Method for recovering valuable metals

Abstract

To provide a method that allows efficient separation and recovery of tin and valuable metals from a target material containing tin and valuable metals.SOLUTION: The method for recovering valuable metals according to the present invention includes heating a mixture which contains a target material containing insoluble tin compounds and insoluble compounds of valuable metals other than tin, and a treatment agent with a sodium hydroxide concentration of 1,000 g / L or more to a temperature of 90°C or more; and then leaching tin into an aqueous phase and recovering the valuable metals not leached into the aqueous phase. It is preferable to use 8 to 26 moles of sodium hydroxide per mole of tin. It is also preferable to mix the heated mixture with warm water at 40°C or higher and 90°C or lower to leach tin into the warm water.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for separating and recovering valuable metals from a workpiece containing tin and valuable metals other than tin.

Background Art

[0002] Platinum group metals used in catalysts, electronic materials, etc. are recycled actively because they are scarce resources and have a large environmental impact during smelting. The workpieces to be recycled may contain impurities such as tin in addition to platinum group metals. Therefore, in order to recycle platinum group metals, it is necessary to separate impurities such as tin from platinum group metals. As one such technique, for example, Patent Document 1 proposes a method for separating impurity elements from a platinum group metal solution containing platinum group elements and bismuth, tin, and antimony as impurity elements. In this method, first, potassium chloride is added to the solution of platinum group elements to form potassium salts of platinum group elements, dilute hydrochloric acid is added to the obtained potassium salts of platinum group elements and mixed and washed, and then an aqueous sodium hydroxide solution is added to the washed potassium salts to obtain potassium salt neutralization precipitates. Next, sodium hydroxide and an oxidizing agent are added to the potassium salt neutralization precipitates for leaching, and hydrochloric acid is added to the recovered leaching residue for dissolution to obtain a platinum group metal hydroxide solution.

[0003] Patent Document 2 proposes a method for separating and recovering palladium and tin from an acidic aqueous solution containing palladium, tin, and their compounds. In this method, step (1) of setting the pH of the acidic aqueous solution containing palladium, tin, and their compounds to 3 or more, and step (2) of adding an alkali and at least one of a reducing agent and a metal collector to the aqueous solution having a pH of 3 or more obtained in step (1) to set the pH to 6 to 10 to form a palladium-containing precipitate and a tin-containing precipitate, and step (3) of solid-liquid separating and recovering the palladium-containing precipitate and the tin-containing precipitate obtained in step (2) are performed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As one of the objects for recycling platinum group metals, there is anode slime containing platinum group metals and tin. Conventionally, a leaching method using an acid such as hydrochloric acid or an alkali such as sodium hydroxide has been used to separate platinum group metals and tin from anode slime. However, in these leaching methods, the leaching rate of tin is low and the leaching rate of platinum group metals is high, so platinum group metals and tin could not be efficiently separated. Therefore, an object of the present invention is to provide a method for efficiently separating and recovering tin and valuable metals from a material to be treated containing valuable metals such as platinum group metals and tin.

Means for Solving the Problems

[0006] The present invention provides a method for recovering valuable metals, which comprises heating a mixture containing a material to be treated containing an insoluble tin compound and an insoluble compound of a valuable metal other than tin and a treating agent having a sodium hydroxide concentration of 1000 g / L or more to 90°C or higher, then leaching tin into an aqueous phase, and recovering the valuable metals not leached into the aqueous phase.

Effects of the Invention

[0007] According to the present invention, tin and valuable metals can be efficiently separated and recovered from a material to be treated containing valuable metals such as platinum group metals and tin.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described based on its preferred embodiments. The present invention relates to a method for separating and recovering tin and valuable metals from an object to be treated containing an insoluble tin compound and an insoluble compound of a valuable metal other than tin. The recovery method of the present invention preferably has the following steps (a) to (c). (a) Mixing step: An object to be treated containing an insoluble tin compound and an insoluble compound of a valuable metal other than tin is mixed with a treatment agent containing sodium hydroxide to obtain a mixture. (b) Heating step: The mixture is heated to produce a water-soluble tin compound from the insoluble tin compound contained in the object to be treated. (c) Leaching step: The water-soluble tin compound is mixed with water to leach tin into the aqueous phase and recover the valuable metals that are not leached into the aqueous phase. Hereinafter, each step will be described.

