Method for isolating 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 (hydrochloride). 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, in particular inorganic acids such as nitric acid. The pH of such aqueous hydrochloric acid solutions is usually in the range of less than 2.

[0004] The term "poorly soluble precious metal chloro complex salt" as used herein refers to its low solubility in hydrochloric acid or hydrochloric acid aqueous medium in the pH range below 2. When quantified and expressed as the solubility of the precious metal present in the poorly soluble precious metal chloro complex 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 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 the chloronoble metal acids, in the case of rhodium, hexachlororhodate(III) acid H3RhCl6, in the case of iridium, depending on the redox potential of the solution, hexachloroiridate(III) acid H3IrCl6 and / or hexachloroiridate(IV) acid H2IrCl6, in the case of ruthenium, hexachlororuthenate(IV) acid H2RuCl6, in the case of gold, tetrachloroaurate(III) acid HAuCl4, in the case of platinum, hexachloroplatinate(IV) acid HPtCl6, and in the case of palladium, depending on the redox potential of the solution, tetrachloropalladate(II) acid HPdCl4 and / or hexachloropalladate(IV) acid HPdCl6.

[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 the wet chemical precious metal recycling or the wet chemical precious metal refining, the joint separation of rhodium, iridium and ruthenium, which is carried out by coprecipitation with aliphatic polyamines in the form of sparingly soluble chloro complex salts at relatively low redox potentials, for example in the range of 400-550 mV, is customary in the art. The sparingly soluble chloro complex salts are in particular the corresponding polyamine hexachlororhodate(III), polyamine hexachloroiridate(III), polyamine hexachlororuthenate(III) or polyamine hexachlororuthenate(IV); it is not necessary for the skilled person to take note of the fact that the nitrogen atom of the respective aliphatic polyamine component is protonated in such chloro complex salts. Any gold that may be present can, for example, already be separated reductively beforehand, i.e. before the rhodium / iridium / ruthenium coprecipitation, and the platinum and palladium possibly present can, for example, be separated by precipitation in the form of sparingly soluble chloro complex salts with ammonium chloride or potassium chloride before or after the rhodium / iridium / ruthenium coprecipitation. The sparingly soluble chloro complex salts of rhodium, iridium and ruthenium coprecipitated with aliphatic polyamines can then first be evaporated in aqua regia for further processing. In this case, the organic components are decomposed by oxidation, finally forming an aqueous hydrochloric acid solution containing dissolved chloro complexes of rhodium, iridium and ruthenium, in particular in the form of the aforementioned chloro noble metal acids. A typical method for further refining is to separate rhodium as sparingly soluble chloro complex salts by precipitation with aliphatic polyamines at a relatively high redox potential, followed by further refining of the rhodium to obtain metallic rhodium or purified rhodium compounds, such as hexachlororhodate(III) acid H3RHCl6. Iridium and ruthenium can then be separated from the aqueous hydrochloric acid phase containing dissolved iridium and ruthenium chlorocomplexes at relatively low redox potentials 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 invention is to make it possible to separate rhodium particularly efficiently from aqueous hydrochloric acid solutions which contain rhodium and chlorocomplexes of iridium and / or ruthenium (chlorocomplexes of rhodium and iridium, or of rhodium and ruthenium, or of 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 chloro complex of rhodium and at least one chloro complex of iridium and / or at least one chloro complex of ruthenium (i.e. 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), characterized in that rhodium is precipitated as a sparingly soluble chloro complex salt of rhodium from an aqueous hydrochloric acid solution with a redox potential of ≧950-1050 mV (in the range of redox potential of ≧950-1050 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 according to the invention does not distinguish between nitrosyl complexes of the precious metals rhodium, iridium and ruthenium, as well as any nitrosyl complexes. The method according to the invention does not include any type of nitrosyl complexes. At any time during the method according to the 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 further substances used during the method according to the 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, in the method according to the invention, nitrosyl complexes are not formed or used at any time, nor are there any needs for them.

