US3255119A - Compositions and process for removal of radioactive contaminants - Google Patents

Description

2 ,2 1 48 cross REFERENCE rximmq' United States Patent 0 3,255,119 Patented June 7, 1966 ice acid solution containing sulfamate ions, together with bi- 3,255,119 sulfate or sulfate ions, said last mentioned ions being COMPOSITIONS AND PROCESS FOR REMOVAL OF RADIOACTIVE CONTAMINANTS Paul R. Pariseau, Long Beach, Calif., assignor to Purex Corporation, Ltd., Lakewood, Calif., a corporation of California No Drawing. Filed Oct. 30, 1962, Ser. No. 234,229 19 Claims. (Cl. 252-142) This invention relates to the decontamination of surfaces on which are deposited radioactive materials, and is especially concerned with a novel composition and process for the removal of radioactive elements from surfaces, especially aluminum, substantially without corrosion of such surfaces.

In Patent N 95 assigned to the assignee of the instant application, is described a composition effective for removal of radioactive materials or contaminants from surfaces of metals, concrete, porcelain, and the like, in the form of an aqueous acid solution containing sulfamate and halogen ions, e.g. as provided by sulfamic acid and a water soluble halide such as a chloride or a fluoride, or a mixture of a chloride and a fluoride. The compositions of the above patent in practice have given good results in the decontamination or removal of radioactive materials from surfaces such as aluminum, steel and other metals.

However, the presence in such compositions of halogens, e.g. as provided by fluorides and chlorides, and particularly the fluoride ion, has been found undesirable in certain applications. Particularly, it has been found that the presence of halogen in such compositions tends to cause excessive corrosion of aluminum and zirconium, even when conventional corrosion inhibitors are incorporated in the compositions. Since aluminum and zirconium are frequently employed in the construction of the components of nuclear reactors, this presents a disadvantage to the use of the above described compositions containing halogen or the halogen ion, for decontaminating or removing radioactive contaminants from reactor components composed of such metals.

It is accordingly an object of this invention to provide a composition and process for removal of radioactive contaminants from surfaces of metals, particularly aluminum or zirconium, which possesses efficient decontaminating and scale removal properties yet which is substantially non-corrosive toward such metals. A particular object of the invention is to modify the compositions and process of the above patent to render such compositions useful for radioactive decontamination or removal of radioactive scale deposits from surfaces of metals, particularly the surfaces of nuclear reactor components containing aluminum or zirconium, substantially without any corrosion of the base metal, and without adversely afiecting the decontaminating and scale removal properties of the composition.

These and other objects and advantages of the invention will appear hereinafter.

By the terms aluminum and zirconium employed herein are meant, respectively, aluminum and its alloys, and zirconium and its alloys.

I have now found that an aqueous acid solution containing sulfamate ions, e.g. as provided by an aqueous sulfamic acid solution, and free of halogen ions, is effective for removal of radioactive contaminants from surfaces, and that such solution is safe on aluminum and zirconium, that is, such halogen-free solution is substantially non-corrosive to surfaces of such metals.

According to the invention, I have found that particularly effective radioactive decontamination of aluminum and zirconium is obtained substantially without any corrosion thereof, by treatment with a halogen-free aqueous provided for example, by sodium bisulfate or sulfuric acid. Thus, for example, a halogen-free solution containing sulfamic acid ap d so urn lSll ate, preferably employed 1n certain proportions and within certain pH ranges, as described in detail hereinafter, when applied to an aluminum or zirconium surface contaminated with radioactive materials, provides an unexpectedly high decontamination etficiency, while substantially avoiding any corrosion of the base metal.

It is believed that the sulfamate ions, and the bisulfate or sulfate ions, present in combination in the aqueous acid solution at the proper pH, and in the absence of halogen ions, function in a synergistic manner to achieve highly effective removal of radioactive contaminants, superior to sulfamate alone, or to sulfate or bisulfate alone, while having the additional important advantage, according to the invention, of avoiding corrosion on surfaces of aluminum and zirconium which takes place when employing known compositions containing sulfamic 'acid or sulfamate ions, in the presence of halogen ions.

