Method for removing ferric ions from sulfate-based iron electroplating solutions

Abstract

The present invention relates to a method for effectively removing ferric ions contained in an iron electroplating solution, the method comprising a regeneration step of circulating a sulfate-based iron electroplating solution containing ferric ions through a solution tank charged with metallic iron to reduce the ferric ions, the metallic iron being charged in an amount that satisfies the following formula (1): S≧0.01 I conv / C max (1) In equation (1), S is the total surface area of ​​metallic iron (m 2 ) and C max is the maximum allowable concentration of ferric ions in the solution (g / L), and I conv is the plating time (t p The total current (I) applied to the electroplating cell during the regeneration time (t r , sec) and is expressed by the following formula (2). [0010] TIFF2024509312000010.tif30155

Description

[Technical Field]

[0001] The present invention relates to a method for effectively removing ferric ions contained in iron electroplating solutions. [Background technology]

[0002] Iron is manufactured as steel plate or steel material and is used as a general-purpose structural material. However, because it lacks corrosion resistance and appearance characteristics compared to other metals, its surface has been electroplated to utilize its magnetic properties or to form alloys for special purposes.

[0003] A typical plating solution for iron electroplating on iron surfaces uses ferrous ions to maintain high electroplating efficiency, but there are problems with this, such as the rapid decline in plating efficiency and the generation of sludge as the ferrous ions are oxidized to ferric ions during the continuous electroplating process.

[0004] To solve this problem, conventional methods include reducing ferric ions to ferrous ions or periodically replacing the solution. However, in large-scale continuous electroplating processes, periodically removing and replacing the solution is difficult, which increases production costs.

[0005] Another method to reduce the amount of ferric iron produced is to use a soluble anode. However, when electroplating is performed under high current density conditions exceeding 10 ASD (Amperes per Square Decimal), the overvoltage increases, making it impossible to fundamentally prevent the oxidation of ferrous ions to ferric ions. Furthermore, the dissolution efficiency of the soluble anode is higher than the plating efficiency, resulting in a continuous increase in the concentration of iron ions in the solution. Furthermore, as the soluble anode gradually dissolves and wears out as plating progresses, the electrode distance and electrode surface condition change, making it necessary to periodically replace the soluble anode, making management extremely difficult.

[0006] On the other hand, the generation of ferric ions is inevitable in sulfate-based iron electroplating solutions that use insoluble anodes. Therefore, the ferric ions are usually removed from the plating solution by sludge filtration, or by adding a reducing agent or electrolysis to reduce the ferric ions to ferrous ions.

[0007] For example, Korean Patent Application No. 2011-0137463 discloses a method of reducing ferric ions to ferrous iron by adding ascorbic acid as a reducing agent to a sulfate-based iron electroplating solution. However, when ferric ions are reduced, ascorbic acid is oxidized to produce dihydroascorbic acid, which causes a rapid decrease in iron electroplating efficiency and persistent accumulation of dihydroascorbic acid.

[0008] Other examples include Korean Patent Application No. 2015-0185858 and Japanese Patent Application Nos. 1994-181533 and 1988-259089, which disclose methods for reducing ferric ions to ferrous ions by applying a constant current to an anode and a cathode in an electrolyte. However, when electricity is applied to an electrolyte containing both ferrous and ferric ions, the oxidation of ferrous ions to ferric ions and a small amount of water decomposition reaction occur at the anode, whereas the reaction of electroplating iron occurs primarily at the cathode, with only a limited reduction of ferric ions to ferrous ions occurring, resulting in the accumulation of ferric ions. While these methods can increase the rate of ferric ion reduction at the cathode by using an additive that inhibits iron electroplating in an electrolyte, they are unable to remove ferric ions from an iron electroplating solution, which requires high plating efficiency. Summary of the Invention [Problem to be solved by the invention]

[0009] One embodiment of the present invention provides a method for effectively removing ferric ions, which are generated during long-term continuous plating using an iron electroplating solution, by reducing the ferric ions to ferrous ions and thereby effectively removing the ferric ions, thereby suppressing the generation of sludge due to the oxidation of iron ions, maintaining constant plating efficiency, and eliminating the need for frequent solution changes. [Means for solving the problem]

[0010] The present invention provides a method for removing ferric ions from a sulfate-based iron electroplating solution, which includes a regeneration step of circulating a sulfate-based iron electroplating solution containing ferric ions through a solution tank charged with metallic iron to reduce the ferric ions, wherein the metallic iron is charged in an amount that satisfies the following formula (1): S ≥ 0.01 × I conv / C max (1)

[0011] In equation (1), S is the total surface area of ​​metallic iron (m 2 ) and C max is the maximum allowable concentration of ferric ions in the solution (g / L), and I conv is the plating time (t p The total amount of current (I) applied to the electroplating cell during the regeneration period (t sec) is used to regenerate the electrolyte, i.e., the regeneration time (t r , sec) and is expressed by the following formula (2).

[0012]

number

[0013] The regeneration step can be carried out while the plating process is running.

[0014] The regeneration step is carried out during the plating process, and the regeneration step can be carried out two or more times discontinuously.

[0015] The regeneration step begins while the plating process is in progress and ends during a rest period of the plating process, and the regeneration step can be carried out continuously or discontinuously.

[0016] The regeneration step can begin during a rest period of the plating process and end during or after the plating process.

[0017] The regeneration step is carried out during a rest period of the plating process, and the regeneration step can be carried out continuously or discontinuously.

