Method for separating rhodium

Abstract

A method for separating rhodium from an aqueous hydrochloric acid solution containing at least one chloro complex of rhodium and at least one chloro complex of iridium and / or at least one chloro complex of ruthenium, characterized in that rhodium is precipitated as a poorly soluble chloro complex salt of rhodium from an aqueous hydrochloric acid solution having a redox potential of ≧950-1050 mV using an aliphatic polyamine, while explicitly omitting the simultaneous separation of iridium and / or ruthenium, which has been conventionally carried out.

Description

[Technical Field]

[0001] The present invention relates to an efficient method for separating rhodium as sparingly soluble rhodium chloro complex salts from aqueous solutions containing noble metal chloro complexes (hydrochlorides). Summary of the Invention [Problem to be solved by the invention]

[0002] As used herein, the term "noble metal chloro complex" refers to a chloro complex of the noble metals rhodium, iridium, ruthenium, gold, platinum, or palladium.

[0003] Precipitation of sparingly soluble precious metal chloro complex salts from aqueous hydrochloric acid solutions containing the precious metal chloro complexes is a conventional technique in wet chemical precious metal recycling or wet chemical precious metal refining. In addition to hydrochloric acid, such aqueous hydrochloric acid solutions can also contain other acids, particularly inorganic acids such as nitric acid. The pH of such aqueous hydrochloric acid solutions is typically in the range of less than 2.

[0004] The term "scarcely soluble precious metal chlorocomplex salt" as used herein refers to its low solubility in hydrochloric acid or aqueous hydrochloric acid medium in the pH range of less than 2. When quantified and expressed as the solubility of the precious metal present in the sparingly soluble precious metal chlorocomplex salt, this means a solubility of less than 100 mg per liter of the precious metal.

[0005] The concentration of the noble metal dissolved in the aqueous hydrochloric acid solution can be determined by ICP-OES (inductively coupled plasma optical emission spectrometry).

[0006] Examples of noble metal chloro complexes contained in the aqueous hydrochloric acid solution, i.e. dissolved therein, include in particular chloronoble metal acids, such as hexachlororhodate(III) H3RhCl6 in the case of rhodium, hexachloroiridate(III) H3IrCl6 and / or hexachloroiridate(IV) H2IrCl6 in the case of iridium, depending on the redox potential of the solution, hexachlororuthenate(IV) H2RuCl6 in the case of ruthenium, tetrachloroaurate(III) HAuCl4 in the case of gold, hexachloroplatinate(IV) H2PtCl6 in the case of platinum, and tetrachloropalladate(II) H2PdCl4 and / or hexachloropalladate(IV) H2PdCl6 in the case of palladium, depending on the redox potential of the solution.

[0007] The term "redox potential" as used in this specification and claims means the redox potential of an aqueous solution at 20°C measured against an Ag / AgCl electrode.

[0008] In the case of hydrochemical precious metal recycling or hydrochemical precious metal refining, the joint separation of rhodium, iridium, and ruthenium by coprecipitation with aliphatic polyamines in the form of sparingly soluble chlorocomplex salts at relatively low redox potentials, for example, in the range of 400 to 550 mV, is common in the art. The sparingly soluble chlorocomplex salts are, in particular, the corresponding polyamine hexachlororhodate(III), polyamine hexachloroiridate(III), polyamine hexachlororuthenate(III), or polyamine hexachlororuthenate(IV); those skilled in the art need not take note that the nitrogen atom of the respective aliphatic polyamine component is protonated in such chlorocomplex salts. Any gold present can be separated reductively already, for example, before the rhodium / iridium / ruthenium coprecipitation. Optionally present platinum and palladium can be separated, for example, by precipitation in the form of sparingly soluble chlorocomplex salts with ammonium chloride or potassium chloride before or after the rhodium / iridium / ruthenium coprecipitation. The sparingly soluble chlorocomplex salts of rhodium, iridium, and ruthenium coprecipitated with an aliphatic polyamine can then be evaporated in aqua regia for further processing. In this case, organic components are decomposed by oxidation, ultimately forming an aqueous hydrochloric acid solution containing dissolved chlorocomplexes of rhodium, iridium, and ruthenium, particularly in the form of the aforementioned chloronoble metal acids. A typical method for further purification is to separate rhodium as sparingly soluble chlorocomplex salts by precipitation with an aliphatic polyamine at a relatively high redox potential, followed by further purification of the rhodium to obtain metallic rhodium or purified rhodium compounds, such as hexachlororhodic acid (III) H3RHCl6. Iridium and ruthenium can then be separated from the aqueous hydrochloric acid phase containing dissolved iridium and ruthenium chlorocomplexes at a relatively low redox potential by precipitation with aliphatic polyamines as sparingly soluble chlorocomplex salts, which can then be fed to further iridium or ruthenium refining.

