Method for refining and recycling iridium

Abstract

A method of refining / recycling iridium, the method comprising: adding ammonium chloride to an iridium-containing refining / recycling solution comprising iridium dissolved in hydrochloric acid in a first precipitation vessel to precipitate ammonium hexachloroiridate; filtering the precipitated ammonium hexachloroiridate; washing the filtered ammonium hexachloroiridate with a washing mixture of ammonium chloride and water; and recycling the wash mixture of ammonium chloride and water back to a second precipitation vessel, which may be the same vessel as the first precipitation vessel or a different precipitation vessel, to precipitate any iridium dissolved in the wash mixture during wash of ammonium hexachloroiridate.

Description

Technical Field

[0001] This specification relates to a method for refining / recycling iridium. This method can be applied to a range of iridium-containing refined / recycled feeds, including those produced from membrane materials coated with spent catalysts in fuel cell and hydrogen electrolyzer applications. Background Technology

[0002] Platinum group metal refining methods typically involve one or more pyrometallurgical methods, including smelting to separate the platinum group metals from other materials in the feed, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical methods to separate and purify the individual platinum group metals (platinum, palladium, rhodium, iridium, and / or ruthenium). Such methods are known in the art.

[0003] The demand for iridium is expected to increase, at least in part due to its increased use in fuel cells and hydrogen electrolyzers. Therefore, there is a need for improved methods for recycling iridium. This specification aims to address this need. Summary of the Invention

[0004] According to this specification, a method for refining / recycling iridium is provided, the method comprising:

[0005] In the first precipitation vessel, ammonium chloride is added to an iridium-containing purified / recycled solution containing iridium dissolved in hydrochloric acid to precipitate ammonium hexachloroiridate;

[0006] Filter out the precipitated ammonium hexachloroiridate;

[0007] The filtered ammonium hexachloroiridate was washed with a washing mixture of ammonium chloride and water; and

[0008] The washing mixture of ammonium chloride and water is recycled back to a second precipitation container, which may be the same as or a different one from the first precipitation container, to recover any iridium dissolved in the washing mixture during the washing of ammonium hexachloroiridate.

[0009] This method recovers iridium as a high-purity solid ammonium hexachloroiridate salt while minimizing iridium loss and reducing the use of ammonium chloride reagent in the process. In this regard, it has been found that a small proportion of ammonium hexachloroiridate can dissolve in the washing mixture of ammonium chloride and water during the washing step. This is especially true if there is too much water in the washing mixture. To recover iridium from the washing mixture, it has been found advantageous to recycle the washing mixture back to a precipitation vessel for iridium recovery. In one configuration, the washing mixture is recycled to the same precipitation vessel used for precipitating ammonium hexachloroiridate, the object of the washing step. Alternatively, in another configuration, two or more precipitation vessels can be used. For example, ammonium hexachloroiridate precipitation can be carried out in two precipitation vessels, in which case two washing recirculation routes can be installed to allow the washes to be redirected from one vessel to another, so that the washes can be treated with another portion of the iridium-containing recirculated solution.

[0010] In addition to the advantage of reducing iridium loss during the washing of the precipitated ammonium hexachloroiridate, this method has another advantage: by recycling the washing mixture of ammonium chloride and water back into the precipitation vessel, the need to add fresh ammonium chloride to the vessel for complete precipitation of hexachloroiridate is reduced. Therefore, this method increases the iridium yield while reducing reagent usage. Attached Figure Description

[0011] To better understand the invention and show how it can be implemented, certain embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, wherein:

[0012] Figure 1 A flowchart of a method for refining / recycling iridium according to this specification is shown;

[0013] Figure 2 A flowchart illustrating a first configuration of a method using a single settling vessel and recycling the washing mixture back into the single settling vessel is shown; and

[0014] Figure 3 A flowchart of a second configuration of a method using two settling containers and recycling the washing mixture from each settling container to the other settling container is shown. Detailed Implementation

[0015] As indicated in the summary section of the invention and Figure 1As illustrated in the flowchart, this specification provides a method for recycling iridium, the method comprising: adding ammonium chloride to an iridium-containing purified / recycled solution containing iridium dissolved in hydrochloric acid in a first precipitation container to precipitate ammonium hexachloroiridate; filtering the precipitated ammonium hexachloroiridate; washing the filtered ammonium hexachloroiridate with a washing mixture of ammonium chloride and water; and recycling the washing mixture of ammonium chloride and water back to a second precipitation container, which may be the same container as the first precipitation container or a different precipitation container, to recover any iridium dissolved in the washing mixture during the washing of the ammonium hexachloroiridate.

[0016] In one configuration, such as Figure 2 As shown, the washing mixture is recycled to the same precipitation vessel used to precipitate ammonium hexachloroiridate, which is the object of the washing step. Alternatively, in... Figure 3 In another configuration shown, two or more precipitation containers can be used. For example, ammonium hexachloroiridate precipitation can be carried out in two precipitation containers. Two wash recycling routes can be installed to allow the washes to be redirected from one container to another, so that the washes can be treated with another portion of the iridium-containing recycled solution.

[0017] The washing mixture of ammonium chloride and water can be a mixture of a saturated ammonium chloride solution and water in a volume ratio of 1:2 to 2:1, optionally 1:1. The washing mixture is prepared by filling a container with the saturated ammonium chloride solution and water and bubbling air through the container. If too much water is provided in the washing mixture, this can cause precipitated ammonium hexachloroiridate to dissolve in the washing mixture. The method of the present invention ensures the recovery of any such ammonium hexachloroiridate dissolved in the washing mixture by recycling the washing mixture to a precipitation container.

