JP6162554B2 - Electrolytic purification apparatus for Ag and method for electrolytic purification of Ag using the apparatus - Google Patents

Description

  The present invention relates to a technique for electrolytically purifying Ag, and more particularly to an electrolytic purification apparatus used for electrolytic purification of Ag, and an electrolytic purification method using the electrolytic purification apparatus.

  Ag is widely used in daily goods and industrial products such as tableware, jewelry, dental materials, and various electronic devices. For example, alloys (Ag-containing alloys) with various metals are used for jewelry and wiring of electronic devices. Further, depending on applications, Ag and other metals and non-metals are used together. For example, dental materials are made of non-metal such as gold-silver palladium alloy and ceramics.

  As described above, Ag is widely used in various products, while Ag is collected and recycled from used products. For example, an anode produced by processing a used Ag-containing raw material is electrolytically purified in an electrolytic solution, whereby Ag in the anode is dissolved and Ag is deposited on the cathode to purify Ag (electrolytic purification). Method).

  However, the Ag content in the anode (ratio of Ag to the total metal dissolved in the electrolyte: [Ag mass / (Ag mass + mass of impurity metal element dissolved in the electrolyte) × 100]) is less than 95% by mass. (Hereinafter, sometimes referred to as “low Ag content”), the Ag concentration in the electrolytic solution is lowered, the purity of the purified Ag is lowered, and the shape of the Ag deposited on the cathode is dendritic. Since it changes from (dendritic) to powdery and the volume of precipitated Ag increases by about 10 times, a large electrolytic cell is required, and it is difficult to clean the precipitated Ag after electrolysis. there were.

  Therefore, pretreatment is performed to increase the Ag content in the Ag-containing raw material as much as possible, or chemicals are added during electrolytic purification to control the Ag concentration in the electrolytic solution.

  For example, Patent Document 1 proposes a technique for increasing the Ag content by dry purification or wet purification prior to electrolytic purification.

Patent Document 2 proposes a technique for increasing the Ag concentration in the electrolytic solution by adding a pH adjusting agent (Ag ₂ O).

  In addition, since Ag which could not be recovered by electrolytic purification remained in the electrolytic solution after electrolysis (used electrolytic solution), it was necessary to separately collect Ag. For example, a chlorine component is added to a used electrolytic solution and recovered as AgCl. This is because many impurities other than Ag are dissolved in the used electrolytic solution, but by using AgCl, these impurities can be separated. After the recovered AgCl is reduced, it is returned again to the electrolytic purification process, and Ag is recovered.

JP 07-34147 A JP 2000-38692 A

  All of the above-described conventional techniques require separate processing to obtain high-purity Ag. Therefore, facilities and chemicals for performing the processing must be prepared, and further, the remaining Ag in the used electrolyte can be removed. Equipment and chemicals to collect are also required. Therefore, new problems such as an increase in cost and complicated processing have occurred. The present invention has been made paying attention to the above-described circumstances, and the purpose thereof is a technique in which high-purity Ag can be obtained only by electrolytic purification without performing pretreatment or addition of chemicals as in the prior art. Is to establish. It is preferable to provide a technique capable of purifying high-purity Ag having a purity of 99.9% or more even when an Ag-containing raw material having an Ag content of less than 95% by mass is used for the anode. More preferably, the present invention also provides a technique for collecting Ag from the used electrolyte without separately preparing new equipment and chemicals.

  The electrolytic purification apparatus of the present invention capable of solving the above problems is an Ag electrolytic purification apparatus using an Ag-containing raw material as an anode, and the electrolytic tank of the electrolytic purification apparatus is a first electrolytic tank partitioned by a diaphragm And the second electrolytic cell comprises the anode and the first cathode, the second electrolytic cell comprises the second cathode, and between the anode and the first cathode, and The gist is that a current control mechanism for controlling a current between the anode and the second cathode is provided.

  In another preferred embodiment, the anode includes an anode bag that does not pass through anode mud containing a metal having a smaller ionization tendency than Ag.

  The present invention also includes an Ag electrolytic purification method using the above-described Ag electrolytic purification apparatus, wherein the Ag electrolytic purification method includes the anode and the first cathode, and the anode and the first electrode. The current between the two cathodes is controlled by the current control mechanism to adjust the Ag deposition rate deposited on the first cathode and the Ag dissolution rate eluted from the anode, and are included in the first electrolytic solution of the first electrolytic cell. The main point is to control the Ag concentration.

  In practicing the present invention, it is also a preferred embodiment that the first electrolytic solution after electrolytic purification is filled in the second electrolytic cell, and Ag is electrolytically recovered.

  If the apparatus of this invention is used, the elution amount of Ag in an anode can be raised, suppressing the amount of Ag precipitation in a 1st cathode. Therefore, even when a raw material containing a large amount of impurities dissolved in the electrolytic solution is used for the anode, Ag having the same degree of purity as that of the prior art can be purified only by electrolytic purification without performing the pretreatment or the addition of chemicals.

  Further, according to the present invention, even when a raw material containing an impurity that does not dissolve in the electrolytic solution is used for the anode, the impurity particles (anode mud) generated from the anode can be prevented from being mixed into the precipitated Ag, High purity Ag can be obtained more easily than in the prior art.

  By controlling the current between the anode and the first cathode and between the anode and the second cathode by the current control mechanism of the apparatus of the present invention, and controlling the decrease in the Ag concentration of the first electrolyte, the bulk density is high. Dendritic Ag can be obtained.

