GB2269183A

GB2269183A - Elactrolytic production of metal oxides

Info

Publication number: GB2269183A
Application number: GB9216173A
Authority: GB
Inventors: Charles Bowden
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-07-30
Filing date: 1992-07-30
Publication date: 1994-02-02
Also published as: GB9216173D0

Abstract

Partially-conducting metal oxide, particularly magnetite in finely-divided form, is produced in a cell comprising a first electrode constituted substantially by the metal whose oxide is to be produced an aqueous conductive electrolyte, and another electrode which evolves hydrogen and is inert, preferably austenitic steel. If the first electrode is steel contaminated with radioactive material waste radioactive material in a form which is relatively convenient for handling and long-term storage is produced. The cell may be solar-powered, for use in space.

Description

DESCRIPTION Electrolytic cell The present invention relates to electrochemical cells.

According to the invention, an electrochemical cell for the production of a partially-conducting metal oxide, particularly magnetite, comprises a first electrode constituted substantially by the metal whose oxide is to be produced. In the preferred case of the production of magnetite, the first electrode is iron which may be any scrap iron.

The cell according to the invention may be used to provide waste radioactive material in a form which is relatively convenient for handling and for long-term storage purposes.

The electrolyte in the cell must yield oxygen at the first electrode, in use, and is preferably water made conductive by the addition of a salt which is not itself involved in the electrolysis process. Alkali metal salts are preferred, particularly potassium chloride; relatively low concentrations are required.

The other electrode may be of any convenient material but is preferably such that hydrogen is evolved during electrolysis since this constitutes a further valuable product. Inert metals, such as platinum or palladium, may be used but steel, preferably austenitic steel, is suitable and is preferred for its relative cheapness and resistance to corrosion during idle periods.

One embodiment of the invention will now be more particularly described by way of example with reference to the accompanying drawing which is a purely diagrammatic illustration of an electrochemical cell of the invention.

With reference to the drawing, an electrochemical cell is shown and has a first electrode 1 of scrap iron and a second electrode 2 of austenitic steel connected through a full-wave rectified, A.C. supply 3 capable of supplying an intermittent current at a voltage of from about 4 to 12 amps. Alternatively the current supply may be a D.C. polarised supply, preferably interrupted.

The electrodes 1 and 2 are immersed in an electrolyte 4 constituted by a dilute aqueous potassium chloride solution.

It is found, in use, that, when current is passed through the cell, hydrogen is liberated at the steel electrode 2, the temperature of the electrolyte rises, and a fine dispersion of black powder is formed at the iron electrode 1. The black powder is magnetite (Fe3O4 with an inverse spinel structure) . Some oxygen may also be liberated at the iron electrode. The black powder contains any radioactive material when the first electrode is constituted by contaminated steel, for example from nuclear reactors.

In practice the cell may be arranged to collect or utilise all three products, i.e. hydrogen, heat and magnetite, by means of known technology which will not, therefore, be described. With respect to the finely-divided magnetite, it should be noted that this is currently manufactured by the grinding of coarser particles which is an energy-intensive process.

It is assumed that the cell reactions are essentially: at the steel electrode 8H+ + 8e - > 4H2 at the iron electrode 80H + 3Fe-8e - > Fe304 + 4H2 0.

It is usually considered that the deposition of a non-soluble product on an electrode during electrolysis will cause a gradually-increasing resistance to the passage of current until the electrolysis eventually stops. Surprisingly, this is not the case with the cell of the invention and it is assumed that this is at least partly because the oxide formed is itself a partial-conductor. As stated above, it is also found that the oxide is released into the electrolyte to form a suspension. Furthermore, the current strength rises rather than falls as electrolysis proceeds. It is also found that the initial current strength can be increased by the addition of finely-divided magnetite to the electrolyte at the beginning: this indicates that the suspended magnetite takes some part in the transmission of the current although the mechanism of this transmission is not yet established.

With regard to the current supply, as noted above, this is preferably intermittent since this causes more uniform erosion of the iron electrode than a continuous supply.

Although the invention has been described with reference to a ferritic electrode and the formation of magnetite, it is thought that other partially-conductive metal oxides could be produced in a similar manner, particularly those with a spinel structure.

It is thought that the cell of the invention may have application in space with the use of a solar D.C. power supply. With such a D.C. supply, a chopper circuit would preferably be used to give a square-wave output with a high rise time and a frequency preferably between 50 and 2000 Hertz to give optimum results.

In a specific embodiment of the invention, the electrodes comprised flat rectangular plates, each 5 cm wide by 15 cm long, suspended in a glass jar containing 1 litre of electrolyte. The jar was housed in a vacuum flask to minimise heat loss.

It should be noted that, where chromium and potassium is present in the system as described, precautions should be taken by operators of the process against the possibility of poisoning due to the toxic nature of reaction products.

Claims

1. An electrochemical cell for the production of partially-conducting metal oxide, the cell comprising a first electrode constituted substantially by the metal whose oxide is to be produced.

2. An electrochemical cell according to Claim 1, in which the partially-conducting metal oxide comprises magnetite and the first electrode comprises iron.

3. An electrochemical cell according to Claim 1 or Claim 2, in which the electrolyte comprises water made conductive by the addition of a salt which is not itself involved in the electrolysis process.

4. An electrochemical cell according to Claim 3, in which the salt comprises an alkali metal salt.

5. An electrochemical cell according to any preceding claim, in which the other electrode is formed from a material such that, in use, hydrogen is evolved during electrolysis.

6. An electrochemical cell according to Claim 5, in which the said other electrode is formed from an inert metal such as platinum or palladium.

7. An electrochemical cell according to Claim 5, in which the said other electrode is formed from austenitic steel.

8. An electrochemical cell according to any preceding claim, in conjunction with a solar D.C. power supply.

9. An electrochemical cell according to Claim 8, further including a chopper circuit to give a square-wave output with a high rise time and a frequency preferably between 50 and 2000 Hertz.

10. A method for the production of a partially-conducting metal oxide, the method comprising electrolysis in which a first electrode is constituted substantially by the metal whose oxide is to be produced.

11. A method according to Claim 10, in which the metal oxide has a spinel structure.

12. A method according to Claim 10 or Claim 11, in which the metal oxide comprises magnetite.

13. A method according to any of Claims 10 to 12, for use in the provision of waste radioactive material in a form which is convenient for handling and for long-term storage, in which the said first electrode is constituted by steel contaminated by a radioactive material.

14. A method according to any of Claims 10 to 13, in which partially-conducting metal oxide in finely divided form is added to the electrolyte at the beginning of the process.

15. A process according to any of Claims 10 to 14, in which the current supply is intermittent.

16. An electrochemical cell, substantially as hereinbefore defined.

17. A method for the production of a partially-conducting metal oxide, substantially as hereinbefore defined.