[0010] <(a) Mixing step> In this step, first, an object to be treated is prepared. The object to be treated contains an insoluble tin compound and an insoluble compound of a valuable metal other than tin. Examples of valuable metals include, but are not limited to, platinum group metals such as platinum, palladium, rhodium, ruthenium, iridium, and osmium, and transition metals other than platinum group metals such as copper. Examples of the material to be treated include anode slime, which is a residue obtained by electrolyzing a metal plate obtained from a melt of a conductor (e.g., a lead frame or the like) in which a platinum group metal is plated on the surface of a base material made of phosphor bronze, and eluting and recovering copper in the metal plate. This anode slime contains tin and a platinum group metal. Alternatively, a lead-containing residue generated in the process of treating lead concentrate or fly ash by flotation can be mentioned. This residue contains tin and copper in amounts of several mass% to about several tens of mass%, respectively. However, the types of materials to be treated are not limited to these.

[0011] The tin compound contained in the material to be treated is insoluble in water. Typical examples of such a tin compound include, but are not limited to, tin oxide (SnO2).

[0012] In this step, the material to be treated is mixed with a treatment agent containing sodium hydroxide. The treatment agent may be solid sodium hydroxide itself or an aqueous solution of sodium hydroxide. When an aqueous solution of sodium hydroxide is used as the treatment agent, it is preferable that the aqueous solution is a concentrated aqueous solution from the viewpoint of facilitating the selective recovery of tin contained in the material to be treated. From this viewpoint, the concentration of the aqueous solution of sodium hydroxide as the treatment agent is preferably 700 g / L or more, more preferably 1000 g / L or more, and still more preferably 1200 g / L or more. Also, from the viewpoint of facilitating the leaching of tin into the aqueous phase in the leaching step described later, the concentration of the aqueous solution of sodium hydroxide is preferably 3000 g / L or less, more preferably 2000 g / L or less, and still more preferably 1500 g / L or less. When the concentration of the aqueous solution of sodium hydroxide used as the treatment agent is high, some sodium hydroxide may remain undissolved in water. However, this does not affect the selective recovery of tin contained in the object to be treated. Therefore, the "aqueous solution of sodium hydroxide" referred to in this specification is a concept that includes not only an aqueous solution in which the entire amount of sodium hydroxide is completely dissolved in water, but also a saturated aqueous solution in which some sodium hydroxide remains undissolved in water.

[0013] The modes of mixing the object to be treated and sodium hydroxide to obtain a mixture are roughly classified into the following two: (i) and (ii). (i) After mixing the object to be treated and solid sodium hydroxide, water is mixed to obtain a mixture. (ii) The object to be treated and a concentrated aqueous solution of sodium hydroxide are mixed to obtain a mixture.

[0014] In either case of (i) and (ii), it is preferable that the mixture contains the object to be treated and a treatment agent with a sodium hydroxide concentration of 1000 g / L or more. Therefore, in the case of the mode (i), after mixing the object to be treated and solid sodium hydroxide, an appropriate amount of water is mixed so that the mixture contains an aqueous solution with a sodium hydroxide concentration of 1000 g / L or more. In the case of the mode (ii), it is preferable to mix the object to be treated and a concentrated aqueous solution of sodium hydroxide with a sodium hydroxide concentration of 1000 g / L or more. In this case, after mixing the object to be treated and the concentrated aqueous solution of sodium hydroxide, water can be additionally mixed to adjust the concentration of the aqueous solution of sodium hydroxide.

[0015] In either case of (i) and (ii), from the viewpoint of facilitating the selective recovery of tin contained in the object to be treated, the concentration of the aqueous solution of sodium hydroxide contained in the mixture is more preferably 1000 g / L or more, and even more preferably 1200 g / L or more. From the viewpoint of economy, the concentration of the aqueous sodium hydroxide solution contained in the mixture is preferably 3000 g / L or less, more preferably 2000 g / L or less, and still more preferably 1500 g / L or less.

[0016] In the mixture of the object to be treated and the aqueous sodium hydroxide solution, in either case of (i) and (ii), with respect to the amount A (mol) of tin contained in the object to be treated, the amount B (mol) of sodium hydroxide used is represented by the value of B / A which is the ratio of the number of moles of sodium hydroxide to 1 mole of tin. From the viewpoint of facilitating the selective recovery of tin contained in the object to be treated, it is preferably 8 or more. From this viewpoint, the value of B / A is more preferably 12 or more, and still more preferably 16 or more. Also, from the viewpoint of economy, the value of B / A is preferably 26 or less, may be 22 or less, or may be 18 or less.