  Furthermore, according to the present invention, even when Ag remains in the used electrolyte, it is possible to recover Ag without installing a new recovery facility for collecting Ag or adding a chemical.

FIG. 1 is a schematic configuration diagram of the electrolytic purification apparatus of the present invention. FIG. 2 is another schematic configuration diagram of the electrolytic purification apparatus of the present invention. FIG. 3 is a schematic configuration diagram of a conventional electrolytic purification apparatus. FIG. 4 is a graph showing the relationship between the Ag concentration in the electrolyte solution of Example 1 and the electrolysis time. FIG. 5 is a graph showing the relationship between the Ag concentration in the electrolyte solution of Example 2 and the electrolysis time. FIG. 6 is a graph showing the relationship between the Ag concentration in the electrolyte solution of Example 3 and the electrolysis time. FIG. 7 is a graph showing the relationship between the Ag concentration in the electrolytic solution of the comparative example and the electrolysis time.

  When the present inventors performed electrolytic purification using a low-Ag content raw material for the anode using a conventional electrolytic purification apparatus as shown in FIG. 3, impurity metals such as Cu other than Ag are deposited on the cathode. Thus, the cause of the lower purity of the purified Ag was repeatedly investigated.

  In general, the phenomenon of impurity metal precipitation is considered as follows. First, when the anode contains an impurity metal having a higher ionization tendency than Ag (for example, Cu, Ni, Fe, Cr, Zn, etc., hereinafter referred to as “soluble impurity metal”), the anode is more soluble than Ag. Impurity metals elute preferentially. On the other hand, Ag having a small ionization tendency is preferentially deposited over the soluble impurity metal at the cathode. Therefore, when the Ag content of the anode is low, the Ag concentration in the electrolytic solution decreases as the electrolysis time elapses, and the concentration of the soluble impurity metal increases.

  Then, when the Ag concentration in the electrolytic solution decreases and the soluble impurity metal concentration increases to some extent, a part of the soluble impurity metal starts to be reduced and deposited, so that Ag deposited at the cathode (hereinafter referred to as “electrodeposited Ag”). The purity may decrease.

  As a result of the study by the present inventors based on the above phenomenon, even when a raw material having a low Ag content is used for the anode, the Ag deposition rate and the Ag elution rate are controlled so that the soluble impurity metal does not precipitate. It was concluded that if the Ag concentration is appropriately controlled, precipitation of soluble impurity metals at the cathode can be suppressed, and high-purity Ag can be purified.

  However, in the conventional electrolytic refining apparatus as shown in FIG. 3, when the Ag content of the anode is low, an imbalance between the amount of electricity necessary for dissolution of Ag and the amount of electricity necessary for precipitation of Ag cannot be eliminated. A decrease in Ag concentration in the liquid could not be suppressed.

  Therefore, as a result of intensive studies on the structure of the electrolytic purification apparatus, the present inventors have solved the above problem of unbalance in the amount of electricity, and dissolved Ag and dissolved Ag. Since the current required for the precipitation can be controlled to suppress the decrease in the Ag concentration in the electrolytic solution, it has been found that high-purity Ag can be obtained by preventing the precipitation of the soluble impurity metal, leading to the present invention. . Hereinafter, the electrolytic purification apparatus of the present invention will be described.

  The electrolytic purification apparatus of the present invention comprises an electrolytic cell comprising a first electrolytic cell and a second electrolytic cell separated by a diaphragm, the first electrolytic cell comprises an anode and a first cathode, and The two electrolytic cell has a second cathode. Furthermore, the gist is that a mechanism (current control mechanism) for controlling the current between the anode and the first cathode and between the anode and the second cathode is provided.

  In the electrolytic purification apparatus of the present invention, by providing a plurality of cathodes with a diaphragm so as to be electrically in parallel, a current flowing between the first cathode and the anode (current A) and a current flowing between the second cathode and the anode ( A current (current A + current B) obtained by adding the current B) can flow to the anode. That is, the anode current value can be made larger than the first cathode current value (anode: current A + current B> first cathode: current A). Therefore, by increasing the value of the current flowing through the anode while decreasing the current flowing through the first cathode, the amount of Ag eluted at the anode can be increased while suppressing the amount of Ag deposited at the first cathode. Such a current flow between the electrodes can be appropriately controlled by a current control mechanism.

  FIG. 1 is a schematic configuration diagram of the electrolytic purification apparatus of the present invention. The electrolytic cell 1 is composed of a first electrolytic cell 2 and a second electrolytic cell 3 separated by a diaphragm 4.

  The structure of the electrolytic cell 1 is not particularly limited, and an electrolytic cell having an arbitrary structure can be used. By separating the electrolytic cell 1 with the diaphragm 4, Ag contained in the electrolytic solution (hereinafter referred to as “first electrolytic solution”) filled in the first electrolytic cell 2 can be used as the second cathode even when current flows between the electrodes. It is possible to control the flow of current without precipitating to 7. Therefore, if the current between the anode 6 and the second cathode 7 is controlled, the concentration of Ag contained in the first electrolyte can be easily controlled.

  The diaphragm 4 is not particularly limited as long as it is capable of electrical conduction (ion permeability) and has a property of not allowing the electrolytic solution to pass therethrough. However, when a diaphragm having high permeability of Ag ions from the first electrolytic cell 2 side to the second electrolytic cell 3 side is used, the Ag recovery rate at the first cathode 5 (the recovery rate of Ag eluted from the anode 6) is high. Along with the decrease, the Ag concentration in the electrolytic solution in the first electrolytic cell 2 also decreases. Therefore, as the diaphragm 4, an unglazed wall, a semipermeable membrane, an ion exchange membrane, or the like can be used, but a diaphragm having a low Ag ion permeability is preferably used. Specifically, a diaphragm having a low cation permeability is preferable, and examples of such a diaphragm having a difference in transport number include an anion exchange membrane and a bipolar membrane.

