A METHOD OF RECOVERING IRIDIUM

Abstract

The present invention relates to a method of recovering iridium in the form of iridium solutions, metal, oxides or salts from a body, such as a spent catalyst, comprising iridium oxides.

Claims

1. A method of recovering iridium from a body comprising Ir.sub.xO.sub.y, wherein x is a number between 1 and 2 and y is a number between 1 and 4, wherein said method comprises: contacting said body with a reducing agent, thereby forming a suspension; and dissolving said suspension by exposing said suspension to an acidic solution, thereby forming a solution comprising iridium ions.

2-15. (canceled)

16. The method of recovering iridium according to claim 1, wherein said Ir.sub.xO.sub.y comprises Ir(IV) oxides compounds.

17. The method of recovering iridium according to claim 1, wherein said suspension is a suspension of Ir.sub.xO.sub.y compounds comprising Ir(III) oxides particles.

18. The method of recovering iridium according to claim 1, wherein said reducing agent comprises hydrazine.

19. The method of recovering iridium according to claim 1, wherein said reducing agent comprises formic acid having a concentration between 0.5 M and 3 M.

20. The method of recovering iridium according to claim 1, wherein said reducing agent comprises sodium borohydride having a concentration between 0.5 M and 3 M.

21. The method of recovering iridium according to claim 1, wherein said body is a spent catalyst.

22. The method of recovering iridium according to claim 1, wherein said acidic solution comprises hydrogen halides.

23. The method of recovering iridium according to claim 21, wherein said acidic solution further comprises an halide salt.

24. The method of recovering iridium according to claim 1, wherein said contacting said body with a reducing agent comprises contacting said body with a reducing agent for a period of time between 5 and 30 minutes at room temperature.

25. The method of recovering iridium according to claim 1, wherein said contacting said body with a reducing agent comprises contacting said body with a reducing agent under sonication.

26. The method of recovering iridium according to claim 1, wherein said dissolving comprises dissolving said suspension by exposing said suspension to a solution comprising hydrogen halides for a period of time between 10 minutes to 4 hours at a temperature between 50° C. and 120° C. at the pressure of 1 Atm.

27. The method according to claim 1, further comprising: precipitating said iridium ions as Ir metal particles by exposing said solution containing iridium ions to a reducing agent at a temperature between 60° C. and 100° C. for a period of time between 1 hour and 3 hours.

28. The method according to claim 1, further comprising: precipitating said iridium ions as Ir.sub.xO.sub.y, by contacting said solution containing iridium ions with NaOH at a temperature between 100° C. and 200° C. for a period of time between 10 minutes and 60 minutes at a pressure between 1 and 10 Atm.

29. The method according to claim 1, further comprising: precipitating said iridium ions as Ir salts by contacting said solution containing iridium ions with H.sub.2O.sub.2, and by adding NH.sub.4Cl in a concentration 3M eq. to said oxidized solution containing iridium ions.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0057] The method of recovering iridium according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0058] FIG. 1 shows the absorption spectra of the dissolution of IrO.sub.2 when a first reduction step is performed compared to the one without reduction step.

[0059] FIG. 2 is a bar chart comparing the dissolution of Ir.sub.xO.sub.y compounds without and with using different reducing agents.

[0060] FIG. 3 shows a comparison between Ir.sub.xO.sub.y dissolution without and with using different reducing agents vs reflux time.

[0061] FIG. 4 shows a comparison between Ir.sub.xO.sub.y dissolution using different temperature vs reflux time.

[0062] FIG. 5 and FIG. 6 are flow-charts of the methods according to some embodiments the invention.

[0063] FIG. 7 shows the X-ray diffraction (XRD) pattern of Ir metal particles produced according to one embodiment of the invention.

[0064] FIG. 8 shows UV-vis spectra of the solution containing Ir ions and of the correspondent oxidized solution according to one embodiment of the invention.

