CA1256357A - Method of pickling iron or steel objects - Google Patents
Method of pickling iron or steel objectsInfo
- Publication number
- CA1256357A CA1256357A CA000504493A CA504493A CA1256357A CA 1256357 A CA1256357 A CA 1256357A CA 000504493 A CA000504493 A CA 000504493A CA 504493 A CA504493 A CA 504493A CA 1256357 A CA1256357 A CA 1256357A
- Authority
- CA
- Canada
- Prior art keywords
- pickling
- solution
- iron
- proportion
- acid
- 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.)
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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
- C23G1/36—Regeneration of waste pickling liquors
-
- 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
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- 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)
- Electrolytic Production Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for pickling iron or steel objects before a subsequent surface treatment or mechanical processing. The objects are transported into a pickling bath having a temperature above 250°C and containing a solution of ferrous chloride and a low proportion of free hydrochloric acid. The pickling bath is continuously regenerated in a circulation system with electrolytic cells. These are preferably electrically connected in series and in parallel with the flow of the pickling bath, in order to deposit iron on the cathode and recover free acid.
A method for pickling iron or steel objects before a subsequent surface treatment or mechanical processing. The objects are transported into a pickling bath having a temperature above 250°C and containing a solution of ferrous chloride and a low proportion of free hydrochloric acid. The pickling bath is continuously regenerated in a circulation system with electrolytic cells. These are preferably electrically connected in series and in parallel with the flow of the pickling bath, in order to deposit iron on the cathode and recover free acid.
Description
~2S635~
This invention relates to methods for pickling iron or steel ob~ects, b~fore a subsequent surface treatment or a mechanical processing.
Before the mechanical processing of ob~ects of iron or steel, e.g. by drawing, milling or pressing, or before application of any anti-corrosive film, the surface coating usually must be removed. This coating can comprise various oxides, e.g. rust, being formed by chemical corrosion. Other coatings can consist of scale from a preliminary heat treatment or rolling skin from a preliminary rolling. These different coatings are normally removed by pick~ing in acid baths.
Normally, either sulphuric acid or hydrochloric acid is used for pickling carbon steel or cast iron. The former is less expensive to buy, but the hydrochloric acid presents several technical advantages, often ma~ing the total economy for this acid the most profitable.
A pickling bath intended for pickling with hydrochloric acid normally comprise about 200 g HCl per liter. During pickling, normally performed at a temperature of about 20C, iron is solved as Fe2~. The proportion of iron in the pickling bath rises gradually until it, after some use, reaches about 80-85 g per litre pickling solution. The proportion of acid in the pickling bath is now about 80-100 g per litre pickling solu-tion.
The pickling continues very slowly during these circumstances making it necessary to exchange the pickling solution for regenerating or dumping. In total, 7-8 kg of hydrochloric acid is used per kg of dissolved iron~
The depositing or regenerating of used pickling solution is very important from various points of view. Partly because these pickling baths constitute a dangerous waste, which has to be destructed before deposition. Partly because the pickling baths has a significant value with respect to the ., ~2$~3~7 content o remaining free acid, solved iron and a corresponding amount of negative ions.
The hydrochloric solution can be regenerated through a roasting process within an oil-burning oven. Thereby the solved iron forms iron oxide and hydrogen chlorine. The latter is absorbed while the pickling acid is recovered. One disadvantage with this process is that a certain amount of hydrogen chlorine is lost because also the remaining free acid goes into the oven.
It is also possible to regenerate the pickling solution through electrolysis. The iron in the solution will be deposited at the cathode of the electrolytic cell. The electrolyte (the pickling solution) must form an almost neutral solution of ferrous chloride in order to enable the electrolysis. Since the pickling solution, however, contains a comparatively large proportion of remaining acid, there will mainly be development of hydrogen gas at the cathode, i.e. the deposition of metal will be small in relation to used electric energy.
The solution can be neutralized by evaporation and crystallization of iron chloride and separation of remaining surplus acid, which can be returned to the pickling process.