  The first electrolytic cell 2 of the present invention includes a first cathode 5 and an anode 6. The anode 6 contains Ag, and the balance is a metal other than Ag and / or a nonmetal. The Ag-containing raw material used for the anode 6 is used in a wide range of applications as described above, and various metals other than Ag are contained, and the Ag content is also different. Depending on the application, non-metals (ceramics, glass, etc.) may be included. Therefore, the ratio of Ag, metal other than Ag, and nonmetal constituting the anode 6 is not particularly limited. In particular, according to the present invention, high-purity Ag can be purified even if the Ag content is low, so the Ag content in the anode 6 (the ratio of Ag mass to the total of Ag mass and soluble impurity metal mass; the same applies hereinafter) is 95. It may be less than mass%, and may be 80 mass% or less. The lower limit of the Ag content is not particularly limited, but if the Ag content is too low, it takes time for electrolytic purification and the recovery efficiency deteriorates. Therefore, it is preferably 5% by mass or more, more preferably 20% by mass or more, and still more preferably. Is 30% by mass or more.

  The anode 6 may contain a metal having a smaller ionization tendency than Ag (Au, Pd, Pt: hereinafter referred to as “insoluble impurity metal”), but the total content of insoluble impurity metals is large. If the amount is too large, the dissolution rate of the anode 6 is remarkably reduced. Therefore, the amount is preferably 50% by mass or less, more preferably 35% by mass or less, based on the total metal elements contained in the anode 6.

  The anode 6 may be composed of, for example, a plurality of Ag-containing raw materials having different compositions, and the usage form may be used as the anode 6 by, for example, storing the Ag-containing raw material in a granular container. . The anode 6 may have a desired shape, and can be used after being formed into a desired shape such as a plate shape or a cylindrical shape.

  The first cathode 5 is not particularly limited as long as it does not corrode by the electrolytic solution, and examples thereof include electrode materials such as stainless steel and titanium.

  The second electrolytic cell 3 of the present invention has a second cathode 7. Similar to the first cathode 5, the second cathode 7 may be an electrode material having excellent corrosion resistance against an electrolytic solution such as stainless steel or titanium.

  In addition, the electrode material of the 1st cathode 5 and the 2nd cathode 7 may be the same, or may differ. Moreover, the shape of each cathode is not specifically limited, Arbitrary shapes, such as rod shape, porous shape, and plate shape, are employable. Furthermore, the number of electrodes provided in each electrolytic layer is not particularly limited, and a plurality of electrodes may be provided.

  The electrolytic purification apparatus of the present invention includes a current control mechanism 8 that controls the current between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7. The current control mechanism 8 of the present invention includes a power source that applies a DC voltage between electrodes and a measuring instrument that measures a current value between the electrodes. The power supply has a function of flowing a current by applying a predetermined voltage between the electrodes. The measuring instrument has a function of measuring a current value between the electrodes and controlling the power source based on the measured current value. In particular, the current control mechanism 8 of the present invention is configured to be able to control the current value between any electrodes by stopping energization or changing the voltage as necessary.

  For example, in FIG. 1, the current control mechanism 8 has a configuration in which a power source 8a is provided between the first cathode 5 and the anode 6, a power source 8b is provided between the anode 6 and the second cathode 7, and a measuring instrument (not shown) is included in each power source. The current value between the electrodes can be independently controlled by the power source 8b and the power source 8b. In FIG. 2, the power supply control mechanism 8 includes a variable resistor 9, a power supply 8 c, and a measuring device (not shown), and by adjusting the resistance value of the variable resistor according to the measurement result from the measuring device. The current flow from the power source 8c is controlled so that the current between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 can be controlled.

  In the present invention, metals having a smaller ionization tendency than Ag, such as Au, Pd, and Pt, are insoluble impurities that are liberated from the anode as single particles without being ionized even after electrolytic purification. These insoluble impurities are so-called anode mud (anode slime), and the purity of the purified Ag is lowered when Au or the like is mixed into Ag electrodeposited on the first cathode 5. In the present invention, from the viewpoint of preventing diffusion of anode mud generated from the anode 6 during electrolytic purification into the electrolytic solution, the anode 6 does not permeate anode mud containing a metal having a smaller ionization tendency than Ag, and Ag ions It is preferable to include an anode bag (container) 10 having a property of transmitting water. In addition, non-metals that do not dissolve in electrolytes such as ceramics, or metals that have a higher ionization tendency than Ag but do not dissolve even after electrolytic purification become insoluble impurities. preferable.

  The shape of the anode bag 10 is not particularly limited, and various known shapes such as a basket shape (upper opening) and a bag shape can be adopted. Moreover, the anode bag 10 should just be comprised with the material (For example, resin, such as PET, a metal etc.) which does not melt | dissolve in electrolyte solution. In addition, when the anode bag 10 is used, by providing a gap between the anode 6 and the anode bag 10, poor contact between the electrolyte solution and the anode 6 caused by the generated anode mud can be suppressed. Note that the anode mud in the anode bag is separately collected and purified, so that a desired noble metal or the like can be collected from the anode mud.