[0009] U.S. Pat. No. 5,478,376 discloses a method for separating rhodium and / or iridium from a starting solution containing at least one ruthenium chloro complex, hydrochloric acid, and rhodium and / or iridium chloro complex, which comprises converting the ruthenium chloro complex to a divalent nitrosyl complex and precipitating the rhodium and / or iridium by manipulating the oxidation state.

[0010] The object of the present invention is to enable a particularly efficient separation of rhodium from an aqueous hydrochloric acid solution containing rhodium and chloro complexes of iridium and / or ruthenium (chloro complexes of rhodium and iridium, or rhodium and ruthenium, or rhodium, iridium and ruthenium).

[0011] The present invention achieves this object in a surprisingly simple manner by a method for separating rhodium from an aqueous hydrochloric acid solution containing at least one chlorocomplex of rhodium and at least one chlorocomplex of iridium and / or at least one chlorocomplex of ruthenium (i.e., at least one chlorocomplex of rhodium and at least one chlorocomplex of iridium, or at least one chlorocomplex of rhodium and at least one chlorocomplex of ruthenium, or at least one chlorocomplex of rhodium, at least one chlorocomplex of iridium, and at least one chlorocomplex of ruthenium), characterized in that rhodium is precipitated as a sparingly soluble chlorocomplex of rhodium from an aqueous hydrochloric acid solution having an oxidation-reduction potential of ≥ 950 to 1050 mV (oxidation-reduction potential in the range of ≥ 950 to 1050 mV) using an aliphatic polyamine, while explicitly omitting the conventional simultaneous separation of iridium and / or ruthenium from the aqueous hydrochloric acid solution.

[0012] For the avoidance of doubt, the method of the present invention does not distinguish between nitrosyl complexes of the precious metals rhodium, iridium, and ruthenium, nor any nitrosyl complexes. The method of the present invention does not include any type of nitrosyl complex. At any point during the method of the present invention, no nitrosyl complexes are found in the aqueous hydrochloric acid solution containing at least one chloro complex of rhodium and at least one chloro complex of iridium and / or at least one chloro complex of ruthenium. All additional substances used in the method of the present invention do not include nitrosyl complexes, nor do they include substances capable of forming nitrosyl complexes with the aqueous hydrochloric acid solution. In other words, nitrosyl complexes are not formed or used at any point in the method of the present invention, nor are they necessary.

[0013] The method according to the present invention particularly comprises the following steps (1) to (4): (1) at least one chloro complex of rhodium and at least one chloro complex of iridium, or at least one chloro complex of rhodium and at least one chloro complex of ruthenium, or At least one chloro complex of rhodium, at least one chloro complex of iridium, and at least one chloro complex of ruthenium providing an aqueous hydrochloric acid solution containing: (2) ensuring that the redox potential of the aqueous hydrochloric acid solution is in the range of ≧950-1050 mV; (3) adding an aliphatic polyamine in an amount at least sufficient to completely precipitate at least one rhodium chloro complex as a sparingly soluble rhodium chloro complex salt, or even in excess; (4) separating the precipitated poorly soluble rhodium chloro complex salt from the aqueous hydrochloric acid solution; Includes.