[0018] The regeneration step is carried out discontinuously, including a rest period between plating steps, and can be carried out between two or more plating steps.

[0019] The metallic iron may be an alloy iron containing at least one alloy element selected from the group consisting of Mn, Al, Mg, Li, Na, and K.

[0020] The ferroalloy may be a ferroalloy containing alloying elements in a content of more than 0% by weight and not more than 3% by weight.

[0021] The metallic iron particles may be at least one of particles, spiral chips, plates, and strips.

[0022] The sulfate-based iron electroplating solution may further include a complexing agent.

[0023] The complexing agent may be at least one compound selected from the group consisting of at least one amino acid selected from glycine, glutamic acid, and glutamine, formic acid, acetic acid, lactic acid, gluconic acid, oxalic acid, citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediamine-N,N,N',N'-tetraacetic acid).

[0024] The sulfate-based iron electroplating solution may have a temperature of 80° C. or less and a pH of 1.0 to 4.0.

[0025] The above method can be performed using an iron-based electroplating apparatus that includes an electroplating cell in which electroplating is performed by applying an electric current; a circulation tank in which the electroplating cell and the electroplating solution are circulated; and a dissolution tank in which the circulation tank and the electroplating solution are circulated, in which the metallic iron is charged, and in which the metallic iron is dissolved to remove ferric ions from the electroplating solution, the apparatus being equipped with a pump that supplies the electroplating solution from the circulation tank to the dissolution tank and a filter that prevents the metallic iron from the dissolution tank from flowing into the circulation tank. [Effects of the Invention]

[0026] According to the method of the present invention, the ferric ions that continuously accumulate during continuous electroplating can be effectively removed, thereby preventing a decrease in electroplating efficiency and preventing sludge due to the accumulation of ferric ions.

[0027] In addition, since ferric ions are reduced to ferrous ions and metallic iron dissolves to supply ferrous ions, the ferrous ion concentration in the iron electroplating solution can be maintained constant.

[0028] Furthermore, since there is no need to periodically replace the solution for solution management, the amount of solution wastewater can be reduced, which is environmentally friendly and allows for a significant reduction in production costs. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram showing the time relationship between plating and electrolyte regeneration, and is a diagram showing the continuous regeneration of electrolyte during a continuous plating process. [Figure 2] FIG. 1 is a diagram showing a schematic representation of the temporal relationship between plating and electrolyte regeneration, illustrating an example of discontinuous electrolyte regeneration during a continuous plating process. [Figure 3] FIG. 1 is a diagram showing a schematic diagram of the temporal relationship between plating and regeneration of the electrolyte, showing an example in which the regeneration of the electrolyte is started during the execution of the plating process and the regeneration process of the electrolyte is ended during a rest period of the plating process. [Figure 4] FIG. 1 is a diagram showing a schematic diagram of the temporal relationship between plating and regeneration of the electrolyte, in which regeneration of the electrolyte is started before application of a current for plating and is completed during a rest period after the plating process is completed. [Figure 5] FIG. 1 is a diagram showing a schematic diagram of the time relationship between plating and regeneration of an electrolyte, and is a diagram showing a schematic diagram of an example in which an electrolyte regeneration process is performed during a rest period between plating processes. [Figure 6] FIG. 1 is a diagram showing a schematic representation of the temporal relationship between plating and electrolyte regeneration, illustrating an example of continuous electrolyte regeneration with at least two plating steps and a rest period between plating steps. [Figure 7] 1 shows a schematic diagram of an apparatus according to the method of the present invention; [Figure 8] 1 shows photographs of the initial solution according to Example 1, and the solutions obtained 1 hour, 2 hours, and 3 hours after adding and dissolving pure iron into the initial solution. DETAILED DESCRIPTION OF THE INVENTION

[0030] One embodiment of the present invention provides a method for reducing the concentration of ferric ions accumulated in a sulfate-based iron electroplating solution and supplying ferrous ions consumed during iron electroplating in an electroplating facility using an insoluble anode.

[0031] Since an increase in the concentration of ferric ions in an iron electroplating solution impairs electroplating quality, the present invention reduces the concentration of ferric ions produced during continuous plating operations in an electroplating facility using an insoluble anode by bringing the ferric ions into contact with metallic iron and reducing them.

[0032] When iron electroplating is performed using electroplating equipment that uses insoluble anodes, a sulfuric acid-based electrolyte is usually used, and when electroplating is performed using insoluble anode equipment, the following reaction occurs at the anode.

[0033] 2H2O → O2+4H + +4e - Fe 2+ → Fe 3+ +e -

[0034] That is, at the anode, the water splitting reaction and the oxidation of ferrous ions to ferric ions occur simultaneously. Because the potential at which the oxidation of ferrous ions occurs is lower than the potential at which the water splitting reaction occurs, low current operation reduces the voltage and increases the rate at which the oxidation of ferrous ions occurs. Furthermore, if a complexing agent is used to prevent sludge, the ferric ions remain in a more stable state in the electrolyte, further accelerating the oxidation of ferrous ions.

[0035] On the other hand, if a complexing agent is not used when performing iron electroplating in a sulfuric acid-based electroplating solution, high electroplating efficiency cannot be achieved, and when ferric ions accumulate, they easily turn into sludge, making the solution cloudy, which is difficult to remove by conventional filtration. Therefore, complexing agents are usually used to prevent the formation of sludge.