  The electrolytic purification apparatus of the present invention is configured as described above. Hereinafter, the electrolytic purification method using the electrolytic purification apparatus of this invention is demonstrated based on FIG.

  As a 1st electrolyte solution with which the 1st electrolytic cell 2 divided by the diaphragm 4 is filled, the various well-known electrolyte solution used for the electrolytic purification of Ag can be used. For example, an acid electrolyte such as nitric acid or sulfuric acid is preferable because Ag can exist stably in an ionic state. In particular, nitric acid is more preferable because it is excellent in solubility of Ag.

  In addition, the electrolyte solution which can melt | dissolve the metal (Au, Pt, Pd) whose ionization tendency is smaller than Ag is not preferable as a 1st electrolyte solution. For example, an alkali cyanide solution or aqua regia is also used as an electrolytic solution of Ag. However, when an alkali cyanide solution or aqua regia is used, a metal having a lower ionization tendency than Ag is dissolved, and a metal having a lower ionization tendency is agglomerated. This is because it is difficult to implement the present invention because it is preferentially deposited.

  The acid concentration of the first electrolytic solution is not particularly limited because it varies depending on electrolysis conditions and the like, but is preferably 0.01 to 1.5 mol / L. If the acid concentration of the first electrolytic solution is too low, the purified Ag becomes too fine, and filtration after the electrolytic purification is difficult, and the Ag recovery rate decreases. On the other hand, if the acid concentration of the first electrolyte is too high, the precipitated Ag may be redissolved.

  The method for adjusting the acid concentration is not particularly limited, and various known methods can be employed. It is recommended to dilute with water (more preferably with ion exchange water). The acid concentration can be neutralized with, for example, an alkali agent such as alkali hydroxide, but when the anode contains a heavy metal such as Cu, it is precipitated as a hydroxide when it is eluted in the first electrolyte. In addition, the purity of the purified Ag may decrease, which is not preferable.

  The electrolytic solution (hereinafter sometimes referred to as “second electrolytic solution”) filled in the second electrolytic cell 3 is not particularly limited as long as it is a conductive electrolytic solution, and various known electrolytic solutions can be used. it can. For example, an acid electrolyte solution may be used like the first electrolyte solution. The acid concentration is not particularly limited and may be the same level as the first electrolytic solution. However, the type and content of the metal contained in the second electrolytic solution, such as prevention of re-dissolution of the metal deposited on the second cathode 7. What is necessary is just to set suitably according to. Or you may fill the 2nd electrolytic vessel 3 with the 1st electrolyte solution (used 1st electrolyte solution) after electrolytic purification. From the viewpoint of increasing the Ag recovery rate, after the predetermined electrolytic purification, the used first electrolytic solution is filled in the second electrolytic cell 3, and the first electrolytic cell 2 is filled with a new electrolytic solution, and the electrolytic recovery of Ag is performed. It is desirable to do. As described above, when the second electrolytic cell 3 is filled with the used first electrolytic solution and the electrolytic recovery of Ag is performed, the second electrolytic solution (used first electrolytic solution) is generated by the current flowing between the anode 6 and the second cathode 7. ) Can be deposited on the second cathode 7, the Ag recovery rate can be increased, and the electric power can be effectively utilized.

  In addition, as a 2nd electrolyte solution, the electrolyte solution which has the property to deposit a metal on the surface of the diaphragm 4 is not preferable. Such an electrolytic solution causes Ag ions that have permeated through the diaphragm 4 from the first electrolytic cell 2 side to precipitate on the surface of the diaphragm 4, thereby blocking the diaphragm 4 and inhibiting electrolytic purification. For example, an electrolytic solution containing chlorine ions may precipitate Ag (AgCl) on the surface of the diaphragm 4. The alkaline electrolyte may cause heavy metal hydroxide to precipitate on the surface of the diaphragm 4.

  In the electrolytic purification method of the present invention, the supply method of the electrolytic solution is not particularly limited. After a certain amount of electrolytic solution is supplied to the first electrolytic tank 2 and electrolytically purified for a predetermined time, the used first electrolytic solution is changed to the first electrolytic solution. It may be a batch type that is taken out from the electrolytic cell 2 or may be a continuous type that supplies the electrolytic solution to the first electrolytic cell 2 at a constant speed and extracts the same amount of electrolytic solution from the first electrolytic cell 2. The used first electrolytic solution may be supplied to the second electrolytic cell 3 by being connected to the second electrolytic cell 3 via a pipe line (not illustrated) through a liquid feeding means such as a pump (not illustrated).

  The temperature of the first electrolytic solution and the second electrolytic solution during electrolytic purification is not particularly limited, and may be, for example, about 20 ° C. to 25 ° C.

  In the present invention, electrolytic purification is performed while controlling the concentration of Ag contained in the first electrolyte so that the soluble impurity metal contained in the first electrolyte does not precipitate. Specifically, the current between the anode 6 and the first cathode 5 and between the anode 6 and the second cathode 7 is controlled by the current control mechanism 8 so that the soluble impurity metal does not deposit on the first cathode 5. The Ag concentration contained in the electrolytic solution is controlled.

  The current (current A) that flows between the first cathode 5 and the anode 6 and the current (current B) that flows between the anode 6 and the second cathode 7 can be determined as follows, for example. In order to suppress a decrease in Ag concentration of the first electrolyte solution, it is preferable to control so that the current A consumed for Ag deposition at the first cathode 5 does not exceed the current consumed for Ag elution from the anode 6. Therefore, the current A and the current B may be controlled so that the ratio of the current A (current A / (current A + current B)) is not more than the value D1 determined by the following formula (1).

(In the formula, M (Ag): mole percentage of Ag contained in anode 6 M (i): mole percentage of metal dissolved in electrolyte among elements contained in anode 6 V (i): anode The ionic valence of each element contained in 6 Note that the mole percentage means the percentage of the sum of Ag and soluble impurity metal)

  The current value (current A + current B) that flows through the anode 6 can be arbitrarily determined depending on the electrolysis efficiency and the target Ag production amount. If the voltage is increased too much in order to increase the current flowing through the anode 6, electrolysis of the solvent component (for example, water) in the electrolytic solution occurs, and the current efficiency decreases. Further, the generation of gas accompanying electrolysis of the solvent component makes the Ag deposition state at the first cathode 5 unstable. Therefore, it is desirable to control the current flowing through the anode 6 to be equal to or lower than the voltage at which the solvent component is electrolyzed. The voltage at which the solvent component is electrolyzed varies depending on the composition of the first electrolytic solution. However, since the bubbles are generated in the electrolytic solution when the solvent component is electrolyzed, it is preferable to control so that no bubbles are generated.

  The ratio of the current to be applied to the current A and the current B may be changed as appropriate. Each time so that the Ag precipitation rate and the Ag elution rate are always the same during electrolysis, or the Ag elution rate is higher than the Ag precipitation rate. It is preferable to control the current flowing between the electrodes by the current control mechanism 8. If the Ag concentration can be maintained to such an extent that the soluble impurity metal does not precipitate, it is allowed that the Ag deposition rate is faster than the Ag elution rate during electrolysis.

  It is also desirable to deposit Ag on the first cathode 5 after increasing the Ag concentration in the first electrolyte to a predetermined concentration. If the Ag concentration in the first electrolytic solution is increased in advance, it is easy to maintain the Ag concentration in the first electrolytic solution so high that the soluble impurity metal does not precipitate during electrolytic purification. Therefore, the allowable concentration of the soluble impurity metal can be increased, and the precipitation of the soluble impurity metal can be more effectively suppressed. Therefore, for example, the current control mechanism 8 is controlled, and the current flowing between the first cathode 5 and the anode 6 is suppressed or stopped and the second cathode 7 and the anode 6 are controlled until the Ag concentration of the first electrolyte reaches a predetermined concentration. What is necessary is just to enlarge the electric current which flows between them. For example, in the case of FIG. 1, the current flowing between the first cathode 5 and the anode 6 suppresses the current flowing between the first cathode 5 and the anode 6 by turning off the power supply 8a or controlling the power supply 8a. Do not precipitate Ag or reduce the deposition rate. Further, the current flowing between the second cathode 7 and the anode 6 can increase the Ag concentration of the first electrolyte by controlling the amount of current with the power source 8b so that the Ag elution rate from the anode 6 is increased. Easy to do.

  Then, the current flowing between the first cathode 5 and the anode 6 and the current flowing between the second cathode 7 and the anode 6 after the Ag concentration of the first electrolyte reaches a predetermined concentration are converted into the power supply control mechanism 8 (power supply 8a, power supply 8b). And the Ag concentration of the first electrolyte solution, that is, the Ag elution amount and the Ag deposition amount, may be controlled so that the soluble impurity metal does not deposit on the first cathode 5.

  The electrolytic purification does not need to be continued until all the Ag in the first electrolytic solution is reduced and deposited, and the electrolytic purification may be terminated after an arbitrary electrolytic purification time elapses. For example, even if the current control mechanism 8 is controlled and the Ag concentration during electrolytic purification is maintained at a desired value, the soluble impurity metal concentration increases as the electrolytic purification time elapses, so that the soluble impurity metal is deposited. There are things to do.

  There are still many unclear points about how high the concentration of the soluble impurity metal is, and the precipitation behavior of the soluble impurity metal varies depending on the constituent elements of the anode, the properties of the electrolyte, the current value, and the like. Therefore, although the electrolysis conditions cannot be determined uniquely, the electrolysis conditions are determined by preliminary experiments, or the Ag concentration or soluble impurity metal concentration of the first electrolytic solution is monitored during the electrolytic purification, If the deposit on the one cathode 5 is monitored, electrolytic purification can be performed under the condition that the soluble impurity metal does not precipitate.

  The Ag concentration of the first electrolytic solution during electrolytic purification varies depending on the electrolysis conditions, the properties of the electrolytic solution, the composition of the anode, etc., and is not particularly limited. However, as described above, when the Ag concentration decreases, The metal precipitates and the purity of the refined Ag decreases, and the shape of the electrodeposited Ag also changes from dendritic to powdery. Therefore, it is desirable to appropriately control the Ag concentration of the first electrolytic solution during electrolytic purification so that problems such as precipitation of soluble impurity metals do not occur. In the present invention, it is recommended that the Ag concentration of the first electrolytic solution during electrolytic purification is preferably maintained at 5 g / L or more, more preferably 30 g / L or more.

