Metal treatment system

• US 4,392,888 A
• Filed: 01/07/1982
• Issued: 07/12/1983
• Est. Priority Date: 01/07/1982
• Status: Expired due to Fees

• Current Assignee: Aluminum Company of America (Howmet Aerospace, Inc.)
• Original Assignee: Aluminum Company of America (Howmet Aerospace, Inc.)
• Inventors: Miller, Ronald E., Eckert, Charles E.
• Primary Examiner(s): Andrews, M. J.
• Application Number:
  US06/337,529
• Time in Patent Office: 551 Days
• Field of Search: 75/68 R, 75/93 E, 75/68 A, 75/93 R, 75/93 AC
• US Class Current: 75/407
• CPC Class Codes: C22B 21/066 Treatment of circulating aluminium, e.g. by filtration C22B21/068 takes precedence
• CPC Class Codes: C22B 9/055 while the metal is circulating, e.g. combined with filtration

Abstract

Molten aluminum or other metals are purified by contacting with a fluorocarbon, such as CCl₂ F₂, in order to decrease the amount of impurity metal elements along with gas and inclusions therein preferably in the presence of an agitator to enhance efficiency. An oxidizer, such as oxygen, is employed to prevent the carbon in the fluorocarbon from forming carbide inclusions. Oxidizing the carbon to carbon monoxide is preferred in treating aluminum since the monoxide effectively removes the carbon from the system without oxidizing aluminum. Preferably, a fluorine acceptor is employed to temporarily combine with the fluorine in the fluorocarbon and prevent it from reacting with carbon such that the fluoride is still available to treat the molten metal. The gases employed to treat the molten metal can be passed over a bed of carbon immediately prior to introduction into the melt. The system operates with low skim generation and without providing a salt cover and is capable of substantially fume-free operation.

Claims

1. In a process for treating molten metal wherein said metal is contacted with halogen values from a gas containing a halocarbon the improvement comprising contacting said halocarbon with an oxidizer under conditions to oxidize carbon constituent thereof prior to introducing said halogen values into the molten metal.

4. The improvement according to claim 1 wherein said oxidizer comprises oxygen.

5. The improvement according to claim 1 wherein said oxidizer comprises oxygen provided in an amount stoichiometrically related to the carbon in said halocarbon.

7. The improvement according to claim 1 wherein a nonreactive gas is employed in said process in an amount greater than said halocarbon.

9. The improvement according to claim 1 wherein a nonreactive gas is employed in said process in a volume ratio of at least 2:

1 with said halocarbon.

13. The improvement according to claim 1 wherein said oxidizer is oxygen used in an amount stoichiometrically in excess of that required to oxidize the carbon in said halocarbon to CO by up to about 30% excess whereby some CO₂ is formed and said CO₂ is passed over carbon at an elevated temperature prior to introduction into said molten metal.

14. The improvement according to claim 1 wherein said halocarbon contains fluorine.

15. The improvement according to claim 1 wherein said halocarbon contains fluorine and is contacted with a fluorine acceptor to impede production of CF₄ and favor said oxidation of said carbon.

19. The improvement according to claim 1 wherein said molten metal comprises aluminum or the alloys thereof.

27. The improvement according to claim 1 wherein the carbonaceous-oxidizer reaction product is gaseous.

29. The improvement according to claim 1 wherein said oxidation reaction is substantially effected before the halogenaceous values in said halocarbon contact the molten metal.

31. The improvement according to claim 1 wherein said halocarbon and said oxidizer react within a hollow portion of a rotating agitator shaft prior to introduction into said molten metal.

33. The improvement according to claim 1 wherein said molten metal, after said treatment with said halocarbon, is moved through a filter bed.

37. The improvement according to claim 1 wherein said molten metal contains halogenizable metal impurities which are reacted with said halogen values in said process.

2. In a process for treating molten metal wherein said metal is contacted with fluorine values contained in a halocarbon containing fluorine the improvement comprising contacting said halocarbon with an oxidizer under conditions to oxidize substantial portions of the carbon therein to carbon monoxide and with a fluorine acceptor to impede contacting the molten metal with CF₄ and favor oxidation of carbon to CO, said fluorine acceptor yielding fluorine values for treatment of said molten metal.

6. The improvement according to claim 2 wherein said fluorine acceptor comprises silicon.

8. The improvement according to claim 2 wherein a nonreactive gas is employed in said process in an amount greater than said halocarbon.

10. The improvement according to claim 2 wherein a nonreactive gas is employed in said process in a volume ratio of at least 9:

1 with said halocarbon.

