JP6159297B2 - Silver recovery method - Google Patents

Description

  The present invention relates to a silver recovery method in which silver or a silver-based alloy is dissolved and peeled from the surface of a substrate coated with silver or a silver-based alloy, and silver in the silver or silver-based alloy is recovered from the substrate.

  As an electronic material, it is widely used to apply a silver alloy such as silver solder on an iron alloy base material or to form a silver solder-coated iron alloy. For example, an iron-nickel-cobalt alloy sheet material that exhibits a thermal expansion coefficient close to that of ceramic or glass is coated with silver brazing on both surfaces, and is suitable for joining metal and ceramic or glass. It is used for hermetically sealing a piezoelectric vibrator, a piezoelectric oscillator, etc.

  When an iron alloy coated with silver solder is used as an electronic material, a large amount of processing waste such as punching waste is generated. In particular, when a silver-based alloy silver solder is applied on an expensive iron-based alloy base material such as an iron-nickel-cobalt alloy, the base material itself and the applied silver are also recovered and recycled. It is hoped that.

  In particular, in an iron-based alloy base material, since an expensive metal such as nickel or cobalt is used as an alloy component as described above, it is preferable that only a portion of a silver-based alloy such as a silver solder coated without being completely dissolved is coated. It is desired to separate and recover.

  Separation by a mechanical method such as grinding is not preferable because the separation is incomplete and there is a concern that new contamination may occur.

  As a method for dissolving only the silver alloy on the iron-based alloy substrate, for example, as shown in Patent Document 1, a method using an alkali cyanide solution is generally used.

  Patent Document 1 provides a method of effectively recovering an iron alloy having a silver content of 10 ppm or less and a silver brazing component separately from the processing waste of the silver brazing coated iron alloy.

  Specifically, the method of Patent Document 1 is a pretreatment step in which processing waste of silver braze-coated iron alloy is shredded and deformed so that the surfaces do not adhere to each other; Electrolysis to remove the silver wax component from the iron alloy surface and move to the cathode by electrolytic treatment by immersing the bag in a cyanide aqueous solution, using the bag as an anode, and providing a cathode outside the bag. It has a peeling treatment process. Furthermore, the method of Patent Document 1 is a finish peeling that sufficiently removes the silver brazing component from the surface of the iron alloy by immersing a small piece of the silver solder coated iron alloy that has been subjected to electrolytic treatment in an aqueous solution of a cyanide compound containing oxygen or an oxidizing agent. A treatment step and a water washing step of washing the small piece from which the silver brazing component has been removed from the surface of the iron alloy are washed, and the iron alloy and the silver brazing component from the silver brazing coated iron alloy are recovered.

  The technique using an alkali cyanide solution as in Patent Document 1 can separate and recover only the silver-based alloy by dissolving it all without losing the iron-based alloy substrate. However, in the method of Patent Document 1, in order to use a toxic alkali cyanide, a specific dedicated work facility is provided, and a wastewater treatment facility for completely decomposing cyanide in the generated cleaning liquid is required. There was a problem of increasing labor and cost.

  On the other hand, as a method not using alkali cyanide, a method using an aqueous solution of iron (III) nitrate is disclosed in Patent Document 2 below. This method is characterized in that an iron-based alloy material coated with a metal material is immersed in a stripping solution containing one or more selected from cupric nitrate, cupric nitrate, and ferric nitrate. This is a method for recovering a metal material coated with an iron-based alloy material.

The technique using a solution of iron nitrate (III) as in Patent Document 2 uses a solution of Fe ³⁺ as an oxidant to form silver brazing by a dissolution reaction exemplified for Formula 1 below for silver metal and Formula 2 for copper metal. It dissolves silver metal and copper metal contained. This method has an advantage that there are few restrictions on the facility location because no chemicals corresponding to poisons are used.

Fe ³⁺ (NO ₃ ⁻ ) ₃ + Ag
_{^{→ Fe 2+ (NO 3 -)}} 2 + Ag + (NO 3 -) ··· < Formula 1>
2Fe ³⁺ (NO ₃ ⁻ ) ₃ + Cu
_{^{→ 2Fe 2+ (NO 3 -)}} 2 + Cu 2+ (NO 3 -) 2 ··· < formula 2>

However, the standard electrode potential of the reaction in which Fe ³⁺ acts as an oxidizing agent to become Fe ²⁺ and the reaction in which Ag ⁺ is reduced to return to Ag metal are approximately the same level. For this reason, when the reaction of Formula 1 proceeds and the concentration of Fe ²⁺ and Ag ⁺ in the liquid increases, there is a problem that the reverse reaction of Formula 1, that is, the precipitation reaction of silver once dissolved occurs.

  When reusing an iron-based alloy base material coated with silver brazing, it is generally necessary to reduce the silver quality in the base material to several tens of ppm or less. For this reason, when the reprecipitation phenomenon of silver metal arises on a base material by the reverse reaction of Formula 1, it will become difficult to reuse the collect | recovered base material as an iron-type alloy raw material as it is.

In order to prevent reprecipitation of silver due to the reverse reaction from Equation 1, maintain a state in which a large excess of Fe ³⁺ ions are present in the production system on the left side compared to Fe ²⁺ and Ag ⁺ in the reaction system on the right side of Equation 1. I think that it should be done. However, when the amount of iron (III) nitrate used is increased with respect to the base material to be recovered and valuable materials such as silver, the cost increases. Further, since iron (III) nitrate has a large nitrogen load on the environment, the treatment requires a treatment for reducing the nitrogen load on the environment to an allowable range. For this reason, when the amount of the iron (III) nitrate solution used is increased, it is necessary to process a large amount of solution accordingly, which requires more time and equipment for processing a large amount of solution.

