MXPA98003512A - Method of treatment of a me - Google Patents
Method of treatment of a meInfo
- Publication number
- MXPA98003512A MXPA98003512A MXPA/A/1998/003512A MX9803512A MXPA98003512A MX PA98003512 A MXPA98003512 A MX PA98003512A MX 9803512 A MX9803512 A MX 9803512A MX PA98003512 A MXPA98003512 A MX PA98003512A
- Authority
- MX
- Mexico
- Prior art keywords
- metal
- hydrogen peroxide
- supplied
- nitric acid
- solution containing
- Prior art date
Links
- MHAJPDPJQMAIIY-UHFFFAOYSA-N hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 72
- 239000002184 metal Substances 0.000 claims abstract description 35
- 229910052751 metal Inorganic materials 0.000 claims abstract description 35
- 238000005554 pickling Methods 0.000 claims abstract description 12
- 239000007864 aqueous solution Substances 0.000 claims abstract description 11
- 238000005507 spraying Methods 0.000 claims abstract description 6
- 238000004381 surface treatment Methods 0.000 claims abstract description 6
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 5
- 238000005755 formation reaction Methods 0.000 claims abstract description 5
- GQPLMRYTRLFLPF-UHFFFAOYSA-N nitrous oxide Inorganic materials [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 claims abstract 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 32
- 239000000243 solution Substances 0.000 claims description 22
- 229910002089 NOx Inorganic materials 0.000 claims description 12
- 229910000831 Steel Inorganic materials 0.000 claims description 11
- 239000010959 steel Substances 0.000 claims description 11
- KRHYYFGTRYWZRS-UHFFFAOYSA-N HF Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 8
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 abstract 2
- 238000000034 method Methods 0.000 description 6
- 230000001603 reducing Effects 0.000 description 4
- 239000007921 spray Substances 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 239000007789 gas Substances 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 101710010905 PY01155 Proteins 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000033116 oxidation-reduction process Effects 0.000 description 2
- -1 steel Chemical class 0.000 description 2
- 238000009423 ventilation Methods 0.000 description 2
- 229910001369 Brass Inorganic materials 0.000 description 1
- 235000007575 Calluna vulgaris Nutrition 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- 241000353097 Molva molva Species 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000010951 brass Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 230000000875 corresponding Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000003517 fume Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Abstract
The invention relates to a method for pickling or surface treatment of a metal in an aqueous solution containing nitric oxide where hydrogen peroxide is supplied in order to reduce the formation of nitrous vapors. At least a part of the hydrogen peroxide is supplied by spraying or by spraying an aqueous solution thereof directly on the metal through one or several separate nozzles (18, 18b, 19a, 19).
Description
ES $ METHOD OF TREATMENT OF A METAL
The present invention relates to a method for pickling or surface treatment of a metal in a solution containing nitric acid to which hydrogen peroxide is supplied to reduce the formation of nitrous fumes. In the manufacture of many metals such as steel, particularly stainless steel, an oxide layer is formed on the surface during annealing, and this layer must be removed. This is usually done by pickling which means that the steel is treated in an ethereal oxidation pickling bath to effect some dissolution of metal under the oxide layer which is then loosened. The pickling and surface treatment of metals is often carried out in a solution based on nitric acid as an oxidizing agent, whose treatment, however, involves emissions of nitrous fumes, mainly NO and N? 2. These emissions can be significantly reduced by adding hydrogen peroxide to the solution containing nitric acid, as described in the U.S. Patents. 4938838 and 3945865 as well as in "Control of Nox in Steel Pic ling" by H. T. Karisson et al., Environmental Progress, Vol. 3, No. 1, 1984, p. 40-43. In the steel pickling, the following reactions occur:
2 Fe + 6 H + + 3 N? 3 ^ ---? 2 Fe3 + + 3 N? 2- + 3 H20 N02- + H202 - • > N? 3- + H20