[0036] However, when ferrous ions in the plating solution are oxidized to ferric ions, the concentration of ferrous ions involved in the plating reaction at the cathode decreases, and the current is consumed when ferric ions are reduced to ferrous ions, resulting in a rapid decrease in electroplating efficiency. Therefore, to perform iron electroplating continuously, it is necessary to remove ferric ions from the solution.

[0037] The present inventors have devised a method for preventing a decrease in iron electroplating efficiency by re-reducing ferric ions generated during continuous plating in a sulfate-based iron electroplating solution.

[0038] In particular, the present invention aims to reduce and remove ferric ions that continuously accumulate in iron electroplating equipment using insoluble anodes, thereby suppressing the generation of sludge in the solution, and to maintain a constant iron ion concentration in the solution by supplying iron ions consumed during electroplating, thereby maintaining high electroplating efficiency even when performing continuous plating.

[0039] Furthermore, the present invention can maintain a constant pH of the electroplating solution while reducing the concentration of ferric ions in the electroplating solution, thereby maintaining constant plating efficiency, making it easy to manage the iron electroplating solution and allowing it to be used continuously for a long period of time.

[0040] On the other hand, if a reducing agent is added instead of metallic iron to reduce ferric ions to ferrous ions in order to prevent the accumulation of ferric ions in the electrolyte, the oxidized components of the reducing agent will continuously increase and remain in the electrolyte. However, the accumulation of components unnecessary for electroplating reduces plating efficiency and affects plating quality.

[0041] In order to solve the above problems, the present inventors have devised a method of using metallic iron, which is the main component of iron electroplating solutions, as a reducing agent.

[0042] After evaluating various reducing agents for the reduction of ferric ions in iron electroplating solutions, it was found that using metallic iron as a reducing agent effectively removes ferric ions while maintaining the solution homeostasis. Furthermore, the ferrous ions eluted from metallic iron replenish the iron ions consumed during the iron electroplating process, allowing the iron ion concentration in the electrolyte to be maintained at a constant level, dramatically reducing the amount of solution used.

[0043] When metallic iron and ferric ions come into contact with each other without voltage being applied, the ferric ions are reduced to ferrous ions, and the metallic iron is oxidized and dissolved into ferrous ions, resulting in a corrosion reaction. This reaction can be expressed as follows:

[0044] 2Fe 3+ +Fe → 3Fe 2+

[0045] The present invention preferably uses metallic iron as a reducing agent for removing ferric ions from an iron electroplating solution. When iron is used as a reducing agent, it reacts with and dissolves hydrogen ions or ferric ions in the solution, thereby reducing the ferric ions in the solution to ferrous ions and further supplying ferrous ions.

[0046] The metallic iron used as the reducing agent may be pure iron or an ferroalloy. The alloying element of the ferroalloy may be an element that is more oxidizable than iron and does not easily deposit by electroplating, such as at least one selected from the group consisting of Mn, Al, Mg, Li, Na, and K. When such an ferroalloy is used, the rate of dissolution can be further increased by reacting with hydrogen ions or ferric ions in the solution. More preferably, the alloying element may be at least one selected from the group consisting of Mn and Al.

[0047] In the present invention, the metallic iron used as the reducing agent preferably has an alloying element content of 3 wt. % or less. When an ferroalloy containing more than 3 wt. % of the alloying elements is used, even if there are almost no ferric ions in the solution, the highly oxidizing alloying elements react with oxygen from the atmosphere and hydrogen ions in the solution to continuously dissolve, causing the pH of the plating solution to excessively increase. Furthermore, if such an ferroalloy is used as a reducing agent for a long period of time, the ion concentration of the alloying elements in the solution increases and is mixed into the iron electroplating layer during the electroplating process, preventing the desired pure iron electroplating layer from being obtained.

[0048] The metallic iron used as a reducing agent in the present invention may be pure iron or a ferroalloy, and its shape is not limited. It may be in the form of particles such as spheres, spiral chips, plates, or strips. When the metallic iron is in the form of plates or strips, it can be introduced into the dissolving tank by cutting or other methods to an appropriate size, thereby preventing problems such as the metallic iron stacking on top of each other, slowing down the flow of the solution, or reducing the actual contact area with the solution. Furthermore, by-products generated during the manufacturing process of steel sheets, etc., can be used as the reducing agent, thereby reducing manufacturing costs, which is more preferable. Furthermore, using metallic iron in the form of particles as the reducing agent is preferable because it has a high filling rate, increases the contact area with the solution, and thereby prevents the volume of the dissolving tank from becoming excessively large.

[0049] The size of the metallic iron used as the reducing agent is not particularly limited and can be appropriately selected taking into consideration the plating equipment, reduction efficiency, etc. For example, plate- or strip-shaped metallic iron having a thickness of 0.1 to 5 mm can be used, and the area of ​​the plate or strip is not particularly limited as long as it is arranged in an arrangement that does not obstruct the flow of the solution, such as by cutting it to an appropriate size or stacking the plates or strips at equal intervals.

[0050] When used in particulate form, particles having an average diameter of 0.1 mm to 10 mm, for example, 0.5 mm, 0.7 mm, 1 mm or more and 5 mm, 7 mm or less, or 10 mm or less, can be used.