[0014] The method according to the present invention preferably comprises the further steps (5) to (7) following step (4): (5) adding a reducing agent to set the oxidation-reduction potential of the hydrochloric acid aqueous solution in the range of 400 to 550 mV; (6) if necessary, adding an aliphatic polyamine in an amount at least sufficient to completely precipitate at least one iridium chloro complex as a sparingly soluble iridium chloro complex salt and / or at least one ruthenium chloro complex as a sparingly soluble ruthenium chloro complex salt, or even in an excess amount; (7) separating the precipitated poorly soluble iridium chloro complex salt and / or the precipitated poorly soluble ruthenium chloro complex salt from the hydrochloric acid aqueous solution; Includes.

[0015] In step (1) of the method of the present invention, an aqueous hydrochloric acid solution containing at least one rhodium chloro complex and at least one iridium chloro complex, or at least one rhodium chloro complex and at least one ruthenium chloro complex, or at least one rhodium chloro complex, at least one iridium chloro complex, and at least one ruthenium chloro complex is provided. The proportion of the at least one rhodium chloro complex dissolved in the aqueous hydrochloric acid solution may be, for example, in a range corresponding to 0.5 to 15 g / L of rhodium, preferably hexachlororhodic acid. The proportion of the at least one iridium chloro complex dissolved in the aqueous hydrochloric acid solution may be, for example, in a range corresponding to 0.5 to 15 g / L of iridium, preferably hexachloroiridic acid. The proportion of the at least one ruthenium chloro complex dissolved in the aqueous hydrochloric acid solution may be, for example, in a range corresponding to 0.5 to 15 g / L of ruthenium, preferably hexachlororuthenic acid. With regard to the possible further constituents and pH of the aqueous hydrochloric acid solution, reference is made to what has already been made above.

[0016] It is important for the present invention that the method according to the invention explicitly omits the co-separation of rhodium together with iridium, or together with ruthenium, or together with iridium and ruthenium.

[0017] For this purpose, in step (2) of the method according to the present invention, it is first ensured that the redox potential of the aqueous hydrochloric acid solution is in the range of ≥ 950-1050 mV, for example, ≥ 950-1000 mV. If this is not the case, such a redox potential is set by adding an oxidizing agent. Setting the redox potential can be achieved by mixing the aqueous hydrochloric acid solution with one or more oxidizing agents under potential control, as is customary in the art. The oxidizing agent can be added to the aqueous hydrochloric acid solution as is or as an aqueous solution. Examples of particularly suitable oxidizing agents include chlorine, bromate, chlorate, and perchlorate. When using an oxidizing agent in aqueous solution, those skilled in the art will expediently strive to use one that does not have an unnecessarily low concentration.

[0018] It may be convenient to ensure good mixing, for example by stirring, during step (2), which may conveniently be carried out at a temperature in the range of, for example, 55 to 90°C.

[0019] If a relatively high redox potential of the aqueous hydrochloric acid solution exists or has been established by the addition of an oxidizing agent according to step (2), then in step (3), an aliphatic polyamine is added to the aqueous hydrochloric acid solution in an amount sufficient to completely precipitate at least one rhodium chloro complex as a sparingly soluble rhodium chloro complex salt, or even in an excess amount. The amount of aliphatic polyamine at least sufficient to completely precipitate at least one rhodium chloro complex as a sparingly soluble rhodium chloro complex salt is an amount that does not cause further precipitation even if further addition is made; in this regard, those skilled in the art will understand that the term "complete precipitation" refers to precipitating material in excess of the solubility product. The aliphatic polyamine can be added neat or as an aqueous solution, preferably neutralized with an acid, particularly hydrochloric acid. The aliphatic polyamine can be a single aliphatic polyamine or a combination of two or more aliphatic polyamines, although the use of a single aliphatic polyamine is preferred. The proportion of aliphatic polyamine in such an aqueous solution neutralized with acid can be, for example, in the range of 15 to 25% by weight. One aliphatic polyamine or a combination of two or more aliphatic polyamines can be selected. Examples of aliphatic polyamines suitable as such precipitants include diethylene triamine (DETA), triethylene triamine (TETA), tetraethylene pentamine (TEPA), pentaethylenehexamine, tris(2-aminoethyl)amine (TAEA), dipropylenetriamine, and 1-(2-aminoethyl)piperazine. DETA is particularly suitable, and its use is therefore preferred.

