CA2235976C - Method of treating a metal - Google Patents
Method of treating a metal Download PDFInfo
- Publication number
- CA2235976C CA2235976C CA002235976A CA2235976A CA2235976C CA 2235976 C CA2235976 C CA 2235976C CA 002235976 A CA002235976 A CA 002235976A CA 2235976 A CA2235976 A CA 2235976A CA 2235976 C CA2235976 C CA 2235976C
- Authority
- CA
- Canada
- Prior art keywords
- metal
- hydrogen peroxide
- nitric acid
- supplied
- solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/085—Iron or steel solutions containing HNO3
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/10—Other heavy metals
- C23G1/103—Other heavy metals copper or alloys of copper
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
- Chemical Treatment Of Metals (AREA)
- ing And Chemical Polishing (AREA)
Abstract
The invention relates to a method of pickling or surface treating a metal in an aqueous solution containing nitric acid wherein hydrogen peroxide is supplied to decrease the formation of nitrous fumes. At least a portion of the hydrogen peroxide is supplied by spraying or flushing an aqueous solution thereof directly on the metal through one or several separate nozzles (18a, 18b, 19a, 19b).
Description
METHOD OF TREATING A METAL
The present invention relates to a method of pickling or surface treating a metal in a solution containing nitric acid to which hydrogen peroxide is supplied to decrease the formation of nitrous fumes.
At manufacturing of many metals such as steel, particularly stainless steel, an oxide layer forms at the surface during the annealing, and this layer must be removed.
This is normally done by pickling which means that the steel is treated in an acidic oxidis-ing pickling bath to affect some dissolution of metal under the oxide layer which then comes loose. Pickling and surface treatment of metals is often performed in a solution based on nitric acid as an oxidising agent which treatment, however, involves emissions of nitrous fumes, mainly NO and N02. These emissions can be reduced significantly by adding hydrogen peroxide to the nitric acid containing solution as disclosed in the US
patent 4938838 and 3945865 as well as in H. T. Karlsson et al, "Control of NOx in Steel Pickling", Environmental Progress, Vol. 3, No. 1, 1984, pp. 40-43. In pickling of steel the following reactions occur:
The present invention relates to a method of pickling or surface treating a metal in a solution containing nitric acid to which hydrogen peroxide is supplied to decrease the formation of nitrous fumes.
At manufacturing of many metals such as steel, particularly stainless steel, an oxide layer forms at the surface during the annealing, and this layer must be removed.
This is normally done by pickling which means that the steel is treated in an acidic oxidis-ing pickling bath to affect some dissolution of metal under the oxide layer which then comes loose. Pickling and surface treatment of metals is often performed in a solution based on nitric acid as an oxidising agent which treatment, however, involves emissions of nitrous fumes, mainly NO and N02. These emissions can be reduced significantly by adding hydrogen peroxide to the nitric acid containing solution as disclosed in the US
patent 4938838 and 3945865 as well as in H. T. Karlsson et al, "Control of NOx in Steel Pickling", Environmental Progress, Vol. 3, No. 1, 1984, pp. 40-43. In pickling of steel the following reactions occur:
2 Fe + 6 H+ + 3 N03 ~ 2 Fe3+ + 3 N02- + 3 HZO
2 N02 + 2 H+ ~ NO + NOZ + H20 N02- + H202 ~ N03- + H20 This process generally works very well, but it has been found that in order to decrease the emissions below a certain level far more than stochiometric amounts of hydrogen peroxide must be supplied. At the same time, increasing consciousness of en-vironme~ntal problems call for more effective reduction of nitrous fumes.
The present invention intends to solve the problem of further reducing the emis-sions of nitrous fumes or NOX, particularly NO and N02, without increasing the hydrogen peroxide consumption to unacceptable levels. According to the invention it has surpris-ingly been found that the reduction of NOx emissions can be improved considerably with-out significantly increasing the (hydrogen peroxide consumption if at least a part of the hydrogE:n peroxide is sprayed or flushed directly on the metal instead of being added to the nitric acid containing solution, either directly into a tub in which the metal is treated or into a circulation conduit for the nitric acid containing solution.