  Accordingly, a method for recovering silver from the surface of a base material coated with silver or a silver-based alloy is required to be able to reduce the burden on the environment and to be stable in both safety and cost.

JP 2003-89894 A Japanese Patent Laid-Open No. 02-159324

  Therefore, the present invention has been proposed in view of such circumstances, and without dissolving the base material, the silver or silver alloy coated on the base material can be completely dissolved, and the base material can also be reused. An object of the present invention is to provide a silver recovery method that can be recovered in a form and that can also recover silver. Another object of the present invention is to provide a silver recovery method that stably satisfies environmental load reduction, safety, and cost reduction.

The method for recovering silver according to the present invention for achieving the above-described object includes adding a ferric nitrate (III) -containing solution to a substrate coated with silver or a silver-based alloy, dissolving the silver or silver-based alloy, and Included in dissolution and peeling process for peeling silver or silver-based alloy, silver chloride generating process for adding silver chloride to solution in which silver or silver-based alloy is dissolved to form silver chloride precipitate, and solution after dissolution and peeling process An iron nitrate regeneration process that oxidizes divalent iron ions to trivalent iron ions to regenerate an iron nitrate (III) -containing solution, and contains iron nitrate (III) produced in the iron nitrate regeneration process after the iron nitrate regeneration process An iron nitrate (III) -containing solution adjustment step for adjusting the concentration of the solution to the concentration of the iron nitrate (III) -containing solution used in the dissolution peeling step . In the dissolution peeling step, the iron nitrate after adding the base material (III) ^{Fe 3+} concentration ^{Fe 2+} concentration of the solution containing Maintained as a 1.5 times or more, using the iron (III) nitrate containing solution produced by the iron nitrate regeneration step by dissolving stripping step, the iron (III) nitrate containing solution adjusting step, by dissolving the peeling step Nitrate ions equivalent to dissolved silver alloy components other than dissolved silver are supplemented by adding nitric acid to adjust the nitrate ion concentration of the iron (III) nitrate-containing solution produced in the iron nitrate regeneration step. .

  In the present invention, silver or a silver alloy coated on the base material can be completely dissolved without elution of the base material, and the base material can be recovered in a reusable form, and silver can also be recovered. In the present invention, since cyan is not used, the burden on the environment can be reduced and silver can be recovered economically. Moreover, in this invention, an environmental impact reduction, safety | security reduction, and cost reduction can be satisfy | filled stably by repeatedly using the iron (III) nitrate containing solution used for elution of silver or a silver alloy many times.

It is a flowchart of the collection | recovery method of silver. It is the schematic of the rotation stirring tank used in the Example. It is the figure which graphed the example of a time-dependent change of the measured value of the oxidation-reduction potential at the time of oxidation regeneration.

  Hereinafter, a silver recovery method to which the present invention is applied will be described in detail with reference to the drawings. Note that the present invention is not limited to the following detailed description unless otherwise specified.

1. Dissolution peeling step 2. Silver chloride production process 3. Iron nitrate regeneration process 4. Preparation of iron nitrate (III) -containing solution Metal recovery process other than silver Substrate water washing process

<Silver recovery method>
The silver recovery method is for a substrate whose surface is coated with silver or a silver alloy. Examples of the treatment target include a silver-coated substrate in which silver or a silver-based alloy is applied or formed on the surface of an iron alloy substrate. The object to be processed is subjected to an appropriate pretreatment such as cutting, cutting and crushing according to its shape and size and the form and size of the processing equipment, and then subjected to processing for collecting silver. In addition, when dust, dust, oil, or the like is attached, it is preferable to perform a pre-cleaning process in advance by a method corresponding to the attached matter.

  Specifically, as a processing target, there is a silver solder coated base material in which an iron alloy base material is coated with a silver solder made of an alloy of silver and copper. The processing target silver brazing coated base material includes processing scraps and spec-out products of electronic materials in which silver brazing is applied to the surface of an iron-nickel-cobalt alloy sheet, or scraps of products using this material. Can be mentioned.

  A general silver solder is an alloy obtained by adding copper, zinc, tin, or the like to silver. For example, silver brazing used for electronic materials is an alloy in which 10-30% copper is blended with silver. In addition, the silver wax used for an electronic material does not mix | blend zinc and tin, or it is a trace amount even if it mix | blends.

  The silver recovery method will be described by taking a silver wax-coated substrate as an example. In addition, if this silver collection | recovery method is a base material which coat | covered silver and a silver alloy, it can collect | recover silver similarly.

  As shown in FIG. 1, the silver recovery method includes a dissolving and peeling step of adding an iron (III) nitrate-containing solution to a silver wax-coated base piece that has been subjected to appropriate pretreatment to dissolve and peel the silver wax. , A silver chloride production process for producing dissolved silver as silver chloride, and divalent iron ions contained in the solution after the dissolution and peeling process are oxidized to trivalent iron ions to regenerate the iron (III) nitrate-containing solution. An iron nitrate regeneration step. Moreover, the collection | recovery method of silver has a base-material water-washing process of water-washing the iron alloy base material peeled at the melt | dissolution peeling process. Furthermore, the silver recovery method has an iron nitrate (III) -containing solution adjustment step of adjusting the nitrate ion concentration when reusing the iron nitrate (III) -containing solution.

<1. Dissolution peeling process>
In the dissolution and peeling step, the silver wax is dissolved from the silver wax-coated base piece that has been subjected to an appropriate pretreatment, and the silver wax is peeled off from the iron alloy base material. In this melting and peeling step, the silver solder is peeled in a form that can be recycled as a base material without dissolving the iron alloy base piece and damaging the base piece. Specifically, in the dissolution and peeling step, the silver wax-coated substrate piece is immersed in the dissolution treatment solution to dissolve the silver wax and peel the silver wax from the iron alloy substrate.

