JP5114739B2 - Method and equipment for removing iron ions in displacement plating solution - Google Patents

Description

  The present invention relates to means and equipment for regenerating a replacement plating solution by removing iron ions from a replacement plating solution containing iron in replacement plating of a steel material.

  Many platings are provided for the purpose of ensuring corrosion resistance, conductivity, design, and other performances. In particular, electroplating, electroless plating, and displacement plating for depositing metals from aqueous solutions are easy to handle. Widely manufactured for building materials and household appliance materials.

On the other hand, due to concerns about environmental issues, regulations on waste liquid treatment are becoming stricter, and there is a strong demand for technologies that can be processed easily and at low cost, and the plating liquid can be recycled without being disposed of for a long time. There is a high need to be able to use it.
In the iron and steel industry, metal plating on steel materials is the mainstream, so contamination of the plating solution by iron ions inevitably mixed into the plating solution hinders the targeted metal deposition and reduces its efficiency. The removal of iron ions from the plating solution is an important issue.

  In particular, substitution plating, which causes electron exchange due to the potential difference between iron in steel and the metal in the plating solution to displace and deposit the metal, inevitably contains iron in the plating solution. Only by replenishment of ions, iron ions dissolved in the plating solution are accumulated by the substitution reaction, the contamination of the plating solution continues, and the plating solution needs to be disposed of.

  In order to solve this problem, it is common to perform removal with an ion exchange resin that removes heavy metals and the like, but the cost is high and other heavy metal ions are removed at the same time in addition to iron ions. The plating main component metal is also removed. In Patent Document 1 and Patent Document 2, a method for removing iron in a plating solution using microorganisms is presented. However, there is a restriction that an environment in which microorganisms are used must be ensured.

  In patent document 3, although the removal method of the iron in a plating solution is proposed by using a solid wastewater treatment material, since a solid treatment material has the ability to neutralize an acid, wastewater treatment etc. Although it is suitable for the final treatment of an aqueous solution, extreme pH fluctuations are not preferable in consideration of regeneration treatment of a plating solution for recycling and removal during operation of plating production. Patent Document 4 proposes to irradiate light having a wavelength that excites iron and oxygen to oxidize iron ions in the plating solution to trivalent iron, and to remove the precipitate. Since oxygen in the state has a strong oxidizing action, it damages the device itself, and reliably irradiates iron ions present in a large amount of industrial plating solution with short-wavelength light such as ultraviolet light. It is difficult.

  Patent Document 5 proposes means for using oxygen and a platinum group metal as a catalyst to oxidize divalent iron accumulated in an electroplating solution and separate it as trivalent iron. As the electroplating solution also has in the publication, various organic additives are used for the purpose of obtaining glossiness and smoothness, and there is a problem that the additive is decomposed by normal aeration of oxygen. By using it as a catalyst, the wear of the additive can be minimized. However, platinum group metals are extremely expensive and have a problem in cost. In the first place, in substitution plating that uses the potential difference between metals to substitute and deposit, the organic additive is not only a hindrance to substitution, but in the unlikely event that a very precious platinum group dissolves in the substitution plating solution. It is not preferable to bring a noble metal into the displacement plating system because there is a risk that the platinum group is displaced and deposited.

  Patent Document 6 proposes a means of oxidizing divalent iron by bubbling with oxygen or ozone to remove it as trivalent iron. However, strong oxidizing agent ozone is harmful and is strictly controlled for safety. And request the cost for it. In Patent Document 6, trivalent iron ions generated by oxidation due to the use of a chelate resin are removed by ion exchange without precipitation. Accordingly, since the chelate resin becomes clogged and does not function in the pH range where precipitation or the like occurs, the pH range is limited to a highly acidic aqueous solution in which precipitation of trivalent iron does not occur, that is, low pH as described in the publication Is done.

Now consider a highly acidic aqueous solution. From the solubility product Ksp = 3.16 × 10 ^{−38 of} Fe (OH) ₃ (Chemical Handbook basic edition 3rd edition, page II-179, Maruzen, 1984), the divalent iron ions present in the electroplating solution are Assuming that all 0.1 g / l is oxidized to trivalent iron ions, the pH region where precipitation does not occur is 2.4 or less, and can be removed by keeping such a low pH region. On the other hand, in displacement plating, it is necessary to adjust the bath to maintain a low pH range in this range, so removal of trivalent iron by oxygen bubbling and chelate resin requires extremely high costs. In general, chelate resins have the ability to coordinate and bond many heavy metal ions as well as ion exchange resins, and not only remove the intended trivalent iron, but also remove the main heavy metal ions. There is a bug. In addition, the cost increases due to the addition of the essential chelate resin, and the chelate resin itself is decomposed by the remaining oxygen and ozone, thereby causing the problem of contaminating the plating solution.
JP-A-8-164399 JP-A-8-173990 JP 2004-174327 A JP-A-2-66199 JP-A-3-232999 Japanese Patent Laid-Open No. 3-24298

  In view of the above problems, the present invention provides a method and equipment capable of easily removing iron ions accumulated in a displacement plating solution at low cost.

