) feeding said alkali salt-containing aqueous solution to said catholyte of said electrodialytic cell, said catholyte being separated by an anion permeable membrane from said anolyte of said cell;

(b) controlling the pH of said catholyte by;

the rate of removal of anions from said catholyte to said anolyte, the rate of addition of said aqueous solution to said catholyte and the rate of forming hydroxyl ions at the cell cathode, to insolubilize said metal cation as an insoluble hydroxide in said catholyte and electrotransporting said anions from said catholyte to convert said anions to acids or to halogen in said anolyte.

2. The process of claim 1 wherein said catholyte comprises an alkali cation of potassium or sodium.

3. The process of claim 1 wherein the pH of said catholyte is controlled at a level greater than the pH necessary to insolubilize all metal cations that are electrodepositable on the cell cathode.

4. The process of claim 1 wherein said metal cations are cations of all multivalent metals and monovalent metals that form insoluble hydroxides in the pH range of 1 to 14.

5. A process for the electrodialytic conversion in an electrodialytic cell comprising a first electrolyte, a catholyte and a second electrolyte of salts or complexes of metal cations and anions in an aqueous solution into an insoluble hydroxide of said metal cations and into the acids or halogen of said salt or complex anions, said aqueous solution being selected from solutions of said salts or said complexes or solutions of mixtures of said salts and said complexes which comprises:

(a) feeding said aqueous solution to said first electrolyte of said electrodialytic cell and said first electrolyte being separated by an anion permeable membrane from said catholyte of said cell and by an anion permeable membrane from said second electrolyte in electrical communication with the anode of said cell;

(b) controlling the pH of said first electrolyte by (1) the rate said aqueous solution is added to said first electrolyte;

(2) the rate acid anions are electrotransported from said first electrolyte to said second electrolyte; and

(3) the rate hydroxyl ions are electrotransported from said catholyte to said first electrolyte to insolubilize said metal cations in said first electrolyte and electrotransporting said acid anions from said first electrolyte to said second electrolyte to convert said anions to acids or halogen in said second electrolyte.

6. The process of claim 5 wherein said aqueous solution comprises multivalent or monovalent metal cations that form insoluble hydroxides at a pH of two or greater.

7. The process of claim 5 wherein said first electrolyte comprises an alkali cation of at least one of sodium and potassium.

8. The process of claim 5 wherein said catholyte is an aqueous solution of an alkali hydroxide of sodium or potassium.

9. The process of claim 5 wherein the pH of said first electrolyte is controlled at a pH sufficient to insolubilize cations of one metal and to leave cations of a second metal in solution.

10. The process of claim 5 wherein the pH of said first electrolyte is sufficiently greater than one to insolubilize all metal cations in said aqueous solution.

11. A process using an electrodialytic cell for the electrolytic conversion of salts or complexes of metal cations and anions in an aqueous solution into an insoluble hydroxide of said metal cation and the acid of the anions of the salt or complex or halogen if the anion is a halide which comprises (a) passing an electric current through said cell having a catholyte separated by an anion permeable membrane from an anolyte;

(b) feeding said aqueous solution of a complex or salt of a metal cation to said catholyte;

(c) electrotransporting anions from said catholyte to said anolyte;

(d) and controlling the pH of said catholyte to insolubilize said metal cations in said catholyte and convert anions to acids or halogen in said anolyte.

13. The process of claim 11 wherein said catholyte comprises a cation of an alkali metal of potassium or sodium.

14. The process of claim 11 wherein said catholyte comprises a cation of an alkali metal and preferably a cation of potassium or sodium.

12. A process using an electrodialytic cell for the electrolytic conversion of salts or complexes of metal cations in an aqueous solution into an insoluble hydroxide of said metal cation and the acid of the anions of the salt or complex or halogen if the anion is a halide which comprising (a) passing an electric current through said cell having a catholyte separated by an anion permeable membrane from an anolyte;

(b) feeding said aqueous solution to said catholyte;

(c) electrotransporting anions from said catholyte to said anolyte;

(d) forming hydroxyl ions in said catholyte and hydrogen ions in said anolyte whereby the pH of said catholyte is controlled to insolubilize said metal cations in said catholyte and convert said anions to acids or halogen in said anolyte.

15. A process using an electrodialytic cell for the electrodialytic conversion of salts or complexes of metal cations and anions in an aqueous solution into an insoluble hydroxide of said metal cation and the acid of the anions of said salt or complex or halogen if the anion is a halide which comprises (a) passing an electric current through said cell having at least a catholyte, a first electrolyte and an anolyte separated by anion permeable membrane;

(b) feeding said aqueous solution to said first electrolyte;

(c) electrotransporting anions from said first electrolyte to said anolyte to form hydrogen ions in said anolyte and hydroxyl ions in said catholyte; and

(d) electrotransporting hydroxyl ions from said catholyte to said first electrolyte sufficient to control the pH of said first electrolyte to insolubilize said metal cation in said first electrolyte and electrotransporting said anions from said first electrolyte to said anolyte to convert said anions to acids or halogen in said anolyte.

16. The process of claim 15 wherein said catholyte is an aqueous solution of a hydroxide of an alkali cation of potassium or sodium.

17. The process of claim 15 wherein the pH of said first electrolyte is controlled sufficiently to insolubilize a cation of at least one metal.

18. A process using an electrodialysis cell for the electrodialytic conversion of salts or complexes of metal cations and anions in an aqueous solution into an insoluble hydroxide of said metal cation and the acid of the anions of said salt or complex which comprises (a) passing an electric current through said cell having at least a catholyte, a first electrolyte and an anolyte said anolyte separated by a cation permeable membrane from said first electrolyte and said first electrolyte separated by an anion permeable membrane from said catholyte;

(b) feeding said aqueous solution to said catholyte to form hydroxyl ions in said catholyte, (c) electrotransporting anions from said catholyte through said anion permeable membrane into said first electrolyte to form hydrogen ions in said anolyte and (d) transporting hydrogen ions from said anolyte through said cation permeable membrane into said first electrolyte whereby said metal cation is insolubilized in said catholyte and said anions are converted to acids in said first aqueous solution.

19. The process of claim 18 wherein said catholyte contains a cation of an alkali metal.

20. The process of claim 18 wherein said anolyte is an aqueous solution comprising an acid of sulfur, nitrogen, phosphorous and carbon.

21. The process of claim 18 wherein said aqueous solution comprises salts and complexes of multivalent and monovalent metals that form insoluble hydroxides at a pH greater than 1.

22. The process of claim 18 wherein the pH of said catholyte is controlled at a level greater than the pH necessary to insolubilize all electrodepositable metal cations in said aqueous solution.