Because of the solubility of iron ~hloride, the evaporation of the bath must be complete to enable crys$allization. Furthermore, the subsequent electrolysis will consume a lot of electric energy, since a great deal of the chloride is used up by the development of gas, while oxidation of ferrous chloride to ferric chloride takes place at the anode.
The gradual increase of Fe III changes the polarlty leading to the forming of basic salts, while the electrolytic efficiency declines steeply.
From this, an electrolytic cell for recovPry of pickling acid must have a ion-exchange membranes as a partltion
This invention relates to methods for pickling iron or steel ob~ects, b~fore a subsequent surface treatment or a mechanical processing.
Before the mechanical processing of ob~ects of iron or steel, e.g. by drawing, milling or pressing, or before application of any anti-corrosive film, the surface coating usually must be removed. This coating can comprise various oxides, e.g. rust, being formed by chemical corrosion. Other coatings can consist of scale from a preliminary heat treatment or rolling skin from a preliminary rolling. These different coatings are normally removed by pick~ing in acid baths.
Normally, either sulphuric acid or hydrochloric acid is used for pickling carbon steel or cast iron. The former is less expensive to buy, but the hydrochloric acid presents several technical advantages, often ma~ing the total economy for this acid the most profitable.
A pickling bath intended for pickling with hydrochloric acid normally comprise about 200 g HCl per liter. During pickling, normally performed at a temperature of about 20C, iron is solved as Fe2~. The proportion of iron in the pickling bath rises gradually until it, after some use, reaches about 80-85 g per litre pickling solution. The proportion of acid in the pickling bath is now about 80-100 g per litre pickling solu-tion.
The pickling continues very slowly during these circumstances making it necessary to exchange the pickling solution for regenerating or dumping. In total, 7-8 kg of hydrochloric acid is used per kg of dissolved iron~
The depositing or regenerating of used pickling solution is very important from various points of view. Partly because these pickling baths constitute a dangerous waste, which has to be destructed before deposition. Partly because the pickling baths has a significant value with respect to the ., ~2$~3~7 content o remaining free acid, solved iron and a corresponding amount of negative ions.
The hydrochloric solution can be regenerated through a roasting process within an oil-burning oven. Thereby the solved iron forms iron oxide and hydrogen chlorine. The latter is absorbed while the pickling acid is recovered. One disadvantage with this process is that a certain amount of hydrogen chlorine is lost because also the remaining free acid goes into the oven.
It is also possible to regenerate the pickling solution through electrolysis. The iron in the solution will be deposited at the cathode of the electrolytic cell. The electrolyte (the pickling solution) must form an almost neutral solution of ferrous chloride in order to enable the electrolysis. Since the pickling solution, however, contains a comparatively large proportion of remaining acid, there will mainly be development of hydrogen gas at the cathode, i.e. the deposition of metal will be small in relation to used electric energy.
The solution can be neutralized by evaporation and crystallization of iron chloride and separation of remaining surplus acid, which can be returned to the pickling process.
Because of the solubility of iron ~hloride, the evaporation of the bath must be complete to enable crys$allization. Furthermore, the subsequent electrolysis will consume a lot of electric energy, since a great deal of the chloride is used up by the development of gas, while oxidation of ferrous chloride to ferric chloride takes place at the anode.
The gradual increase of Fe III changes the polarlty leading to the forming of basic salts, while the electrolytic efficiency declines steeply.
From this, an electrolytic cell for recovPry of pickling acid must have a ion-exchange membranes as a partltion
- 2 -~ .
35~7 be-tween anode and cathode, so that the acid ~ormed at the anode will not prevent the deposition of metal at -the cathode.
An usefule pickling solution may comprise between 100 200 g free hydrochloric acid per liter solution wi~h between 0-80 g Fe2+ and usually attacks the base metal furiously. When objects of iron or steel with scales, normally comprising Fe203 FeO-oxides, are pickled, pittings occur. This happens because the surface of the base metal usually is rather small compared to the oxide surface, i.e. the cathode, whereln the oxide has the high electric potential in relation to the iron within sald solution and is cathodic in relation to the base metal, which becomes the dissolving electrode, because of its anodic potential. Therefore, the scales are not dissolved in the acid, but rather "explodes" away from its surface, because the acid penetrates below the scale and lifts it away. The consequence is severe pittings on the base metal, because of the anodic current density (corrosive current~ is very high. Whils the proportion of acid in the solution declines, the difference of potential also declines and thereby the pickling effect of the solution.