[0051] The smaller the size of the metallic iron used, the greater the contact area between the metallic iron and the solution, making it more effective at reducing ferric ions. However, excessively small metallic iron particles can actually hinder the flow of the solution, and if added in excess, they can react with hydrogen ions in the solution even in the absence of ferric ions, causing an excessive increase in pH and causing iron particles to enter the electroplating cell and damage the plating surface. On the other hand, if the size of the metallic iron is excessively large, the reaction area decreases, making it difficult to effectively remove ferric ions, and a large amount of metallic iron must be added. Therefore, it is preferable to select metallic iron having an appropriate size within the above range depending on the capacity and plating speed of the iron electroplating equipment.

[0052] Ferrous ions in electroplating solutions are reduced to metallic iron below -0.44 V versus the standard hydrogen electrode, and oxidized to ferric ions above 0.77 V. Meanwhile, water is electrolyzed above 1.23 V, generating oxygen gas. Therefore, when iron electroplating is performed using electroplating equipment equipped with an insoluble anode, the anode undergoes a ferrous oxidation reaction in which ferrous ions are oxidized to ferric ions, and a water splitting reaction in which water is split. At the cathode, ferrous ions are reduced to metallic iron and plated, and some of the ferric ions are reduced to ferrous ions.

[0053] The rate of reaction occurrence in the above electrode reactions may vary slightly depending on the current density, electrode, and solution characteristics. However, when iron electroplating is performed using electroplating equipment equipped with an insoluble anode, the rate of iron electroplating at the cathode is higher than the rate of ferric reduction reaction, and ferrous oxidation and water decomposition reactions occur at the anode. Therefore, when electroplating is performed by applying a current, the concentration of ferric ions in the solution inevitably increases continuously.

[0054] The rate at which ferric ions are produced in an iron electroplating solution increases in proportion to the amount of current applied for iron electroplating or the plating rate. Therefore, it is preferable to control the rate at which ferric ions are produced by electroplating so that it does not exceed the rate at which ferric ions are removed by metallic iron, thereby preventing a continuous increase in ferric ions.

[0055] Through numerous experiments, the inventors have confirmed that the continuous accumulation and increase of ferric ions can be prevented by using metallic iron as a reducing agent in an appropriate amount according to the electroplating speed. That is, by sufficiently increasing the contact area between metallic iron and the solution, the reaction rate of ferric ions being reduced to ferrous ions increases, thereby suppressing the increase of ferric ions.

[0056] When a current is applied for iron plating, ferric ions are generated in proportion to the current. The rate of ferric ion generation is a·I conv where a is the rate constant for the formation of ferric ions and I conv is the converted current per unit time, and the converted current I conv is the plating time (t p The total amount of current (I) applied during the regeneration of the electrolyte, i.e., the regeneration time (t r , sec) and can be expressed as follows, with the unit being A:

[0057]

number

[0058] At this time, the time during which the current (I) is applied in the plating process (current application time, i.e., plating time t p ) and regenerating time (t r) may be the same or different. That is, the plating process and the regeneration process may be carried out in various forms. For example, they may be in the form of continuous plating and continuous regeneration, continuous plating and discontinuous regeneration, discontinuous plating and continuous regeneration, discontinuous plating and discontinuous regeneration, etc. The plating process and the regeneration process may be carried out in various forms, some examples of which will be described in more detail with reference to FIGS. 1 to 6.

[0059] FIG. 1 shows an embodiment of continuous plating and continuous regeneration, in which regeneration for the reduction of ferric ions is continuously performed while applying a current (I) to perform the plating process. In this case, the regeneration process can be performed during the plating process. In this case, the current application time (t p ) and playback time (t r ) are the same, and in this case, the reduced current I conv is equal to the average current applied to the plating cell per unit time.

[0060] FIG. 2 shows an embodiment of continuous plating and discontinuous regeneration, in which a current (I) is applied to continuously perform the plating process, and if the concentration of ferrous ions in the electrolyte exceeds the allowable value, a regeneration process is performed intermittently. In this case, the current application time (t p ) and playback time (t r =tr1+t r2 ) are different. FIG. 2 shows an example in which regeneration is performed twice, but it can be performed three or more times if necessary.

[0061] FIG. 3 shows an embodiment of discontinuous plating and continuous regeneration. In the plating process, a current (I) is applied to the electrolytic solution, and the regeneration process is initiated when the concentration of ferrous ions in the electrolytic solution exceeds a permissible value. The regeneration process is continued for a certain period of time during the rest period of the plating process, and then terminated. In this case, the current application time (t p ) and playback time (t r) may be the same or different. Although Fig. 3 shows a case where one regeneration step is performed continuously, a person skilled in the art can easily understand that the embodiment of Fig. 2 can be combined and performed intermittently.

[0062] FIG. 4 shows another embodiment relating to discontinuous plating and continuous regeneration, in which the regeneration process is started before applying current (I) to perform the plating process, i.e., during the rest period of the plating process when current (I) is not applied, and is maintained during the plating process. The regeneration process is continued for a certain period of time until the rest period after the plating process is completed, and then terminated. This embodiment is suitable for use when using an electrolyte used in a previous plating process. In this case, the current application time (t p ) and playback time (t r 4 shows that one regeneration step is performed continuously, but a person skilled in the art can easily understand that the embodiment of FIG. 2 can be combined to perform the regeneration step intermittently. In this case, the current application time (t p ) and playback time (t r ) may be identical.