I have also found that the presence of oxalate ions, e.g. as provided by gxalic acid, preferably in certain proportions, as described in detail hereinafter, in the aqueous acid halogen-free solutions of the invention containing sulfamate ions, in combination with bisulfate or sulfate ions as described above, enhances decontamination results, without adversely affecting the properties of such halogen-free solution with respect to inhibiting corrosion on aluminum and zirconium. In fact, it appears that the presence of oxalic acid aids in the inhibition ofcorrosion of such metal In order to achieve best results according to the invention, the compositions of the invention are preferably also maintained free of materials such as ferric or ferrous ions, or salts thereof, since such salts tend to reduce the effectiveness of the sulfamate ions, and also the bisulfate or sulfate ions' which may be present according to the invention. However, particularly when oxalate is present in the invention compositions, the presence of iron salts is especially avoided due to the tendency toward formation of undesirable iron oxalate films on the surface of the base metal when treating such surface for radioactive decontamination thereof.

To provide the sulfamate ion, I may employ any water soluble sulfamate or sulfamic acid, preferably the latter, since it also simultaneously produces the hydrogen ion required to obtain the proper acidity or pH. I can also use mixtures of sulfamic acid and sulfamates. Where sulfamate salts are employed these can be alkali metal, e.g. sodium or potassium, or ammonium sulfamates, or other inorganic sulfamates that are soluble in a concentration at least within the broad range noted below, and which ionize to produce sulfamate ions in acid media without producing undesirable precipitates in acid media or with the radioactive elements being removed. The sulfamic acid or sulfamates can be employed in a concentration or proportion of as low as about 0.2% and as high as about 15% by weight of the solution, although such range is not to be considered critical. In preferred operation, I employ a concentration of sulfamic acid or sulfamate of from about 2% to about 8% by weight of the solution.

I can employ together with the sulfamic acid or sulfamate according to the invention, sulfuric acid or any water soluble bisulfate, such as alkali metal, e.g. sodium or potassium bisulfate, or ammonium bisulfate. If desired, a mixture of sulfuric acid and water soluble, e.g. alkali metal, bisulfate, can be employed, in combination with the sulfamic acid or water soluble sulfamate described above. The sulfuric acid (calculated as H or bisulfate can be employed in a concentration or proportion in a range of about 0.2% to about by weight of solution, preferably about 2% to about 8% by weight of solution.

Where oxalic acid is incorporated in the invention composition, such material preferably is employed in a concentration of about 0.1% to about 5% by weight of the solution.

It has been found that in order to produce effective decontamination, the halogen-free solution containing sulfamate and sulfuric acid or bisulfate, should also contain a sufficient concentration of hydrogen ions so that the solution has a pH not greater than about 3, and in preferred operation not greater than about 1.5. The use of free sulfamic acid for this purpose is preferred and is economical since this material furnishes the required sulfamide ion and at the same time is a strong acid which also aids to supply sufficient concentration of hydrogen ion to produce the low pH within the aforementioned range. The sulfuric acid or bisulfate employed in combination with the sulfamic acid compound, and also the oxalic acid, when employed, also materially aid in achieving the proper pH. Under these conditions the use of an additional hydrogen ion producing material is usually unnecessary to obtain the proper pH of the solution. However, where for example, a combination of a sulfamate salt and a bisulfate are employed, or where the amount of sulfamate acid used is insuflicient to afford the desired acidity, an additional hydrogen ion producing material may be employed for this purpose. Such additional material may be an acidic substance such as phosphoric acid, an acid phosphate or sodium diacetate, provided such acidic substances do not react with the sulfamic acid or sulfamate to precipitate the latter materials out of solution, or to form deleterious reaction products therewith, and do not adversely affect the decontamination properties of the solution, or reduce the corrosion-free properties of the solution, especially towards aluminum and zirconium.