  The inventors first focused on the chemical nature of iron. The iron ion dissolved in the displacement plating solution is a divalent ion, which is characterized in that it has an ability to be oxidized. That is, iron can become a trivalent ion in the presence of some oxidizing agent. Trivalent iron ions are unstable in an aqueous solution, and are calculated in the form of hydroxide when the pH exceeds 2.4 as described above.

The present inventors studied to oxidize iron and remove the precipitate by utilizing the property of precipitation of the trivalent iron. The simplest is oxidation using oxygen, but the reaction when divalent iron is oxidized. Fe ²⁺ → Fe ³⁺ + e ⁻ standard electrode potential +0.771 V is oxygen reduction reaction 1 / 2O ₂ + H ₂ O + 2e ^Since it is located nobler than the standard electrode potential +0.401 V of ⁻ → 2OH ⁻ , oxidation by oxygen simply does not proceed. This is the reason for using strong oxidizing agents such as ozone, oxidizing microorganisms, and light irradiation as means for oxidizing divalent iron ions, and further combining ion exchange and chelating resin. However, ozone itself is toxic, and even microorganisms require strict facility management and safety management, which increases costs. In addition, as a means for removing trivalent iron ions, expensive metal ion removal equipment such as ion exchange resin and chelate resin increases in cost, and also causes problems in resin regeneration cost and disposal.

  In terms of facility management, it is desirable that the means be simple and safe, and the present inventors have reexamined the above-described method for removing iron using oxygen. The magnitude of the standard electrode potential indicates which direction the equilibrium is inclined to. The oxidation reaction of divalent iron using oxygen as an oxidizing agent does not occur, but the trivalent It does not exist permanently and stably, but it means that it returns to divalent iron in an infinite time. Therefore, we thought that there was a possibility of proceeding the reaction if the trivalent iron ions were immediately discharged from the aqueous solution system. Based on this inference, when the plating solution was adjusted so that the pH range where trivalent iron can precipitate was blown, oxygen was blown, and as the oxygen was supplied, the divalent iron ions in the plating solution became trivalent iron ions. It has been found that it is oxidized to produce a yellow precipitate as a hydroxide.

However, as the reaction progressed, the solution acidified, and after acidifying to a certain pH, the iron precipitation reaction did not proceed. This is because the reaction of the following formula (1) proceeds, the solution is acidified, and the trivalent iron ions generated by oxidation can remain in the solution system without precipitating. It became possible to return to the ion, and as a result, it was speculated that the reaction of the following formula (1) did not proceed.
Fe ²⁺ +1/4 O ₂ + 5 / 2H ₂ O → Fe (OH) ₃ + 2H ⁺ (1)

  Therefore, in order to precipitate the generated trivalent iron ions, the solution was maintained at pH 2.5 or higher, which is a precipitation region of the trivalent iron ions, and it was found that the precipitation removal of the trivalent iron ions proceeded. . FIG. 1 shows the amount of decrease in divalent iron ions and the amount of precipitation of trivalent iron ions and the change in pH with respect to the oxygen blowing time. As oxygen was blown in, the pH decreased, divalent iron ions decreased, and the amount of precipitated trivalent iron ions increased. However, below pH 2.5, the decrease in divalent iron ions and the precipitation of trivalent iron ions stagnated. After 24 hours, when the pH was readjusted to 4, reduction of divalent iron ions and precipitation of trivalent iron ions proceeded again.

In general, the solution used for electroplating, for example, when a high current density such as 100 A / dm ² is applied, the diffusion of metal ions that receive electrons to the electrode surface is not in time, so that the burning phenomenon of plating (called plating or scorching) ( For the purpose of preventing this, a large amount of protons are present as a strong acidic solution such as pH 1, and hydrogen is generated when the diffusion of metal ions is not in time. Conversely, adjustment of pH from a weak acid with few protons to a neutral side (for example, pH 3 to 5) causes quality deterioration such as plating burn, so that it is difficult to employ the present invention for an electroplating solution.

  However, substitution plating based on a natural electron exchange reaction between metal ions and iron does not generate plating or scorching, so it is rather possible to use a pH range from a weak acid to a neutral pH range (for example, pH 3 to 5) to prevent hydrogen generation. It is preferable in terms of plating efficiency and is well suited to a pH range where iron ions are precipitated and removed.