  In the case where Ag remains in the used first electrolytic solution after performing the predetermined electrolytic purification, from the viewpoint of increasing the Ag recovery rate, the used first electrolytic solution is subjected to various treatments such as chemical reduction and the like. Recovery may be performed. As a method for recovering Ag, it is preferable to fill the second electrolytic cell 3 with the used first electrolytic solution and to purify the first electrolytic cell 2 with a new electrolytic solution. Since electrolytic purification and Ag recovery can be performed in parallel, it is not necessary to add a chemical to Ag recovery or provide a new recovery facility as in the prior art, and efficient use of electric power can be achieved. In addition, when filling the used 1st electrolyte solution in the 2nd electrolytic vessel 3, if the Ag density | concentration of the used 1st electrolyte solution (2nd electrolyte solution) with which the 2nd electrolytic vessel 3 was filled falls to predetermined | prescribed density | concentration, What is necessary is just to extract electrolyte solution from the 2nd electrolytic vessel 3, and to fill the 2nd electrolytic vessel 3 with the newly used 1st electrolytic solution. Further, when the purity of Ag deposited on the second cathode 7 is low, further purification of Ag may be performed. For example, purification by a known method is possible, but purification may be performed by returning to the manufacturing process of the anode 6.

  Ag deposited on the first cathode 5 and the second cathode 7 may be collected by any means, and can be easily collected by scraping means such as a scraper. The collected Ag may be subjected to various known processes. For example, high-purity purified Ag can be obtained by washing with pure water (including operations such as filtration) and then drying.

  When the anode bag 10 is used as the anode 6, the anode mud in the anode bag 10 is dissolved in, for example, aqua regia, hydrochloric acid to which hydrogen peroxide is added, and then wet-purified to obtain a desired metal (for example, Au, Pt, Pd, etc.) can be separated and recovered.

  According to the electrolytic purification method of the present invention, high purity Ag can be purified from a raw material having a low Ag content.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1
Based on the apparatus and method of the present invention, electrolytic purification of Ag was performed using a low Ag-containing raw material for the anode. Specifically, the following experiment was conducted using an electrolytic purification apparatus having the configuration shown in FIG. As the diaphragm 4, an anion exchange membrane (a company name LANXESS, product name MA-3475) was used. As the anode 6, 120 g of an Ag-containing alloy plate having the composition shown in Table 1 cast into a plate shape (length and width size: 2 cm × 3.5 cm, electrode area: 14 cm ² (front and back two surfaces)) was used. The first cathode 5 was made of stainless steel (length and width size 2 cm × 3.5 cm, electrode area 7 cm ² ). In addition, the anode 6 was installed in the state inserted in the anode bag 10 (PET cloth bag).

The first electrolytic cell 2 was filled with a 0.3 mol / L nitric acid aqueous solution (100 mL) as the first electrolytic solution. The second electrolytic cell 3 was filled with 100 mL of a 0.3 mol / L nitric acid aqueous solution and then subjected to electrolytic purification. The current between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 was controlled by the current control mechanism 8. The upper limit of the ratio of the current (current A) flowing between the first cathode 5 and the anode 6 was calculated by the above formula (1) based on the mole percentage of the Ag-containing alloy plate constituting the anode.
D1 = {8.2 / (8.2 × 1 + 1.7 × 3 + 74.8 × 2 + 2.7 × 2 + 4.5 × 2 + 3.8 × 3 + 1.5 × 2 + 2.8 × 2)} × 100 = 4.1%

  During electrolytic purification, the Ag concentration in the first electrolytic solution was measured by ICP emission spectroscopy and monitored. The temperature of the electrolytic solution during electrolytic purification was 20 to 25 ° C. for both the first electrolytic cell 2 and the second electrolytic cell 3.

  Before depositing Ag on the first cathode 5, the power source 8b provided on the second electrolytic cell 3 side is turned on until the Ag concentration in the electrolytic solution of the first electrolytic cell 2 reaches 30 g / L. A current (0.77 A) was passed between the second cathode 7. Since the power supply 8a was turned off until the Ag concentration reached a predetermined concentration and no current was passed between the first electrode 5 and the anode 6, Ag was not deposited on the first cathode 5 (about 20 hours from the start). .

  When the Ag concentration of the first electrolytic solution reaches 30 g / L, an electric current (0.03 A) is passed from the power source 8 a between the first cathode 5 and the anode 6 to start electrolysis of Ag in the first electrolytic cell 2. did. Further, the ratio of the current value flowing between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 (first electrode: second electrode) is maintained by the power supplies 8a and 8b so as to maintain 0.4: 9.6. Electrolysis was continued while controlling the current (about 46 hours from the start).

  The change with time of the Ag concentration in the first electrolyte solution was measured. As shown in FIG. 4, when electrolytic purification is performed by appropriately controlling the current after the Ag concentration in the electrolytic solution reaches 30 g / L, the Ag concentration in the electrolytic solution should be maintained at 25 g / L or more. I was able to.

  After the completion of electrolytic purification, the impurity content contained in the Ag electrodeposited on the first cathode 5 was examined using an ICP emission spectroscopic device. As a result, as shown in Table 2, the purity of the electrodeposited Ag was 99.98%. The crystal state of electrodeposited Ag was dendritic.

  Further, Ag was deposited on the second cathode 7 after completion of the electrolytic purification, and the Ag concentration in the electrolytic solution in the second electrolytic cell 3 was less than 0.1 g / L. In this example, Ag can also be recovered from the second electrolytic solution, so that a high Ag recovery rate was achieved as a whole.

Example 2
Similar to Example 1, the following experiment was conducted using an electrolytic purification apparatus having the configuration shown in FIG. The same diaphragm 4 and first cathode 5 as those in Example 1 were used except that 120 g of an Ag alloy plate having the composition shown in Table 1 cast into a plate shape (electrode area 14 cm ² ) was used as the anode 6. The anode 6 was installed in the state inserted in the anode bag 10 (PET cloth bag). The upper limit of the ratio of the current (current A) flowing between the first cathode 5 and the anode 6 was calculated based on the above formula (1).
D1 = {41.9 / (41.9 × 1 + 2.1 × 3 + 37.3 × 2 + 3.3 × 2 ++ 5.5 × 2 + 4.7 × 3 + 1.8 × 2 + 3.5 × 2)} × 100 = 25.4%

  The first electrolytic cell 2 was filled with a 0.3 mol / L nitric acid aqueous solution (400 mL) as a first electrolytic solution. The second electrolytic cell 3 was filled with 400 mL of the used electrolytic solution (Ag 10 g / L, Cu 50 g / L, Pd 3 g / L) generated in Example 1 as the second electrolytic solution, and then electrolytic purification was performed. The current flowing between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 was controlled by the current control mechanism 8.

  During the electrolytic purification, the Ag concentration in the first electrolytic solution was monitored in the same manner as in Example 1. The temperature of the electrolytic solution during electrolytic purification was 20 to 25 ° C. for both the first electrolytic cell 2 and the second electrolytic cell 3.

  Before depositing Ag on the first cathode 5, the power source 8 b provided on the second electrolytic cell 3 side is turned on until the Ag concentration in the first electrolytic solution of the first electrolytic cell 2 reaches 30 g / L. A current (0.64 A) was passed between 6 and the second cathode 7. Since the power supply 8a was turned off until the Ag concentration reached a predetermined concentration and no current was passed between the first electrode 5 and the anode 6, Ag was not deposited on the first cathode 5 (about 20 hours from the start). .

  When the Ag concentration of the first electrolytic solution reaches 30 g / L, an electric current (0.16 A) is passed from the power source 8 a between the first cathode 5 and the anode 6 to start electrolysis of Ag in the first electrolytic cell 2. did. Further, the currents are controlled by the power supplies 8a and 8b so that the ratio of the current values flowing between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 (first electrode: second electrode) is maintained at 2: 8. The electrolysis was continued (about 46 hours from the start).

  The change with time of the Ag concentration in the first electrolyte solution was measured. As shown in FIG. 5, when electrolysis is performed by appropriately controlling the current after the Ag concentration in the electrolytic solution reaches 30 g / L, the Ag concentration in the electrolytic solution may be maintained at 20 g / L or more. did it.

  After the completion of electrolytic purification, the impurity content contained in the Ag electrodeposited on the first cathode 5 was examined using an ICP emission spectroscopic device. As a result, as shown in Table 2, the purity of the electrodeposited Ag was 99.97%. The crystal state of electrodeposited Ag was dendritic.

  Ag was deposited on the second cathode 7 after completion of the electrolytic purification, and the Ag concentration in the electrolytic solution in the second tank 3 was less than 0.1 g / L. In this example, Ag can also be recovered from the second electrolytic solution, so that a high Ag recovery rate was achieved as a whole.

Example 3
Similar to Example 1, the following experiment was conducted using an electrolytic purification apparatus having the configuration shown in FIG. The same diaphragm 4 and first cathode 5 as those in Example 1 were used except that 120 g of an Ag alloy plate having the composition shown in Table 1 cast into a plate shape (electrode area 14 cm ² ) was used as the anode 6. In Example 3, the anode bag 10 was not used for the anode 6. The upper limit of the ratio of current (current A) flowing between the first cathode 5 and the anode 6 was calculated in the same manner as in Example 1.
D1 = {84.1 / (84.1 × 1 + 15.9 × 2)} × 100 = 72.6%

  The first electrolytic cell 2 was filled with a 0.3 mol / L nitric acid aqueous solution (400 mL) as a first electrolytic solution. The second electrolytic cell 3 was filled with 400 mL of the used electrolytic solution (Ag 10 g / L, Cu 50 g / L, Pd 3 g / L) generated in Example 1 as the second electrolytic solution, and then electrolytic purification was performed. The current between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 was controlled by the current control mechanism 8.

  During the electrolytic purification, the Ag concentration in the first electrolytic solution was monitored in the same manner as in Example 1. The temperature of the electrolytic solution during electrolytic purification was 20 to 25 ° C. for both the first electrolytic cell 2 and the second electrolytic cell 3.

  Before depositing Ag on the first cathode 5, the power source 8 b provided on the second electrolytic cell 3 side is turned on until the Ag concentration in the first electrolytic solution of the first electrolytic cell 2 reaches 30 g / L. A current (0.24 A) was passed between 6 and the second cathode 7. The power source 8a was turned off until no Ag concentration reached a predetermined concentration, and no current was passed between the first electrode 5 and the anode 6, so that no Ag was deposited on the first cathode 5 (about 12 hours from the start). .

  When the Ag concentration of the first electrolytic solution reaches 30 g / L, an electric current (0.56 A) is passed from the power source 8 a between the first cathode 5 and the anode 6 to start electrolysis of Ag in the first electrolytic cell 2. did. In addition, the current is controlled by the power supplies 8a and 8b so that the ratio of the current value flowing between the first cathode 5 and the anode 6 and between the anode 6 and the second cathode 7 (first electrode: second electrode) is maintained at 7: 3. The electrolysis was continued (about 46 hours from the start).

  The change with time of the Ag concentration in the first electrolyte solution was measured. As shown in FIG. 6, when electrolysis is performed by appropriately controlling the current after the Ag concentration in the first electrolytic solution reaches 30 g / L, the Ag concentration in the electrolytic solution is maintained at 25 g / L or more. I was able to.