  The dissolution treatment liquid used in the dissolution and peeling step includes an aqueous solution containing iron nitrate (III) or an aqueous solution containing iron nitrate (III) obtained in the iron nitrate regeneration step described later (hereinafter, each of which is iron nitrate (III). ) Containing solution).

In the dissolution and peeling step, reactions shown in the following formulas 1 and 2 occur. In addition, most of silver alloy components other than silver are silver solder used for an electronic component. Therefore, Formula 2 shows the reaction formula of copper.
Fe (NO ₃ ) ₃ + Ag → Fe (NO ₃ ) ₂ + Ag (NO ₃ )
... <Formula 1>
2Fe (NO ₃ ) ₃ + Cu
→ 2Fe (NO ₃ ) ₂ + Cu (NO ₃ ) ₂ ... (Formula 2)

That is, in the dissolution and peeling step, iron (III) nitrate acts as an oxidizing agent, so that silver in the silver wax is dissolved as silver nitrate and copper is dissolved as copper nitrate. Here, the standard redox potential of the reaction in which Fe ³⁺ becomes Fe ²⁺ and the standard redox potential of the reaction in which Ag ⁺ is reduced to return to Ag metal are substantially the same. For this reason, in the dissolution and peeling step, when the reaction shown in Formula 1 proceeds and the concentration of Fe ²⁺ or Ag ⁺ increases, the reverse reaction of Formula 1 occurs, and the precipitated silver precipitates once.

Therefore, the inventors obtained the conditions for suppressing the reverse reaction of Formula 1 in the dissolution and peeling step, and as a result of repeated tests, the inventors have immersed the silver wax-coated substrate in the dissolution treatment liquid, that is, during the dissolution reaction. It has been found that the amount of Fe ³⁺ ions in the dissolution treatment liquid is preferably maintained to be always 1.5 times or more of Fe ²⁺ ions, and more preferably 2.5 times or more. .

The dissolution treatment liquid is maintained so that the amount of Fe ³⁺ ions in the dissolution treatment liquid is always 1.5 times or more, preferably 2.0 times or more, more preferably 2.5 times or more of Fe ²⁺ ions. There is a need. That is, in the dissolution and peeling process, the iron nitrate (III) that is the minimum necessary for suppressing the reduction reaction of silver is not used, but the concentration of iron (III) is not increased so that Fe ³⁺ in the dissolution treatment liquid is excessive. The concentration is (III). As a result, in this dissolution and peeling step, since only a necessary amount of the iron (III) nitrate-containing solution needs to be used, when processing the iron (III) nitrate-containing solution, the nitrogen load on the environment is reduced to an allowable range. Time and cost can be reduced. Moreover, in this Embodiment, although the iron nitrate (III) containing solution is reused so that it may mention later, since it can be used repeatedly in a required quantity, cost can be reduced.

To maintain the Fe ³⁺ concentration to be always 1.5 times or more the Fe ²⁺ concentration, for example, in the case of a batch-type dissolution and peeling treatment, silver contained in a silver brazing-coated substrate piece processed in one batch The amount of metal to be dissolved, such as copper and copper, is grasped in advance, and iron (III) nitrate containing Fe ³⁺ ions that are 2.5 times the amount of Fe ²⁺ ions that are estimated to be generated when all of these metals are dissolved That is, it is necessary to start the dissolution treatment using the containing solution starting solution. To always maintained so as to be more than 2.5 times the amount of ^{Fe 2+} ions Fe ³⁺ ion content is estimated to occur ^{Fe 2+} ion content of 3.5 iron nitrate containing times more ^{Fe 3+} ions (III ) Start the treatment with the solution starting solution.

Even if the iron concentration of Fe ²⁺ and Fe ³⁺ in the iron (III) nitrate-containing solution is 10 g / l (0.18 mol / l) or less, the reaction to dissolve the silver wax can be performed, but the treatment is performed. This is not realistic because the amount of liquid required per amount of the silver wax-coated substrate becomes too large. On the other hand, if the iron concentration is 150 g / l (2.67 mol / l) or more, the viscosity and specific gravity of the liquid increase, which is not preferable in terms of operation. Therefore, the iron concentration is preferably 60 to 90 g / l (1.07 to 1.60 mol / l), more preferably 60 to 70 g / l (1.07 to 1.25 mol / l).

In the dissolution and peeling process, silver is not reduced and deposited again on the iron alloy base material by dissolving silver wax in a state where the Fe ³⁺ concentration is maintained at 1.5 times the Fe ²⁺ concentration or more during the dissolution reaction. Can be completely dissolved, and the iron alloy substrate can be separated from the silver solder in a reusable form.

<2. Silver chloride production process>
Next, the silver chloride production | generation process which produces | generates and collect | recovers silver as silver chloride from the solution which silver and copper melt | dissolved is performed. Specifically, in the silver chloride production step, silver chloride is produced and precipitated by adding hydrochloric acid in an amount equal to or less than an equivalent amount of Ag ⁺ ions dissolved in the solution. And a silver chloride production | generation process collect | recovers silver derived from a silver wax by carrying out solid-liquid separation of the silver chloride deposit from a solution. The reaction formula is shown in the following formula 3.
Ag (NO ₃ ) + HCl → AgCl ↓ + HNO ₃ (Formula 3)

In this silver chloride production step, when hydrochloric acid exceeding the equivalent of dissolved Ag ⁺ ions is added, chloride ions (Cl ⁻ ions) remain in the liquid after the addition. The residual chloride ions cause the precipitation of silver chloride when the iron (III) -containing solution is regenerated as described later and used again in the dissolution and peeling process to dissolve the silver wax. In the dissolution and peeling step, if silver chloride is deposited on the surface of the silver wax being dissolved, the contact between the silver wax and the iron (III) nitrate-containing solution may be hindered, which is not preferable. Therefore, in the silver chloride production step, it is preferable to control the amount of hydrochloric acid added so that a small amount of Ag ⁺ ions remain in the solution after silver chloride production.