[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 invention preferably comprises the further steps (5) to (7) following step (4): (5) adding a reducing agent to set the redox potential of the hydrochloric acid aqueous solution in the range of 400 to 550 mV; (6) further optionally adding an aliphatic polyamine in an amount at least sufficient or even in excess to completely precipitate at least one chloro complex of iridium as a sparingly soluble iridium chloro complex salt and / or at least one chloro complex of ruthenium as a sparingly soluble ruthenium chloro complex salt; (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 according to the present invention, an aqueous hydrochloric acid solution containing 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 is prepared. The proportion of the at least one dissolved chloro complex of rhodium in the aqueous hydrochloric acid solution may be, for example, in a range corresponding to 0.5 to 15 g / l of rhodium, and is preferably hexachlororhodium acid. The proportion of the at least one dissolved chloro complex of iridium in the aqueous hydrochloric acid solution may be, for example, in a range corresponding to 0.5 to 15 g / l of iridium, and is preferably hexachloroiridic acid. The proportion of the at least one dissolved chloro complex of ruthenium in the aqueous hydrochloric acid solution may be, for example, in a range corresponding to 0.5 to 15 g / l of ruthenium, and is preferably hexachlororuthenic acid. With regard to the possible further constituents and the pH of the aqueous hydrochloric acid solution, reference is made to those already mentioned above.

[0016] It is important for the invention that the process according to the invention explicitly omits the co-isolation 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 invention, it is first ensured that there is an oxidation-reduction potential of the aqueous hydrochloric acid in the range of ≧950-1050 mV, for example in the range of ≧950-1000 mV. If this is not the case, such an oxidation-reduction potential is set by adding an oxidizing agent. Said setting of the oxidation-reduction potential can be carried out by mixing the aqueous hydrochloric acid with one or more oxidizing agents under potentiometric control as is customary in the art. The oxidizing agents can be added to the aqueous hydrochloric acid as such or as an aqueous solution. Examples of particularly suitable oxidizing agents include chlorine, bromate, chlorate and perchlorate. When using an oxidizing agent as an aqueous solution, the skilled person will expediently try to use one that does not have an unnecessarily low concentration.

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

[0019] According to step (2), if a relatively high redox potential of the aqueous hydrochloric acid solution exists or has been set by the addition of an oxidizing agent, in step (3), an aliphatic polyamine is added to the aqueous hydrochloric acid solution in an amount sufficient or even in excess to completely precipitate at least one rhodium chloro complex as a sparingly soluble rhodium chloro complex salt. The amount of aliphatic polyamine that is 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 added; in this respect, the skilled artisan will understand that the term "completely precipitate" refers to precipitating material in excess of the solubility product. The aliphatic polyamine can be added as is or as an aqueous solution, preferably as an aqueous solution neutralized with an acid, in particular hydrochloric acid. The aliphatic polyamine can be one 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 an 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 may 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 therefore its use is preferred.

[0020] In other words, rhodium is directly and at least largely selectively precipitated as sparingly soluble rhodium chlorocomplex salts using aliphatic polyamines in the redox potential range of ≧950-1050 mV, for example ≧950-1000 mV, and is therefore first 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 trihydrohexachlororhodic 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 during step (3), for example by stirring. Step (3) 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 rest, 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 chloro complex salt can be separated from the supernatant aqueous hydrochloric acid solution in step (4) of the process according to the invention by a typical solid-liquid separation. 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 combinations 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 provided in step (1), which 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 provided in step (1).

[0026] The separated sparingly soluble rhodium chloro complex salts can be fed into 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 process according to the invention are consecutive steps. As already mentioned, the process according to the invention preferably comprises the further steps (5) to (7), of which steps (5) and (6) can be carried out in the step sequence (5)-(6) or (6)-(5), although the step sequence (5)-(6) is preferred.

[0029] In step (5), the relatively low redox potential of the aqueous hydrochloric acid solution is set in the range of 400-550 mV, preferably 440-470 mV, by adding a reducing agent. The redox potential can be conveniently set by mixing the aqueous hydrochloric acid solution with the reducing agent under potential difference control. The reducing agent can be added to the aqueous hydrochloric acid solution as is or as an aqueous solution. The reducing agent can be one 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 especially iron(II) salts such as iron(II) chloride, iron(II) sulfate and iron(II) nitrate. When using a reducing agent as an aqueous solution, the skilled person will expediently strive to use one that does not have an unnecessarily low concentration.