  After the completion of electrolytic purification, the impurity content contained in Ag electrodeposited on the first cathode 5 was examined. As a result, as shown in Table 2, the purity of the electrodeposited Ag was 99.98%. The crystal state of electrodeposited Ag was dendritic.

  Ag was deposited on the second cathode 7 after completion of the electrolytic purification, and the Ag concentration in the electrolytic solution in the second tank 3 was less than 0.1 g / L. In this example, Ag can also be recovered from the second electrolytic solution, so that a high Ag recovery rate was achieved as a whole.

Comparative Example Based on a conventional apparatus and method, electrolytic purification of Ag using an Ag-containing raw material as an anode was performed. Specifically, the following experiment was conducted using an electrolytic purification apparatus having the configuration shown in FIG. As the anode 16, 120 g of an Ag-containing alloy plate cast into a plate shape (length and width size 2 cm × 3.5 cm, electrode area 7 cm ² ) was used. The composition of the anode 16 is the same as in Example 2. The cathode 15 was made of stainless steel (length and width size 2 cm × 3.5 cm, electrode area 7 cm ² ). In addition, the anode 16 was installed in the state inserted in the anode bag 10 (PET cloth bag).

  The electrolytic bath 12 was filled with 0.3 mol / L nitric acid aqueous solution (400 mL) as an electrolytic solution. The current between the cathode 15 and the anode 16 was controlled by the current control mechanism 8. Specifically, the value of the current passed was calculated based on the composition of the Ag-containing alloy plate constituting the anode 16. During electrolytic purification, the Ag concentration in the electrolytic solution was measured by ICP emission spectroscopy and monitored. The temperature of the electrolytic solution during electrolytic purification was 20 to 25 ° C.

  The power source 18 provided in the electrolytic cell 12 was turned on, and the electrolytic purification was continued while supplying a current (0.35 A) between the anode 16 and the cathode 15 (about 46 hours from the start).

  The time-dependent change of Ag concentration in electrolyte solution was measured. As shown in FIG. 7, the Ag concentration in the electrolytic solution during electrolytic purification was 5 g / L or less.

  After the completion of electrolytic purification, the impurity content contained in the Ag electrodeposited on the cathode 15 was examined. As a result, as shown in Table 2, the purity of the electrodeposited Ag was 97.5%. The crystal state of the electrodeposited Ag was powdery.

  In Examples 1 to 3, high-purity Ag having a purity of 99.9% or more could be purified, whereas in Comparative Examples, the Ag purity was about 97.5%. Examples 1 to 3 also had higher Ag recovery rates than the comparative examples.

DESCRIPTION OF SYMBOLS 1 Electrolysis tank 2 1st electrolysis tank 3 2nd electrolysis tank 4 Diaphragm 5 1st cathode 6, 16 Anode 7 Second cathode 8 Current control mechanism 8a, 8b, 8c, 18 Power supply 9 Variable resistor 10 Anode bag 12 Electrolysis tank 15 cathode

Claims (5)

An Ag electropurification apparatus using an Ag-containing raw material for an anode,
The electrolytic cell of the electrolytic purification apparatus is composed of a first electrolytic cell and a second electrolytic cell partitioned by a diaphragm,
The first electrolytic cell includes the anode and a first cathode,
The second electrolytic cell includes a second cathode,
A current control mechanism for controlling a current between the anode and the first cathode and between the anode and the second cathode ;
The current control mechanism controls the current between the electrodes to adjust the Ag deposition rate deposited on the first cathode and the Ag elution rate eluted from the anode so that the Ag purity becomes 99.9% or more. electrorefining apparatus Ag characterized that you control the Ag concentration contained in the first electrolytic solution of the first electrolytic cell.   The said electrolytic anode is an electrolysis refinement | purification apparatus of Ag of Claim 1 provided with the anode bag which does not permeate | transmit the anode mud containing the metal whose ionization tendency is smaller than Ag. An Ag electrolytic purification method using the Ag electrolytic purification apparatus according to claim 1 or 2,
By controlling the current between the anode and the first cathode and between the anode and the second cathode by the current control mechanism, the Ag deposition rate deposited on the first cathode and the Ag dissolution rate eluted from the anode are as follows. A method for electrolytically purifying Ag, which adjusts and controls the concentration of Ag contained in the first electrolytic solution of the first electrolytic cell so that the Ag purity is 99.9% or more . An Ag electropurification method using the Ag electropurification apparatus according to claim 3,
The ratio (current A / (current A + current B)) of the current A obtained from the current A between the anode and the first cathode and the current B between the anode and the second cathode is obtained by the following formula (1). The current A and the current B are respectively controlled by the current control mechanism so as to be less than or equal to a value D1 to adjust the Ag deposition rate deposited on the first cathode and the Ag dissolution rate eluted from the anode, A method for electrolytic purification of Ag, which controls the concentration of Ag contained in a first electrolytic solution of one electrolytic cell.
D1 = M (Ag) / Σ (M (i) × V (i)) (1)
(Wherein M (Ag): mole percentage of Ag contained in the anode
M (i): Mole percentage of metal dissolved in electrolyte solution among each element contained in anode
V (i): Ion valence of each element contained in the anode
(Mole percentage means the percentage of the sum of Ag and soluble impurity metal)) The method for electrolytically purifying Ag according to claim 3 or 4 , wherein the first electrolytic solution after electrolytic purification is filled in the second electrolytic cell, and Ag is electrolytically recovered.