This process generally works very well, but it has been found that in order to reduce emissions below a certain level, much larger quantities than stoichiometric hydrogen peroxide must be supplied. At the same time, the increasing awareness of environmental problems demands more effective reduction of nitrous fumes. The present invention aims to solve the problem by further reducing the emissions of nitrous fumes or NOx, particularly NO and N? 2 without increasing the consumption of hydrogen peroxide to unacceptable levels. In accordance with the invention it has surprisingly been found that the reduction of Nox emissions can be considerably improved without significantly increasing the hydrogen peroxide consumption if at least a part of the hydrogen peroxide is sprayed or flooded directly on the metal instead of being added to the metal. the solution containing nitric acid, either directly in a tub in which the metal is treated or to a circulation conduit for the solution containing nitric acid. In this way, the present invention relates to a method of pickling or surface treatment of a metal in an aqueous solution containing nitric acid in which hydrogen peroxide is supplied to reduce the formation of nitrous fumes. At least a portion of the hydrogen peroxide is supplied by spraying or flooding an aqueous solution thereof directly on the metal through one or several separate nozzles. Preferably the hydrogen peroxide is sprayed in a manner to obtain as small droplets as possible which makes the reaction with NOx more efficient. Although it is possible to supply substantially all of the hydrogen peroxide through the separate nozzles, the preferred portion is from about 20 to about 80%, more preferably from about 40 to about 60% of the total amount of the hydrogen peroxide supplied. . Without being limited to any theory, it is assumed that the hydrogen peroxide which is contacted with the metal ions in an etching solution is catalytically decomposed to water and oxygen and thus consumed until no use. It is also assumed that the main part of the nitrous fumes are generated on the surface of the metal and that hydrogen peroxide, therefore, is more likely to make contact with the Nox before it comes into contact with metal ions if it is spray or flood directly on the metal. This is supposed to be
* particularly true when nitric acid-containing solution is sprayed or flooded directly on the metal in which process considerable amounts of fumes
Nitroses are released even at very low concentrations of dissolved Nox. The nitric acid solution typically contains from about 0.1 to about 4 moles / 1, preferably from about 0.5 to
About 3 moles / 1 of nitric acid, and also suitable hydrofluoric acid, for example from about 0.01 to about 5 moles / 1, preferably from about 0.1 to about 3 moles / 1. The content of dissolved Nox is usually around
0.01 to about 0.7 g / 1, preferably from about 0.1 to about 0.4 g / 1. The invention is particularly advantageous when the content of dissolved Nox is less than about 0.7 g / 1. Normally, most of the dissolved NOx is in the form of N? 2-. According to the invention, it is generally possible to keep the Nox gas emissions below about 7 g of NOx per m2 of treated metal and often still less than about 4 g of NOx per m2 of treated metal at a consumption of hydrogen peroxide of from about 2 to about 60 g of H 2 O 2, preferably from about 5 to about 40 g of H 2 O 2 per square meter of treated metal. The amount of added hydrogen peroxide can be controlled by conventional method such as by measuring the reduction potential by oxidation in the nitric acid-containing solution or by measuring the NOx content in the discharged gas. Preferred oxidation reduction potential control methods are described in US 4938838 and EP 442250. The invention is advantageous in all processes for surface treatments of metals such as steel, copper or brass with solutions containing nitric acid. It is particularly advantageous in the pickling of steel, especially stainless steel. The invention will now be described with reference to the accompanying Figure which schematically shows one embodiment of a process for treating a metal. The Figure shows a tub 1 containing a bath 2 for surface treatment or pickling of an aqueous solution containing nitric acid and preferably also hydrofluoric acid through which a moving strip 3 of a metal, preferably stainless steel, It is driven continuously. The solution containing nitric acid is supplied through lancets 5a, 5b, 6a, 6b each containing a
* plurality of nozzles 7a, 7b, 8a, 8b which spray the solution on each side of the metal strip 3 so that
is distributed over substantially the entire width thereof. The solution of the bath 2 is removed to a tank 4 and fed to the lancets 5a, 5b, 6a, 6b at sufficiently high pressure through a circulation conduit 10 and a pump 11. The process is also
involves the supply of an aqueous solution of hydrogen peroxide from a storage tank 12. A portion of the hydrogen peroxide is carried by a pump 13a to the separate lancets 16a, 16b, 17a, 17b, each containing a plurality of
nozzles 18a, 18b, 19a, 18b which spray the solution on each side of the metal strip 3 so that it is distributed over the substantially complete width thereof. The appropriate number of nozzles depends on the size of the metal strip 3 and the type of nozzles,
