Method for recovering precious metals

Abstract

To provide a method for recovering a noble metal, in which the noble metal is absorbed into a metal melt side, and further, produced slag is uniformly melted and has low viscosity and excellent handleability, in the method for separating and recovering the desired noble metal by using a flux and iron as a metallic material for melting, and melting them at a high temperature.SOLUTION: A method for recovering noble metals contained in a noble metal-containing material, the method including heating and melting a noble metal-containing material containing aluminum and titanium, a metal material for melting containing iron, a reducing agent, and a flux containing lime and silica together at 1300 °C or higher and 1600 °C or lower to form a slag and a metal melt, and controlling respective masses of alumina, titania, lime, and silica in the formed slag so that the respective masses satisfy the following formulae (1) to (3): 0.45 ≤ S / (C + S) ≤ 0.55 (1) 0.2 ≤ A / (A+ T) ≤ 0.6 (2) 0.4 <(A+ T) / (A+ T + C + S) ≤ 0.6 (3) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for efficiently recovering precious metals, particularly platinum group metals, from materials containing aluminum and titanium as primary components. [Background technology]

[0002] Precious metals are utilized in various industrial fields due to their element-specific characteristics and properties, such as heat resistance, corrosion resistance, catalytic activity, etc. In particular, in the field of catalysts, platinum group metals (hereinafter referred to as "PGM") are often used supported on supports made of alumina, titania, or both. However, precious metals, especially PGMs, are unevenly distributed and their supply is unstable. Therefore, if catalysts that have been used for a certain period of time (hereinafter referred to as "spent catalysts") could be recovered and the precious metals could be recovered from the recovered catalysts, it is thought that this would lead to a stable supply of precious metals and a reduction in catalyst costs.

[0003] When useful precious metals are recovered from such precious metal-containing waste catalysts, a dry recovery method is widely used in which a carrier made of ceramics such as alumina or titania and a waste catalyst containing the precious metal to be recovered are melted at high temperature to recover the precious metal. In the dry recovery method, a waste catalyst consisting of precious metals and carriers is mixed with a metal material for melting, such as copper or iron, a reducing agent, and a flux, and the mixture is melted at high temperature. The desired precious metals are absorbed into the molten metal, while non-precious metal components such as the carriers are transferred to the slag phase, and the slag is removed to produce a molten metal containing the desired precious metals. The metal melt is then subjected to a standard acid treatment or the like to separate and recover the desired precious metals (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6541947 [Patent Document 2] Patent Publication No. 2005-113193 [Patent Document 3] Patent Publication No. 2009-179839 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional dry recovery methods, the slag phase may not form a homogeneous molten mass, but may contain a mixture of unmelted solid material and molten material, due to the influence of the composition of the mixture of spent catalyst, melting metal, and flux, the melting temperature conditions, etc. In such cases, the presence of the solid material increases the viscosity of the slag phase, reducing the efficiency of separation of the molten mass containing precious metals from the slag during removal of the slag. The present invention provides a method for separating and recovering useful precious metals from precious metal-containing materials, such as spent catalysts containing alumina and titania as carriers, by melting the materials at high temperatures using silica and lime as fluxes and iron as a melting metal material to separate and recover the desired precious metals, in which the precious metals are absorbed into the molten metal and the resulting slag phase is uniformly melted, resulting in a low viscosity and easy handling. [Means for solving the problem]

[0006] The present inventors discovered that in the above-mentioned method for recovering precious metals, by controlling the amounts of alumina, titania, silica, and lime in the slag produced during heating and melting, the slag can be made easier to handle, and thus completed the present invention. That is, the present invention has the following aspects. [1] A method for recovering precious metals contained in the precious metal-containing material, comprising: heating and melting a precious metal-containing material containing aluminum and titanium, a metal material for melting containing iron, a reducing agent, and a flux containing lime and silica at a temperature of 1300°C to 1600°C to form a slag phase and a metal melt phase; and controlling the masses of alumina, titania, lime, and silica in the formed slag phase so that the masses of these components satisfy the following formulas (1) to (3): 0.45≦S / (C+S)≦0.55 (1) 0.2≦A / (A+T)≦0.6 (2) 0.4<(A+T) / (A+T+C+S)≦0.6 (3) In the formulas (1) to (3), the total amount of alumina, titania, lime, and silica is 100% by mass, and A represents the mass % of alumina, T represents the mass % of titania, C represents the mass % of lime, and S represents the mass % of silica. [2] The method for recovering precious metals according to [1] above, wherein the precious metals are platinum group metals. [3] The recovery method according to [1] or [2], wherein A, T, C, and S in the formulas (1) to (3) are each within the following ranges. 5≦A≦40 15≦T≦50 15≦C≦35 15≦S≦35 [4] The method for recovering precious metals according to any one of [1] to [3], wherein the slag is separated from the metal melt phase. [Effects of the Invention]