  The separated silver chloride precipitate is reused as a raw material for silver metal after removing the adhering liquid by washing with water. Metal elements other than silver derived from silver wax accumulate in the liquid without being removed in the silver chloride production step.

<3. Iron nitrate regeneration process>
In the iron nitrate regeneration step, the Fe ²⁺ ions generated by the dissolution reaction of silver or copper in the dissolution and peeling step are oxidized to Fe ³⁺ ions to regenerate the iron (III) nitrate-containing solution. This iron nitrate oxidation process is not limited to the process after the silver chloride production process, and there is no problem even if it is performed after the dissolution and peeling process and before the silver chloride production process.

In the iron nitrate regeneration step, an oxidizing agent is supplied to a solution after dissolution of silver or copper, for example, a solution after desilvering after removing silver as shown in FIG. 1 to oxidize Fe ²⁺ ions. Air (internal oxygen) is suitable as the oxidant to be supplied. Examples of other oxidizing agents include oxygen-enriched air, pure oxygen, ozone, and hydrogen peroxide through an oxygen concentrator. The iron nitrate regeneration step is not particularly limited as long as the Fe ²⁺ ions can be changed to Fe ³⁺ ions. In addition, it is preferable to warm the solution because the reaction can proceed more easily than at room temperature, and the processing time can be shortened.

Specifically, aeration of blowing air is performed while oxidizing the Fe ²⁺ ions while maintaining the temperature of the post-desilvering solution (iron nitrate solution) after removing silver at 45 ° C. or higher and 70 ° C. or lower. In such a method, the iron nitrate (II) solution can be efficiently oxidized and regenerated into the iron nitrate (III) solution in a short time of about 3 hours or 1 to 2 hours.

  If the liquid temperature is lower than 45 ° C., the oxidation treatment cannot be performed in a short time, and even if aeration is performed using the same equipment, it takes more than 3 hours and the variation increases. On the other hand, when the liquid temperature is set to 45 ° C. or higher, the oxidation reaction is accelerated, and the oxidative regeneration treatment can be stably performed in a short time within 3 hours.

  In addition, the higher the liquid temperature, the faster the oxidation proceeds. However, even if it exceeds 75 ° C, the amount of decrease in the solution due to evaporation increases, the amount of heat required for heating increases, and the cost increases to increase the regeneration rate. Does not increase significantly. Therefore, it is suitable to oxidize at a temperature of 75 ° C. or lower.

The end point of oxidation is preferably determined by quantifying the residual amount of Fe ²⁺ ions by a redox titration method using potassium permanganate.

  As the aeration means, in addition to the combination of the air supply pipe 4 and the stirring blade 3 illustrated in FIG. 2, use of an ejector type gas-liquid mixer, use of a microbubble generator, etc. can be considered. It is not limited to this.

  In addition, in the silver recovery method, the obtained iron nitrate (III) -containing solution may be reused as it is in the dissolution and peeling step. However, as described below, nitric acid or the like is added to adjust the concentration and liquid volume. You may adjust.

<4. Step of preparing a solution containing iron (III) nitrate>
While the number of reuse of the iron (III) nitrate-containing solution is small, the obtained iron (III) nitrate-containing solution can be reused as it is in the dissolution and peeling step. However, in order to repeatedly use the iron nitrate (III) -containing solution more many times, by adding nitric acid equivalent to the silver alloy components other than silver dissolved in the dissolution peeling step after the iron nitrate regeneration step, nitric acid is added. It is necessary to replenish and adjust the concentration of nitrate ions in the iron (III) nitrate-containing solution produced in the iron nitrate regeneration step. Note that, for example, silver brazing used for electronic materials is mostly made of copper, and the following description will be made by taking copper as an example.

  That is, in the iron nitrate (III) -containing solution adjustment step, the iron nitrate concentration is adjusted so that the iron nitrate (III) -containing solution generated in the iron nitrate regeneration step can be reused in the dissolution and peeling step. In the iron nitrate (III) -containing solution adjustment step, the solution containing iron nitrate (III) obtained in the iron nitrate regeneration step is supplemented with nitric acid, water, or nitric acid for supplementing nitrate ions consumed by copper. Iron (III) may be added to adjust the liquidity and volume of the solution to an iron (III) nitrate-containing solution that can be reused in the dissolution and peeling step.

  Here, replenishment of nitrate ions in the iron (III) nitrate-containing solution adjustment step will be described. Almost all of the silver dissolved by the reaction represented by Formula 1 in the dissolution and peeling process is recovered in the silver chloride production process. The total amount of copper dissolved by the reaction represented by Formula 2 remains in the iron (III) nitrate-containing solution after the iron nitrate regeneration step. That is, in the iron nitrate (III) -containing solution after the iron nitrate regeneration step, the equivalent amount of nitrate ions of copper dissolved in the dissolution peeling step is insufficient.

The inventors used the iron nitrate (III) -containing solution after the iron nitrate regeneration step without adding nitric acid for supplementing nitrate ions to the iron nitrate (III) -containing solution after the iron nitrate regeneration step. A test was conducted in which the treatment from the dissolution peeling step to the iron nitrate regeneration step was repeated many times. As a result, it was confirmed that when the deficiency of nitrate ions exceeded a certain level, a part of Fe ³⁺ ions was hydrolyzed during the oxidation and precipitation occurred during oxidation in the iron nitrate regeneration step.

In addition, if nitric acid addition is performed before the iron nitrate regeneration step to add the equivalent amount of nitrate ions to the silver alloy components other than silver dissolved in the dissolution and peeling step, the Fe ²⁺ ions are oxidized to Fe ³⁺ ions. It has also been confirmed that the reaction rate is significantly slow.