[0063] FIG. 5 shows yet another embodiment of discontinuous plating and continuous regeneration, in which the regeneration step is carried out during the rest period of the plating step when no current (I) is applied. In this case, the current application time (t p ) and playback time (t r ) may be the same or different. Although FIG. 5 shows that one regeneration step is performed continuously, it is also possible to perform the regeneration step intermittently by combining the embodiment of FIG. 2, and the regeneration step may continue during the rest period or may be performed for a part of the rest period. In this case, the current application time (t p ) and playback time (t r ) may be the same or different.

[0064] FIG. 6 shows yet another embodiment of discontinuous plating and continuous regeneration, in which the plating process is discontinuously performed in the order of plating, resting period, and plating, and the regeneration process is continuously performed during the plating and resting periods. In this case, the current application time (t p ) and playback time (t r ) may be different. Although FIG. 6 shows a continuous regeneration step, the embodiment of FIG. 2 may be combined to perform the regeneration step intermittently, and the regeneration step may start or end during the plating step. In this case, the current application time (t p ) and playback time (t r ) may be identical.

[0065] On the other hand, the concentration of ferric ions in the iron electroplating solution is C (g / L), and the total surface area of ​​metallic iron added as a reducing agent is S (m 2 ), the ferric ions are reduced by the reducing agent, and the concentration of ferric ions decreases. The rate at which the ferric ions decrease can be expressed as bCS (b = reaction rate constant between ferric ions and metallic iron).

[0066] If the concentration of ferric ions is to be maintained constant during continuous plating, the following relationship holds:

[0067] a·I conv = b C S S=(a / b)·I avg / C

[0068] When such a relationship exists, the above C indicates the equilibrium concentration.

[0069] Meanwhile, a / b is a value that can be determined experimentally. As a result of measurements by the present inventors, even if the solution changes, a has a nearly constant value regardless of the solution and electrode, and b tends to increase as the content of alloying elements such as Mn and Al in metallic iron added as a reducing agent increases, and it was confirmed that a / b is 0.01 in the case of pure iron.

[0070] When ferric ions are produced by an electrode reaction, the ferrous ions in the solution are directly oxidized, and other additive components are not involved in the reaction, so a remains almost constant. However, when ferric ions react with metallic iron and are reduced, the reaction rate varies greatly depending on the composition of the metallic iron. Therefore, it is believed that the higher the content of alloying elements that are highly reactive with metallic iron, the greater the increase in b.

[0071] From the above relationship, the current I conv Applying a voltage to the solution, the maximum allowable concentration of ferric ions in the solution is set to C max When the above formula is satisfied, it is preferable that the metallic iron is added so that the total surface area S of the metallic iron satisfies the following formula:

[0072] S ≥ 0.01 × I conv / C max

[0073] When metallic iron containing alloying elements is used as a reducing agent, the reaction rate constant b increases and a / b decreases, even if the surface area of ​​the metallic iron (reducing agent) is smaller than when pure iron is used as a reducing agent under the same conditions, because the ferroalloy has a faster reaction rate for reducing ferric ions to ferrous ions. Therefore, if the surface area (S) of the reducing agent satisfies the condition for the surface area of ​​metallic iron, it can provide the effect of reducing and removing ferric ions in the iron electroplating solution to ferrous ions, thereby achieving the intended purpose of controlling the allowable concentration of ferric ions below a critical value.

[0074] For example, in an operation pattern in which electroplating is performed by applying a current of 9000 A for 20 minutes, followed by a 40-minute rest period without applying current, if the concentration of ferric ions is to be maintained at 3 g / L or less, the converted current is 3000 A and the total surface area is 10 m 2 By adding metallic iron in an amount equal to or greater than this, the average concentration of ferric ions in the solution can be maintained at 3 g / L or less.

[0075] On the other hand, when a large amount of ferric ions is contained in a sulfate-based iron electroplating solution, the ferric ions form hydroxides, generating sludge. However, even when the generated ferric ion sludge comes into contact with metallic iron, no reduction reaction occurs with metallic iron, and therefore, the reducing power of metallic iron is not exhibited in a typical plating solution. Therefore, in order for the ferric ions to be reduced by a corrosion reaction with metallic iron, it is preferable to use a complexing agent to prevent the ferric ions from precipitating in the form of sludge.

[0076] The complexing agent that can be used in the present invention is not particularly limited, and any complexing agent commonly used in electroplating can be suitably used in the present invention. For example, a compound having a carboxyl group can be used. Specific examples include amino acids such as glycine, glutamic acid, and glutamine; acids containing one carboxyl group such as formic acid, acetic acid, lactic acid, and gluconic acid; and acids having two or more carboxyl groups such as oxalic acid, citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediamine-N,N,N',N'-tetraacetic acid).

[0077] A method for effectively removing ferric ions from a sulfate-based iron electroplating solution using metallic iron according to the present invention will now be described in detail.

[0078] 7, the method of the present invention includes an electroplating cell 1 to which iron electroplating is performed by applying a current, and a circulation tank 2 to which an electroplating solution is supplied to the electroplating cell 1 and from the electroplating cell 1. In other words, the electroplating solution circulates between the electroplating cell 1 and the circulation tank 2.

[0079] More specifically, ferrous ions are supplied to the circulation tank 2, and the electroplating solution containing these ferrous ions is supplied to the electroplating cell 1, thereby maintaining a constant concentration of ferrous ions in the electroplating solution in the electroplating cell 1. Furthermore, the electroplating solution in which the concentration of ferric ions has increased due to electroplating in the electroplating cell 1 is sent to the circulation tank 2.