11. The improvement according to claim 2 wherein said fluorine acceptor comprises silicon provided as SiCl₄.

12. The improvement according to claim 2 wherein said fluorine acceptor comprises silicon provided as SiO₂.

16. The improvement according to claim 2 wherein said fluorine acceptor'"'"'s fluoride is more stable than CF₄ and the oxide of said acceptor.

17. The improvement according to claim 16 wherein said fluorine acceptor'"'"'s fluoride is gaseous.

18. The improvement according to claim 16 wherein said fluorine acceptor'"'"'s fluoride is less stable than the fluoride of one or more metals present in the molten metal being treated.

20. The improvement according to claim 2 wherein said molten metal comprises aluminum or the alloys thereof.

21. The improvement according to claim 2 wherein said oxidizer is oxygen used in an amount stoichiometrically in excess of that required to oxidize the carbon in said halocarbon to CO by up to about 30% excess whereby some CO₂ is formed and said CO₂ is passed over carbon at an elevated temperature prior to introduction into said molten metal, said excess of oxidizer not being in excess of that required to oxidize all the carbon to CO₂.

28. The improvement according to claim 2 wherein the carbonaceous-oxidizer reaction product is gaseous.

30. The improvement according to claim 2 wherein said oxidation reaction is substantially effected before the halogenaceous values in said halocarbon contact the molten metal.

32. The improvement according to claim 2 wherein said halocarbon and said oxidizer react within a hollow portion of a rotating agitator shaft prior to introduction into said molten metal.

34. The improvement according to claim 2 wherein said molten metal, after said treatment with said halocarbon, is moved through a filter bed.

38. The improvement according to claim 2 wherein said molten metal contains fluoridizable metal impurities which are reacted with said fluorine values in said process.

3. In a process for treating molten metal wherein said metal is contacted with halogen values from a gas comprising a halocarbon, the improvement comprising reacting carbon in said halocarbon to produce a carbonaceous reaction product more stable in the treatment process than said halocarbon, but non-deleterious to said metal and said treatment process, prior to contacting said metal with said halogen values.

22. A process for treating molten aluminum with reactive fluorine values in a fluorocarbon gas comprising:

(a) contacting said fluorocarbon with oxygen to oxidize carbon values therein to one or more carbon oxides, said oxygen being provided in excess of the stoichiometric equivalent to react said carbon values to CO, but insufficient to react all said carbon values to CO₂, thereby forming both CO and CO₂ ;

(b) contacting said fluorine values with a fluorine acceptor to substantially impede introduction of CF₄ to the molten aluminum;

(c) combining said fluorine values with a nonreactive gas, the amount by volume of said nonreactive gas exceeding the amount of said fluorine values as gas to form a mixture of said gases; and

(d) introducing said gas mixture into said molten aluminum.

23. The improvement according to claim 22 wherein said fluorine acceptor comprises silicon.

24. The improvement according to claim 22 wherein said CO₂ is passed over carbon before introduction into said molten aluminum.

25. The improvement according to claim 22 wherein said fluorine acceptor'"'"'s fluoride is gaseous and less stable than the fluoride of one or more metals contained in said molten aluminum.

35. The improvement according to claim 22 wherein said molten metal, after said treatment with said halocarbon, is moved through a filter bed.

26. A process for treating molten aluminum with reactive fluorine values in a fluorocarbon gas comprising:

(a) contacting said fluorocarbon with oxygen, SiCl₄ and a nonreactive gas;

(b) providing a treatment chamber for said molten aluminum including therein a rotating agitator having a hollow shaft therein to provide a hollow space in said shaft, said hollow space being provided with an exit in the region of said agitator;

(c) introducing said fluorocarbon, oxygen, SiCl₄ and nonreactive gas into the said hollow space in said agitator shaft;

(d) heating said gases in said agitator shaft to a temperature exceeding 1000°

F.;

(e) said oxygen being provided in an amount stoichiometrically in excess by 10 to 30% of the amount required to react the carbon constituent in said fluorocarbon to CO, thereby to react said carbon values to form both CO and CO₂ ;

(f) said SiCl₄ combining with said fluorine values to form substantial amounts of SiF₄ and Cl₂ while substantially reducing the amount of CF₄ which would enter the molten aluminum but for the action of said SiCl₄ ;

(g) moving said carbon oxides, fluorine values, chlorine and nonreactive gas through a reducing media to reduce the substantial portions of said CO₂ to CO;

(h) passing said gases from said hollow chamber into said molten aluminum.

36. The improvement according to claim 26 wherein said molten metal, after said treatment with said halocarbon, is moved through a filter bed.