The Fe304- oxide is deposited as a sludge on the bottom of the pickling bath. The proportion of iron rises during conventional pickling, while the proportion of acid declines. ~t the beginning of the process the difference of potential between the iron oxides is at least 1000 mV. The base metal Fe then acts as anode, meaning that the iron oxides from FeO~ Fe2+. The surface of the metal is therefore pitted when it is exposed by fractures and pores in the oxide coating. It is normal to use an inhibitor or restrainer in the pickling bath to reduce the pitting damage on the base metal.
The present invention provides a method for pickling objects of iron and steel, whlch enables a continuous regenerating of the pickling solution, at a high level of electrolytic efficiency, wherein the pickling can be performed in a closed process having as residual products pickled ob;ects of
35~7 be-tween anode and cathode, so that the acid ~ormed at the anode will not prevent the deposition of metal at -the cathode.
An usefule pickling solution may comprise between 100 200 g free hydrochloric acid per liter solution wi~h between 0-80 g Fe2+ and usually attacks the base metal furiously. When objects of iron or steel with scales, normally comprising Fe203 FeO-oxides, are pickled, pittings occur. This happens because the surface of the base metal usually is rather small compared to the oxide surface, i.e. the cathode, whereln the oxide has the high electric potential in relation to the iron within sald solution and is cathodic in relation to the base metal, which becomes the dissolving electrode, because of its anodic potential. Therefore, the scales are not dissolved in the acid, but rather "explodes" away from its surface, because the acid penetrates below the scale and lifts it away. The consequence is severe pittings on the base metal, because of the anodic current density (corrosive current~ is very high. Whils the proportion of acid in the solution declines, the difference of potential also declines and thereby the pickling effect of the solution.
The Fe304- oxide is deposited as a sludge on the bottom of the pickling bath. The proportion of iron rises during conventional pickling, while the proportion of acid declines. ~t the beginning of the process the difference of potential between the iron oxides is at least 1000 mV. The base metal Fe then acts as anode, meaning that the iron oxides from FeO~ Fe2+. The surface of the metal is therefore pitted when it is exposed by fractures and pores in the oxide coating. It is normal to use an inhibitor or restrainer in the pickling bath to reduce the pitting damage on the base metal.
The present invention provides a method for pickling objects of iron and steel, whlch enables a continuous regenerating of the pickling solution, at a high level of electrolytic efficiency, wherein the pickling can be performed in a closed process having as residual products pickled ob;ects of
- 3 -iron and steel and pure electrolytic iron corresponding to the amount of dissolved iron.
The method according to the present invention is characterized in that the objects are transported into a pickling solution having a temperature above 25C and con~aining ferrous chloride and a low proportion of free hydrochloride acid, and that said solution is continuously regenerated in a circulation system with electrolytic cells, which are connected to a source of direct-current, in order to deposite iron electrolytically and recover free acid.
Preferably, the pickling fluid contains at least 300 g FeC12 per liter and no more than 50 g of frPe acid reckoned as HCl per liter.
Preferably the electrolytic cells are electrically connected in series with the source of direct-current and in parallel with the flow of pickling solution in said circulatlon system.
Preferably, the proportion of ferrous chloride sinks no more than 10 g per liter solution during its passage through any of the electrolytic cells, and the current intensity at each of their respective cathode is especially between 0.2-10 A per dm2 of cathodic surface.
A solution for pickling ob~ects of iron or steel, before a subsequent surface treatment or mechanical processing, comprising: FeC12, Fe2 and HCl, preferably contains the following proportions: FeC12 between 250 and 450 g/l, Fe2 between 110 and 200 g/l and HCl between 5 and 50 g/l.