[0007] According to the present invention, when separating and recovering useful precious metals from a material containing precious metals, silica and lime are used as a flux and iron is used as a molten metal material, and the materials are melted at high temperatures to separate and recover the desired precious metals. In this method, the precious metals are absorbed into the molten metal, and the resulting slag is uniformly melted, has a low viscosity, and is easy to handle. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of an embodiment of the recovery method of the present invention. [Figure 2] FIG. 2 is a schematic diagram of a mullite tube used in the examples. [Figure 3] 1 is an SEM photograph of a sample collected in Example 7. [Figure 4] 1 is an SEM photograph of a sample collected in Comparative Example 1. [Figure 5] FIG. 2 is a schematic diagram showing how to determine the liquid phase ratio in the case of two-phase equilibrium. [Figure 6] FIG. 2 is a schematic diagram showing how to determine the liquid phase ratio in the case of three-phase equilibrium. [Figure 7] FIG. 2 is a schematic diagram showing how to determine the liquid phase ratio in the case of four-phase equilibrium. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not to be construed as being limited to these descriptions. The method for recovering precious metals of the present invention (hereinafter also referred to as "this recovery method") involves heating and melting a precious metal-containing material containing aluminum and titanium (hereinafter also referred to as "this material"), a metal material for melting containing iron (hereinafter also referred to as "this melting material"), a reducing agent, and a flux containing lime and silica (hereinafter also referred to as "this flux") at a temperature of 1300°C to 1600°C, forming two phases, a slag phase and a metal melt phase, for example in a furnace, and controlling the masses of alumina, titania, lime, and silica in the formed slag phase so that they satisfy the following formulas (1) to (3), thereby recovering the precious metals contained in this material. 0.45≦S / (C+S)≦0.55 (1) 0.2≦A / (A+T)≦0.6 (2) 0.4<(A+T) / (A+T+C+S)≦0.6 (3) In the formulas (1) to (3), the total amount of alumina, titania, lime, and silica is 100% by mass, and A represents the mass % of alumina, T represents the mass % of titania, C represents the mass % of said lime, and S represents the mass % of said silica.

[0010] In this recovery method, the present material, the present melting material, the reducing agent, and the present flux are heated together and melted, so that the precious metals contained in the present material form a metal melt phase with the iron contained in the present melting material, as described below. If the material contains elements that are less oxidizable than iron, such as nickel or cobalt, these elements are also included in the metal melt phase. Meanwhile, components other than the precious metals, iron, and elements less oxidizable than iron are oxidized and form a slag phase. The metal melt phase and the slag phase are separated due to the difference in specific gravity, so the precious metals can be separated from the material.

[0011] The precious metals contained in this material are rare metals that are chemically stable and difficult to form compounds with, specifically gold, silver, platinum, palladium, rhodium, iridium, ruthenium, and osmium. These precious metals are utilized in various industrial fields and are used in large quantities, so recovering them using this recovery method can help stabilize the supply of precious metals.

[0012] Among the above-mentioned precious metals, PGM is used in various chemical processes and in the treatment of exhaust gases from automobiles, etc., and the present recovery method is suitably applied to the recovery of these PGMs. PGM refers to Group VIII elements of the periodic table, including platinum, palladium, rhodium, iridium, ruthenium, and osmium.

[0013] The material contains aluminum and titanium, and examples include catalysts for chemical processes, catalysts for purifying exhaust gases from automobiles and other vehicles, and substrates for electronic devices such as ceramic IC boards.These materials include waste catalysts and waste substrates that have been used for a certain period of time. The aluminum contained in the material of the present invention may be, for example, aluminum contained in alumina used as a catalyst carrier, or aluminum contained in organoaluminum used as a promoter. Examples of titanium contained in the material include titanium in titania used as a catalyst carrier, titanium contained in organic titanium or titanium halide used as a promoter, and titanium used as an insoluble electrode.

[0014] This recovery method can be more suitably applied to spent catalysts in which the present material uses alumina and titania as carriers. In addition to the noble metals, aluminum, titanium, and elements that are less likely to be oxidized than iron, the material may contain elements that become oxides through the oxidation-reduction reaction described below and are contained in the slag. Examples include base metals other than aluminum and titanium, such as zinc and nickel, and their salts, or organic substances consisting of carbon and hydrogen. In addition to carbon and hydrogen, the organic substances may also contain oxygen, nitrogen, sulfur, etc. Typically, these organic substances volatilize during heating in this recovery method.

[0015] From the viewpoint of the recovery efficiency of the present recovery method, the content of the precious metal in the present material is preferably 0.1% by mass or more, and more preferably 1% by mass or more, with the mass of the present material being 100% by mass. Furthermore, from the viewpoint of suitably applying the present recovery method, the content of precious metals in the present material is preferably 50% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 2% by mass or less, with the mass of the present material being 100% by mass.

[0016] The melting material used in this recovery method is used as an absorbent for the precious metal in the material, and is used to form a metal melt with the precious metal to absorb the precious metal. In this recovery method, iron absorbs the precious metal in the material. The iron contained in the melting material may be metallic iron or may be in the form of a salt such as an oxide. When used in the form of salt, magnetite, hematite, limonite, pyrite, etc. may be used as is. Of these, magnetite is preferred. When magnetite is used, it is preferably in the form of a powder with an average particle size of 0.1 μm to 100 μm. The average particle size is usually the volume average particle size. The volume average particle size is the D50 value, which can be measured using a laser diffraction particle size analyzer, etc. D50 can be measured by dynamic light scattering using a laser particle size analyzer, etc. The volume average particle size of particles is the particle size at which the cumulative volume distribution curve reaches 50% of the cumulative volume when plotted from the smallest diameter side in the particle size distribution. In addition to the iron, the material for main melting may contain, for example, sodium, aluminum, titanium, silicon, phosphorus, sulfur, calcium, chromium, manganese, etc. These may be contained as metals or as salts such as oxides, chlorides, and hydroxides.

[0017] From the viewpoint of the recovery efficiency of the present recovery method, the iron content in the present melting material is preferably 4 to 20 times, and more preferably 4 to 10 times, the amount of precious metal contained in the present material, in terms of metallic iron.