Thus, the present invention concerns a method of pickling or surface treating a metal in an aqueous solution containing nitric acid wherein hydrogen peroxide is supplied to decrease the formation of nitrous fumes. At least a portion of the hydrogen peroxide is supplied by spraying or flushing an aqueous solution thereof directly on the metal through one or several separate nozzles. Preferably the hydrogen peroxide is sprayed in a way to obtain as small droplets as possible which makes the reaction with the NOX
more effi-cient. Although it is possible to supply substantially all the hydrogen peroxide through the separate nozzles, the preferred portion is from about 20 to about 80%, most preferably from about 40 to about 60% of the total amount of hydrogen peroxide supplied.
Without being bound to any theory it is assumed that hydrogen peroxide coming into contact with metal ions in a pickling solution decomposes catalytically into water and oxygen and is thus consumed to no use. It is also assumed that the main part of the ni-trous fumes are generated at the surface of the metal and that the hydrogen peroxide therefore is most likely to contact the NOX before it comes into contact with metal ions if it is sprayed or flushed directly on the metal. This is supposed to be particularly true when nitric acid containing solution is sprayed or flushed directly on the metal in which proc-esses considerable amounts of nitrous fumes evolve even at very low concentrations of dissolved NOx.
The nitric acid solution normally contains from about 0.1 to about 4 mols/l, pref-erably from about 0.5 to about 3 molsll of nitric acid, and suitably also hydrofluoric acid, for example from about 0.01 to about 5 molsll, preferably from about 0.1 to about 3 mols/I. The content of dissolved NOX is normally from about 0.01 to about 0.7 g/I, pref-erably from about 0.1 to about 0.4 g/l. The invention is particularly advantageous when the content of dissolved NOX is below about 0.7 gll. Normally most of the dissolved NOX
is in the form of NOZ .
According to the invention it is generally possible to maintain the emissions of NOX gas below about 7 g NOX per m2 treated metal and often even below about 4 g NOX
per m2 treated metal at a hydrogen peroxide consumption from about 2 to about 60 g H20z, preferably from about 5 to about 40 g H202 per m2 treated metal.
The amount of hydrogen peroxide added can be controlled by conventional method such a by measuring the redox potential in~the nitric acid containing solution or measuring the content of NOX in the exhaust gas. Preferred redox 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 nitric acid containing solutions. It is particularly advan-tageous in pickling of steel, especially stainless steel.
The invention will now be described in connection with the enclosed Figure schematically showing an embodiment of a process of treating a metal.
The figure shows a tub 1 containing a surface treating or pickling bath 2 of an aqueous solution containing nitric acid and preferably also hydrofluoric acid through which a running strip 3 of a metal, preferably stainless steel, is conducted continuously.
Nitric acid containing solution is supplied through lances 5a, 5b, 6a, 6b, each containing a plurality of nozzles 7a, 7b, 8a, 8b spraying the solution on each side of the metal strip 3 so it is distributed over substantially the entire width thereof. Solution from the bath 2 is withdrawn to a tank 4 and is fed ~;o the lances 5a, 5b, 6a, 6b at sufficiently high pressure via a circulation conduit 10 and a pump 11. The process also involves supply of an aque-ous solution of hydrogen peroxide from at storage tank 12. A portion of the hydrogen peroxide is brought by a pump 13a to separate lances 16a, 16b, 17a, 17b, each contain-ing a plurality of nozzles 18a, 18b, 19a, 19b spraying the solution on each side of the metal strip 3 so it is distributed over substantially the entire width thereof. The suitable number of nozzles depends on the size of the metal strip 3 and on the type of nozzles, but normally from about 4 to about 12 nozzles per lance is sufficient. Any conventional nozzle can be used, for example nozzles also blowing air which prevents clogging at in-terruption of the hydrogen peroxide flow. The remaining part of the hydrogen peroxide supplied is added by pumps 13b, 13c to the nitric acid containing solution in the tank 4 and the circulation conduit 10 at the suction side of the pump 11. The hydrogen peroxide from the pump 13c is preferably mixed with the solution from the bath 2 just before it en-ters the 'tank 4. Above the tub 1 a hood 25 containing a vent 26 is arranged.