Since the pickling is carried through at a high proportion of lron and therefore at a low proportion of free acid and also at rised temperature, the oxides are dissolved ~\
~:~5;635~
efficiently, without any pitting of the base metal. This very favourabl2 pickling effect, in spite of the high proportion of iron in the solution, is a result of the ability of chloride to form large complexes. That is, a large proportion of the iron in the pickliny solution is bound in anion form as:
~FeC14 ) ~
This complex ion is in balance with other ions in the solution tanks to the rised temperature, which results in an increased proportion of free hydrogen ions.
Since the ionization energy is comparatively low in a solution of ferrous chloride with a low proportion of free acid it is possible to electrolytically deposit the iron with a high electrolytic efficiency, and cathodically within a simple electrolytic cell, without any partitioning ion-exchanging membrane between anode and cathode.
The invention will now be described in further detail, with reference to the accompanylng drawing, which represents a schematic elevation of a pickling plant for using the method according to the invention with continuous regenerating of the pickling solution in a closed circuit.
The figure shows a pilot plant for pickling of cast iron and hot rolled objects before hot zinc coating. A tank containing pickling solution is generally denoted 10. Ob~ects represented by the arrow 11 are transported down into the solution after a preliminary degreasing and rinsing. Pickled obejcts are represented by the arrow 12.
The pickling solution is continuously pumped, by means of a pump 13 r from the tank 10, into five electrolytic cells 14, connected in parallel with the flow ~rom the pump 13, and returns to the tank 10 by means of a return pump 15. The electrolytic cells are electrically connected in series to the positlve and . , .
~2563~
negative terminals 16 and 17, respectively, of a direct-current source. Each electrolytic cell 14 conventionally comprises one anode 18 and one cathode 19.
These conditions prevail:
In the Picklinq solution Volume: 10 m3 Flow of objects: 2 tons/h Dissolved iron: 10 kg/h Theoretical amount of acid used per hour ~ 15 kg HCl at 100 % ~50 kg acid at 30 %
Concentrations: FeC12 340 g/l Fe 150 g/l free Hcl 20 g/l Temperature: 40C
Among others, the following chemical reactions take place in the 20 solution: FeO~ Fe2+, Fe3+ . ~Fe2 In the reqeneratinq section Dimensions: 1500xlOOOx1200 mm Electrode system: 5 cells with blpolar electrodes anode: graphite cathode: stainless, acid resistant Voltage drop per cell: 2.5 V
Current density: 2 A/dm2 Static current changer 16 V, 1000 A
Amperage per cell: 900 A
Total quantity of current: 4500 Ah Theorectical amount of dissolved Fe: 4680 g Real amount of dissolved Fe: 4300 g Estimated electrolytic efficiency: 91 %
Amount of recovered acid: 22 kg at 30 ~56:357 The following reactions take place in the electrolytic cells:
Cathode: Fe2~ ~ FeO, Anode: Fe2+--~3 Fe3+
The cathode plates 19 are made of 0.1 mm thin stainless, acid resistant sheet. The cathodes are changed regularily in the cells 14. By bending the sheets, the electrolytic iron can be removed from said sheets.
The pickling solution circulates through the cell lo system during the electrolysis at a rate of about 30 liter per minute. This implies that the difference in concentration of iron in the solution leaving vs. entering the tank is between 2.0-2.5 g/l. In the present cass, when the dissolving rate or iron the pickling solution is 10 kg/h, 40% of the acid is recovered.
In order to get a full recovery of acid, a cell system with a total current of 10000 A is therefore required. This means that the static current changer must be rated at, e.g. 16 v and 200 A or 24 V and 1000 - 1500 A. The latter alternative i5 preferable, since the cost of a static current exchanger malnly depends on current capacity and not on output or voltage.
The above described method radically alters the properties of the pickling solution. The iron oxides Fe304 becomes the dissolving electrode and the base metal is not attacked by pitting. The sludge or iron oxides is completely dissolved leavlng no remains at the bottom of the tank. At the same time the ob~ects are cleaned with no trace of dirt film.
The surrounding pickling solution is strongly reducing at the conditions according to the invention.
The very high electrolytic efficiency during the process according to the invention results from the relation between the overpotential of the hydrogen towards the cathode and the dissolving potential of the iron. The overpotential of i63X~
hydrogen is preferably as high as possible, since the electrolytic efficiency declines with a rising proportlon of free acid in the solution.