[0080] Meanwhile, the electroplating solution containing ferric ions supplied from the electroplating cell 1 to the circulation tank 2 is circulated to the dissolution tank 3. Metallic iron is charged into the dissolution tank 3. The electroplating solution supplied to the dissolution tank 3 dissolves the metallic iron in the dissolution tank 3, and in this process, the ferric ions in the electroplating solution are reduced to ferrous ions by the metallic iron, thereby reducing the content of ferric ions in the electroplating solution.

[0081] When circulating the electroplating solution from the circulation tank 2 to the dissolution tank 3, the pump 4 can be driven as shown in FIG.

[0082] The electroplating solution in the dissolution tank 3 with a reduced content of ferric ions is supplied to the circulation tank 2 and then to the electroplating cell 1 .

[0083] When the electroplating solution in the dissolution tank is supplied to the circulation tank 2, it is preferable that the solution passes through a filtering means 5. The filtering means 5 is intended to prevent metallic iron particles and impurity particles charged in the dissolution tank 3 from flowing into the circulation tank 2 together with the electroplating solution. In particular, in a continuous electroplating process in which a strip passes between rolls, if metallic iron particles are present in the electroplating solution, they may get caught between the roll and the strip and poke the strip, thereby causing dent defects.

[0084] The filtering means 5 can be suitably applied to the present invention as long as it is a means for separating solids in a solution, and is not particularly limited, and examples thereof include a filter or a filtering net.

[0085] As described above, the present invention circulates a sulfate-based iron electroplating solution containing ferric ions through a solution tank containing metallic iron. This allows the ferric ions present in the iron electroplating solution to react with the metallic iron, reducing the ferric ions to ferrous ions, which then dissolve into the ferrous ions, thereby removing the ferric ions from the solution.

[0086] In this case, the sulfate-based iron electroplating solution to which the present invention is applied is not particularly limited as long as it is at a temperature of 80°C or less, as long as it does not cause freezing of the plating solution or changes in viscosity, and more preferably, the plating can be carried out at a temperature of 0°C or higher and 80°C or lower.

[0087] On the other hand, the pH of the electroplating solution does not have a significant effect on the reduction of ferric iron and is not particularly limited, but from the viewpoint of electroplating efficiency, the pH is preferably 1.0 to 4.0, and more preferably 2.0 to 3.0. [Example]

[0088] The present invention will be described in more detail below through examples.

[0089] [Reference Examples 1 and 2] Using ferrous sulfate as the ferrous source and ferric sulfate as the ferric source, sulfate-based iron electroplating solutions were prepared having the ferrous ion concentrations, ferric ion concentrations, and total ferrous and ferric ion concentrations (T-Fe) shown in Table 1 below.

[0090] The pH of the iron electroplating solution was adjusted using sulfuric acid and sodium hydroxide as shown in Table 1, and glutamine was added as a complexing agent at a concentration 0.5 times the molar concentration of the iron ions to prevent ferric ions from precipitating as sludge.

[0091] 1 dm 2 Ten pure iron metal plates each having an area of ​​0.7 mm and a thickness of 0.7 mm were immersed in the solution at regular intervals so as not to overlap each other, and after 3 hours, the concentration of ferric ions and the total iron concentration (total Fe, T-Fe), which is the sum of the concentrations of ferrous ions and ferric ions, in the iron electroplating solution were measured.

[0092] In addition, electroplating was carried out at a current density of 40 ASD using the solution immediately after preparation and the solution after removing ferric iron using a metal iron plate with a reducing agent, and the plating efficiency was measured.

[0093] The measurement results are shown in Table 1.

[0094] [Table 1]

[0095] As can be seen from Table 1 above, in Reference Examples 1 and 2, the iron electroplating solutions prepared to contain a large amount of ferric ions had plating efficiencies of 54% and 63%, respectively, and the lower the pH, the lower the plating efficiency.

[0096] [Examples 1 and 2] The initial solutions of Reference Examples 1 and 2 containing a large amount of ferric ions shown in Table 1 above were each added with 1 dm 2 A pure iron metal plate having an area of ​​1.5 mm and a thickness of 0.7 mm was introduced into the solution, and ferric iron was reduced and removed for 3 hours to obtain a reduced iron electroplating solution. Example 1 is an example in which the initial solution of Reference Example 1 was used, and Example 2 is an example in which the initial solution of Reference Example 2 was used.

[0097] The iron electroplating solutions obtained above were each measured for ferric ion concentration and T-Fe concentration, which is the sum of the ferrous ion concentration and the ferric ion concentration. The results are shown in Table 2.

[0098] Furthermore, the pH of the iron electroplating solution was adjusted using sulfuric acid and sodium hydroxide as shown in Table 2, and amino acids or citric acid were added to the solution at a concentration 0.5 times the molar concentration of the iron ions to prevent ferric ions from precipitating as sludge.

[0099] The resulting solution was electroplated at a current density of 40 ASD immediately after preparation and after removing ferric iron using a reducing agent, and the plating efficiency was measured.

[0100] The measurement results are shown in Table 2.

[0101] [Table 2]

[0102] As can be seen from Table 2 above, when metallic iron was used as a reducing agent as in Examples 1 and 2, the ferric concentration decreased, the pH increased, and the plating efficiency increased significantly to 82% and 85%, respectively. Meanwhile, the state of the solution prepared in Example 1 after being kept for 1 hour, 2 hours, and 3 hours is shown in Figure 8. As can be seen from Figure 8, it was confirmed that the color gradually changed from reddish brown due to ferric iron to light green due to ferrous iron over time.