[0017] Conventionally, to separate and recover tin and valuable metals other than tin from an object to be treated containing tin and valuable metals other than tin, a leaching method using an aqueous hydrochloric acid solution or an aqueous sodium hydroxide solution has often been used. However, in the leaching method using an aqueous hydrochloric acid solution, the separation between tin and valuable metals other than tin was not good, and moreover, the filterability during solid-liquid separation was not good, so satisfactory results could not be obtained (see Comparative Example 3 described later). The leaching method using an aqueous sodium hydroxide solution has better separation between tin and valuable metals other than tin than the leaching method using an aqueous hydrochloric acid solution. However, the degree of separation between the two did not reach an industrially satisfactory level (see Comparative Example 2 described later). In contrast, according to the present invention, in the leaching method using a concentrated aqueous sodium hydroxide solution, the separation between tin and valuable metals other than tin is extremely good, and the leaching of tin can be carried out with high selectivity.

[0018] <(b) Heating step> In this process, the mixture obtained in the mixing process is heated to a predetermined temperature to react the insoluble tin compound contained in the object to be treated in the mixture with sodium hydroxide to produce a water-soluble tin compound. Although the details of this reaction are not clear, the inventor believes that the following reactions (1) and / or (2) occur. However, the scope of the present invention is not restricted by this theory. SnO2 + 2NaOH + 2H2O → Na2SnO3·3H2O (1) SnO2 + 2NaOH → Na2SnO3 + H2O (2)

[0019] From the viewpoint of surely causing the production reaction of the water-soluble tin compound, the heating temperature of the mixture in this process is preferably 90°C or higher, more preferably 100°C or higher, and still more preferably 105°C or higher. Also, from the viewpoint of economy, the heating temperature of the mixture is preferably 250°C or lower, more preferably 200°C or higher, and still more preferably 150°C or higher.

[0020] The heating of the mixture may be carried out in an open system, that is, under atmospheric pressure, or in a closed system such as in an autoclave.

[0021] From the viewpoint of surely causing the production reaction of the water-soluble tin compound, it is preferable to maintain the above-mentioned heating temperature for 1 hour or more, more preferably 3 hours or more, and still more preferably 5 hours or more. Also, from the viewpoint of economy, the above-mentioned heating temperature can be maintained for 24 hours or less, may be maintained for 18 hours or less, or may be maintained for 12 hours or less.

[0022] By heating the mixture under the above-described conditions, the mixture changes into a gel state. During heating, a water-soluble tin compound is formed even without stirring, but from the viewpoint of promoting the formation reaction of the water-soluble tin compound, it is preferable to stir this gel-like mixture. Note that if heating is carried out over a long period of time, the water in the mixture may volatilize and the fluidity of the mixture may be lost. In that case, a small amount of water sufficient to maintain the gel state of the mixture may be additionally added to the mixture.

[0023] <(c) Leaching step> In this step, the water-soluble tin compound generated in the mixture by the heating step and water are mixed. By mixing the two, tin is leached into the aqueous phase. On the other hand, metals other than tin, such as platinum group metals such as platinum, palladium, and rhodium, and transition metals other than platinum group metals such as copper, remain in an insoluble state and thus do not leach into the aqueous phase and remain in the solid phase. Therefore, by performing solid-liquid separation, tin is leached and recovered into the aqueous phase, and metals other than tin are recovered as solid components.

[0024] From the viewpoint of ensuring the leaching of tin into the aqueous phase, the amount of water used is preferably 230 parts by mass or more with respect to 100 parts by mass of the mixture after heating. From this viewpoint, the amount of water used is more preferably 260 parts by mass or more with respect to the mass of the mixture after heating, and even more preferably 320 parts by mass or more. Also, the amount of water used can be 450 parts by mass or less with respect to the mass of the mixture after heating, may be 410 parts by mass or less, or may be 360 parts by mass or less.

[0025] The water used in this step may be at room temperature (25 °C) or may be heated, that is, warm water. From the viewpoint of efficiently leaching the water-soluble tin compound into the aqueous phase, it is preferable to use warm water. This is because sodium stannate (Na2SnO3), which is a kind of water-soluble tin compound, has a higher solubility as the temperature is higher. From the perspective of efficiently leaching the water-soluble tin compound into the aqueous phase, the temperature of the warm water is preferably 40 °C or higher, more preferably 50 °C or higher, and still more preferably 60 °C or higher. Also, from the perspective of economy, the temperature of the warm water is preferably 90 °C or lower, more preferably 80 °C or lower, and still more preferably 75 °C or lower.

[0026] The time for leaching the water-soluble tin compound into the aqueous phase is preferably 0.5 hours or more, more preferably 1 hour or more, and still more preferably 1.5 hours or more when using warm water at the above-mentioned temperature, from the perspective of sufficiently performing the leaching and increasing the leaching rate of tin. Also, from the perspective of economy, it can be leached for 6 hours or less, may be leached for 4 hours or less, or may be leached for 2 hours or less.

[0027] In this step, while leaching the water-soluble tin compound into the aqueous phase, it is preferable to stir the liquid from the perspective of promoting the leaching.

[0028] In this way, by mixing the heated mixture with water, tin is leached into the aqueous phase. In this case, most of the valuable metals other than tin remain in the solid phase as insoluble compounds, but a part of the valuable metals may be leached into the aqueous phase together with tin. This is one of the reasons for reducing the selective separation efficiency of tin. Therefore, in this step, it is preferable to add a reducing agent that has no reducing ability for tin and has a reducing ability for valuable metals to the liquid obtained by mixing the heated mixture with water. By this operation, the valuable metals once leached into the aqueous phase are reduced by the reducing agent and return to the solid phase. As a result, the proportion of tin in the metals present in the aqueous phase increases, and it becomes possible to separate tin and valuable metals with high efficiency.

[0029] Examples of the reducing agent that has no reducing ability for tin and has a reducing ability for valuable metals include hydrazine-based compounds such as hydrazine and hydrazine hydrate, and sodium borohydride.

[0030] The amount of the reducing agent used is such that the oxidation-reduction potential (ORP) of the leachate obtained by mixing the mixture after heating with water is preferably -800 mV or more and -400 mV or less, more preferably -750 mV or more and -500 mV or less, still more preferably -700 mV or more and -550 mV or less. This is preferable from the viewpoint of not reducing tin and efficiently reducing valuable metals other than tin. The oxidation-reduction potential is a potential based on Ag / AgCl.

[0031] In this way, tin contained in the object to be treated can be separated from valuable metals other than tin and recovered. For example, when the object to be treated contains a plurality of platinum group metals, tin and the plurality of platinum group metals are separated and recovered. In order to separate the plurality of platinum group metals recovered in this way into individual metals, known methods can be used.

Examples

[0032] Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[0033] 〔Example 1〕 (a) Mixing step Anode slime was used as the object to be treated. This anode slime is a residue obtained by electrolyzing a metal plate obtained from a melt of a lead frame in which a platinum group metal is plated on the surface of a base material made of phosphor bronze, and eluting and recovering copper in the metal plate. The tin grade and platinum group metal grades (platinum, palladium, and rhodium) in this anode slime were as shown in Table 1 below. The result of X-ray diffraction measurement of this anode slime is shown in FIG. 1. As shown in the figure, it can be seen that the anode slime contains tin oxide (SnO2). 100 g of anode slime and 250 g of sodium hydroxide (solid) were mixed, and further 200 mL of water was mixed to obtain a mixture. The concentration of the sodium hydroxide aqueous solution in the mixture was 1250 g / L.

[0034]

Table 1

[0035] (b) Heating process The mixture obtained in the mixing process was heated at 110 °C for 6 hours. The heating was carried out under atmospheric pressure. The results of X-ray diffraction measurement of the heated mixture are shown in Figure 2. As shown in the figure, no diffraction peak of tin oxide (SnO2) was observed in the mixture. Instead, diffraction peaks of sodium stannate (Na2SnO3) and its hydrate were observed. This means that sodium stannate was formed from tin oxide by heating the mixture.

[0036] (c) Leaching process The heated mixture was mixed with warm water at 70 °C. The amount of warm water was 1500 mL. This amount was 270 parts by mass with respect to 100 mass of the heated mixture. While mixing the mixture and warm water and stirring both, a solution obtained by diluting 98% hydrazine 5 times with water was added. The addition amount was such that the redox potential of the aqueous phase became -600 mV (vs. Ag / AgCl). Subsequently, stirring was carried out for 60 minutes. Then, solid-liquid separation was performed, and the amounts of tin and platinum group metals contained in the aqueous phase were measured by ICP emission spectrometry. Based on the measurement results, the leaching rate of each metal was calculated. The results are shown in Table 2 below. The following formula (3) was used to calculate the leaching rate. (Amount of metal dissolved in the liquid [g]) / (Amount of metal dissolved in the liquid [g] + Amount of metal in the residue after extraction [g]) (3)

[0037] The results of X-ray diffraction measurement of the warm water extraction residue after solid-liquid separation are shown in Figure 3. As shown in the figure, it can be seen that the diffraction peaks of sodium stannate (Na2SnO3) and its hydrate observed in Figure 2 disappeared due to warm water leaching. The reason is presumed to be that in the heating process, the formed sodium stannate (Na2SnO3) and its hydrate were undissolved because they had reached the saturation concentration, whereas the solubility of sodium stannate increased due to the addition of warm water and it dissolved in the warm water.

[0038] [Example 2] In the heating step of Example 1, the mixture was heated at 200°C for 3 hours. Otherwise, tin and platinum group metals were separated and recovered in the same manner as in Example 1. The amounts of tin and platinum group metals contained in the aqueous phase obtained in the leaching step were measured in the same manner as in Example 1, and the leaching rates of the respective metals were calculated. The results are shown in Table 2.

[0039] [Comparative Example 1] In the heating step of Example 1, the mixture was heated at 80°C for 6 hours. Otherwise, tin and platinum group metals were separated and recovered in the same manner as in Example 1. The amounts of tin and platinum group metals contained in the aqueous phase obtained in the leaching step were measured in the same manner as in Example 1, and the leaching rates of the respective metals were calculated. The results are shown in Table 2.

[0040] [Comparative Example 2] This comparative example is a method of leaching tin using an aqueous sodium hydroxide solution having a lower concentration than in the examples. 300 g of sodium hydroxide (solid) and water were mixed to obtain 1 L of a mixed solution. 100 g of anodeslime similar to that used in Example 1 was added to this mixed aqueous solution. The concentration of the aqueous sodium hydroxide solution in the mixture was 300 g / L. This mixture was heated at 70°C for 76 hours to leach tin into the aqueous phase. The total amount of tin and the total amount of platinum group metals leached into the aqueous phase were measured in the same manner as in Example 1, and the leaching rates of the respective metals were calculated. The results are shown in Table 2.

[0041] [Comparative Example 3] This comparative example is a method of leaching tin using an aqueous hydrochloric acid solution. The anodeslime used in Example 1 and a 3 mol / L aqueous hydrochloric acid solution were mixed to prepare a slurry having a concentration of 100 g / L. This slurry was heated to 70 - 80°C and maintained at that temperature for 6 hours to leach tin into the aqueous phase. The amounts of tin and platinum group metals leached into the aqueous phase were measured in the same manner as in Example 1, and the leaching rates of the respective metals were calculated. The results are shown in Table 2.

[0042] [Table 2]

[0043] As is clear from the results shown in Table 2, it can be seen that in the methods of each example, tin was selectively leached into the aqueous phase at a high leaching rate. It can be seen that in the method of Comparative Example 3 using an aqueous hydrochloric acid solution, the leaching rate of tin is low and the separability between tin and platinum group metals is also poor. It can be seen that the method of Comparative Example 2 using a low-concentration aqueous sodium hydroxide solution was able to achieve a higher leaching rate of tin than the method of Comparative Example 3 using an aqueous hydrochloric acid solution, but the separability between tin and platinum group metals is not good.

Claims

1. A method for recovering valuable metals, comprising heating a mixture containing a material to be treated containing an insoluble tin compound and an insoluble compound of a valuable metal other than tin and a treating agent having a sodium hydroxide concentration of 1000 g / L or more to 90°C or higher, then leaching tin into an aqueous phase and recovering the valuable metal not leached into the aqueous phase.

2. The recovery method according to claim 1, wherein 8 moles or more and 26 moles or less of sodium hydroxide are used per mole of tin.

3. The recovery method according to claim 1 or 2, wherein the mixture after heating is mixed with warm water at 40°C or higher and 90°C or lower to leach tin into the warm water.

4. The recovery method according to claim 1 or 2, wherein a reducing agent having no reducing ability for tin and having a reducing ability for the valuable metal is added to a liquid obtained by mixing the mixture after heating with water to separate tin and the valuable metal.

5. The recovery method according to claim 1 or 2, wherein the valuable metal contains a platinum group metal.

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