Any nitrous fumes farmed is evacuated through the vent 26. The supply of hydrogen peroxide is preferably controlled on basis of the NOx content in the gas stream in the vent 26 or of the redox potential in the bath 2. It is also possible to have fixed flow of hydrogen perox-ide added through the nozzles 1 F3a, 18b, 19a, 19b and only regulate the pumps 13b, 13c supplying hydrogen peroxide to the tank 4 and the circulation conduit 10.
Although not shown in the Figure it is possible to treat the metal strip 3 without immersing it into the bath 2. It is also possible to convey the metal strip 3 vertically and spray the nitric acid containing :solution and the hydrogen peroxide on the vertical sur-faces.
The invention is further illustrated through the following example. If not otherwise stated all contents and percentages refer to wt%.
EXAMPLE: In a plant according to the Figure stainless steel was pickled in a an aqueous. solution of 2.9 molsll nitric acid and 2.7 molsll hydrofluoric acid.
When all the hydrogen peroxide was added to the nitric acid containing solution in the tank 4 and the circulation conduit a hydrogen peroxide consumption of 60-70 ml 35% aqueous H20z per m2 pickled steel was required to (keep a NOX concentration below 280 ppm in the vent 26 (corresponding to 3.5 g NOX per m2 pickled steel). When the process was operated ac-cording to the invention and about 45% of the hydrogen peroxide supplied was sprayed directly on the steel surface through the separate lances 16b, 17b above the steel strip 3, each containing six nozzles 18b, 19b, the consumption required to keep a NOX
concen-tration below 280 ppm in the vent 26 was only 40-45 ml 35% aqueous H202 per m2 pick-led steel.
2 N02 + 2 H+ ~ NO + NOZ + H20 N02- + H202 ~ N03- + H20 This process generally works very well, but it has been found that in order to decrease the emissions below a certain level far more than stochiometric amounts of hydrogen peroxide must be supplied. At the same time, increasing consciousness of en-vironme~ntal problems call for more effective reduction of nitrous fumes.
The present invention intends to solve the problem of further reducing the emis-sions of nitrous fumes or NOX, particularly NO and N02, without increasing the hydrogen peroxide consumption to unacceptable levels. According to the invention it has surpris-ingly been found that the reduction of NOx emissions can be improved considerably with-out significantly increasing the (hydrogen peroxide consumption if at least a part of the hydrogE:n peroxide is sprayed or flushed directly on the metal instead of being added to the nitric acid containing solution, either directly into a tub in which the metal is treated or into a circulation conduit for the nitric acid containing solution.
Thus, the present invention concerns a method of pickling or surface treating a metal in an aqueous solution containing nitric acid wherein hydrogen peroxide is supplied to decrease the formation of nitrous fumes. At least a portion of the hydrogen peroxide is supplied by spraying or flushing an aqueous solution thereof directly on the metal through one or several separate nozzles. Preferably the hydrogen peroxide is sprayed in a way to obtain as small droplets as possible which makes the reaction with the NOX
more effi-cient. Although it is possible to supply substantially all the hydrogen peroxide through the separate nozzles, the preferred portion is from about 20 to about 80%, most preferably from about 40 to about 60% of the total amount of hydrogen peroxide supplied.
Without being bound to any theory it is assumed that hydrogen peroxide coming into contact with metal ions in a pickling solution decomposes catalytically into water and oxygen and is thus consumed to no use. It is also assumed that the main part of the ni-trous fumes are generated at the surface of the metal and that the hydrogen peroxide therefore is most likely to contact the NOX before it comes into contact with metal ions if it is sprayed or flushed directly on the metal. This is supposed to be particularly true when nitric acid containing solution is sprayed or flushed directly on the metal in which proc-esses considerable amounts of nitrous fumes evolve even at very low concentrations of dissolved NOx.