but normally it's around 4 to about 12 nozzles per lancet is enough. Any conventional nozzle can be used, for example nozzles that also blow air which prevents plugging in the interruption of the flow of hydrogen peroxide. The remaining part of the hydrogen peroxide supplied is added by pumps 13b, 13c to the solution containing nitric acid in tank 4 and circulation conduit 10 on the suction side of pump 11. Hydrogen peroxide from the pump 13c is preferably mixed with the solution of the bath 2 just before it enters the tank 4. Above the tub 1, a cap 25 is provided which contains a vent 26. Any nitrous fumes formed are evacuated through the vent 26 The supply of hydrogen peroxide is preferably controlled on the basis of the NOx content in the gas stream in the vent 26 or the oxidation reduction potential in the bath 2. It is also possible to have fixed flow of hydrogen peroxide added to the through the nozzles 18a, 18b, 19a, 19b and only regulate the pumps 13b, 13c, supplying the hydrogen peroxide to the tank 4 and the circulation duct 10. Even when not shown in the Figure, it is possible to treat the metal strip 3 without immersing it in the bath 2. It is also possible to transfer the metal strip 3 vertically and spray the solution containing nitric acid and hydrogen peroxide on the vertical surfaces. The invention is further illustrated by the following example. If not stated otherwise, all contents and percentages refer to% by weight.
EXAMPLE: In a plant according to Figure 1, stainless steel was decanted in an aqueous solution of 2.9 mol / l of nitric acid and 2.7 mol / l of hydrofluoric acid. When all the hydrogen peroxide was added to the solution containing nitric acid in tank 4 and the circulation conduit, a hydrogen peroxide consumption of 60-70 ml of aqueous H2O2 per square meter of pickling steel was required to maintain a NOx concentration of less than 280 ppm in ventilation 26 (corresponding to 3.5 g of NOx per m.2 of pickled steel). When the process was operated in accordance with the invention and about 45% hydrogen peroxide sprayed directly onto the steel surface was supplied through the lancets 16b, 17b spaced above the steel strip 3, each containing six nozzles 18b, 19b, the consumption required to maintain a NOx concentration of less than 280 ppm in ventilation 26 was only 40-45 ml of aqueous H 2 O 2 per square meter of pickled steel.
Claims (10)
1. - A method for stripping or superficially treating a metal in an aqueous solution containing nitric acid, wherein the hydrogen peroxide is supplied to decrease the formation of nitrous fumes, characterized in that at least a portion of the hydrogen peroxide is supplied by spraying or by flooding an aqueous solution thereof directly onto the metal through a plurality of separate nozzles.
2. A method according to claim 1, characterized in that from about 20 to about 80% of the total amount of hydrogen peroxide supplied through the separate nozzles.
3. A method according to claim 2, characterized in that from about 40 to about 60% of the total amount of hydrogen peroxide supplied is supplied through the separate nozzles.
4. A method according to any of claims 1 to 3, characterized in that from about 2 to about 60 g of H2O2 per square meter of treated metal is supplied.
5. - A method according to any of claims 1 to 4, characterized in that the solution containing nitric acid is sprayed directly on the metal.
6. A method according to any of claims 1 to 5, characterized in that the nitric acid solution contains from about 0.1 to about 4 moles / 1 of nitric acid.
7. A method according to any of claims 1 to 6, characterized in that the content of NOx dissolved in the solution containing nitric acid is less than about 0.7 g / 1.
8. A method as claimed in any of claims 1 to 7, characterized in that the metal is steel.
9. A method as claimed in any of claims 1 to 8, characterized in that the NOx emissions are maintained at less than about 7 g per square meter of pickling metal.
10. A method as claimed in any of claims 1 to 9, characterized in that the solution containing nitric acid also contains hydrofluoric acid. SUMMARY OF THE INVENTION The invention relates to a method for pickling or surface treatment of a metal in an aqueous solution containing nitric acid where hydrogen peroxide is supplied in order to reduce the formation of nitrous vapors. At least a part of the hydrogen peroxide is supplied by spraying or by spraying an aqueous solution thereof directly on the metal through one or several separate nozzles.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP97850075.9 | 1997-05-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| MXPA98003512A true MXPA98003512A (en) | 1999-02-24 |
Family
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