The addiiton of surface active agents to the aqueous acid solution of the invention often improves the effectiveness of such solution. By the term surface active agent, I mean those compounds which are characterized by an appreciable reduction in surface tension of water when used in small quantities in aqueous solution or dispersion and which are known to be useful as wetting agents, detergents, penetrating agents, emulsifying agents, and the like. For this purpose I may employ, for example, cationic or non-ionic surface active agents. The surface active agents which I employ are those which are stable chemically in acid solutions at a pH of 3 or less. Specific illustrative examples of suitable non-ionic surface active agents which I may employ are alkylarylpolyether alcohols, marketed as Triton X-l00 by Rohm & Haas, Co., polyoxyethylene sorbitan monolaurate, marketed as Tween 21 by Atlas Powder Co., and polyoxyethylene lauryl ether, marketed as Brij 35 by Atlas Powder Co. Specific examples of suitable cationic surface active agents are the fatty acid tertiary amines marketed as Ethomeen by Armour & Co., and the quaternary ammonium compounds such as the alkyl dimethyl benzyl ammonium chlorides, e.g., Roccal marketed by Winthrop Sterns, and di-isobutyl (p-tert. cetyl) phenoxy ethoxy ethyl dimethyl benzyl ammonium chloride, such as Hyamine 1622 marketed by Rohm & Haas Co. The amount of surface active agent employed may vary over wide ranges, but generally about 0.001 to about 0.2% by weight of the solution is used.

The surface active agent may be employed in my composition to aid in removing non-radioactive oily materials such as fats and greases so that the decontamination compound can more readily dissolve the radioactive materials, to improve the rate of penetration of the decontamination composition so that the time of decontamination is reduced, and to permit the aqueous decontami nation composition to more readily wet the surface being decontaminated in order to morerapidly and completely effect the decontamination or removal of the radioactive materials from such surface. However, it is to be understood that the surface active agent is not an essential component of my composition, and may be omitted therefrom if desired.

Small amounts of other materials which do not affect the functioning of the main ingredients of my compositions for removal of radioactive contamination, and which do not adversely affect the corrosion inhibiting properties of such compositions towards aluminum and zirconium, may be present in the compositions or solutions of the invention, such as small amounts of materials usually associated as impurities with the main ingredients, such as sulfates present with the sulfamates. Also, there may be added small amounts of conventional organic corrosion inhibitors such as, for example, di ortho tolyl thiourea, diphenyl thiourea and alkyl dimethyl benzyl ammonium chloride, which may be employed in amounts of about 0.001 to about 0.2% by weight of the solution. Certain of these inhibitors, such as, for example, alkyl dimethyl benzyl ammonium chloride, also function as suitable surface active agents according to the invention.

In formulating the acid aqueous solutions of the invention, I may mix together the ingredients in concentrated liquid or dry form, for example, the sulfamic acid or sulfamate compound, the sulfuric acid or the bisulfate, the oxalic acid, when employed, and also the surface active agent and/or corrosion inhibitor, if used, to form a single composition which can be packaged and when ready for use, added to water. Preferably, dry concentrated compositions containing bisulfate, rather than sulfun'c acid, are employed, due to greater convenience and safety in packaging and handling. If desired, however, the ingredients may be separately dissolved in water to give the solutions of the invention.

In the above concentrated liquid or dry compositions the amount of sulfamic acid or sulfamate present may range from about 10 parts to about 90 parts by weight of said composition, and the amount of sulfuric acid (calculated as H or bisulfate can also range from about 10 parts to about parts by weight of the composition. A preferred composition is one which contains approximately equal parts by weight of sulfamic acid and sodium bisulfate. When oxalic acid is employed, the amount thereof can be in the range of about 1 to about 25 parts by weight of the composition. The concentrated compositions of the above type can be added to water in an amount generally ranging from about /2 to about 12 ounces, usually about 2 to about 7 ounces, per gallon of solution, depending on the amount of sulfamic acid or sulfamate, and sulfuric acid or bisulfate contained in the concentrate or solid mixture of ingredients. The amount of such mixture added to water is such as to produce an acid solution having a concentration of the components and a pH within the ranges noted above.

The acid solutions of the invention used for decontamination of surfaces containing radioactive elements or emitters, can be applied to the surface at normal or at elevated temperatures, e.g., from about 20 C. up to C. or more. Greater effectiveness, that is, a greater percentage of decontamination, is usually realized at the elevated temperatures, employing the invention compositions, substantially without adversely affecting the corrosion inhibiting properties of such compositions on aluminum or zirconium. Contact time of the solution with the surface being decontaminated will vary with such factors as composition of the solution, temperature thereof, type of material undergoing treatment, the percentage of decontamination desired, etc. It is preferred to obtain as large a measure of decontamination per surface area as is possible in a relatively short period of treatment by the solution, say on the order of about 15 to about 90 minutes.