  Therefore, in order to repeatedly use the iron (III) nitrate-containing solution more many times, after the iron nitrate regeneration step, nitric acid equivalent to the silver alloy component such as copper other than silver dissolved in the dissolution and peeling step is equivalent to nitric acid. It is necessary to adjust the nitrate ion concentration of the iron (III) nitrate-containing solution generated in the iron nitrate regeneration step by making up for the addition. Thus, in the silver recovery method, the occurrence of precipitation is suppressed in the iron nitrate regeneration step and the iron nitrate (III) -containing solution can be reused, so that the iron nitrate regeneration step can be performed efficiently at low cost.

  In addition, the iron nitrate (III) -containing solution adjustment process is also performed by adding iron nitrate (III) and water lost due to adhesion during solid-liquid separation between the dissolution peeling process and the iron nitrate regeneration process. The liquidity and liquid volume may be adjusted to a solution containing iron (III) nitrate that can be reused in the peeling step.

<5. Metal recovery process other than silver>
In the metal recovery step other than silver, a metal other than silver such as copper contained in the regenerated iron nitrate (III) -containing solution is recovered. Examples of the recovery method include a method of depositing by electrolysis or a method of recovering by precipitation as a hydroxide. In this metal recovery step, impurities such as copper can be removed from the aqueous solution adjusted in the iron nitrate (III) solution adjustment step. Thereby, the iron nitrate (III) containing solution which does not contain impurities can be reused in the dissolution and peeling step.

<6. Substrate water washing process>
In the base water washing step, the base piece after the silver wax separation obtained in the dissolution and peeling step is washed with water. In this base water washing step, the base piece is washed with water to remove the attached liquid. Thereby, the cleaned base material piece can be reused as the iron-based alloy of the base material.

  In the silver recovery method described above, the silver wax-coated base material has been described as a processing target. However, even in the case of a base material coated with silver or a silver alloy, silver is recovered without damaging the base material. can do. For example, in the case of a substrate coated with silver, it is not necessary to remove other metals from the iron nitrate (III) -containing solution obtained by the iron nitrate regeneration process, so that it can be reused in the dissolution and peeling process as it is. It can be reused only by adjusting the density as required. In the case of an alloy of silver and another metal other than silver brazing, the method is almost the same as that described above, and a metal recovery method may be selected in accordance with the other metal contained.

The silver recovery method as described above can suppress the reprecipitation of Ag by maintaining the amount of Fe ³⁺ ions at least 1.5 times the amount of Fe ²⁺ ions in the dissolution and peeling step. The amount of silver remaining on the substrate can be stably reduced. Further, in this silver recovery method, silver or a silver alloy can be completely dissolved and peeled off from the substrate without dissolving the substrate in the dissolving and peeling step. As a result, in this silver recovery method, the silver quality required for reusing the base material can be reduced, and the base material can be recovered in a form that is not damaged and can be reused.

  Further, in the silver recovery method, silver or a silver alloy coated on the base material can be completely dissolved and reprecipitation of silver can be suppressed, so that almost all silver can be recovered.

  Furthermore, in this silver recovery method, by oxidizing the divalent iron ions contained in the solution after the peeling of the silver or silver alloy into trivalent iron ions, a solution containing iron (III) nitrate is obtained. It can be reused many times in the dissolution and peeling process. For this reason, since the solution containing nitric acid generated by this silver recovery method is not disposable, it is possible to reduce the labor and cost of treating nitric acid and further reduce the nitrogen load on the environment. In addition, since this silver recovery method does not use cyan, there is no need to provide wastewater treatment equipment. From the above, this silver recovery method can reduce the burden on the environment, and can recover silver safely and economically.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

In the examples and comparative examples, the raw material was a silver wax-coated substrate piece, which is a processing waste of a material in which a surface of a plate made of an Fe—Ni—Co alloy was coated with silver wax. The quality of this raw material is shown in Table 1 below. The analysis was performed using ICP (Inductively Coupled Plasma). The amount of the silver wax component contained in 1 kg of the silver wax-coated substrate piece is 200 g for silver and 47 g for copper. The amount of Fe ²⁺ ions generated when this amount of the silver wax component is dissolved is about 3.3 mol.

<Example 1>
In Example 1, 1 kg of a silver wax-coated base piece and an iron (III) nitrate solution having a concentration and a liquid amount shown in Table 2 were placed in a rotary stirring tank 1 with a baffle plate for stirring as shown in FIG. The mixture was stirred and mixed for 3 hours at a rotation speed of 20 rpm, and the silver wax was dissolved and peeled to form a slurry composed of the dissolved solution and the dissolved residue.

  The stirring tank 1 shown in FIG. 2 is a stirring tank with a capacity of 30 L provided with a baffle plate 2 for stirring. The stirring tank 1 is provided with a disc-shaped stirring blade 3 and an air supply pipe 4 for sending air into the tank from the center of the bottom of the stirring tank 1. In addition, a temperature sensor 5 for measuring the liquid temperature of the solution is attached to the stirring tank 1.

  Next, in Example 1, using a Nutsche and a filter bottle, the dissolved solution and the leaching residue were separated, and the leaching residue was washed with a total of 3 L of water to recover 753 g of the base material piece. The silver quality of this base material piece was less than 10 ppm, and it was a quality that can be regenerated as a raw material for a new silver solder coated base material. The dissolution loss of the base material was less than 0.2%. Furthermore, no precipitate was observed in the 9.7 L recovered solution or the substrate cleaning solution.