[0103] [Comparative Examples 1 to 2] In Comparative Examples 1 and 2, reduced iron electroplating solutions were obtained by the same reduction treatment as in Example 1, except that 16 g / L of ascorbic acid was added as a reducing agent to the initial solutions of Reference Examples 1 and 2 to reduce ferric ions to ferrous ions. Comparative Example 1 is an example in which the initial solution of Reference Example 1 was used, and Comparative Example 2 is an example in which the initial solution of Reference Example 2 was used.

[0104] The ferric ion concentration and T-Fe, which is the sum of the ferrous ion concentration and the ferric ion concentration, of the prepared iron electroplating solution were measured, and the results are shown in Table 3.

[0105] [Table 3]

[0106] Immediately after adding ascorbic acid, the plating solution changed color from reddish-brown to light green, and the concentration of ferric ions decreased significantly. However, after 3 hours of storage, the solution gradually turned red due to reaction with oxygen in the air. Meanwhile, as can be seen from Table 3 above, when iron electroplating was performed using a solution that had been stored for 3 hours after adding ascorbic acid, the plating efficiency actually decreased, even though the concentration of ferric ions decreased significantly.

[0107] [Comparative Examples 3 to 4] In Comparative Examples 3 and 4, reduced iron electroplating solutions were prepared by the same method as in Example 1, except that 12 g / L of sodium sulfite was added as a reducing agent to the initial solutions of Reference Examples 1 and 2 and then maintained at 50°C for 3 hours. Comparative Example 3 is an example in which the initial solution of Reference Example 1 was used, and Comparative Example 4 is an example in which the initial solution of Reference Example 2 was used.

[0108] The ferric ion concentration and the T-Fe concentration, which is the sum of the ferrous ion concentration and the ferric ion concentration, of the prepared iron electroplating solution were measured, and the results are shown in Table 4.

[0109] [Table 4]

[0110] The addition of sodium sulfite did not change the color of the solution. Furthermore, as can be seen from Table 4 above, there was no significant change in the concentration of ferric ions compared to Reference Examples 1 and 2, and the plating efficiency actually decreased further.

[0111] [Examples 3 to 5 and Comparative Examples 5 to 12] The iron electroplating solution was prepared by dissolving ferrous sulfate to a concentration of iron ions (T-Fe) of approximately 50 g / L, and adding glutamine, an amino acid, as a complexing agent to a molar concentration of 0.5 times that of the iron ions. Sulfuric acid was added to adjust the pH to 2-3, and the initial solutions shown in Table 5 below were prepared.

[0112] As a reducing agent, 0.5 mm thick metal iron plates of pure iron or ferroalloys with different Mn contents were placed on a 1 dm 2 The surface area of ​​the metallic iron in contact with the solution was adjusted by varying the number of metallic iron plates placed in the dissolution tank, and the surface area of ​​the reducing agent (dm 2 ) are as shown in Table 5.

[0113] As a base metal for plating, 1dm 2A copper plate having a plating area of ​​100 mm was degreased in advance and continuously plated at a current of 40 A for 2 minutes at regular intervals, for a total of 5 plating sessions per hour, with an average current of 6.7 A.

[0114] After plating at regular intervals for 3 hours using the above method, the iron ion concentration (T-Fe and ferric ion, unit: g / L), manganese ion concentration (mg / L), pH, and plating efficiency (%) in the solution were measured, and the presence or absence of sludge generation in the plating solution (O: sludge generation, X: no sludge generation) was observed. The results are shown in Table 5.

[0115] Furthermore, the area of ​​metallic iron used as a reducing agent (S, unit: m 2 ) and the converted current (I conv ) and the maximum allowable ion concentration of ferric ions in the solution (C max ) using the above formula (1) (unit: m 2 The results are also shown in Table 5.

[0116] [Table 5]

[0117] In Examples 3 and 4 and Comparative Examples 6 and 7, pure iron was used as a reducing agent at 1 dm 2 This is an example in which the number of iron plates cut to the size of 100 mm was changed and they were charged at regular intervals, and the effect of suppressing the generation of ferric ions due to the surface area of ​​metallic iron can be confirmed.

[0118] Specifically, in Comparative Examples 6 and 7, the surface area of ​​the metal iron plate was 2 dm 2 and 4dm 2 Unlike Comparative Example 5 in which metallic iron was not added, the ferric ion concentration did not increase significantly and the plating efficiency did not decrease significantly, but the ferric ion concentration tended to gradually increase compared to the initial solution.

[0119] In contrast, the surface area of ​​the steel plate is 8 and 16 dm 2In Examples 3 and 4, in which the ferric ion concentration in the electroplating solution was increased to 100%, the ferric ion concentration in the electroplating solution decreased gradually compared to the initial solution as the plating progressed, and the plating efficiency also increased slightly. Furthermore, no sludge was generated in the solution during the electroplating process.

[0120] In Examples 5 to 7 and Comparative Example 8, an alloy iron plate containing about 3% Mn as a reducing agent was used. 2 This is an example in which metal iron plates cut to the size of 100 mm were charged at regular intervals with different numbers of pieces added, and the effect of suppressing the generation of ferric ions due to the surface area of ​​the Mn ferroalloy can be confirmed.

