Removal of copper containing incrustations from ferrous surfaces

Abstract

.Iadd.The invention concerns a method of removing copper from a ferrous metal surface without excessive corrosion of the ferrous metal surface. In the method, the copper is dissolved with an aqueous alkaline solution containing a ferric chelate of an alkylene polyamine polyacetic acid chelating agent. .Iaddend.

What is claimed is: 
     
       1. A process for removing copper from a ferrous metal surface containing copper thereon by contacting said surface with an aqueous alkaline solution wherein the solution employed contains as an essential constituent at least one member of the group consisting of ferric chelates of .[.polycarboxylic.]. .Iadd.alkylene polyamine polyacetic .Iaddend.acid chelating agents and mixtures of ferric and ferrous chelates of .[.polycarboxylic.]. .Iadd.alkylene polyamine polyacetic .Iaddend.acid chelating agents in amount sufficient and for a time sufficient at a reaction temperature above about 68° F. and up to about 300° F., to dissolve said copper.Iadd., wherein said solution may also contain a salt of the group consisting of ammonium, amine, and hydroxyalkylamine salts of alkylene polyamine polyacetic acid chelating agents.Iaddend.. .[. 
     
     
       2.  A process as claimed in claim 1 wherein the said solution may also contain a salt of the group consisting of ammonium, amine and hydroxyalkylamine salts of polycarboxylic acid chelating agents..]. 
     
     
       3. A process as claimed in claim .[.2.]. .Iadd.1 .Iaddend.wherein the total iron chelate originally present ranges between about 60 and about 100 weight percent of total salt form and iron chelate and the solution originally contains a total of between ca. 0.5 weight percent and up to a saturated solution of salt form and iron chelated chelating agent. 
     
     
       4. A process as claimed in claim 3 wherein some iron chelate is maintained in the ferric form by the addition of a water-soluble compatible oxidizing agent. 
     
     
       5. A process as claimed in claim 3 wherein some iron chelate is maintained in the ferric form by bubbling air through said aqueous alkaline solution. .[.6. A process as claimed in claim 3 wherein the iron chelate and 
     
     
        chelating agent salt are those of ethylenediaminetetraacetic acid..]. 7. A process as claimed in claim 3 wherein the reacted ferrous surface is 
     
     
        rinsed with rinse water containing a water-soluble oxidant. 8. A process as claimed in claim 3 wherein the reacted ferrous surface is rinsed with 
     
     
        rinse water while air is bubbled therethrough. 9. A process for removing copper from a ferrous metal surface containing copper thereon by contacting said surface with an aqueous alkaline solution wherein the solution contains as an essential constituent ammoniated ethylenediaminetetraacetic acid adjusted to a pH of about 9 with free ammonia and iron chelate thereof wherein the iron chelate originally present ranges between about 60 and ca. 100 weight percent of total salt form ethylenediaminetetraacetic acid and iron chelate thereof and the solution originally contains between about 0.5 weight percent and up to a saturated solution of total salt form and iron chelate of ethylenediaminetetraacetic acid while air is being bubbled therethrough at a reaction temperature above about 68° F. and up to about 300° F. in amount sufficient and for a time sufficient to dissolve said copper, removing said solution from said ferrous metal surface, contacting said surface with rinse water while bubbling air therethrough and removing said rinse water. .Iadd.10. A process for removing copper from a ferrous metal surface containing copper thereon by contacting said surface with an aqueous alkaline solution wherein the solution employed contains as an essential constituent at least one member of the group consisting of ferric chelates of ethylenediaminetetraacetic acid and mixtures of ferric and ferrous chelates of ethylenediaminetetraacetic acid in amount sufficient and for a time sufficient at a reaction temperature above about 68° F. and up to about 300° F. to dissolve said copper, wherein said solution may also contain a salt of the group consisting of ammonium, amine and hydroxyalkylamine salts of ethylenediaminetetraacetic acid and wherein the total iron chelate originally present ranges between about 60 and about 100 weight percent of total salt form and iron chelate and the solution originally contains a total of between ca. 0.5 weight percent and up to a saturated solution of salt form and iron chelated chelating agent. .Iaddend. .Iadd.11. The process of claim 10, wherein the reaction temperature ranges from about 140° to about 180° F. .Iaddend. .Iadd.12. The process of claim 11, wherein at least 67 percent of the chelating agent is complexed 
     
     
        with iron. .Iaddend. .Iadd.13.  The process of claims 11 or 12 wherein the salt consists of the ammonium salt of ethylenediaminetetraacetic acid. .Iaddend. .Iadd.14. The process of claim 13 wherein the pH of the solution is in excess of 7 and up to about 10. .Iaddend. .Iadd.15. The process of claim 10 wherein the pH of the solution is in excess of 7 and up to about 10. .Iaddend. .Iadd.16. The process of claim 1 wherein said reaction temperature ranges from about 140° F. to about 180° F. .Iaddend. .Iadd.17. The process of claim 16 wherein at least 67 percent of the chelating agent is complexed with iron. .Iaddend. .Iadd.18. The process of claim 16 or 17 wherein the salt consists of an ammonium salt of alkylene polyamine polyacetic acid chelating agent. .Iaddend. .Iadd.19. The process of claim 17 wherein the pH of the solution is in excess of 7 and up to about 10. .Iaddend. .Iadd.20. The process of claim 16 wherein the pH of the solution is in excess of 7 and up to about 10. .Iaddend. .Iadd.21. The process of claim 1 wherein the chelate is a compound corresponding to the formula (HOOCCH 2 ) 2  N[(CH 2 ) n  NCH 2  COOH] m  CH 2  COOH wherein n and m are each independently 1, 2, 3 or 4 and up to two of the carboxymethyl groups may be replaced with a β-hydroxyethyl group and one or more of the carboxymethyl groups may be replaced with a carboxyethyl group. .Iaddend. .Iadd.22. The process of claim 21 wherein the solution may also contain an ammonium salt of said chelate. .Iaddend.     
     
     
        .Iadd.23.  The process of claim 10 wherein said salt consists of the ammonium salt of ethylene diaminetetraacetic acid said reaction temperature ranging between about 140° F. to 180° F. and wherein some iron chelate is maintained in the ferric form by the addition of a water soluble compatible oxidizing agent. .Iaddend. .Iadd.24. The process of claim 23 wherein the solution also contains some chelating agent which is not chelated with iron. .Iaddend. .Iadd.25. The process of claims 23 or 24 wherein air is employed as the oxidant. .Iaddend. .Iadd.26. The process of claims 23 or 24 wherein an alkali metal nitrite is employed as the oxidant. .Iaddend. .Iadd.27. The process of claim 10 wherein said ferrous metal surface also contains iron oxide scale wherein said iron oxide is first dissolved with an alkaline solution of the ammonium salt of ethylene diaminetetraacetic acid, and the copper-containing metal surface is then contacted with the solution obtained from the removal of the iron oxide at a temperature of about 140° F. to 180° F., said solution containing from 60 to 100 percent of the ammonium salt in the form of iron chelate while adding to such solution a water soluble compatible oxidizing agent to maintain some of said iron chelate in the ferric form said solution having a pH within the range in excess of 7 and up to about 10. .Iaddend. .Iadd.28. The process of claim 27 wherein the oxidant comprises at least air which is bubbled through the copper-dissolving solution. .Iaddend.