  Subsequently, in Example 1, the solution after dissolution was placed in a coagulating sedimentation tank with a stirring blade having a capacity of 15 L, and 130 ml of 36% by weight hydrochloric acid (concentrated hydrochloric acid) was added while stirring at 200 rpm to produce silver chloride. 9.2 L of liquid after desilvering with a silver concentration of 3.1 g / L was obtained.

Next, this desilvered solution is put into a 20-liter rotating stirring tank 1 having the same configuration as that shown in FIG. 2, and the air aeration amount is supplied from the air supply pipe 5 while heating and maintaining the solution temperature at 45 ° C. Air was supplied at 10 L / min over 3 hours to regenerate iron (III) nitrate. As a result, it was confirmed that the Fe ²⁺ concentration remaining in the liquid was less than 0.1 g / L, which was reduced to a level that does not hinder reuse.

<Example 2>
In Example 2, the same silver wax-coated base piece as in Example 1 and the iron nitrate (III) solution having the concentrations and liquid amounts shown in Table 2 were put into the same rotating stirring tank as in Example 1, and Example 1 The silver wax was dissolved and peeled under the same stirring conditions as in.

  Next, the base material piece after silver wax separation was washed with water in the same manner as in Example 1 to recover 752 g of the base material piece. The silver quality of this base material piece was less than 10 ppm, and it was a quality that could be regenerated as a silver wax-coated base material without problems. It was also confirmed that the dissolution loss of the substrate was less than 0.2%.

  In Example 2, since slight precipitation of silver powder was observed in the solution after dissolving the silver wax, suction filtration using a hard filter paper, Nutsche and a filter bottle was performed. As a result, 9.5 L of the dissolved solution was recovered, and the precipitated silver powder was washed and dried to recover 4.8 g of silver powder in a dry state.

  Subsequently, in Example 2, the solution after dissolution was placed in the same coagulation sedimentation tank as in Example 1, and 180 ml of 36 wt% hydrochloric acid was added under the same stirring conditions as in Example 1 to produce silver chloride. Liquid separation was performed to obtain 9.2 L of a solution after desilvering with a silver concentration of 4.7 g / L.

In Example 2, when this desilvered solution was put into the same rotary stirring tank as in Example 1 and iron (III) nitrate was regenerated in the same manner as in Example 1, the residual Fe ²⁺ concentration in the solution was 0.00. It was confirmed that the level could be reduced to a level of less than 1 g / L with no trouble in reuse.

<Comparative Example 1>
In Comparative Example 1, a silver wax-coated base piece having a weight of 1 kg and an iron nitrate (III) solution having the concentrations and liquid amounts shown in Table 2 were put into the same rotating stirring tank as in Example 1, and the same as in Example 1. Silver wax was dissolved and peeled under stirring conditions.

  Next, the base material piece after silver wax separation was washed with water in the same manner as in Example 1 to recover 752 g of the base material piece. The silver quality of this base material piece was 100 ppm, and it was a quality that could not be regenerated as a raw material for the silver solder coated base material.

  Furthermore, in Comparative Example 1, a large amount of silver powder was precipitated in the solution after dissolution, and therefore silver powder was collected in the same manner as in Example 2. As a result, 11.3 g of silver powder was separated.

  Table 2 summarizes the silver quality of the recovered base material pieces, the amount of silver powder contained in the solution after the dissolution and peeling step, and the silver concentration in the solution after the dissolution and peeling step in Examples and Comparative Examples. It can be said that the amount of silver powder contained in the solution after the dissolution and peeling step is the amount of precipitated Ag once dissolved by the reduction precipitation reaction of silver.

  From the results shown in Table 2, in Example 1, all of the silver contained in the silver wax-coated substrate piece was dissolved, and the solution after dissolution and peeling did not contain silver powder. It can be seen that no reaction has occurred. Therefore, in Example 1, it turns out that all the silver in a silver wax can be collect | recovered. Moreover, in Example 1, it turns out that the silver quality of a base material piece is very low.

  In Example 2, although some silver was precipitated, most of the silver was dissolved, and it can be seen that the silver can be sufficiently recovered. Moreover, in Example 2, like Example 1, it turns out that the silver quality remaining on a base material piece is very low.

  On the other hand, in Comparative Example 1, the amount of silver that can be recovered was small because the amount of silver deposited was large and the amount of silver dissolved was small compared to the Examples. Moreover, in the comparative example 1, the silver quality of the base material piece became very high.

(Example 3)
In Example 3, the silver wax-coated substrate was dissolved by the same method as in Example 1 using the same apparatus and materials as in Example 1, and a desilvered post-desilvered solution (iron nitrate solution) was obtained. 900 ml of this desilvered solution (iron nitrate solution) is taken, put in a rotating stirring tank 1 as shown in FIG. 2 having a capacity of 2 L, and heated, and at the same time, from the air supply pipe 4 to the center of the bottom of the stirring tank 1. Aeration was performed, and the mixture was oxidized by stirring using a stirring blade 3 with a disk.

  The degree of oxidation was determined by charging the redox potential (ORP) measured in the stirring tank 1 using a silver / silver chloride electrode as a reference electrode and using the silver-silver chloride electrode as a reference electrode. The time until reaching ORP810 mV was evaluated. The change in redox potential is shown in FIG. In addition, the value of the oxidation-reduction potential shown below is a measured value using a silver-silver chloride electrode.

  As shown in FIG. 3, when the solution after desilvering is maintained at 60 ° C., it reaches in a short time of about 1 to 2 hours until the oxidation-reduction potential becomes 810 mV or more, and from 3 hours in Example 1 I was able to oxidize as soon as possible.

  In addition, as shown in Table 3, the concentration of iron (II) in the post-desilvering solution (iron nitrate solution) at the end of oxidation decreased from 19 g / l before oxidation to less than 0.1 g / l, and reused. It has been confirmed that the level has been reduced to a level at which there is no problem.