[0020] In other words, rhodium is directly and at least largely selectively precipitated as a sparingly soluble rhodium chlorocomplex salt using an aliphatic polyamine in the redox potential range of ≧950-1050 mV, for example ≧950-1000 mV, and is therefore initially separated from iridium and / or ruthenium.

[0021] The material precipitated during step (3) is a sparingly soluble salt of an aliphatic polyamine, such as DETA, with a chloro complex of rhodium, such as trihydrohexachlororhodium acid, i.e., for example, diethylenetriammonium hexachlororhodium salt of formula H3(DETA)RhCl6 or (H3NC2H4NH2C2H4NH3)(RhCl6).

[0022] It may be convenient to ensure good mixing, for example by stirring, during step (3), which may conveniently be carried out at a temperature in the range of, for example, 55 to 90°C.

[0023] At the end of step (3) or between steps (3) and (4), it may be advantageous to allow the mixture formed to stand, for example by leaving it for 1 to 3 hours, thus effectively supporting the settling of the precipitated material and the formation of a supernatant in the form of an aqueous hydrochloric acid solution.

[0024] Following its precipitation, the sparingly soluble rhodium chlorocomplex salt can be separated from the supernatant aqueous hydrochloric acid solution by a typical solid-liquid separation in step (4) of the process according to the present invention. Examples of suitable solid-liquid separation methods include those known to those skilled in the art, such as decantation, squeezing, filtration, suction filtration, centrifugation, or a combination thereof.

[0025] It has been found that rhodium separations on the order of 80-99% can be achieved, based on the rhodium content of the aqueous hydrochloric acid solution provided in step (1), and this is achieved at least largely selectively, in the sense that co-precipitation of iridium or ruthenium does not occur, or occurs only to the order of, for example, >0-15%, based on the iridium or ruthenium content of the original aqueous hydrochloric acid solution provided in step (1).

[0026] The separated sparingly soluble rhodium chloro complex salt can be fed to a typical rhodium refining process.

[0027] The separated aqueous hydrochloric acid solution further contains iridium and / or ruthenium in the form of dissolved, non-precipitated chloro complexes.

[0028] Steps (1) to (4) of the method according to the invention are consecutive steps. As already mentioned, the method according to the invention preferably comprises further steps (5) to (7), of which steps (5) and (6) can be carried out in the order (5)-(6) or (6)-(5), with the order (5)-(6) being preferred.

[0029] In step (5), the relatively low redox potential of the aqueous hydrochloric acid solution is adjusted to a range of 400 to 550 mV, preferably 440 to 470 mV, by adding a reducing agent. Adjusting the redox potential is conveniently achieved by mixing the aqueous hydrochloric acid solution with the reducing agent under potential control. The reducing agent can be added to the aqueous hydrochloric acid solution as is or as an aqueous solution. The reducing agent may be a single reducing agent or a combination of two or more reducing agents. Examples of suitable reducing agents include tin(II) salts such as tin(II) chloride and tin(II) sulfate, but particularly iron(II) salts such as iron(II) chloride, iron(II) sulfate, and iron(II) nitrate. When using a reducing agent as an aqueous solution, those skilled in the art will expediently strive to use one that does not have an unnecessarily low concentration.

[0030] It may be convenient to ensure good mixing, for example by stirring, during step (5).Step (5) may conveniently be carried out at a temperature in the range of, for example, 50 to 70°C.

[0031] Furthermore, if necessary, in step (6), which is optionally optional in this respect, further aliphatic polyamine, i.e., an amount at least sufficient or even an excess amount of aliphatic polyamine to completely precipitate at least one iridium chloro complex as a sparingly soluble iridium chloro complex salt and / or at least one ruthenium chloro complex as a sparingly soluble ruthenium chloro complex salt, can be added to the aqueous hydrochloric acid solution before or preferably after the low redox potential is established in step (5). The amount of aliphatic polyamine at least sufficient to completely precipitate at least one iridium or ruthenium chloro complex as a sparingly soluble chloro complex salt is an amount that will not cause further precipitation if further added; in this regard, those skilled in the art will understand that the term "completely precipitate" refers to precipitating material in excess of the solubility product. The need to add an aliphatic polyamine, and therefore the need to perform step (6), depends on whether there is a shortage of aliphatic polyamine necessary for complete precipitation, more precisely, on whether and to what extent the aliphatic polyamine resulting from the addition in step (2) is present in the aqueous hydrochloric acid solution. If this is not the case, or if the amount is not sufficient or even excessive, step (6) is performed. In this case, the aliphatic polyamine can be added as is or in the form of an aqueous solution, preferably in the form of an acid, particularly an aqueous solution neutralized with hydrochloric acid. The proportion of the aliphatic polyamine in such an aqueous solution neutralized with acid can be, for example, in the range of 15 to 25% by weight. Examples of aliphatic polyamines suitable as such precipitants include the aliphatic polyamines already mentioned above.

[0032] If step (6) is unnecessary and can be omitted, that is, if a sufficient amount of the aliphatic polyamine added in step (2) is contained in the aqueous hydrochloric acid solution in step (5), the precipitation of iridium and / or ruthenium occurs "automatically," so to speak.

[0033] In this regard, the material precipitated during or after completion of step (5) or step (6) is a sparingly soluble salt of an aliphatic polyamine and a chloro complex of iridium and / or a chloro complex of ruthenium.

[0034] During step (6), it may be advantageous to ensure good mixing, for example by stirring. Step (6) may be conveniently carried out at a temperature in the range of, for example, 55 to 90°C. At the end of step (6), or between steps (6) and (7), it may be advantageous to allow the mixture formed to stand, for example by leaving it for 1 to 6 hours. This can effectively assist the settling of the precipitated material and the formation of a supernatant in the form of an aqueous hydrochloric acid solution.

[0035] Following the precipitation, the precipitated poorly soluble iridium chlorocomplex salt and / or the precipitated poorly soluble ruthenium chlorocomplex salt can be separated from the aqueous hydrochloric acid solution by a typical solid-liquid separation in step (7). Examples of suitable solid-liquid separation methods include those known to those skilled in the art, such as decantation, squeezing, filtration, suction filtration, centrifugation, or a combination thereof.

[0036] The separated sparingly soluble iridium chloro complex salt and / or sparingly soluble ruthenium chloro complex salt can be fed to a typical iridium or ruthenium refining process.

[0037] The advantages of the process according to the invention compared to the prior art processes mentioned at the outset are a low consumption of chemicals and a high efficiency: unlike the prior art, the separated rhodium and iridium and / or ruthenium can be processed in parallel, essentially without time delay.

[0038] Exemplary embodiments 1-3, general procedure: 200 mL of an aqueous precious metal hydrochloric acid solution, the redox potential of which was set to 950 mV by adding sodium chlorate solution (acid content: 3 mol / L, dissolved precious metals: platinum, palladium, rhodium, iridium, and ruthenium), was added dropwise to a beaker at 75 °C while stirring, along with a 1.5-fold stoichiometric excess of DETA calculated relative to the rhodium content. For this purpose, an aqueous DETA solution neutralized with hydrochloric acid and containing 19% DETA by weight was used. The mixture was then stirred for another 5 minutes, and the beaker, covered with a watch glass, was allowed to cool. The precipitate, consisting essentially of DETA hexachlororhodate, was filtered off with suction and washed with a small amount of distilled water. The filtrate volume and the respective precious metal contents of the filtrates were determined on the one hand and, on the other hand, related to the volume and precious metal content of the original 200 mL precious metal solution by ICP-OES. The following table shows the precious metal contents of the original precious metal solution and the respective yields of the precipitated precious metals. [Table 1]

Claims

1. A method for separating rhodium from an aqueous hydrochloric acid solution containing at least one chloro complex of rhodium and at least one chloro complex of iridium and / or at least one chloro complex of ruthenium, comprising precipitating the rhodium as a sparingly soluble chloro complex salt of rhodium from the aqueous hydrochloric acid solution having a redox potential of ≥ 950-1050 mV using an aliphatic polyamine; 10. A method according to claim 9, wherein the simultaneous separation of the rhodium and the iridium and / or the ruthenium by coprecipitating them in the form of sparingly soluble chlorocomplex salts is not carried out prior to the precipitation of the rhodium.

2. Steps (1) to (4): (1) at least one chloro complex of rhodium and at least one chloro complex of iridium, or at least one chloro complex of rhodium and at least one chloro complex of ruthenium, or At least one chloro complex of rhodium, at least one chloro complex of iridium, and at least one chloro complex of ruthenium providing an aqueous hydrochloric acid solution containing: (2) ensuring that the redox potential of the aqueous hydrochloric acid solution is in the range of ≧950-1050 mV; (3) adding an aliphatic polyamine in an amount at least sufficient to completely precipitate the at least one rhodium chloro complex as a sparingly soluble rhodium chloro complex salt, or even in an excess amount; (4) separating the precipitated poorly soluble rhodium chloro complex salt from the aqueous hydrochloric acid solution; The method of claim 1 , comprising:

3. Steps (5) to (7) following step (4): (5) adding a reducing agent to set the oxidation-reduction potential of the hydrochloric acid aqueous solution in the range of 400 to 550 mV; (6) if necessary, adding an aliphatic polyamine in an amount at least sufficient to completely precipitate the at least one iridium chloro complex as a sparingly soluble iridium chloro complex salt and / or the at least one ruthenium chloro complex as a sparingly soluble ruthenium chloro complex salt, or even in an excess amount; (7) separating the precipitated poorly soluble iridium chloro complex salt and / or the precipitated poorly soluble ruthenium chloro complex salt from the hydrochloric acid aqueous solution; The method of claim 2 , comprising:

4. 4. The method according to claim 2 or 3, wherein the proportion of said at least one dissolved chloro complex of rhodium in said aqueous hydrochloric acid solution is in the range corresponding to 0.5 to 15 g / l of rhodium.

5. 4. The method according to claim 2 or 3, wherein the proportion of said at least one dissolved iridium chloro complex in said aqueous hydrochloric acid solution is in the range corresponding to 0.5 to 15 g / l of iridium.

6. 4. The method according to claim 2 or 3, wherein the proportion of said at least one dissolved chloro complex of ruthenium in said aqueous hydrochloric acid solution is in the range corresponding to 0.5 to 15 g / l of ruthenium.

7. 3. The method of claim 2, wherein the redox potential in step (2) is set by adding an oxidizing agent.

8. 3. The method of claim 2, wherein in step (3), the aliphatic polyamine is added as an aqueous solution neutralized with hydrochloric acid.

9. 4. The method of claim 2 or 3, wherein the aliphatic polyamine is one aliphatic polyamine, two aliphatic polyamines, or a combination of two or more aliphatic polyamines selected from the group consisting of diethylenetriamine (DETA), triethylenetriamine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine, tris(2-aminoethyl)amine (TAEA), dipropylenetriamine, and 1-(2-aminoethyl)piperazine.

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