The regenerating cells can be built as a modular system, which can be adpated to most existing pickling plants, while changing from a conventional process to the pickling process according to the invention.
0 The above mentioned dimensions, rates and values can obviously be varied within the scope of the following claims.
The method according to the invention can be used in combination with conventional pickling methods. An actiyator can be added to the above described pickling solution, comprising a surface active agent with a high affinity to the base me-tal surface, to facilitate the penetration of the pickling fluid beneath the scales. Further, the electrolytic current between terminals 16, 17 can be pulsed at low frequency, givlng a lower electrolytic polarization and therefore a higher electrolytic efficiency.
The pickling effect of the solution according to the invention can be even more improved by addition of any of the salts: magnesium chloride, calcium chloride or aluminium chloride. This increases the overpotential at any given proportion of free acid and therefore the electrolytic efficiency. An additive of 50 g/l MgC12 reduces tensile stress at the iron deposited at the cathode, so that a ductile film of iron is formed. The iron can be plated to form any desired thickness. The growth of about 1 m/min. at a current density of 5 A/dm2 and 90% electrolytic eEficiency. This addition of magnesium chloride also improves the pickling process.
The method according to the present invention is characterized in that the objects are transported into a pickling solution having a temperature above 25C and con~aining ferrous chloride and a low proportion of free hydrochloride acid, and that said solution is continuously regenerated in a circulation system with electrolytic cells, which are connected to a source of direct-current, in order to deposite iron electrolytically and recover free acid.
Preferably, the pickling fluid contains at least 300 g FeC12 per liter and no more than 50 g of frPe acid reckoned as HCl per liter.
Preferably the electrolytic cells are electrically connected in series with the source of direct-current and in parallel with the flow of pickling solution in said circulatlon system.
Preferably, the proportion of ferrous chloride sinks no more than 10 g per liter solution during its passage through any of the electrolytic cells, and the current intensity at each of their respective cathode is especially between 0.2-10 A per dm2 of cathodic surface.
A solution for pickling ob~ects of iron or steel, before a subsequent surface treatment or mechanical processing, comprising: FeC12, Fe2 and HCl, preferably contains the following proportions: FeC12 between 250 and 450 g/l, Fe2 between 110 and 200 g/l and HCl between 5 and 50 g/l.
Since the pickling is carried through at a high proportion of lron and therefore at a low proportion of free acid and also at rised temperature, the oxides are dissolved ~\
~:~5;635~
efficiently, without any pitting of the base metal. This very favourabl2 pickling effect, in spite of the high proportion of iron in the solution, is a result of the ability of chloride to form large complexes. That is, a large proportion of the iron in the pickliny solution is bound in anion form as:
~FeC14 ) ~
This complex ion is in balance with other ions in the solution tanks to the rised temperature, which results in an increased proportion of free hydrogen ions.
Since the ionization energy is comparatively low in a solution of ferrous chloride with a low proportion of free acid it is possible to electrolytically deposit the iron with a high electrolytic efficiency, and cathodically within a simple electrolytic cell, without any partitioning ion-exchanging membrane between anode and cathode.
The invention will now be described in further detail, with reference to the accompanylng drawing, which represents a schematic elevation of a pickling plant for using the method according to the invention with continuous regenerating of the pickling solution in a closed circuit.
The figure shows a pilot plant for pickling of cast iron and hot rolled objects before hot zinc coating. A tank containing pickling solution is generally denoted 10. Ob~ects represented by the arrow 11 are transported down into the solution after a preliminary degreasing and rinsing. Pickled obejcts are represented by the arrow 12.
The pickling solution is continuously pumped, by means of a pump 13 r from the tank 10, into five electrolytic cells 14, connected in parallel with the flow ~rom the pump 13, and returns to the tank 10 by means of a return pump 15. The electrolytic cells are electrically connected in series to the positlve and . , .
~2563~
negative terminals 16 and 17, respectively, of a direct-current source. Each electrolytic cell 14 conventionally comprises one anode 18 and one cathode 19.
These conditions prevail:
In the Picklinq solution Volume: 10 m3 Flow of objects: 2 tons/h Dissolved iron: 10 kg/h Theoretical amount of acid used per hour ~ 15 kg HCl at 100 % ~50 kg acid at 30 %
Concentrations: FeC12 340 g/l Fe 150 g/l free Hcl 20 g/l Temperature: 40C
Among others, the following chemical reactions take place in the 20 solution: FeO~ Fe2+, Fe3+ . ~Fe2 In the reqeneratinq section Dimensions: 1500xlOOOx1200 mm Electrode system: 5 cells with blpolar electrodes anode: graphite cathode: stainless, acid resistant Voltage drop per cell: 2.5 V
Current density: 2 A/dm2 Static current changer 16 V, 1000 A
Amperage per cell: 900 A
Total quantity of current: 4500 Ah Theorectical amount of dissolved Fe: 4680 g Real amount of dissolved Fe: 4300 g Estimated electrolytic efficiency: 91 %
Amount of recovered acid: 22 kg at 30 ~56:357 The following reactions take place in the electrolytic cells:
Cathode: Fe2~ ~ FeO, Anode: Fe2+--~3 Fe3+
The cathode plates 19 are made of 0.1 mm thin stainless, acid resistant sheet. The cathodes are changed regularily in the cells 14. By bending the sheets, the electrolytic iron can be removed from said sheets.
The pickling solution circulates through the cell lo system during the electrolysis at a rate of about 30 liter per minute. This implies that the difference in concentration of iron in the solution leaving vs. entering the tank is between 2.0-2.5 g/l. In the present cass, when the dissolving rate or iron the pickling solution is 10 kg/h, 40% of the acid is recovered.
In order to get a full recovery of acid, a cell system with a total current of 10000 A is therefore required. This means that the static current changer must be rated at, e.g. 16 v and 200 A or 24 V and 1000 - 1500 A. The latter alternative i5 preferable, since the cost of a static current exchanger malnly depends on current capacity and not on output or voltage.
The above described method radically alters the properties of the pickling solution. The iron oxides Fe304 becomes the dissolving electrode and the base metal is not attacked by pitting. The sludge or iron oxides is completely dissolved leavlng no remains at the bottom of the tank. At the same time the ob~ects are cleaned with no trace of dirt film.
The surrounding pickling solution is strongly reducing at the conditions according to the invention.
The very high electrolytic efficiency during the process according to the invention results from the relation between the overpotential of the hydrogen towards the cathode and the dissolving potential of the iron. The overpotential of i63X~
hydrogen is preferably as high as possible, since the electrolytic efficiency declines with a rising proportlon of free acid in the solution.
The regenerating cells can be built as a modular system, which can be adpated to most existing pickling plants, while changing from a conventional process to the pickling process according to the invention.
0 The above mentioned dimensions, rates and values can obviously be varied within the scope of the following claims.
The method according to the invention can be used in combination with conventional pickling methods. An actiyator can be added to the above described pickling solution, comprising a surface active agent with a high affinity to the base me-tal surface, to facilitate the penetration of the pickling fluid beneath the scales. Further, the electrolytic current between terminals 16, 17 can be pulsed at low frequency, givlng a lower electrolytic polarization and therefore a higher electrolytic efficiency.
The pickling effect of the solution according to the invention can be even more improved by addition of any of the salts: magnesium chloride, calcium chloride or aluminium chloride. This increases the overpotential at any given proportion of free acid and therefore the electrolytic efficiency. An additive of 50 g/l MgC12 reduces tensile stress at the iron deposited at the cathode, so that a ductile film of iron is formed. The iron can be plated to form any desired thickness. The growth of about 1 m/min. at a current density of 5 A/dm2 and 90% electrolytic eEficiency. This addition of magnesium chloride also improves the pickling process.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for pickling iron or steel objects before a subsequent surface treatment or a mechanical processing, in which objects are transported into a pickling solution having a temperature above 25°C and containing ferrous chloride and a low proportion of free hydrochloric acid, and said solution is continuously regenerated in a circulation system with cells, which are connected to a source of direct-current, in order to deposite iron electrolytically and recover free acid.