[0121] As in Examples 5 to 7, the Mn-containing alloy iron plates have a surface area of ​​4 dm 2 Even if the above amount was added, the concentration of ferric ions decreased compared to the initial solution. However, when the area of ​​the alloy iron plate was 2 dm 2 In Comparative Example 8, in which the plating solution was charged so that the pH was 0.05, the pH decreased as plating progressed, and the concentration of ferric ions gradually increased.

[0122] In Comparative Examples 9 to 12, an ferroalloy plate containing approximately 5 wt. % Mn was used as a reducing agent, and the Mn content was found to have an inhibitory effect on the generation of ferric ions. Thus, when an ferroalloy plate containing a large amount of Mn was used, the concentration of ferric ions was significantly reduced even with the use of a small amount of Mn ferroalloy, and the plating efficiency remained constant. However, as the Mn content in the solution increased, the pH rose sharply, and fine sludge formed in the electroplating solution during plating.

[0123] Based on the above results, when a dissolving tank containing pure iron or a ferroalloy containing 3% or less of Mn is provided in an iron electroplating apparatus and circulated, it is possible to prevent the accumulation of ferric ions in the iron electroplating solution, suppress a decrease in pH, and replenish iron ions consumed during electroplating. This makes it possible to maintain constant plating efficiency and maintain the homeostasis of the iron electroplating solution when performing continuous iron electroplating using an insoluble anode. [Explanation of symbols]

[0124] 1: Electroplating cell 2: Circulation tank 3:Dissolution tank 4: Pump 5:Filtration means

Claims

1. 1. A method for removing ferric ions in a sulfate-based iron electroplating solution, comprising: a regeneration step of circulating a sulfate-based iron electroplating solution containing ferric ions through a solution tank containing metallic iron to reduce the ferric ions; The method for removing ferric ions in a sulfate-based iron electroplating solution, wherein the metallic iron is charged in an amount that satisfies the following formula (1): S≧0.01 I ｃｏｎｖ / C ｍａｘ (1) In formula (1), S is the total surface area of ​​metallic iron (m ２ ) and C ｍａｘ is the maximum allowable ferric ion concentration in the solution (g / L), and I ｃｏｎｖ is the plating time (t ｐ The total amount of current (I) applied to the electroplating cell during the regeneration time (t ｒ , sec) and is expressed by the following equation (2). [Equation 1]

2. 10. The method for removing ferric ions in a sulfate-based iron electroplating solution according to claim 1, wherein said regeneration step is performed during the plating process.

3. 2. The method for removing ferric ions from a sulfate-based iron electroplating solution according to claim 1, wherein the regeneration step is performed during the plating process, and the regeneration step is performed two or more times discontinuously.

4. 2. The method for removing ferric ions from a sulfate-based iron electroplating solution according to claim 1, wherein the regeneration step is initiated during an ongoing plating process and terminated during a rest period of the plating process, and the regeneration step is performed continuously or discontinuously.

5. 2. The method for removing ferric ions from a sulfate-based iron electroplating solution according to claim 1, wherein the regeneration step is initiated during a rest period of the plating process and terminated during or after the plating process.

6. 10. The method for removing ferric ions from a sulfate-based iron electroplating solution according to claim 1, wherein a regeneration step is performed during a rest period of the plating process, said regeneration step being performed continuously or discontinuously.

7. 2. The method for removing ferric ions from a sulfate-based iron electroplating solution according to claim 1, wherein the plating steps are performed discontinuously, including rest periods, and a regeneration step is performed between two or more plating steps.

8. 2. The method for removing ferric ions in a sulfate-based iron electroplating solution of claim 1, wherein the metallic iron is a ferroalloy containing at least one alloying element selected from the group consisting of Mn, Al, Mg, Li, Na, and K.

9. 9. The method for removing ferric ions in a sulfate-based iron electroplating solution according to claim 8, wherein the ferroalloy is a ferroalloy containing alloying elements in a content of more than 0 wt. % and not more than 3 wt. %.

10. 10. The method for removing ferric ions in a sulfate-based iron electroplating solution of claim 1, wherein the metallic iron is in the form of at least one of particles, spiral chips, plates, and strips.

11. 10. The method for removing ferric ions in a sulfate-based iron electroplating solution of claim 1, wherein the sulfate-based iron electroplating solution further comprises a complexing agent.

12. 12. The method of claim 11, wherein the complexing agent is at least one compound selected from the group consisting of at least one amino acid selected from glycine, glutamic acid, and glutamine, formic acid, acetic acid, lactic acid, gluconic acid, oxalic acid, citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediamine-N,N,N',N'-tetraacetic acid).

13. 2. The method for removing ferric ions in a sulfate-based iron electroplating solution according to claim 1, wherein the sulfate-based iron electroplating solution has a temperature of 80° C. or less and a pH of 1.0 to 4.

0.

14. The method comprises: an electroplating cell to which an electric current is applied to perform electroplating; a circulation tank for circulating the electroplating cell and the electroplating solution; a dissolving tank through which the electroplating solution is circulated, into which the metallic iron is charged, and which dissolves the metallic iron to remove ferric ions from the electroplating solution, 14. The method according to claim 1, wherein the method is performed by an iron-based electroplating apparatus including a pump that supplies the electroplating solution in the circulation tank to a dissolving tank and a filter that prevents metallic iron from the dissolving tank from flowing into the circulation tank.

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