Following treatment of the contaminated surface with the acid solution, the spent solution can be conducted to another zone, and therein suitably treated, to recover, for example, sulfamic acid and radioactive isotopes.

concentration, temperature and time of treatment, re-

sulted in substantial corrosion of the aluminum components. It is also noteworthy from the above table that aqueous solutions of compositions C and D of the inven- The tests on removability of radioactive contamination 5 tion had superior decontamination effectiveness as comaccording to my invention were conducted mainly on secpared to aqueous solutions of compositions A and B, contions of aluminum components removed from an atomic taining sulfamic acid but without sodium bisul-fate. Also, reactor pile assembly. A determination of the level of it is noted in the table above that the radioactive deconbeta-gamma radiation from a unit surface area was made tamination efiiciency of the aqueous solution of composibefore treatment with the acid solutions and after such 10 tion C of the invention containing oxalic acid, was supetreatment. The materials emitting beta and gamma rays rior to that of the aqueous solution of composition D of were included in a single category because the counting the invention in the absence of oxalic acid, without any devices determined the radiation level of both of these sacrifice incorrosion resistance properties of the composirays together. The measure of the eificiency of the comtion on aluminum. positions for radioactive decontamination was made in Although the actual decontamination factors obtained terms of the decontamination factor (D.F.), defined as in the above runs employing the invention compositions follows: were of the order of about 2, the aluminum components DR: tested were highly radioactively contaminated, and other original radiation in counts per minute tests run on aluminum parts contamlnated with radioactive materials, employing the mventron compositions final radlaton counts per mmute under substantially the same conditions with respect to Hence, it is desirable to Obtain a maximum decofltamiflaconcentration, temperature and time of treatment as in fiOl'i factor with minimum COI'I'OSiOlJ. Of the base metal. Example ,1 above, have resulted in decontamination The following examples illustrate Practiw 0f t e factors ranging upwardly from about 8 to about 15 and V fi higher, with the same high corrosion inhibition as indi- EXAMPLE 1 cated in Table I above.

Aluminum pigtails" or piping components (formed EXAMPLE 2 of 1100 aluminum) of a nuclear reactor system, which were removed from the reactor after a period of opera- An aqueous solution similar to that formed using comtion and which were contaminated with radioactive maposition D of Example 1 is prepared, except that in place terials, were subjected to treatment by immersion in five of sodium bisulfate, sulfuric acid is employed in an separate aqueous treating solutions, formed by addition amount, based on the H 80 content, equal to the amount of compositions A to B, respectively, of the table below of sodium bisulfate in the aqueous solution of composito water in a quantity of 3 ounces of each such composition D prepared as in Example 1. tion per gallon of solution, such solutions each being Decontamination results and corrosion resistance on maintained at C. Time of treatment in each case 1100 aluminum parts of the .type treated in Example 1, was one hour. The pH of the solutions was in the range contaminated with radioactive materials, employing the of about 1 to about 2. The data and results are set forth above solution containing sulfuric acid, are similar to the in Table I below. results noted in the table above for composition D.

Table I Compositions A B c D E Components NaHSOt plus sulfamic acid Suliamie acid sulfamic acid Suliamic acid oxalic acid plus oxalic acid plus N aHSOi plus N aHSO plus halogens plus oxalic acid (Prior Art) 0 0 0 o 8.9 NaCl 0 0 0 0 40.0 Diortho tolyi thiourea (Corrosion Inhibitor) 2. 1 1. 6 1. 8 1. 3 1. 1

Decontamination Factor- 1. 6 1. 4 2. 1 1. 8 1. 7 Corrosion (mils oi Penetration) 0. 003 0. 001 0. 001 0. 001 0. 200

From the table above, it is seen that the decontarnina- 60 EXAMPLE 3 tion efllciency of aqueous solutions of compositions C and Zircaloy 2 components contaminated with radio- D of the invention, both containing sulfamic acid and active materials are treated with the aqueous solution of sodium bisulfate, and free of halogens, are as effective or composition D prepared as in Example 1. Decontaminaare superior in effectiveness for radioactive decontamination and corrosion resistance results comparable to those tion, as compared to an aqueous solution of composition 55 obtained in Example 1 employing the solution of compo- Eodof the prior art containing halogens in the form of sition D thereof are obtainable.