[0018] The reducing agent used in this recovery method is intended to reduce the oxidation state of the precious metals in the material, such as salts and oxides, so that the precious metals can be efficiently absorbed into the melting material. At the same time, the base metals and their salts contained in the material, the melting material, or the flux (described later) are also oxidized and taken up into the slag.

[0019] The reducing agent used in this recovery method is, for example, carbon. Examples of carbon include carbon materials such as artificial graphite and coke, with artificial graphite and coke being more preferred, and artificial graphite being even more preferred.

[0020] This flux contains lime and silica, and is used to remove components other than precious metals from the material when the material and the melting material are molten, to form a slag phase to extract impurities from the molten metal, and to reduce the melt viscosity of the slag phase that is formed.

[0021] The lime may be quicklime obtained by artificial synthesis or purification, or may be naturally occurring lime, such as lime containing at least one of CaO, CaCO3, or Ca(OH)2 as a main component. It can be artificially produced by the thermal decomposition of calcium carbonate as described below. CaCO3 → CaO + CO2 In the present recovery method, lime is preferably naturally occurring lime.

[0022] The silica may be naturally occurring silica sand or synthetic silica, which can be produced by methods such as the sol-gel method. The lime and silica contained in the flux are commercially available powders and granules, and examples of commercially available powders and granules include those with particle sizes of 5000 μm or less.

[0023] In this recovery method, the material, melting material, reducing agent, and flux are heated together at a temperature between 1300°C and 1600°C, resulting in the melting of the material, melting material, reducing agent, and flux. As described above, reduction and oxidation reactions also occur during melting, and the precious metals contained in the material, along with the iron in the melting material, form a heavy metal melt phase. Meanwhile, the aluminum and titanium in the material are oxidized within the temperature range, almost entirely becoming alumina and titania. The alumina and titania produced during melting, along with the lime and silica in the flux, form a slag phase, which has a relatively low specific gravity compared to the metal melt phase. If the material contains alumina or titania, the alumina and titania are retained in the slag phase.

[0024] When the melting material, reducing agent and flux contain alumina or titania, they also form a slag phase when melted. If lime or silica is contained in the melting material and reducing agent, these also form a slag phase when melted. Furthermore, aluminum components (hereinafter also referred to as "alumina precursors") that become alumina through oxidation reactions during melting in the melting material, reducing agent, and flux also become alumina and form a slag phase when melted. Similarly, titania, lime, and silica also form slag when melted; titanium components (hereinafter also referred to as "titania precursors") that become titania, calcium components (hereinafter also referred to as "lime precursors") that become lime, and silicon components (hereinafter also referred to as "silica precursors") that become silica also become titania, lime, and silica, respectively, when melted.

[0025] Furthermore, oxides of base metals other than alumina, titania, lime, and silica, inorganic oxides, and oxides of base metals and inorganic oxides produced by oxidation during melting also form a slag phase. The slag phase formed as described above usually has a lower specific gravity than the metal melt phase, and therefore separates from the metal melt, with the slag phase at the top and the metal melt phase at the bottom. As described above, the metal melt and the slag are phase-separated, so that the metal melt and the slag can be separated, and the precious metal in the metal melt can be recovered.

[0026] If the viscosity of the resulting slag is too high, the interface between the slag phase and the molten metal phase will be unclear, and the fluidity of the slag will be poor, which may reduce the efficiency of separation between the slag phase and the molten metal phase. Furthermore, if the melting point of the slag increases during this recovery process, the slag will solidify, reducing its fluidity and, in some cases, causing blockage of the slag outlet.

[0027] In this recovery method, by controlling the composition of the components in the slag formed, particularly the alumina, titania, lime, and silica components, it is possible to form slag that is easy to handle and does not easily form a solid phase at relatively low temperatures of between 1300°C and 1600°C. As a result, the separation efficiency between the slag and the molten metal can be improved. Furthermore, since the melting point of the slag formed in this recovery method can be lowered, it is preferable from the viewpoint of energy efficiency to heat and melt the material, melting material, reducing agent, and flux at 1500°C or less.

[0028] In this recovery method, the concentrations of the components alumina, titania, lime, and silica in the slag formed as described above are controlled so as to satisfy the following formulas (1) to (3).

[0029] 0.45≦S / (C+S)≦0.55 (1) 0.2≦A / (A+T)≦0.6 (2) 0.4<(A+T) / (A+T+C+S)≦0.6 (3) In the above formulas (1) to (3), the total amount of alumina, titania, lime, and silica in the slag is 100% by mass, and A represents the mass % of alumina, T represents the mass % of titania, C represents the mass % of lime, and S represents the mass % of silica. A, T, C, and S in the above formulas (1) to (3) are the masses of alumina, titania, lime, and silica present in the slag formed by this recovery method, and also include the masses of alumina, titania, lime, and silica contained in the Material, Melting Material, Reducing Agent, and Flux at the start of this recovery method, as well as the masses of alumina, titania, lime, and silica produced by heating, melting, etc. in this recovery method.

[0030] As described above, alumina is formed when the aluminum contained in the material is melted, and in addition, the melting material, reducing agent, and flux may contain alumina or an alumina precursor. When the melting material, reducing agent, and flux contain alumina or an alumina precursor, A is the sum of the mass of the contained alumina or the mass of the alumina precursor when it becomes alumina, and the mass of alumina produced from the aluminum contained in the material. Furthermore, when the material contains alumina, the above-mentioned A also includes the amount of alumina contained in the material.

[0031] Furthermore, when the melting material, reducing agent, and flux contain titania or a titania precursor, T is the sum of the mass of the contained titania or the mass of the titania precursor converted to titania and the mass of titania produced from the titanium contained in the material. When the material contains titania, T also includes the content of titania contained in the material.

[0032] Similarly, the C and S are the sum of the mass of lime and the mass of lime precursor when lime is formed from the material, the melting material, and the reducing agent, respectively, when the material, the melting material, and the reducing agent contain lime or silica, and the mass of silica and the mass of silica precursor when silica is formed from the material, the melting material, and the reducing agent contain lime or silica, respectively, when the material, the melting material, and the reducing agent contain lime or silica, and the mass of lime and the mass of silica contained in the flux, respectively.

[0033] Therefore, in the present recovery method, it is preferable to previously determine the masses of the present material, the present melting material, the present reducing agent, the alumina, titania, lime, silica, and their precursors contained in the present flux. The quantitative determination method may be, for example, a method in which the amounts of aluminum, titanium, calcium, and silicon are determined by ICP analysis, and the masses of alumina, titania, lime, and silica, respectively, are calculated from the determined values.

[0034] From the quantitative values, the compositions of the present material, the present melting material, the reducing agent, and the present flux can be adjusted to satisfy the above formulas (1) to (3). For example, the amounts and ratios of the present material, the present melting material, the reducing agent, and the present flux supplied can be adjusted based on the quantitative values ​​of the amounts of aluminum, titanium, calcium, and silicon so as to satisfy the formulas (1) to (3), or any or all of alumina, titania, lime, and silica can be added separately so as to satisfy the formulas (1) to (3), thereby making it possible to make the alumina, titania, lime, and silica in the formed slag satisfy the formulas (1) to (3).

[0035] The above formula (1) means controlling the mass of lime relative to the total mass of lime and silica in the slag. By controlling in this way, it is possible to form a slag phase with a high liquid phase ratio, as described below, at a low temperature.

[0036] The above formula (2) means controlling the mass of alumina relative to the total mass of alumina and titania in the slag. By controlling in this way, a slag phase with a high liquid phase ratio can be formed at a low temperature. The ratio of alumina to titania varies depending on the content of the material and supply and demand trends, so this range indicates a range that can accommodate fluctuations due to material variations.

[0037] The above formula (3) means that the total mass of alumina and titania relative to the total mass of alumina, silica, lime, and silica in the slag is controlled. By controlling in this way, a slag phase with a high liquid phase ratio can be formed at a low temperature, and more of this material can be processed with less flux. From the above viewpoint, it is more preferable that the total mass of alumina and titania satisfies the following formula (4). 0.50≦(A+T) / (A+T+C+S)≦0.6 (4) In the present recovery method, from the viewpoints of operational stability, processing costs, and energy conservation, it is preferable that the alumina, titania, lime, and silica in the slag satisfy the above formula (4).

[0038] In terms of ease of adjusting the compositions so as to satisfy the formulas (1) to (3), A in the formulas (1) to (3) preferably satisfies the following formula (5). 5≦A≦40 (5) By satisfying the formula (5), the formulas (1) to (3) are satisfied, and a slag phase exhibiting a high liquid phase ratio is formed at a lower temperature. From the viewpoint of the processing cost per unit mass of precious metal, it is more preferable that A in the formulas (1) to (3) satisfies the following formula (6): 10≦A≦40 (6)

[0039] In terms of ease of adjusting the compositions so as to satisfy the formulas (1) to (3), T in the formulas (1) to (3) preferably satisfies the following formula (7). 15≦T≦50 (7) By satisfying the formula (7), the formulas (1) to (3) are satisfied, and a slag phase exhibiting a high liquid phase ratio is formed at a lower temperature. From the viewpoint of the processing cost per unit mass of precious metal, it is more preferable that T in the formulas (1) to (3) satisfies the following formula (8): 20≦T≦50 (8)

[0040] In terms of ease of adjusting the compositions so as to satisfy the formulas (1) to (3), C in the formulas (1) to (3) preferably satisfies the following formula (9). 15≦C≦35 (9) By satisfying the formula (9), the formulas (1) to (3) are satisfied, and a slag phase exhibiting a high liquid phase ratio is formed at a lower temperature. From the viewpoint of the processing cost per unit mass of precious metal, it is more preferable that C in the formulas (1) to (3) satisfies the following formula (10): 15≦C≦30 (10)

[0041] In view of ease of adjusting the compositions so as to satisfy the formulas (1) to (3), S in the formulas (1) to (3) preferably satisfies the following formula (11). 15≦S≦35 (11) By satisfying the formula (11), the formulas (1) to (3) are satisfied, and a slag phase that exhibits a high liquid phase ratio at a lower temperature is formed. More preferably, S in the above formulas (1) to (3) satisfies the following formula (12) from the viewpoint of the treatment cost per unit mass of precious metal. 15≦S≦30 (12)

[0042] From the viewpoint of ease of adjusting the compositions so as to satisfy formulas (1) to (3), it is preferable that at least one of A, T, C, and S satisfies any of formulas (5) to (12), it is more preferable that all of A, T, C, and S satisfy formulas (5), (7), (9), and (11), and it is even more preferable that all of A, T, C, and S satisfy formulas (6), (8), (10), and (12).

[0043] The recovery method may be carried out in a batch or continuous manner. When this recovery method is carried out batchwise, it is generally considered that the A, T, C, and S contents in the slag do not change significantly during the heating and melting process, and the compositions of the material, melting material, reducing agent, and flux can be determined based on the quantitative values.

[0044] When this recovery method is carried out continuously, the material, melting material, reducing agent, and flux are continuously supplied, and the composition of the slag may change during the recovery method. Therefore, the alumina, titania, lime, and silica are measured before using the material, melting material, reducing agent, and flux, and the recovery method is carried out continuously while adjusting the compositions of the material, melting material, reducing agent, and flux so that the above formulas (1) to (3) are satisfied. Preferably, during the present recovery method, slag is extracted and analyzed as appropriate, and the amounts of the present material, the present melting material, the reducing agent, and the present flux used are adjusted, or any or all of alumina, titania, lime, and silica are added, so that the amounts of alumina, titania, lime, and silica in the slag satisfy the above formulas (1) to (3). This recovery method may be a batch method or a continuous method, but from the viewpoint of the recovery efficiency of the precious metals, a continuous method is preferred.

[0045] The present recovery method can be suitably carried out, for example, by placing the present material, the present melting material, the reducing agent, and the present flux, the compositions of which have been adjusted as described above, into a furnace whose temperature has been adjusted to 1300°C or higher and 1600°C or lower, where they are heated and melted together. The present material, the present melting material, the reducing agent and the present flux may be charged separately into the furnace in that order, or they may be mixed in advance and then charged into the furnace. Alternatively, a part of these may be mixed in advance and then charged into the furnace, and the rest may be charged into the furnace separately.

[0046] The flux may be a mixture of both lime and silica, or a lime-containing flux and a silica-containing flux may be prepared separately and mixed in advance, and then charged into the furnace either simultaneously or separately. During this recovery method, the slag is recovered and its composition is analyzed. If it appears that the above formulas (1) to (3) are no longer satisfied, any of the present material, the present melting material, the present reducing agent, and the present flux may be added to the furnace as needed, or any or all of alumina, titania, lime, and silica may be added to the furnace to adjust the composition of the slag.

[0047] The furnace used in this recovery method can be, for example, an electric furnace, a plasma furnace, etc. The material, the melting material, the reducing agent, and the flux are charged into the furnace, the temperature of which is adjusted to 1300°C or higher and 1600°C or lower, and when heated and melted together, a slag phase is formed, which is separated from the metal melt phase containing the precious metal. Due to the difference in specific gravity between the slag and the molten metal, the slag phase and the molten metal phase separate, with the upper part being slag and the lower part being molten metal.

[0048] Most of the precious metals contained in this material form a molten metal with iron. Therefore, by removing the molten metal in the lower phase, for example, from near the bottom of the furnace, it is possible to separate and recover almost all of the precious metals contained in this material from the alumina and titania. Furthermore, the efficiency of separating and recovering the molten metal can be increased by removing the slag in the upper phase, for example, by overflowing it from the furnace.

[0049] Since the recovered metal melt contains precious metals and iron as described above, the precious metals can be further separated from the iron to recover the precious metals. Before recovering the precious metals from the metal melt, the metal melt may be subjected to gravity separation, magnetic separation, or the like to further increase the content of precious metals in the metal melt. Methods for recovering precious metals from metal melts include, for example, a hydrometallurgical method using an acid solution such as hydrochloric acid, and a pyrometallurgical method in which the metal is melted at a high temperature.

[0050] A schematic diagram of an example of an embodiment of the recovery method of the present invention is shown in FIG. 1, but the recovery method of the present invention is not limited to this embodiment. Figure 1 is a schematic diagram of a plasma furnace 1 whose temperature is adjusted to between 1300°C and 1600°C. A supply tank 2 is used to supply the material, the melting material, the reducing agent, and the flux to the plasma furnace 1. The supply tank may store the present material, the present melting material, the reducing agent, and the present flux individually, or, as described above, a mixture of some of these may be premixed and stored in supply tank 2. If necessary, alumina, titania, lime, silica, etc. may also be stored in supply tank 2 separately. The material, the melting material, the reducing agent, and the flux may be supplied from the supply tank 2 to the plasma furnace 1 all at once or separately. The supply may be continuous or intermittent. A normal powder feeder or the like is used to supply powder from the supply tank 2 to the plasma furnace 1 . The inside of the plasma furnace 1 is usually a mixed atmosphere of an inert gas such as nitrogen, helium, or argon and a reducing gas such as carbon monoxide.

[0051] The material, melting material, reducing agent, and flux supplied into the plasma furnace 1 are heated to 1300°C or higher and 1600°C or lower, and the oxidation-reduction reaction proceeds while melting as described above. The precious metals contained in this material, together with the iron in the melting material, form a heavy metal melt phase 8. On the other hand, the aluminum and titanium in this material are oxidized within the above temperature range, and almost all of them become alumina and titania. The alumina and titania produced during melting and the lime and silica in this flux form a slag phase 7 that has a relatively low specific gravity compared to the metal melt phase 8.

[0052] The formed slag phase 7 is formed above the metal melt layer 8, and as shown schematically in FIG. 1, the slag is discharged from the slag discharge pipe 4 by means of overflow or suction (not shown).

[0053] Since the metal melt phase 8 is formed below the slag phase 7, it is usually discharged by its own weight or the like from the metal melt discharge pipe 6 formed at the bottom of the plasma furnace 1. The metal melt separated and recovered as described above is subjected to hydrometallurgy or pyrometallurgy to recover precious metals. The gas in the plasma furnace 1 is exhausted from the plasma furnace 1 through an exhaust pipe 5 and sent to necessary processes such as a gas recovery process, a purification process, a separation process, etc.

[0054] The present recovery method can be carried out continuously by continuously or intermittently supplying the present material, the present melting material, the reducing agent, and the present flux from the supply tank 2 and continuously or intermittently discharging the formed slag phase 7 and metal melt phase 8.

[0055] As described above, the present recovery method allows the precious metals contained in the material to be separated from aluminum, titanium, and other components and recovered.

[0056] As described above, by controlling the concentrations of the alumina, titania, lime, and silica components in the slag so as to satisfy the above formulas (1) to (3), it is possible to obtain slag that is uniformly melted and has excellent handleability. Therefore, the composition for recovering precious metals of the present invention (hereinafter also referred to as "the present recovery composition") contains alumina, titania, lime, and silica, and satisfies the following formulas (13) to (15). 0.45≦S / (C+S) ≦0.55 (13) 0.2≦A / (A+T)≦0.6 (14) 0.4<(A+T) / (A+T+C+S)≦0.6 (15) In the formulas (13) to (15), the total amount of alumina, titania, lime, and silica is 100% by mass, and A represents the mass % of alumina, T represents the mass % of titania, C represents the mass % of lime, and S represents the mass % of silica.

[0057] By using the recovery composition for precious metals, the precious metals can be suitably separated from precious metal-containing materials containing precious metals, particularly aluminum and titanium. Specifically, as described in the present recovery method, a precious metal-containing material containing aluminum and titanium, a metal material for melting containing iron, a reducing agent, and a flux containing lime and silica are heated and melted together at 1300°C to 1600°C, and the masses of alumina, titania, lime, and silica in the resulting slag satisfy the formulas (13) to (15), thereby enabling the precious metal to be recovered in an appropriate manner.

[0058] The above equation (13) means that the mass of lime relative to the total mass of lime and silica in the slag is controlled. By controlling in this way, a slag phase with a high liquid phase ratio can be formed at a low temperature.

[0059] Equation (14) above means controlling the mass of alumina relative to the total mass of alumina and titania in the slag, and by controlling in this way, a slag phase with a high liquid fraction can be formed at a low temperature. The ratio of alumina to titania varies depending on the contents of the material and supply and demand trends, so this range indicates a range that can accommodate fluctuations due to material variations.

[0060] The above formula (15) means that the total mass of alumina and titania relative to the total mass of alumina, silica, lime, and silica in the slag is controlled. By controlling in this way, a slag phase with a high liquid phase ratio can be formed at a low temperature, and more of this material can be processed with less flux. From the above viewpoint, it is more preferable that the total mass of alumina and titania satisfies the following formula (16). 0.50≦(A+T) / (A+T+C+S)≦0.6 (16) When the present recovery composition is used in the present recovery method, it is preferable that the alumina, titania, lime, and silica in the slag satisfy the above formula (16) from the viewpoints of the operational stability of the present recovery method, processing costs, and energy saving.

[0061] In view of ease of adjusting the compositions so as to satisfy the formulas (13) to (15), A in the formulas (13) to (15) preferably satisfies the following formula (17). 5≦A≦40 (17) By satisfying the formula (17), the present recovery composition satisfies the formulas (13) to (15) and exhibits a high liquid phase ratio at a lower temperature. From the viewpoint that applying the present recovery composition to the present recovery method can reduce the processing cost per unit mass of precious metal, it is preferable that A in the formulas (13) to (15) satisfies the following formula (18). 10≦A≦40 (18)

[0062] In view of ease of adjusting the compositions so as to satisfy the formulas (13) to (15), T in the formulas (13) to (15) preferably satisfies the following formula (19): 15≦T≦50 (19) By satisfying the formula (19), the present recovery composition satisfies the formulas (13) to (15) and exhibits a high liquid phase ratio at a lower temperature. From the viewpoint that applying the present recovery composition to the present recovery method can reduce the processing cost per unit mass of precious metal, it is preferable that T in the formulas (13) to (15) satisfies the following formula (20): 20≦T≦50 (20)

[0063] In view of ease of adjusting the compositions so as to satisfy the formulas (13) to (15), C in the formulas (13) to (15) preferably satisfies the following formula (21). 15≦C≦35 (21) By satisfying the formula (21), the present recovery composition satisfies the formulas (13) to (15) and exhibits a high liquid phase ratio at a lower temperature. From the viewpoint that applying the present recovery composition to the present recovery method can reduce the processing cost per unit mass of precious metal, it is preferable that C in the formulas (13) to (15) satisfies the following formula (22): 15≦C≦30 (22)

[0064] In view of ease of adjusting the compositions so as to satisfy the formulas (13) to (15), S in the formulas (13) to (15) preferably satisfies the following formula (23). 15≦S≦35 (23) By satisfying the formula (23), the present recovery composition satisfies the formulas (13) to (15) and exhibits a high liquid phase ratio at a lower temperature. From the viewpoint that applying the present recovery composition to the present recovery method can reduce the processing cost per unit mass of precious metal, it is preferable that S in the formulas (13) to (15) satisfies the following formula (24): 15≦S≦30 (24)

[0065] From the viewpoint of facilitating the adjustment of the respective components of the recovery composition so as to satisfy formulas (13) to (15), it is preferable that at least one of A, T, C, and S satisfies any of the formulas (17) to (24), it is more preferable that all of A, T, C, and S satisfy the formulas (17), (19), (21), and (23), and it is even more preferable that all of A, T, C, and S satisfy the formulas (18), (20), (22), and (24).

[0066] In the present recovery composition, the masses of alumina, titania, lime, and silica in formulas (13) to (15) are the same as those in the present recovery method and can be determined in the same manner. As described above, the present recovery composition is produced in the slag formed by heating and melting a precious metal-containing material containing alumina and titania, a molten metal material containing iron, a reducing agent, and a flux containing lime and silica at a temperature of 1300°C or higher and 1600°C or lower. Furthermore, in the same manner as in the present recovery method for controlling the masses of alumina, titania, lime, and silica so as to satisfy the above formulas (1) to (3), the masses of alumina, titania, lime, and silica in the recovery composition can be controlled so as to satisfy the above formulas (13) to (15). In addition to alumina, titania, lime, and silica, the recovery composition of the present invention may contain base metals, their salts and oxides, inorganic oxides, organic substances, etc., as in the recovery method of the present invention.

[0067] As described above, this recovery method can efficiently recover desired precious metals from various items containing precious metals, such as spent catalysts, that have been in use for a long period of time. The precious metals recovered by this recovery method can be used in various new items, such as other catalysts. The recovery composition can also be suitably used in the recovery method.

[0068] Although the present recovery method and recovery composition have been described above, the present invention is not limited to the above-described embodiments. In the recovery method of the present embodiment, any other steps may be added to the configuration of the above embodiment, or any other steps that produce the same effect may be substituted. In addition, in the constitution of the present recovery composition according to the embodiment, any other constitution may be added, or any constitution that exerts the same function may be substituted. [Example]

[0069] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, in order to confirm the properties of the molten slag, alumina, titania, silica and lime were used without adding PGM, and attention was paid to the properties of the slag formed by these.

[0070] (Examples 1 to 9 and Comparative Example 1) In the examples and comparative examples, a mullite reaction tube shown in Figure 2 was used. As shown in Figure 2, a mullite reaction tube with a sealed top and bottom was used, which contained an iron crucible corresponding to the melting material inside. 8.0 g of a sample containing alumina, titania, silica, and lime adjusted to the mass % shown in Table 1 was placed in the iron crucible. While argon gas was passed from the bottom to the top of the mullite reaction tube, the mullite reaction tube was maintained at a temperature 50°C higher than the target temperature for 30 minutes, and then cooled to the target temperature of 1350°C or 1450°C and maintained there for 24 hours. Thereafter, the mullite reaction tube was cooled to room temperature by water cooling, and the cooled sample was recovered.

[0071] A portion of the collected sample was cut using a fine cutter, and the cross section was observed using SEM-EDS (JEOL, JSM-6510A) to observe the liquid and solid phases and quantitatively analyze each phase. For example, FIG. 3 shows an SEM photograph of the sample recovered in Example 7, and FIG. 4 shows an SEM photograph of the sample recovered in Comparative Example 1. The SEM photograph in Figure 3 shows that the entire sample is a single phase, while the SEM photograph in Figure 4 shows a mixture of areas with the same color tone as the SEM photograph in Figure 3 and areas with different color tones. The elemental composition ratios of each part were measured by quantitative analysis using EDS for each part with a different color tone.

[0072] A part of the collected sample was crushed and the crystalline phase was identified using XRD. When the liquid phase in the molten state is rapidly cooled, it becomes an amorphous solid, so for samples in which no crystalline phase was observed, it can be seen that the entire sample was in the liquid phase. For samples in which crystalline phases were observed, the elemental ratio information measured by EDS in the previous section was compared with the composition ratio of the identified crystals, and parts with matching color tones were determined to be solid phases in the molten state before cooling, while parts with different color tones were determined to be liquid phases. A comparison of FIG. 3 and FIG. 4 reveals that the recovered sample of Comparative Example 1 had a solid phase dispersed in a liquid phase.

[0073] The liquid fraction of the recovered sample was calculated from the quantitative determination of the atoms in the solid and liquid phases. The results are shown in Table 1.

[0074] From the above examples and comparative examples, it is believed that the recovered samples reflect the state of alumina, titania, silica, and lime at the time of melting, and the state of alumina, titania, silica, and lime at the time of melting can be known from the analysis of the recovered samples. In other words, it is believed that the state at the time of melting and the ratio of liquid phase to solid phase can be measured from the recovered samples.

[0075] [Table 1]

[0076] The measurement conditions for SEM-EDS and XRD are as follows. [SEM-EDS] Using a JEOL JSM-6510A, electron beam reflection images were taken at an accelerating voltage of 20 keV or less. EDS (energy dispersive X-ray spectroscopy) was quantitatively analyzed with ZAF correction.

[0077] [XRD] (X-ray diffraction method) Measurements were performed using a RIGAKU SmartLab under the following conditions: X-ray source: sealed tube type Cu tube Kα ray Output: 1.5kW Detector: 2D semiconductor X-ray detector HI-PIX3000 Scan speed: 3° to 5° / min For powder samples, the focusing method was used.

[0078] [Liquid phase ratio] The liquid phase ratio is the proportion of the sample that is in a liquid phase when melted, and is a value between 0 and 1. A larger liquid phase ratio indicates a higher proportion of the sample that is in a liquid phase when melted, and a liquid phase ratio of 1 indicates that the sample is completely in a liquid phase when melted. If no diffraction peaks are observed in XRD and the SEM photographs indicate that the entire phase is liquid, as shown in Figure 3, the liquid phase ratio is 1. Conversely, if diffraction peaks are observed in XRD, the phases observed in the SEM photographs are all determined to be identified crystalline phases, and no phases that are determined to be liquid are observed in the SEM photographs, the liquid phase ratio is 0.