2. A method according to claim 1, in which the pickling solution contains at least 300 g ferrous chloride per liter.
3. A method according to claim 1, in which the pickling solution contains no more than 50 g free acide, calucalated as HCl, per liter.
4. A method according to claim 1,2 or 3, in which the electrolytic cells are electrically connected in series with the source of direct-current.
5. A method according to claim 1,2 or 3, in which the electrolytic cells are connected in parallel with the flow of pickling solution in said circulation system.
6. A method according to claim 1,2 or 3, in which the proportion of ferrous chloride is reduced no more than 10 g per liter solution, during its passage through any of the electroylic cells.
7. A method according to claim 1,2 or 3, in which the amperage at each cathode in the electrolytic cells is between 0.2 - 10 per dm2 cathodic surface.
8. A solution for pickling of orion or steel objects before a subsequent surface treatment or a mechanical processing, containing: FeCl2, Fe2 and HCl, in which the proportion of FeC2 in the solution is between 250 and 450 g/l, the proportion of Fe2 in the solution is between 110 and 240 g/litre and the proportion of free acid, HCl is between 5 and 50 g/l.
9. A solution according to claim 8, in which contains a magnesium or calcium chloride, in order to improve the pickling process, increase the electroyltic efficiency and reduce the tensile stress at the iron deposited on the cathode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8501329.0 | 1985-03-19 | ||
| SE8501329A SE452481B (en) | 1985-03-19 | 1985-03-19 | METHOD OF REGULATING BEDBATH AND REGENABLE SOLUTION FOR BETTING IRON AND STEEL FORM |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1256357A true CA1256357A (en) | 1989-06-27 |
Family
ID=20359547
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000504493A Expired CA1256357A (en) | 1985-03-19 | 1986-03-19 | Method of pickling iron or steel objects |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0244417B1 (en) |
| JP (1) | JPS62502268A (en) |
| CA (1) | CA1256357A (en) |
| DE (1) | DE3671042D1 (en) |
| SE (1) | SE452481B (en) |
| WO (1) | WO1986005523A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0762575A (en) * | 1993-08-27 | 1995-03-07 | Unitika Ltd | Purifying equipment and purifying method for bath liquid |
| NL9302035A (en) * | 1993-11-24 | 1995-06-16 | Piet De Vries | Pickling method and a device therefor. |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE637287C (en) * | 1935-01-20 | 1936-10-24 | Georg Agde Dr | Process for refreshing pickling solutions containing trivalent iron salts |
| US2423385A (en) * | 1944-07-27 | 1947-07-01 | Chemical Foundation Inc | Process of pickling and of recovering pickling agent |
| US4113588A (en) * | 1976-03-09 | 1978-09-12 | Solex Research Corporation Of Japan | Process for recovery of waste H2 SO4 and HCl |
| ATE7050T1 (en) * | 1980-01-18 | 1984-04-15 | Boliden Aktiebolag | METHOD OF REGENERATION OF PICKLING SOLUTIONS. |
| CS218296B1 (en) * | 1980-10-30 | 1983-02-25 | Antonin Stehlik | Method of continuous regeneration of the iron trichloride solution |
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1985
- 1985-03-19 SE SE8501329A patent/SE452481B/en not_active IP Right Cessation
-
1986
- 1986-03-17 WO PCT/SE1986/000116 patent/WO1986005523A1/en active IP Right Grant
- 1986-03-17 JP JP50188686A patent/JPS62502268A/en active Pending
- 1986-03-17 EP EP19860902076 patent/EP0244417B1/en not_active Expired
- 1986-03-17 DE DE8686902076T patent/DE3671042D1/en not_active Expired - Fee Related
- 1986-03-19 CA CA000504493A patent/CA1256357A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SE452481B (en) | 1987-11-30 |
| SE8501329D0 (en) | 1985-03-19 |
| WO1986005523A1 (en) | 1986-09-25 |
| EP0244417A1 (en) | 1987-11-11 |
| JPS62502268A (en) | 1987-09-03 |
| EP0244417B1 (en) | 1990-05-09 |
| DE3671042D1 (en) | 1990-06-13 |
| SE8501329L (en) | 1986-09-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |