Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Utility Patent
1998-09-17
2001-01-02
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S003000, C134S010000, C134S041000, C205S471000, C205S583000
Utility Patent
active
06168670
ABSTRACT:
FIELD OF THE INVENTION
Our present invention relates to a method of pickling articles of copper and metals less noble than copper, especially articles of copper and brass.
BACKGROUND OF THE INVENTION
In the pickling of copper-containing articles it is known to make use of an aqueous peroxosulfate-containing a pickling solution which, in regeneration, is subjected first to a cathodic reduction to deposit out copper that has been dissolved in the pickling solution in a cathodic deposition and then to anodic oxidation to reform the peroxosulfate from sulfate ions contained in the used pickling solution.
It is also known in this regenerating process to increase the current efficiency of the anodic peroxosulfate formation, to introduce additives which can be organic sulfur compounds, inorganic sulfur compounds, organic sulfur-free nitrogen compounds or inorganic sulfur-free nitrogen compounds.
The technique has been used for the pickling of copper as well as for the pickling of copper alloys, especially brass. Brass is an alloy of copper and zinc and zinc is in this case an example of a metal less noble than copper.
In the pickling of copper and brass with peroxodisulfate containing pickling solutions, where the pickling solution after use is subjected to regeneration in the manner described, initially involving a cathodic reduction in which most of the copper dissolved in the pickle is cathodically deposited out, some of the peroxosulfate which remains is invariably cathodically reduced. In the subsequent process step the peroxodisulfate is electrochemically regenerated by anodic oxidation of the sulfate ions usually on smooth platinum electrodes. To ensure a sufficiently high current yield for the anodic oxidation, the sulfate ion concentration in the solution must be relatively high. In prior systems, this can be achieved by adding to the pickling solution to be regenerated, a solution with a high concentration of alkali metal sulfate ions or ammonium sulfate ions. To increase the current yield (current efficiency) of the anodic peroxodisulfate formation, solutions of such additives which are so-called potentially-raising substances can be supplied. The usual additives for the purpose have included, for example, ammonium thiocyanate, sodium thiocyanate or thiourea. These additives are usually supplied in concentrations of 0.5×10
−3
mol/l to 5×10
−3
mol/l.
In such earlier processes, problems have been encountered when copper alloys e.g. brass, have been pickled and especially when the pickling is carried out of both articles composed of copper and articles composed of brass.
In pickling with solutions of the aforedescribed type, brass has a tendency to dissolve more rapidly in the pickling solution than does copper. In fact, one cannot obtain satisfactory results if, for example, a system designed for the pickling of copper articles is then used for the pickling of brass articles without modification, or for the pickling of both copper and brass articles. When such solutions are used to pickle brass articles, the composition of the pickling solution and/or the pickling duration or exposure time must be altered. Such modification is necessary if one wishes to have a satisfactory surface quality of the metal articles and prevent the so-called over-pickling of the brass.
When articles composed of both brass and copper are to be pickled, the problem becomes more acute since conditions at which copper is satisfactorily pickled can result in an overpickling of the brass with detriment to the surface quality. If, however, the conditions are designed for the pickling of brass, the copper surface can be insufficiently pickled so that again the surface quality may be detrimentally affected.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to provide a pickling method which can be used to obtain satisfactory quality surfaces for articles of copper and copper alloys with metals less noble than copper, especially copper and brass.
Another object of the invention is to provide a method of pickling such articles in which the same conditions can be used for the pickling of both articles of copper and articles of brass in terms of the composition of the pickling solution, the duration of the pickling operation or the exposure time, and the like.
Still another object of this invention is to provide a pickling method which overcomes drawbacks of prior art techniques.
SUMMARY OF THE INVENTION
These objects are attained, in accordance with the invention by providing an enhanced concentration of the additive promoting the anodic peroxosulfate formation, by inhibiting the velocity of dissolution of the less noble metal in addition to the current yield enhancement, and by adding at least one organic complex former to the pickling solution.
More particularly, the method of pickling articles of copper and articles of copper with a metal less noble than copper, especially copper and brass, can comprise the steps of:
(a) treating the articles with an aqueous peroxosulfate pickling solution, thereby forming a used pickling solution;
(b) cathodically reducing the used pickling solution with cathodic deposition of copper from the used pickling solution, thereby forming a reduced solution;
(c) adding to the reduced solution a relatively high concentration of at least one additive promoting anodic peroxosulfate formation and selected from the group which consists of organic sulfur compounds, inorganic sulfur compounds, organic sulfur-free nitrogen compounds, inorganic sulfur-free nitrogen compounds and mixtures thereof;
(d) anodically oxidizing the reduced solution to which the additive has been added to regenerate peroxosulfate from sulfate ion therein, thereby forming a regenerated pickling solution, and recycling the regenerated pickling solution to step (a);
(e) inhibiting a dissolution velocity of the metal less noble than copper during treatment of the articles in step (a); and
(f) adding to the solution in step (a) at least one organic complex-forming substance.
In a preferred embodiment of the invention, a peroxodisulfate, preferably sodium peroxodisulfate, and/or a peroxomonosulfate, preferably sodium peroxomonosulfate, can be added to the pickling solution, The peroxosulfate additive is preferably supplied in an amount of 30 to 100 g/l, most preferably in an amount of 50 to 80 g/l.
Of course in order to ensure a high current yield during the anodic oxidation and for the anodic peroxosulfate formation, there must be a sufficiently high concentration of sulfate ions present. During the anodic oxidation, sulfate ion is oxidized especially to peroxodisulfate ions and alkali sulfate and/or ammonium sulfate can be added to the pickling solution to increase the sulfate ion concentration. The alkali sulfate and/or ammonium sulfate is added in an amount of 50 to 350 g/l; preferably an amount of 100 to 300 g/l.
It has also been found to be advantageous to add to the pickling solution zinc sulfate and/or copper sulfate and/or iron sulfate. The latter compound can be added alone or in combination with the above-mentioned alkali sulfates and/or ammonium sulfate.
The goals of the invention can be achieved by adjusting the sulfate ion content with the aid of zinc sulfate and/or copper sulfate and/or iron sulfate. Preferably the zinc sulfate and/or copper sulfate and/or iron sulfate is supplied in an amount of 20 to 250 g/l, more preferably in an amount of 50 to 200 g/l and most preferably in an amount of 100 to 200 g/l.
According to a preferred embodiment of the invention, in order to increase the current yield of the anodic peroxosulfate formation in the pickling solution to be recycled, an additive from the group of thiocyanates, thioureas, thiocarbaminates and thiosemicarbazides is supplied.
The thiocyanates are preferably ammonium thiocyanate and/or sodium thiocyanate.
It is also possible to utilize an additive from the group of cyanides, cyanates, cyanamides, hexamethylenetetramine and urotropin. The additive is preferably provided in an amount w
Möbius Andreas
Thiele Wolfgang
Chaudhry Saeed T.
Dubno Herbert
Gulakowski Randy
LPW-Blasberg Anlagen GmbH
Myers Jonathan
LandOfFree
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