The present invention has been made based on the above knowledge, and is a method for removing iron ions in a displacement plating solution that removes iron ions dissolved in a displacement plating solution when a metal other than iron is displacement plated on a steel material. Then, the metal carbonate to be subjected to displacement plating as an alkaline agent is added to the displacement plating solution, while maintaining the pH of the displacement plating solution in the displacement plating solution main tank or its spare tank at 2.5 or more , By ventilating oxygen or oxygen-containing gas of 0.01 L / min or more per 1 m ^{3 of} plating solution , the reaction of the following formula is promoted, and iron ions are removed from the reaction system as precipitates of hydroxide. It is what.
Fe ²⁺ +1/4 O ₂ + 5 / 2H ₂ O → Fe (OH) ₃ + 2H ⁺
It is.

  As described above, the present invention enables iron ions accumulated in the displacement plating solution to be easily removed at a low cost by an extremely easy means of aeration of oxygen or oxygen-containing gas. The contribution to industry is extremely large.

Hereinafter, the present invention will be described in detail.
First, the plating solution according to the present invention is most effective for displacement plating in which iron ions dissolve one after another. In addition, as shown in FIG. 1, it is essential that the pH is 2.5 or more, which is different from the region where pH is 2.4 or less, where trivalent iron ions are not precipitated, and substitution plating in this pH region is the most. Great effect.

  Displacement plating is an electrochemical reaction in which a metal precipitates due to a potential difference between iron and a metal ion having a potential nobler than iron and the iron dissolves, and an electric current is forcibly applied to exchange electrons with iron. The electroplating is different from electroplating that does not need to be performed, and is different from electroless plating that does not cause electron exchange between the base material and metal ions in the solution by adding a reducing auxiliary agent.

  There is no limitation on the type of the displacement plating solution, and any displacement plating solution may be used as long as it is a displacement plating of a metal nobler than iron, for example, copper or nickel. Further, the concentration of metal ions to be subjected to displacement plating does not have any influence on the removal of iron ions in the present invention, and a solution having a concentration as required such as several mg / l to several tens g / l should be used. Can do. Furthermore, various additives may be added to the replacement plating solution for the purpose of improving the smoothness and adhesion of the plating. Further, even if various counter ions such as sulfate ion, nitrate ion and halide ion are selected as counter ions of metal ions to be subjected to displacement plating, there is no influence.

  The effect of the present invention can be greatly expected when the substitution plating solution contains 0.1 g / l or more of iron ions. If the dilute iron ion concentration is less than 0.1 g / l, the deterioration of the displacement plating solution due to the iron ions does not progress greatly, and the displacement plating solution continues to maintain a good state without carrying out the present invention. The removal effect of the present invention is poor. Although an upper limit is not defined, 20 g / l or less is appropriate considering the upper limit of the solubility of divalent iron ions in an aqueous solution.

  The oxygen used for the oxidation of iron may be pure oxygen or an oxygen-containing gas such as air. The ventilation method is not limited.

When the amount of oxygen blown is less than 0.01 L / min per 1 m ³ of the plating solution, the reaction is difficult to proceed, so the lower limit is set to 0.01 L / min. In consideration of improvement in reactivity, 1 L / min or more is preferable per 1 m ^{3 of} the plating solution, and iron oxidation and precipitation can proceed extremely rapidly. An upper limit is not set, but it is preferably up to 600 L / min in consideration of equipment space, equipment cost, generation of bubbles, and the like. Moreover, the one where a bath temperature is also high is advantageous, and reactivity can be improved above 40 degreeC. FIG. 2 shows the relationship between the amount of oxygen blown and the amount of divalent iron ions decreased. The decrease of iron ions markedly progressed from around 0.01 L / min.

The pH of the solution needs to be kept at 2.5 or higher. When the pH is less than 2.5, trivalent iron ions are difficult to precipitate, and thus the trivalent iron ions generated in the solution return to divalent iron ions. FIG. 3 shows a pH-potential curve of iron ions (Atlas of Electrochemical Equilibria in Aqueous Solutions, Marcel Pourbaix, p313, edited by NACE International, 1996). The dotted line in FIG. 3 indicates the pH limit for precipitation at a certain iron concentration. The precipitation pH of Fe (OH) ₃ generated varies depending on the iron ion concentration in the solution, but is pH 1.8 at an iron ion concentration of 1 mol / l and pH 2.4 at an iron ion concentration of 0.01 mol / l. Therefore, precipitation does not occur in a strongly acidic region such as pH 1.5 because it exists as trivalent iron ions.

  The means for maintaining the pH at 2.5 or higher is a carbonate of a metal to be subjected to displacement plating. For example, copper carbonate is most preferable for copper displacement plating, and nickel carbonate is most preferable for nickel displacement plating. Carbonate is generated in an acidic solution and is emitted to the outside of the plating solution. In addition, since only metal ions and water are supplied, the third component generated by other alkaline agents, such as hydroxide, is used. PH adjustment and ion replenishment can be carried out at the same time without losing the ion balance.