(Comparative Example 2)
In Comparative Example 2, the same process as in Example 3 was performed except that the post-desilvering solution (iron nitrate solution) was oxidized at a room temperature. In Comparative Example 2, the oxidation took 10 hours or more.

From the results of Example 3 and Comparative Example 2, it can be seen that it is possible to more efficiently oxidize Fe ²⁺ by heating the liquid temperature of the solution after desilvering (iron nitrate solution) to 45 ° C. or higher.

<Example 4>
In Example 4, 1 kg of a silver wax-coated base piece and 10 L of an iron (III) nitrate solution prepared to an iron concentration of 67 g / L with the composition shown in Table 4 were attached with a baffle for stirring having a capacity of 30 L shown in FIG. The slurry was put into the rotary stirring tank 1 and stirred and mixed at a rotational speed of 20 rpm for 3 hours to dissolve and peel the silver wax to obtain a slurry composed of the dissolved solution and the dissolved residue.

  Next, in Example 4, the solution after dissolution and the leaching residue were separated using a Nutsche and a filter bottle, and the leaching residue was washed with a total of 3 L of water to recover 753 g of the base material piece. The silver quality of this base material piece was less than 10 ppm, and it was a quality that could be regenerated as a new base material. The dissolution loss of the base material was less than 0.2%. Furthermore, no precipitate was observed in the 9.7 L recovered solution or the substrate cleaning solution. Table 4 shows the concentrations of silver and copper in the collected solution after dissolution (solution after dissolution).

  Subsequently, in Example 4, the solution after dissolution was placed in a coagulation sedimentation tank with a stirring blade having a capacity of 15 L, and 145 ml of 36 wt% hydrochloric acid (concentrated hydrochloric acid) was added while stirring at 200 rpm to produce silver chloride. 9.5 L of liquid after desilvering with a silver concentration of 1.1 g / L was obtained.

Next, the solution after desilvering is placed in a stirred aeration tank 1 having a capacity of 20 L as in the configuration shown in FIG. 2, and the air aeration rate is 10 L / min from the air supply pipe 5 while heating and maintaining the liquid temperature at 55 ° C. Then, air was supplied and iron (III) nitrate was regenerated over 3 hours. As a result, the Fe ²⁺ concentration remaining in the liquid was less than 0.1 g / L, and was reduced to a level that does not hinder reuse.

  Since the concentration of 8.8 L of iron and copper in the post-regeneration solution obtained in the iron nitrate regeneration step was the value shown in Table 4, the amount of copper added to the solution and the equivalent amount of nitric acid ( 0.68 mol) and the iron (III) nitrate reagent for 45 g of trivalent iron lost due to liquid loss during the solid-liquid separation were supplemented, and the liquid volume was adjusted to 10.0 L. Then, it repeated to the 2nd melt | dissolution peeling process. Table 4 shows the composition of the adjusted iron (III) nitrate solution (adjusted solution).

  Except for using an iron (III) nitrate solution as a repetitive solution, 1 kg of the raw material was dissolved and peeled under the same conditions as the first time. The silver quality of the recovered and washed base piece was less than 10 ppm. It was of a quality that can be recycled as a base material. From this result, by adjusting the nitrate ion concentration of the iron nitrate (III) solution after the iron nitrate regeneration step, even a reused iron nitrate (III) solution can dissolve and reuse the silver alloy. It can be seen that a piece of wood is obtained.

<Example 5>
In Example 5, the same stripping treatment as in Example 4 was performed except that the iron (III) nitrate solution after the fifth regeneration was used in total four times more in accordance with Example 4 and used. went. The composition of the liquid after the fifth regeneration is as shown in Table 4. The silver quality of the base material pieces collected after the 6th total dissolution treatment and subjected to the same cleaning treatment as in Example 4 was less than 10 ppm, which was reproducible as a new base material. The dissolution loss of the base material was less than 0.2%. In addition, no precipitate was observed in the recovered solution or the substrate cleaning solution. Table 4 shows the concentrations of silver and copper in the collected solution after dissolution (solution after dissolution).

Subsequently, the recovered silver chloride solution was subjected to the treatment of the silver chloride production step under the same conditions as in Example 4 to obtain 9.3 L after silver removal. Further, the iron (III) nitrate regeneration treatment for 3 hours was performed on the solution after desilvering under the same treatment conditions as in Example 4. As a result, the Fe ²⁺ concentration remaining in the solution became less than 0.1 g / L, The level has been reduced to a level that does not hinder use.

  The concentration of 8.8 L of iron and copper in the post-regeneration solution obtained in the iron nitrate regeneration step was the value shown in Table 4, so that 0.67 mol of nitric acid and trivalent iron 63 g of iron nitrate (III ) After supplementing the reagent, the liquid volume was adjusted to 10.0L. Then, the 7th melt | dissolution peeling process was performed in total. Table 4 shows the composition of the adjusted iron (III) nitrate solution (adjusted solution).

  Except for using an iron (III) nitrate solution as a repetitive solution, 1 kg of the raw material was dissolved and peeled under the same conditions as the first time. The silver quality of the recovered and washed base piece was less than 10 ppm. It was of a quality that can be recycled as a base material. From this result, by adjusting the nitrate ion concentration of the iron nitrate (III) solution in the iron nitrate regeneration process, even in the iron nitrate (III) solution that has been reused and regenerated multiple times, the silver alloy is dissolved, It can be seen that a reusable substrate piece is obtained.

<Comparative Example 3>
In Comparative Example 3, the dissolution peeling process and the silver chloride production process were performed according to Example 4. The silver quality of the base material piece collected after the dissolution and peeling treatment and subjected to the same cleaning treatment as in Example 4 was less than 10 ppm, and it was a quality that could be regenerated as a new base material. The dissolution loss of the base material was less than 0.2%. Furthermore, no precipitate was observed in the recovered solution after dissolution (solution after dissolution) or in the substrate cleaning solution. Table 4 shows the concentrations of silver and copper in the recovered solution after dissolution.

  Subsequently, the recovered silver chloride solution was subjected to a silver chloride production step under the same conditions as in Example 4 to obtain 9.5 L of a solution after desilvering.

Here, in Comparative Example 3, the same amount of nitric acid (0.68 mol) as the amount of copper added to the solution in the dissolution and peeling step was added before the iron nitrate regeneration treatment, and then the same processing conditions as in Example 4 The iron nitrate (III) regeneration treatment was carried out for 3 hours. As a result, the Fe ²⁺ in the liquid was 3.2 g / L, which was a level that could not be reused in the next dissolution and peeling process. Therefore, it can be seen that if the nitric acid supplementation is performed before the iron nitrate regeneration treatment, the reaction efficiency of the oxidation regeneration process deteriorates, and the recycling of the iron (III) nitrate solution is inefficient and cannot be economically performed. From this result, it can be seen that if the concentration of nitrate ions is adjusted before the iron nitrate regeneration treatment, the efficiency of regeneration of Fe (III) ions and recycling of the iron nitrate (III) solution is deteriorated.

<Comparative example 4>
In Comparative Example 4, the dissolution peeling process and the silver chloride production process were performed according to Example 5.
The silver quality of the base material piece collected after the dissolution and peeling treatment and subjected to the same cleaning treatment as in Example 4 was less than 10 ppm, and it was a quality that could be regenerated as a raw material for a new base material. The dissolution loss of the base material was less than 0.2%. Further, no precipitate was observed in the recovered solution after dissolution or in the substrate cleaning solution. Table 4 shows the concentrations of silver and copper in the collected solution after dissolution (solution after dissolution).

  Subsequently, the recovered solution after dissolution was subjected to a silver chloride production process under the same conditions as in Example 4 and Example 5 to obtain 9.4 L of a solution after desilvering.

Here, in Comparative Example 4, as in Comparative Example 1, before the iron nitrate regeneration treatment, after adding the equivalent amount of nitric acid (0.67 mol) to the amount of copper added in the solution in the dissolution and peeling step, the test was performed. As a result of the iron nitrate (III) regeneration treatment for 3 hours under the same treatment conditions as in Examples 4 and 5, Fe ^{2+ in} the liquid was 5.4 g / L, which was a level that could not be reused in the next dissolution and peeling process. It was. From this result, when the concentration of nitrate ions is adjusted before the iron nitrate regeneration treatment and the silver chloride production step is repeated several times from the dissolution and peeling step, the concentration of Fe ²⁺ is further increased, and the regeneration of Fe (III) ions and It can be seen that the recycling efficiency of the iron (III) nitrate solution becomes worse.

From the above, by applying the present invention, the silver-based alloy applied or formed on the surface of the iron-based alloy base material is dissolved and separated without damaging the base material without using toxic substances such as cyanide. Thus, it can be seen that the silver recovery rate is high, and both the base material and silver can be recovered economically and recycled. In addition, by applying the present invention, when oxidizing Fe ²⁺ , the temperature of the solution after desilvering can be within a range of 45 ° C. or higher and 70 ° C. or lower so that the oxidation can be performed in a short time. It can be seen that silver can be recovered efficiently. In addition, by applying the present invention, the iron (III) solution is repeatedly used many times by replenishing the silver alloy components other than silver dissolved in the dissolution and peeling step and equivalent nitrate ions after the iron nitrate regeneration step. And the iron oxide regeneration step can be performed efficiently.

  1 rotating stirring tank, 2 baffle plate for stirring, 3 stirring blade with disc, 4 air supply pipe, 5 temperature sensor

Claims (5)

Adding a solution containing iron nitrate (III) to a substrate coated with silver or a silver-based alloy, dissolving the silver or silver-based alloy, and removing the silver or silver-based alloy from the substrate;
Adding a hydrochloric acid to a solution in which the silver or silver-based alloy is dissolved to form a silver chloride precipitate;
An iron nitrate regeneration step of oxidizing the divalent iron ions contained in the solution after the dissolution and peeling step into trivalent iron ions to regenerate the iron nitrate (III) -containing solution ;
After the iron nitrate regeneration step, the concentration of the iron nitrate (III) -containing solution produced in the iron nitrate regeneration step is adjusted to the concentration of the iron nitrate (III) -containing solution used in the dissolution and stripping step. A solution adjustment step,
In the dissolution and peeling step, the Fe ³⁺ concentration in the iron nitrate (III) -containing solution after the addition of the base material is maintained to be 1.5 times the Fe ²⁺ concentration or more,
Using the iron nitrate (III) -containing solution generated in the iron nitrate regeneration step in the dissolution and peeling step ,
In the iron nitrate (III) -containing solution adjustment step, nitric acid equivalent to silver alloy components other than silver dissolved in the dissolution and peeling step is supplemented by adding nitric acid, and the nitric acid produced in the iron nitrate regeneration step A method for recovering silver, comprising adjusting a nitrate ion concentration of an iron (III) -containing solution . The method for recovering silver according to claim 1, wherein the Fe ³⁺ concentration is maintained at 2.5 times or more of the Fe ²⁺ concentration.   3. The silver recovery method according to claim 1, wherein the iron nitrate regeneration step is performed after the silver chloride production step. The method for recovering silver according to any one of claims 1 to 3 , wherein the base material coated with the silver-based alloy is an iron alloy coated with silver brazing. In the above iron nitrate regeneration step, the dissolving separation step after the above solution of a liquid temperature of 45 ° C. or more, of silver according to any one of claims 1 to 4, characterized in that the 70 ° C. or less Collection method.

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