[0065] FIG. 9 shows the XRD pattern of the precipitate formed following the addition of NH.sub.4Cl according to one embodiment of the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0066] FIG. 1 shows a comparison 1 between absorption spectra of the solution following the dissolution step, when a first reduction step is performed 7 compared to the absorption spectrum when the first reduction step is not performed 8.

[0067] An absorption spectrum 9 of IrCl.sub.3 in aqueous solution is also shown as reference.

[0068] The comparison reveals that the IrO.sub.2 dissolved after the reduction step shows no absorption peaks between 200 and 1200 nm, while the IrO.sub.2 dissolved without reduction step shows a series of characteristic peaks between 400 and 550 nm.

[0069] This reveals formation of different chemical species when no reduction step is performed, suggesting possibly two different dissolution routes.

[0070] During the reduction step, higher oxidation state iridium, such as Ir(IV) oxide is transformed into lowever oxidation state iridium, such as Ir(III) oxide species as shown by the resemblance of the IrCl.sub.3 spectrum with the one of the dissolution of IrO.sub.2 when the reduction step was performed.

[0071] This is clearly not the case of the solution of IrO.sub.2 when the reduction step is not performed.

[0072] FIG. 2 is a bar chart 2 comparing the dissolution of Ir.sub.xO.sub.y compounds without and with using different reducing agents.

[0073] From the chart it appears clear that using a pre-reduction step improves the final dissolution by several orders of magnitude; moreover performing a first reduction step using hydrazine produces a better dissolution of Ir.sub.xO.sub.y compounds compared to the use of NaBH.sub.4 or formic acid.

[0074] All processes were performed by subjecting the Ir.sub.xO.sub.y samples to ultrasonication for 5 min in ultrapure water solution of the corresponding reducing agent, i.e. 35% hydrazine or 1 M formic acid or 1 M NaBH.sub.4 in a reducing agent/Ir molar ratio of >1, such as 10 and a Ir.sub.xO.sub.y/water ratio of 20 mg Ir.sub.xO.sub.y/1 mL of water

[0075] When using 1 M formic acid, a heating step of 100° C. for 5 minutes was introduced to facilitate reduction.

[0076] The dissolution step was then performed in 1M HCl, 3M NaCl heated under reflux for 60 minutes.

[0077] FIG. 3 shows a comparison 3 between Ir.sub.xO.sub.y dissolution without and with using different reducing agents vs reflux time.

[0078] The first reduction step was perform as in the earlier experiment with ultrasonication at room temperature for ˜5 minutes.

[0079] For the case of formic acid, ultrasonication at room temperature for ˜5 minutes was followed by holding the temperature of the suspension at 100° C. for 5 minutes.

[0080] The second dissolution step was performed in an aqueous solution of 1 M HCl and 3M NaCl in a Ir.sub.xO.sub.y/solution ratio of 3 mg Ir.sub.xO.sub.y/1 mL of the solution and the dissolution was measured at different reflux time.

[0081] It appears clear that hydrazine has the best performance as dissolution close to 90% was already achieved after only 10 minutes of reflux.

[0082] FIG. 4 shows a comparison between Ir.sub.xO.sub.y dissolution using different temperature vs reflux time when hydrazine was employed in the first reduction step.

[0083] It appears clear that the higher the temperature employed, the better the dissolution of Ir.sub.xO.sub.y.

[0084] FIG. 5 is a flow-chart of the method 5 according to some embodiments of the invention.

[0085] The method 5 of recovering iridium from a body comprising Ir.sub.xO.sub.y, wherein x is a number between 1 and 2 and y is a number between 1 and 4 comprises: [0086] S1, treating the body with a reducing agent, thereby forming a suspension; [0087] S2, dissolving the suspension by exposing the suspension to an acidic solution, thereby forming a solution comprising iridium ions.

[0088] FIG. 6 is another flow-chart of the method 6 according to some embodiments of the invention.