The nitric acid solution normally contains from about 0.1 to about 4 mols/l, pref-erably from about 0.5 to about 3 molsll of nitric acid, and suitably also hydrofluoric acid, for example from about 0.01 to about 5 molsll, preferably from about 0.1 to about 3 mols/I. The content of dissolved NOX is normally from about 0.01 to about 0.7 g/I, pref-erably from about 0.1 to about 0.4 g/l. The invention is particularly advantageous when the content of dissolved NOX is below about 0.7 gll. Normally most of the dissolved NOX
is in the form of NOZ .
According to the invention it is generally possible to maintain the emissions of NOX gas below about 7 g NOX per m2 treated metal and often even below about 4 g NOX
per m2 treated metal at a hydrogen peroxide consumption from about 2 to about 60 g H20z, preferably from about 5 to about 40 g H202 per m2 treated metal.
The amount of hydrogen peroxide added can be controlled by conventional method such a by measuring the redox potential in~the nitric acid containing solution or measuring the content of NOX in the exhaust gas. Preferred redox 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 nitric acid containing solutions. It is particularly advan-tageous in pickling of steel, especially stainless steel.
The invention will now be described in connection with the enclosed Figure schematically showing an embodiment of a process of treating a metal.
The figure shows a tub 1 containing a surface treating or pickling bath 2 of an aqueous solution containing nitric acid and preferably also hydrofluoric acid through which a running strip 3 of a metal, preferably stainless steel, is conducted continuously.
Nitric acid containing solution is supplied through lances 5a, 5b, 6a, 6b, each containing a plurality of nozzles 7a, 7b, 8a, 8b spraying the solution on each side of the metal strip 3 so it is distributed over substantially the entire width thereof. Solution from the bath 2 is withdrawn to a tank 4 and is fed ~;o the lances 5a, 5b, 6a, 6b at sufficiently high pressure via a circulation conduit 10 and a pump 11. The process also involves supply of an aque-ous solution of hydrogen peroxide from at storage tank 12. A portion of the hydrogen peroxide is brought by a pump 13a to separate lances 16a, 16b, 17a, 17b, each contain-ing a plurality of nozzles 18a, 18b, 19a, 19b spraying the solution on each side of the metal strip 3 so it is distributed over substantially the entire width thereof. The suitable number of nozzles depends on the size of the metal strip 3 and on the type of nozzles, but normally from about 4 to about 12 nozzles per lance is sufficient. Any conventional nozzle can be used, for example nozzles also blowing air which prevents clogging at in-terruption of the hydrogen peroxide flow. The remaining part of the hydrogen peroxide supplied is added by pumps 13b, 13c to the nitric acid containing solution in the tank 4 and the circulation conduit 10 at the suction side of the pump 11. The hydrogen peroxide from the pump 13c is preferably mixed with the solution from the bath 2 just before it en-ters the 'tank 4. Above the tub 1 a hood 25 containing a vent 26 is arranged.
Any nitrous fumes farmed is evacuated through the vent 26. The supply of hydrogen peroxide is preferably controlled on basis of the NOx content in the gas stream in the vent 26 or of the redox potential in the bath 2. It is also possible to have fixed flow of hydrogen perox-ide added through the nozzles 1 F3a, 18b, 19a, 19b and only regulate the pumps 13b, 13c supplying hydrogen peroxide to the tank 4 and the circulation conduit 10.
Although not shown in the Figure it is possible to treat the metal strip 3 without immersing it into the bath 2. It is also possible to convey the metal strip 3 vertically and spray the nitric acid containing :solution and the hydrogen peroxide on the vertical sur-faces.
The invention is further illustrated through the following example. If not otherwise stated all contents and percentages refer to wt%.
EXAMPLE: In a plant according to the Figure stainless steel was pickled in a an aqueous. solution of 2.9 molsll nitric acid and 2.7 molsll hydrofluoric acid.
When all the hydrogen peroxide was added to the nitric acid containing solution in the tank 4 and the circulation conduit a hydrogen peroxide consumption of 60-70 ml 35% aqueous H20z per m2 pickled steel was required to (keep a NOX concentration below 280 ppm in the vent 26 (corresponding to 3.5 g NOX per m2 pickled steel). When the process was operated ac-cording to the invention and about 45% of the hydrogen peroxide supplied was sprayed directly on the steel surface through the separate lances 16b, 17b above the steel strip 3, each containing six nozzles 18b, 19b, the consumption required to keep a NOX
concen-tration below 280 ppm in the vent 26 was only 40-45 ml 35% aqueous H202 per m2 pick-led steel.
Claims (10)
1. A method of pickling or surface treating a metal in an aqueous solution containing nitric acid wherein hydrogen peroxide is supplied to decrease the formation of nitrous fumes characterised in that at least a portion of the hydrogen peroxide is supplied by spraying or flushing an aqueous solution thereof directly on the metal through one or several separate nozzles.
2. A method as claimed in claim 1, characterised in that from about 20 to about 80% of the total amount of hydrogen peroxide supplied is supplied through said one or several separate nozzles.
3. A method as claimed in claim 2, characterised in that from about 40 to about 60% of the total amount of hydrogen peroxide supplied is supplied through said one or several separate nozzles.
4. A method as claimed in any one of claims 1 to 3, characterised in that from about 2 to about 60 g H2O2 per m2 treated metal is supplied.
5. A method as claimed in any one of claims 1 to 4, characterised in that nitric acid containing solution is sprayed directly on the metal.
6. A method as claimed in any one of claims 1 to 5, characterised in that the nitric acid solution contains from about 0.1 to about 4 mols/1 of nitric acid.
7. A method as claimed in any one of claims 1 to 6, characterised in that the content of dissolved NO X in the nitric acid containing solution is below about 0.7 g/l.
8. A method as claimed in any one of claims 1 to 7, characterised in that the metal is steel.
9. A method as claimed in any one of claims 1 to 8, characterised in that emission of NO X is maintained below about 7 g per m2 pickled metal.
10. A method as claimed in any one of claims 1 to 9, characterised in that the nitric acid containing solution also contains hydrofluoric acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP97850075 | 1997-05-05 | ||
| EP97850075.9 | 1997-05-05 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2235976A1 CA2235976A1 (en) | 1998-11-05 |
| CA2235976C true CA2235976C (en) | 2001-06-05 |
Family
ID=8230959
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002235976A Expired - Fee Related CA2235976C (en) | 1997-05-05 | 1998-04-28 | Method of treating a metal |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPH10317181A (en) |
| KR (1) | KR100292792B1 (en) |
| BR (1) | BR9801536A (en) |
| CA (1) | CA2235976C (en) |
| RU (1) | RU2131484C1 (en) |
| TW (1) | TW373035B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20190089705A (en) * | 2018-01-23 | 2019-07-31 | 피에스테크놀러지(주) | Process of cleaning metal for reducing nox |
| CN112831785B (en) * | 2020-12-28 | 2023-03-21 | 江苏兴达钢帘线股份有限公司 | Iron-based micro monofilament sharpening liquid and using method thereof |
-
1998
- 1998-04-28 TW TW087106495A patent/TW373035B/en active
- 1998-04-28 CA CA002235976A patent/CA2235976C/en not_active Expired - Fee Related
- 1998-04-30 JP JP10134229A patent/JPH10317181A/en active Pending
- 1998-04-30 RU RU98108593/02A patent/RU2131484C1/en not_active IP Right Cessation
- 1998-04-30 BR BR9801536A patent/BR9801536A/en unknown
- 1998-05-04 KR KR1019980015906A patent/KR100292792B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| TW373035B (en) | 1999-11-01 |
| BR9801536A (en) | 1999-03-02 |
| KR100292792B1 (en) | 2001-11-26 |
| KR19980086733A (en) | 1998-12-05 |
| RU2131484C1 (en) | 1999-06-10 |
| CA2235976A1 (en) | 1998-11-05 |
| JPH10317181A (en) | 1998-12-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |