EP0885985A1 - Method of treating a metal - Google Patents

Method of treating a metal Download PDF

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Publication number
EP0885985A1
EP0885985A1 EP98201206A EP98201206A EP0885985A1 EP 0885985 A1 EP0885985 A1 EP 0885985A1 EP 98201206 A EP98201206 A EP 98201206A EP 98201206 A EP98201206 A EP 98201206A EP 0885985 A1 EP0885985 A1 EP 0885985A1
Authority
EP
European Patent Office
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.)
Withdrawn
Application number
EP98201206A
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German (de)
French (fr)
Inventor
Troy Berglind
Arne Frestad
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Akzo Nobel NV
Nouryon Pulp and Performance Chemicals AB
Original Assignee
Akzo Nobel NV
Eka Chemicals AB
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Akzo Nobel NV, Eka Chemicals AB filed Critical Akzo Nobel NV
Priority to EP98201206A priority Critical patent/EP0885985A1/en
Publication of EP0885985A1 publication Critical patent/EP0885985A1/en
Withdrawn legal-status Critical Current

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    • 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
    • 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

Definitions

  • 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.
  • an oxide layer forms at the surface during the annealing, and this layer must be removed. This is normally done by picking which means that the steel is treated in an acidic oxidising picking bath to affect some dissolution of metal under the oxide layer which then comes loose.
  • Picking 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 NO 2 . 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.
  • the present invention intends to solve the problem of further reducing the emissions of nitrous fumes or NO x , particularly NO and NO 2 , without increasing the hydrogen peroxide consumption to unacceptable levels.
  • NO x nitrous fumes or NO x
  • NO and NO 2 nitrous fumes or NO x
  • the reduction of NO x emissions can be improved considerably without significantly increasing the hydrogen peroxide consumption if at least a part of the hydrogen 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.
  • the present invention concerns a method of picking 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 NO x more efficient. 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.
  • the nitric acid solution normally contains from about 0.1 to about 4 mols/l, preferably from about 0.5 to about 3 mols/l of nitric acid, and suitable also hydrofluoric acid, for example from about 0.01 to about 5 mols/l, preferably from about 0.1 to about 3 mols/l.
  • the content of dissolved NO x is normally from about 0.01 to about 0.7 g/l, preferably from about 0.1 to about 0.4 g/l. The invention is particularly advantageous when the content of dissolved NO x is below about 0.7 g/l. Normally most of the dissolved NO x is in the form of NO 2 - .
  • the invention it is generally possible to maintain the emissions of NO x gas below about 7 g NO x per m 2 treated metal and often even below about 4 g NO x per m 2 treated metal at a hydrogen peroxide consumption from about 2 to about 60 g H 2 O 2 , preferably from about 5 to about 40 g H 2 O 2 per m 2 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 NO x 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 advantageous in pickling of steel, especially stainless steel.
  • 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 to 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 aqueous 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 containing 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 interruption 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 enters the tank 4.
  • a hood 25 containing a vent 26 is arranged above the tub 1 . Any nitrous fumes formed is evacuated through the vent 26.
  • the supply of hydrogen peroxide is preferably controlled on basis of the NO x 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 peroxide added through the nozzles 18a, 18b, 19a, 19b and only regulate the pumps 13b, 13c supplying hydrogen peroxide to the tank 4 and the circulation conduit 10.
  • EXAMPLE In a plant according to the Figure stainless steel was pickled in a an aqueous solution of 2.9 mols/l nitric acid and 2.7 mols/l 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 H 2 O 2 per m 2 pickled steel was required to keep a NO x concentration below 280 ppm in the vent 26 (corresponding to 3.5 g NO x per m 2 pickled steel).

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

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 picking which means that the steel is treated in an acidic oxidising picking bath to affect some dissolution of metal under the oxide layer which then comes loose. Picking 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 NO2. 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 picking of steel the following reactions occur: 2 Fe + 6 H+ + 3 NO3 - ⇄ 2 Fe3+ + 3 NO2 - + 3 H2O 2 NO2 - + 2 H+ ⇄ NO + NO2 + H2O NO2 - + H2O2 ⇄ NO3 - + H2O
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 environmental problems call for more effective reduction of nitrous fumes.
The present invention intends to solve the problem of further reducing the emissions of nitrous fumes or NOx, particularly NO and NO2, without increasing the hydrogen peroxide consumption to unacceptable levels. According to the invention it has surprisingly been found that the reduction of NOx emissions can be improved considerably without significantly increasing the hydrogen peroxide consumption if at least a part of the hydrogen 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 picking 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 efficient. 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 nitrous 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 processes 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, preferably from about 0.5 to about 3 mols/l of nitric acid, and suitable also hydrofluoric acid, for example from about 0.01 to about 5 mols/l, preferably from about 0.1 to about 3 mols/l. The content of dissolved NOx is normally from about 0.01 to about 0.7 g/l, preferably 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 g/l. Normally most of the dissolved NOx is in the form of NO2 -.
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 H2O2, preferably from about 5 to about 40 g H2O2 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 advantageous 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 to 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 aqueous 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 containing 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 interruption 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 enters the tank 4. Above the tub 1 a hood 25 containing a vent 26 is arranged. Any nitrous fumes formed 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 peroxide added through the nozzles 18a, 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 surfaces.
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 mols/l nitric acid and 2.7 mols/l 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 H2O2 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 according 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 concentration below 280 ppm in the vent 26 was only 40-45 ml 35% aqueous H2O2 per m2 pickled 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 (18a, 18b, 19a, 19b).
  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 the separate nozzles (18a, 18b, 19a, 19b).
  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 the separate nozzles (18a, 18b, 19a, 19b).
  4. A method as claimed in any one of the claims 1-3, 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 the claims 1-4, characterised in that nitric acid containing solution is sprayed directly on the metal.
  6. A method as claimed in any one of the claims 1-5, characterised in that the nitric acid solution contains from about 0.1 to about 4 mols/l of nitric acid.
  7. A method as claimed in any one of the claims 1-6, characterised in that the content of dissolved NOx in the nitric acid containing solution is below about 0.7 g/l.
  8. A method as claimed in any one of the claims 1-7, characterised in that the metal is steel.
  9. A method as claimed in any one of the claims 1-8, characterised in that the emissions of NOx is maintained below about 7 g per m2 pickled metal.
  10. A method as claimed in any one of the claims 1-9, characterised in that the nitric acid containing solution also contains hydrofluoric acid.
EP98201206A 1997-05-05 1998-04-15 Method of treating a metal Withdrawn EP0885985A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP98201206A EP0885985A1 (en) 1997-05-05 1998-04-15 Method of treating a metal

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EP97850075 1997-05-05
EP97850075 1997-05-05
EP98201206A EP0885985A1 (en) 1997-05-05 1998-04-15 Method of treating a metal

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0974682A1 (en) * 1998-07-18 2000-01-26 Henkel Kommanditgesellschaft auf Aktien Method and apparatus for the chemical treatment of metalsurfaces

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB375599A (en) * 1931-08-15 1932-06-30 Thomas Watts Coslett Improvements in or relating to processes for pickling or cleaning iron or steel
FR2253103A1 (en) * 1973-11-26 1975-06-27 Hitachi Ltd
FR2279447A1 (en) * 1974-07-22 1976-02-20 Dart Ind Inc IMPROVEMENTS TO METHODS AND SOLUTIONS CONTAINING NITRIC ACID FOR DISSOLVING OR TREATING METALLIC OR METALLIC MATERIALS
DD124660A1 (en) * 1976-02-24 1977-03-09
EP0053719A1 (en) * 1980-12-10 1982-06-16 Gebr. Schmid GmbH & Co. Process for etching metal surfaces
EP0259533A1 (en) * 1986-09-11 1988-03-16 Eka Nobel Aktiebolag Method of reducing the emission of nitrogen oxides from a liquid containing nitric acid
EP0442250A2 (en) * 1990-01-17 1991-08-21 Eka Nobel Ab Control method with redox-potential
EP0529332A1 (en) * 1991-08-23 1993-03-03 Degussa Aktiengesellschaft Process for automatically controllable lowering the nitrite content in nitrite containing aqueous solutions to a concentration of less than 1 mg/l

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB375599A (en) * 1931-08-15 1932-06-30 Thomas Watts Coslett Improvements in or relating to processes for pickling or cleaning iron or steel
FR2253103A1 (en) * 1973-11-26 1975-06-27 Hitachi Ltd
FR2279447A1 (en) * 1974-07-22 1976-02-20 Dart Ind Inc IMPROVEMENTS TO METHODS AND SOLUTIONS CONTAINING NITRIC ACID FOR DISSOLVING OR TREATING METALLIC OR METALLIC MATERIALS
US3945865A (en) * 1974-07-22 1976-03-23 Dart Environment And Services Company Metal dissolution process
DD124660A1 (en) * 1976-02-24 1977-03-09
EP0053719A1 (en) * 1980-12-10 1982-06-16 Gebr. Schmid GmbH & Co. Process for etching metal surfaces
EP0259533A1 (en) * 1986-09-11 1988-03-16 Eka Nobel Aktiebolag Method of reducing the emission of nitrogen oxides from a liquid containing nitric acid
US4938838A (en) * 1986-09-11 1990-07-03 Eka Nobel Ab Method of reducing the emission of NOx gas from a liquid containing nitric acid
EP0442250A2 (en) * 1990-01-17 1991-08-21 Eka Nobel Ab Control method with redox-potential
EP0529332A1 (en) * 1991-08-23 1993-03-03 Degussa Aktiengesellschaft Process for automatically controllable lowering the nitrite content in nitrite containing aqueous solutions to a concentration of less than 1 mg/l

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
KARLSSON H. T.: "Control of NOX in steel pickling", ENVIRONMENTAL PROGRESS, vol. 3, no. 1, 1 February 1984 (1984-02-01), NEW YORK (US), pages 40 - 43, XP002042842 *
SANDERS N J: "Environmentally friendly stainless steel pickling", ANTI-CORROSION METHODS AND MATERIALS, vol. 44, no. 1, January 1997 (1997-01-01), Bradford (GB), pages 20 - 25, XP002074174 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0974682A1 (en) * 1998-07-18 2000-01-26 Henkel Kommanditgesellschaft auf Aktien Method and apparatus for the chemical treatment of metalsurfaces

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