[0089] The method 6 of recovering iridium from a body comprising Ir.sub.xO.sub.y, wherein x is a number between 1 and 2 and y is a number between 1 and 4, comprises: [0090] S1, treating the body with a reducing agent, thereby forming a suspension; [0091] S2, dissolving the suspension by exposing the suspension to an acidic solution, thereby forming a solution comprising iridium ions; [0092] S3, precipitating the iridium ions as Ir metal particles or Ir.sub.xO.sub.y or Ir salt.

[0093] In some embodiments, the recovery of the dissolved Ir ions in the form of iridium metal (Ir.sup.0) particles may be achieved by reducing the Ir ions through the use of a reducing agent.

[0094] The Ir ions in acidic aqueous solution obtained by dissolving iridium oxides through steps S1 and S2 may be reduced through the addition of NaOH at pH 13 and an aqueous solution of hydrazine having a concentration of 35 wt % in a Hydrazine/Ir ions molar ratio of >1, such as 10

[0095] The solution is then held at 80° C. for 2 hours producing precipitation of Ir metal particles that can be separated from the solution by centrifugation and purified by washing with ultrapure water.

[0096] FIG. 7 shows a XRD pattern 12 of the precipitate collected, which exhibits the diffraction peaks corresponding to iridium metal (Ir.sup.0), confirming the formation of Ir metal (Ir.sup.0).

[0097] In some other embodiments, the recovery of the dissolved Ir ions in the form of iridium oxides (Ir.sub.xO.sub.y) electrocatalyst may be achieved using a microwave synthesis route.

[0098] The Ir ions in acidic aqueous solution, obtained by dissolving iridium oxides through steps S1 and S2, may be reduced through the addition of NaOH at pH 13 and ethylene glycol (EG) in a EG/Ir ions molar ratio of 20.

[0099] The solution is then held at 150° C. for 15 minutes in a microwave oven. However, any other source of heating may be use, adjusting temperature and time of heating accordingly.

[0100] This produces precipitation of Ir oxides (Ir.sub.xO.sub.y) that can be separated from the solution by centrifugation and purified by washing with ultrapure water.

[0101] The Ir.sub.xO.sub.y, produced through this method, shows catalytic activity in oxygen evolution reactions comparable to the Ir oxides commercially used in water electrolyzers.

[0102] In some further embodiments, the recovery of the dissolved Ir ions, in the form of iridium salts such as ammonium hexachloroiridate (NH.sub.4).sub.2IrCl.sub.6, may be achieved through the use of an oxidation agent.

[0103] The Ir ions in acidic aqueous solution obtained by dissolving iridium oxides through steps S1 and S2 may be oxidized through the addition of H.sub.2O.sub.2 in a H.sub.2O.sub.2/Ir ions molar ratio of >1, such as 2.5 under refluxing for 20 minutes.

[0104] Addition of NH.sub.4Cl powder to a concentration >2M, such as 3M produces the precipitation of (NH.sub.4).sub.2IrCl.sub.6 that can be separated from the solution and purified by washing with methanol.

[0105] FIG. 8 shows UV-vis spectra 13 of the solution containing Ir ions obtained by dissolving iridium oxides through steps S1 and S2 and of the corresponding oxidized solution by refluxing with H.sub.2O.sub.2.

[0106] The spectrum of the oxidized solution 10 shows the appearance of absorption peaks between 400 and 550 nm. This indicates the formation of Ir.sup.4+ ions originated by the oxidation of the Ir.sup.3+ ions present in the solution formed through step S1 and S2, which shows a characteristic spectrum 11 having a flat profile.

[0107] FIG. 9 shows the XRD pattern 14 of the precipitate formed following the addition of NH.sub.4Cl.

[0108] The XRD pattern 14 of FIG. 9 exhibits the diffraction peaks corresponding to the finger print of (NH.sub.4).sub.2IrCl.sub.6, confirming the formation of the iridium salt.

[0109] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.