s ium fluoride and sodium chloride, as indicated by the DP. factor for the respective compositions given in the EXAMPLE 4 table. Of particular significance, it is further noted from An additional series of runs were made on 1100 aluthe data in the table above, that treatment with aqueous minum parts specifically for the purpose of testing corsolutions of compositions C and D of the invention rerosion eifects of the invention compositions both with and sulted in an insignificant amount of corrosion of the alu- Without corrosion inhibitor added, as against. a sulfamic minum components treated, whereas treatment of such acid composition containing halides and inhibitor. In

components with an aqueous solution of composition E these runs separate aluminum pieces were immersed respectively in the separate aqueous treating solutions of the prior art under the same conditions with respect to formed by adding compostions F to J, respectively, of Table H below in water, employing a concentration of 6 ounces of each of such compositions per gallon of solution. The solutions were each maintained at temperature of 65 C., and time of treatment in each case was one hour. The inhibitor" noted in compositions H to J of Table H was a corrosion inhibitor composed of 50% diphenyl thiourea and 50% alkyl dimethyl benzyl ammonium chloride. The data and results are set forth in Table II below.

Table II Composition Components Corrosion, mils oi Penetration 607 sulfamic acid a 0. 01s

45% sulfamic acid 45% NaHS04. 0. 015

I o. 012 I 3 N 0.006 1 (Prior Art g C 0.439

All of the 1100 aluminum parts treated in the solutions of the invention compositions F, G, H and I had no visible corrosion on their surfaces, whereas the 1100 aluminum parts treated in the solution of composition I containing halides, had visible corrosion on the surface.

From Table II, it is seen that corrosion on the 1100 aluminum parts treated with the solutions of the invention compositions F and G without any corrosion inhibitor incorporated therein, was far less than the high 0.439 value obtained from treatment with the solution of composition containing halides, even with the corrosion inhibitor present therein. The amount of corrosion obtained employing the invention compositions H and I containing the same amount of corrosion inhibitor as composition J, was reduced even below that obtained from invention compositors F and G. However, the corrosion resistance results obtained using the solutions of invention compositions F and G not containing inhibitor, on the 1100 aluminum parts, are deemed completely satisfactory.

In addition to their effectiveness on 1100 aluminum, the decontaminating compositions of the invention are effective on aluminum alloys such as for example, 2024 aluminum, 7075 aluminum and 6061 aluminum alloy. The invention compositions are effective on zirconium and its various alloys including the Zircaloys such as Zircaloy 2 which contains a major amount of zirconium and minor amounts of tin.

From the foregoing, it is seen that the invention provides novel decontaminating compositions and procedure for rapid and efficient removal of radioactive contaminants from surfaces of metals, particularly aluminum and zirconium, with the particular advantage of effecting such removal substantially without corrosion of the base metal.

While I have described particular embodiments of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention, as set forth in the appended claims.

I claim:

1. A process for removal of radioactive contaminants from surfaces of a metal selected from the group consisting of aluminum and zirconium, which comprises treating said surface with an aqueous acid solution consisting essentially of about 0.2% to about 15% by weight of sulfamic acid and about 0.2% to about 15 by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and water,

said solution having a pH not greater than about 3 and being substantially free of halides.

2. A process for removal of radioactive contaminants from surfaces of a metal selected from the group consisting of aluminum and zirconium, which comprises treating said surface with an aqueous acid solution consisting-essentially of about 0.2% to about 15 by weight of sulfamic acid, about 0.2% to about 15% by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and about 0.1% to about 5% by weight of oxalic acid, and water, said solution having a pH not greater than about 3, and being substantially free of halides.

3. A process as defined in claim 1, employing sulfamic acid and an alkali metal bisulfate.

4. A process as defined in claim 2, employing sulfamic acid and an alkali metal bisulfate.

5. A process for removal of radioactive contaminants from surfaces of a metal selected from the group consisting of aluminum and zirconium, which comprises treating said surface at a temperature from about 20 C. to about C. with an aqueous acid solution consisting essentially of about 2% to about 8% by weight of sulfamic acid and about 2% to about 8% by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and water, said solution having a pH not greater than about 1.5 and being substantially free of halides and of iron salts.

6. The process as defined in claim 5, employing sulfamic acid and sodium bisulfate.

7. A process for removal of radioactive contaminants from surfaces of a metal selected from the group consisting of aluminum and zirconium, which comprises treating said surface at a temperature from about 20 C. to about 100 C. with an aqueous acid solution consisting essentially of about 2% to about 8% by weight of sulfamic acid about 2% to about 8% by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and about 0.1% to about 5% by weight of oxalic acid, and water, said solution having a pH not greater than about 1.5 and being substantially free of halides and of iron salts.

8. A process as defined in claim 7, employing sulfamic acid and sodium bisulfate.

9. An aqueous acid solution for removal of radioactive contaminants from a surface, consisting essentially of about 0.2% to about 15% by weight of sulfamic acid and about 0.2% to about 15% by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and water, said solution being substantially free of halides.

10. An aqueous acid solution for removal of radioactive contaminants from a surface, consisting essentially of about 0.2% to about 15 by weight of sulfamic acid about 0.2% to about 15 by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and about 0.1% to about 5% by weight of oxalic acid, and water, said solution being substantially free of halides.

11. An aqueous acid solution for removal of radioactive contaminants from a surface, consisting essentially of about 2% to about 8% by weight of sulfamic acid and about 2% to about 8% by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and water, said solution being substantially free of halides and iron salts.

12. An aqueous acid solution for removal of radioactive contaminants from a surface, consisting essentially of about 2% to about 8% by weight of sulfamic acid about 2% to about 8% of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and about 0.1% to about 5% by weight of oxalic acid, and water, said solution being substantially free of halides and iron salts.

13. An aqueous acid solution as defined in claim 9, employing sulfamic acid and sodium bisulfate.

14. A composition of matter for removal of radioactive contaminants from a surface, consisting essentially of about 10 to about 90 parts by weight of sulfamic acid and about 10 to about 90 parts by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, said composition being substantially free of halides.

15. A composition of matter for removal of radioactive contaminants from surfaces, consisting essentially of about 10 to about 90 parts by weight of sulfamic acid and about 10 to about 90 parts by weight of a member chosen from the group consisting of sulfuric acid and the alkali metal and ammonium bisulfates, and about 1 to about 25 parts by weight of oxalic acid, said composition being substantially free of halides.

16. A solid composition of matter for removal of radioactive contaminants from a surface, consisting essentially of about 10 to about 90 parts by weight of sulfamic acid and about 10 to about 90 parts by weight of alkali metal bisulfate, said composition being substantialy free of halides.

17. A solid composition of matter for removal of radioactive contaminants from a surface, consisting essentially of about 10 to about 90 parts by weight of sulfamic acid and about 10 to about 90 parts by weight of sodium bisulfate, said composition being substantially free of halides and iron salts.

18. A solid composition of matter for removal of radioactive contaminants from a surface, consisting essentially of about 10 to about 90 parts by weight of sulfamic acid, about 10 to about 90 parts by weight of sodium bisulfate, and about 1 to about 25 parts by weight of oxalic acid, said composition being substantially free of halides and iron salts.

19. A solid composition of matter for removal of radioactive contaminants from a surface, consisting essentially of about equal parts by weight of sulfamic acid and sodium bisulfate, said composition being substantially free of halides and iron salts.

References Cited by the Examiner UNITED STATES PATENTS JULIUS GREENWALD, Primary Examiner.

W. E. SCHULZ, Assistant Examiner.

Claims (1)

1. A PROCESS FOR REMOVAL OF RADIOACTIVE CONTAMINANTS FROM SURFACES OF A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND ZIRCONIUM, WHICH COMPRISES TREATING SAID SURFACE WITH AN AQUEOUS ACID SOLUTION CONSISTING ESSENTIALLY OF ABOUT 0.2% TO ABOUT 15% BY WEIGHT OF SULFAMIC ACID AND ABOUT 0.2% TO ABOUT 15% BY WEIGHT OF A MEMBER CHOSEN FROM THE GROUP CONSISTING OF SULFURIC ACID AND THE ALKALI METAL AND AMMONIUM BISULFATES, AND WATER, BEING SUBSTANTIALLY FREE OF HALIDES.