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

[0031] Furthermore, if necessary, in step (6), which is optionally optional in this respect, a further aliphatic polyamine, i.e., an amount at least sufficient or even an excess amount of aliphatic polyamine to completely precipitate at least one chloro complex of iridium as a poorly soluble iridium chloro complex salt and / or at least one chloro complex of ruthenium as a poorly soluble ruthenium chloro complex salt, can be added to the aqueous hydrochloric acid solution before or preferably after the low redox potential is set in step (5). The amount of aliphatic polyamine at least sufficient to completely precipitate at least one chloro complex of iridium or ruthenium as a poorly soluble chloro complex salt is an amount that will not cause further precipitation even if further added; in this respect, the skilled person will understand that the term "completely precipitate" refers to precipitating materials in excess of the solubility product. The need to add an aliphatic polyamine, and therefore the need to carry out 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 contained in the aqueous hydrochloric acid. If this is not the case, or if it is not present in sufficient or even excessive amounts, step (6) is carried out. In this case, the aliphatic polyamine can be added as such or in aqueous solution, but preferably in the form of an acid, in particular in the form of an aqueous solution neutralized with hydrochloric acid. 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. Examples of aliphatic polyamines suitable as such precipitants include the aliphatic polyamines already mentioned above.

[0032] When step (6) is unnecessary and can be omitted, i.e., when a sufficient amount of the aliphatic polyamine added during step (2) is contained in the aqueous hydrochloric acid solution during 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 expedient to ensure good mixing, for example by stirring. Step (6) may conveniently be carried out at a temperature range, for example, from 55 to 90° C. At the end of step (6), or between step (6) and step (7), it may be expedient to allow the mixture formed to rest, for example by leaving it for 1 to 6 hours. Thus, settling of the precipitated material and the formation of a supernatant in the form of an aqueous hydrochloric acid solution may be effectively supported.

[0035] Following the precipitation, the precipitated poorly soluble iridium chloro complex salt and / or the precipitated poorly soluble ruthenium chloro complex 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 salts and / or sparingly soluble ruthenium chloro complex salts 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 beginning are the low consumption of chemicals and the high efficiency.Unlike the prior art, the separated rhodium and iridium and / or ruthenium can be processed in parallel with virtually no 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 the addition of sodium chlorate solution (acid content 3 mol / l, dissolved precious metals: platinum, palladium, rhodium, iridium, ruthenium), together with a 1.5-fold stoichiometric excess of DETA calculated relative to the rhodium content, were added dropwise to the beaker at 75 °C under stirring. For this purpose, an aqueous DETA solution with a DETA content of 19% by weight, neutralized with hydrochloric acid, was used. The mixture was then stirred for a further 5 minutes and the beaker, covered with a watch glass, was left 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 on the one hand and the respective precious metal content of the filtrate on the other hand were determined and related by ICP-OES to the volume and precious metal content of 200 mL of the original precious metal solution. The following table shows the precious metal content 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, characterized in that the rhodium is precipitated 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, while explicitly omitting the conventional simultaneous separation of the iridium and / or the ruthenium.

2. Steps (1) to (4): (1) at least one rhodium chloro complex and at least one iridium chloro complex, 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 excess; (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) setting the redox potential of the hydrochloric acid solution in the range of 400 to 550 mV by adding a reducing agent; (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 aqueous hydrochloric acid 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 rhodium chloro complex in said aqueous hydrochloric acid solution is in the range corresponding to 0.5 to 15 g / l of rhodium.

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

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

7. The method according to any one of claims 2 to 6, wherein the redox potential in step (2) is set by adding an oxidizing agent.

8. The method according to any one of claims 2 to 7, wherein in step (3), the aliphatic polyamine is added as an aqueous solution neutralized with hydrochloric acid.

9. 9. The method of any one of claims 2 to 8, 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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