  Even if a buffer solution is used as the displacement plating solution so as to maintain a pH of 2.5 or more, there is no problem in the manifestation of the effect of the present invention. Rather, trivalent iron ions can be precipitated efficiently, which is preferable. The type of the buffer solution is not particularly limited, and those having a buffering action such as phosphoric acid, halide, nitric acid, and sulfuric acid can be used. The upper limit of the pH is not particularly defined, and the precipitation limit of the metal to be plated, for example, about pH 5 is preferable.

  An example of equipment for removing iron ions is shown in FIG. In the oxygen aeration apparatus, pure oxygen or air or a non-reactive gas (for example, nitrogen, argon, etc.) + an oxygen-containing gas adjusted to an arbitrary oxygen concentration with oxygen is ventilated by the oxygen aeration apparatus 2 into the replacement plating solution main tank 1. The In FIG. 4, oxygen is ventilated in the replacement plating solution main tank 1 storing the plating solution, but another spare tank installed for ventilation may be provided and oxygen may be vented there.

  The displacement plating solution in which oxygen is passed is sent to the pH adjusting device 3 for maintaining the pH, and the pH is adjusted. In this pH adjuster, ion replenishment may be performed simultaneously. Further, in order to confirm whether the pH adjustment is performed as intended, a pH meter is installed at the outlet of the pH adjusting device 3 and / or the replacement plating solution main tank 1 and / or the above-mentioned another auxiliary tank, and the pH is adjusted. More preferably, the control is automatically controlled.

  In the precipitation removing device 4, iron ions precipitated by filtration or the like are removed. By attaching an automatic washing device or the like that flows backward to the flow of the plating solution to the precipitation removing device 4, clogging due to deposit accumulation can be avoided. Furthermore, by installing a plurality of precipitation removing devices 4 and operating them sequentially, it is possible to prevent a decrease in operation efficiency due to clogging. The precipitation removing device 4 and the pH adjusting device 3 may be installed in parallel or in series.

Next, the Example of this invention is given with a comparative example.
An oxidation removal test of iron ions was carried out using the displacement plating metal components shown in Table 1, the aeration conditions, and various pH adjusting agents. Evaluation was carried out by changing the Fe concentration in the plating solution, the plating adhesion efficiency, and the bath life. As for the Fe concentration in the plating solution, the concentration of iron in the plating solution after 24 hours and 48 hours after the removal test was analyzed by ICP emission spectrometry. The change in plating adhesion efficiency was measured by measuring the amount of plating deposited before and after removal of iron ions. Those that did not exist were marked with Δ, and those that decreased were marked with ×. The bath life is that the phenomenon that the change in plating adhesion efficiency recovers more than 0% was possible even after repeated 6 times or more. X. The results are also shown in Table 1.

  In all of the inventive examples, after 24 hours, a marked decrease in iron ions was observed, and the plating deposition efficiency was improved. On the other hand, Comparative Example 9 with little initial iron ions, Comparative Example 10 in which the gas to be aerated does not contain oxygen, Comparative Example 11 with a small amount of gas passed through, and Comparative Example 12 with a low adjusted pH, almost have the effect of removing iron ions. The plating deposition efficiency was not improved.

  As described above, according to the present invention, iron ions accumulated in the displacement plating solution can be removed easily, safely and inexpensively, which greatly contributes to the industry.

It is explanatory drawing of the iron ion removal by the blowing of oxygen. It is a relationship diagram of the amount of oxygen blowing and the amount of decrease of divalent iron ions present in the displacement plating solution. It is explanatory drawing of pH of precipitation generation | occurrence | production of a trivalent iron ion. It is explanatory drawing which shows an example of an iron ion removal installation.

Explanation of symbols

1 Displacement plating solution main tank 2 Oxygen ventilation device 3 pH adjustment device 4 Precipitation removal device

Claims (1)

A method for removing iron ions in a displacement plating solution that removes iron ions dissolved in a displacement plating solution when a metal other than iron is plated on a steel material ,
Put the carbonate of the metal to be replaced as an alkaline agent into the replacement plating solution,
While maintaining the pH of the replacement plating solution in the replacement plating solution main tank or its spare tank at 2.5 or more,
By passing oxygen or oxygen-containing gas at a rate of 0.01 L / min or more per 1 m ³ of the plating solution into the replacement plating solution ,
A method for removing iron ions in a displacement plating solution, wherein the reaction of the following formula is promoted and iron ions are removed from the reaction system as precipitates of hydroxide .

Fe ²⁺ +1/4 O ₂ + 5 / 2H ₂ O → Fe (OH) ₃ + 2H ⁺

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