Method of removing Cr(VI) ions from an aqueous electrolyte solution

Patent metadata

Field	Value
Publication number	US-11389887-B2
Application number	US-202016748876-A
Country	US
Kind code	B2
Filing date	Jan 22, 2020
Priority date	Jan 24, 2019
Publication date	Jul 19, 2022
Grant date	Jul 19, 2022

Abstract

The invention relates to a method for removing Cr(VI) ions from an aqueous electrolyte solution, particularly an electrolyte solution for electrochemical metal machining, which comprises the reduction of Cr(VI) to Cr(III) with Fe(II) ions. The Fe(II) ions are added to the electrolyte solution in the form of an aqueous salt solution which has been brought into contact with an ion exchange resin loaded with Fe(II) ions. The invention further relates to a device (1) for electrochemical machining of a workpiece (2) by means of an aqueous electrolyte solution (6), which has an ion exchanger (11) which has been loaded with an ion exchange resin charged with Fe(II) ions.

First claim

What is claimed is:

1. A method for removing Cr(VI) ions from an aqueous electrolyte solution, wherein the method comprises reducing Cr(VI) ions in the aqueous electrolyte solution to Cr(III) ions with Fe(II) ions, the Fe(II) ions being added to the electrolyte solution in the form of an aqueous salt solution which has been contacted with an ion exchange resin loaded with Fe(II) ions.

2. The method of claim 1 , wherein the aqueous electrolyte solution is neutral or basic.

3. The method of claim 1 , wherein the aqueous electrolyte solution has been used for electrochemical metal machining (ECM/PECM).

4. The method of claim 1 , wherein the aqueous Fe(II)-containing salt solution is fresh.

5. The method of claim 1 , wherein the aqueous Fe(II)-containing salt solution is a processed electrolyte solution for electrochemical metal machining.

6. The method of claim 3 , wherein the electrochemical metal machining comprises machining a workpiece comprising a chromium-containing alloy.

7. The method of claim 3 , wherein the electrochemical metal machining comprises machining a workpiece comprising a chromium-containing nickel-based alloy.

8. The method of claim 1 , wherein the electrolyte solution comprises sodium nitrate.

9. The method of claim 1 , wherein the ion exchange resin loaded with Fe(II) ions has been produced by treating an acidic ion exchange resin with an aqueous Fe(II) salt solution.

10. The method of claim 9 , wherein the acidic ion exchange resin comprises a resin in Na form.

11. The method of claim 9 , wherein the aqueous Fe(II) salt solution is an Fe(II) sulfate solution.

12. The method of claim 1 , wherein metal hydroxide precipitate formed during reduction is removed.

13. The method of claim 12 , wherein the precipitate is removed by filtration and/or centrifugation.

14. The method of claim 1 , wherein the method is carried out continuously.

15. The method of claim 1 , wherein the method is carried out discontinuously.

16. The method of claim 3 , wherein the Fe(II)-containing solution is metered into the electrolyte solution continuously and dependent on the amount of Cr(VI) ions produced during the electrochemical metal machining.

17. The method of claim 16 , wherein a chromium content of the electrolyte solution is set to a defined target value by controlling an addition of the Fe(II)-containing solution.

18. The method of claim 1 , wherein the method is carried out such that a concentration of Cr(VI) ions in the electrolyte solution is not more than 1 g/l.

19. The method of claim 1 , wherein the method is carried out such that more than 50% of the Cr(VI) ions present in the electrolyte solution are reduced.

20. A device for the electrochemical machining of a workpiece, wherein the device comprises:
a work table adapted to support the workpiece to be machined;
an electrode tool;
a storage tank for feeding an electrolyte solution;
a feed line for feeding the electrolyte solution from the storage tank to the workpiece to be machined by at least one pump;
an intermediate container for collecting the electrolyte solution which has been fed to the workpiece;
a return line for recycling the electrolyte solution to the storage tank from the intermediate container, and
optionally, a bypass line for circulating the electrolyte solution via the intermediate container to the storage tank bypassing the workpiece,
and wherein in at least one of the feed line, the return line and the bypass line an ion exchanger with an ion exchange resin loaded with Fe(II) ions is positioned.

Assignees

• MTU Aero Engines AG

Inventors

• Feiling Nicole
• Niegl Max
• Koenitzer Martin
• Rast Norbert
• Hill Rudolf
• Mauer Dieter

Classifications

• C02F2101/22

  Chromium or chromium compounds, e.g. chromates · CPC title

• B23H3/10 Primary

  Supply or regeneration of working media · CPC title

• C02F1/5245

  using basic salts, e.g. of aluminium and iron · CPC title

• C02F1/42

  by ion-exchange (ion-exchange in general B01J) · CPC title

• C02F1/705

  Reduction by metals · CPC title