[0079] The liquid phase ratio can be determined as follows, where A, T, C, and S are the same as above. The amounts of alumina, titania, lime, and silica in the solid phase and liquid phase of the sample are quantified by the SEM-EDS, and the amounts of A, T, C, and S are calculated as mass % with the total amounts of alumina, titania, lime, and silica in the solid phase and liquid phase, respectively, being 100 mass %. As mentioned above, the composition ratio of the liquid and solid phases can be determined from the EDX composition of each area with different color tones in the SEM and the crystalline phase identification results of the XRD. The liquid phase ratio can be calculated from the obtained A, T, C, and S of the liquid and solid phases using the following method.

[0080] In a quaternary phase diagram, the coordinates of a regular tetrahedron are displayed with each element (compound) that makes up the quaternary system as a vertex. For example, the point in the liquid phase with coordinates A, T, C, and S is represented as P1(A, T, C, S), and the point in the solid phase with coordinates A, T, C, and S is represented as P2(A, T, C, S). If there are n solid phases, the points in the solid phase whose coordinates are A, T, C, and S are P n+1 (A, T, C, S), where n is 1 or greater.

[0081] For example, as shown in Figure 5, in the case of a two-phase equilibrium in which a liquid phase and one type of solid phase are confirmed, two points are taken: P1 (A, T, C, S) and P2 (A, T, C, S). If the initial composition is I, ideally I should lie on the line segment P1P2, but due to factors such as analytical errors, I deviates from the line segment. Therefore, the foot of the perpendicular line dropped from composition I to the line segment P1P2 is designated as H, and using the principle of leverage, the ratio of the amounts of P1 and P2, P1:P2, was calculated as the length of the line segment P2H:P1H. In other words, the product of the amount of P1 and P1H is equal to the product of the amount of P2 and P2H. Therefore, the proportion of the liquid phase, P1, is given by the following formula: Liquid phase ratio=P2H / (P1H+P2H)

[0082] In the case of three-phase equilibrium, where a liquid phase and two solid phases were confirmed by SEM observation, as shown in Figure 6, a perpendicular line was dropped from the initial composition I to a triangle with vertices P1 (A, T, C, S), P2 (A, T, C, S), and P3 (A, T, C, S). H was the foot of the perpendicular line, and the points from P1, P2, and P3 through H and intersecting with the opposite side were designated Q1, Q2, and Q3, respectively. The quantitative ratio P1:P2:P3 was calculated as the length of the line segment Q1H / P1Q1:Q2H / P2Q2:Q3H / P3Q3. Therefore, the proportion of the liquid phase, P1, is given by the following formula: Liquid phase ratio = (Q1H / P1Q1) / (Q1H / P1Q1+Q2H / P2Q2+Q3H / P3Q3)

[0083] In the case of a four-phase equilibrium where a liquid phase and three solid phases were confirmed by SEM observation, as shown in Figure 7, in a tetrahedron with vertices P1 (A, T, C, S), P2 (A, T, C, S), P3 (A, T, C, S), and P4 (A, T, C, S), the initial composition I passes through P1, P2, P3, and P4, and the intersection points with the opposite faces are defined as Q1, Q2, Q3, and Q4, respectively. The quantitative ratio P1:P2:P3:P4 was calculated as the length of the line segment Q1I / P1Q1:Q2I / P2Q2:Q3I / P3Q3:Q4I / P4Q4. Therefore, the proportion of the liquid phase, P1, is given by the following formula: Liquid phase ratio = (Q1I / P1Q1) / (Q1I / P1Q1+Q2I / P2Q2+Q3I / P3Q3+Q4I / P4Q4)

[0084] As can be seen from Table 1, when the composition of alumina, titania, lime, and silica during melting is within the range satisfying the formulas (1), (2), and (3), a high liquid phase ratio is exhibited. From this result, it is considered that the rate of solid phase generation during melting is low and the viscosity is also low. The results in Table 1 are from a model experiment that did not contain PGM. However, even with this recovery method, if the alumina, titania, lime, and silica in the slag produced during melting have a composition that satisfies formulas (1), (2), and (3), it is thought that the slag will have a high liquid phase ratio, a low solid phase ratio during melting, and a low viscosity. Therefore, this recovery method is thought to absorb the precious metal into the molten metal, and the resulting slag is uniformly melted, has low viscosity, and is easy to handle. [Explanation of symbols]

[0085] 1: Plasma furnace 2: Supply Tank 3: Plasma exhaust tube 4: Slag discharge pipe 5: Exhaust pipe 6: Metal molten material discharge pipe 7: Slag phase 8: Metal molten phase

Claims

1. A method for recovering precious metals contained in a precious metal-containing material, comprising heating and melting a precious metal-containing material containing aluminum and titanium, a metal material for melting containing iron, a reducing agent, and a flux containing lime and silica at a temperature of 1300°C to 1600°C to form a slag phase and a metal melt phase, and controlling the masses of alumina, titania, lime, and silica in the formed slag phase so that the masses of each satisfy the following formulas (1) to (3): 0.45≦S / (C+S)≦0.55 (1) 0.2≦A / (A+T)≦0.6 (2) 0.4<(A+T) / (A+T+C+S)≦0.6 (3) In the formulas (1) to (3), the total amount of alumina, titania, lime, and silica is 100% by mass, and A represents the mass % of alumina, T represents the mass % of titania, C represents the mass % of lime, and S represents the mass % of silica.

2. 2. The method of claim 1, wherein the precious metal is a platinum group metal.

3. 3. The recovery method according to claim 1, wherein A, T, C, and S in the formulas (1) to (3) are each within the following ranges. 5≦A≦40 15≦T≦50 15≦C≦35 15≦S≦35

4. 3. The method for recovering precious metals according to claim 1, wherein the slag is separated from the metal melt phase.

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