[0018] The recycled wash mixture can be mixed with another portion of the iridium-containing purified / recycled solution in a precipitation vessel to precipitate ammonium hexachloroiridate. Ammonium chloride is added to the iridium-containing recycled solution in an amount sufficient to provide ammonium ions exceeding iridium. The recycled wash mixture provides at least a portion of the ammonium ions, thereby reducing or eliminating the need to add fresh ammonium chloride to obtain excess ammonium ions in the precipitation vessel.

[0019] Precipitation, filtration, and washing steps can be carried out in one or more precipitation vessels or within a series of vessels. The purified / recycled iridium-containing solution can have an iridium concentration in the range of 40 g / L to 100 g / L and / or an HCl concentration in the range of 4 molar strength to 5 molar strength. Furthermore, precipitation of ammonium hexachloroiridate is carried out under one or more of the following conditions: a temperature in the range of 90°C to 100°C; ambient pressure; and / or a time period of 24 to 48 hours.

[0020] The methods described herein can be applied to a range of iridium-containing recycling feeds, including feeds from fuel cells and hydrogen electrolyzer waste (manufacturing waste and / or end-of-life components). For example, a method for recycling iridium from a catalyst-coated membrane used in a fuel cell or electrolyzer can be provided, the method comprising: dissolving iridium in hydrochloric acid to produce an iridium-containing recycling solution; and treating the iridium-containing recycling solution using the method according to any of the preceding claims.

[0021] In light of the foregoing, it should be understood that this specification provides a route for returning the final iridium filter cake wash to the process for reprocessing with the next batch of iridium and for recovering lost iridium. Following the final ammonium hexachloroiridate precipitation during the PGM refining process, the salt is filtered and washed with a mixture of ammonium chloride and water (e.g., a 1:1 solution of saturated ammonium chloride and water).

[0022] The washing mixture can be prepared by filling a saturated ammonium chloride solution and water into a precipitation vessel, drawing the mixture into a vacuum transfer flask, and mixing it in the flask by bubbling air through the bottom outlet (e.g., manually). Adding too much water to the washing mixture will cause the iridium salt to redissolve during washing. That is, some iridium redissolves during washing, and this is typically lost to the waste liquid.

[0023] Therefore, a new process route has been installed that allows the washes to be redirected back to the precipitation vessel and reprocessed with the next batch. While the final iridium precipitation can be carried out in two vessels, typically only one vessel is in progress at a time. Two new routes have been installed to allow the washes to be redirected to empty adjacent vessels, enabling reprocessing with the next final iridium batch. This recycling also eliminates the need to add solid ammonium chloride to ensure the presence of the required excess ammonium ions for complete precipitation.

[0024] The new method avoids the loss of final iridium salt washes into the waste liquid, and the new route allows for the recovery of iridium dissolved during washing, while removing / reducing the need for the addition of fresh ammonium chloride. Therefore, the benefits of this invention include reduced iridium loss from the process and reduced reagent use. Reducing iridium loss in the refining loop improves the recycling rate of this rare resource.

[0025] While the invention has been specifically shown and described with reference to certain examples, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for refining / recycling iridium, the method comprising: In the first precipitation vessel, ammonium chloride is added to an iridium-containing purified / recycled solution containing iridium dissolved in hydrochloric acid to precipitate ammonium hexachloroiridate; Filter out the precipitated ammonium hexachloroiridate; The filtered ammonium hexachloroiridate was washed with a washing mixture of ammonium chloride and water; and The washing mixture of ammonium chloride and water is recycled back to a second precipitation container, which may be the same as or a different precipitation container from the first precipitation container, to recover any iridium dissolved in the washing mixture during the washing of the ammonium hexachloroiridate.

2. The method according to claim 1, The washing mixture of ammonium chloride and water is a mixture of saturated ammonium chloride solution and water in a volume ratio of 1:2 to 2:1, optionally 1:

1.

3. The method according to claim 1 or 2, The washing mixture is prepared by filling a container with a saturated ammonium chloride solution and water and then bubbling air through the container.

4. The method according to any of the preceding claims, The recycled washing mixture is mixed with another portion of the iridium-containing purified / recycled solution in the second precipitation vessel to precipitate ammonium hexachloroiridate.

5. The method according to any of the preceding claims, The ammonium chloride is added to the iridium-containing purified / recycled solution in an amount sufficient to provide ammonium ions exceeding those of iridium, and the recycled washing mixture provides at least a portion of the ammonium ions, thereby reducing or eliminating the need to add fresh ammonium chloride to obtain excess ammonium ions.

6. The method according to any of the preceding claims, The sedimentation, filtration, and washing steps are carried out in one or more sedimentation containers or in a series of containers.

7. The method according to any of the preceding claims, The first precipitation container and the second precipitation container are two separate containers, and the washing mixture from the first precipitation container is recycled to the second precipitation container for processing together with another portion of the iridium-containing purified / recycled solution.

8. The method according to any of the preceding claims, The iridium-containing purified / recycled solution has an iridium concentration in the range of 40 g / L to 100 g / L.

9. The method according to any of the preceding claims, The iridium-containing purified / recycled solution has an HCl concentration in the range of 4 to 5 molar strength.

10. The method according to any of the preceding claims, The precipitation of the ammonium hexachloroiridate is carried out under one or more of the following conditions: a temperature in the range of 90°C to 100°C; ambient pressure; and / or a time period of 24 to 48 hours.

11. A method for recovering iridium from a catalyst-coated membrane used in a fuel cell or electrolyzer, the method comprising: Iridium is dissolved in hydrochloric acid to produce an iridium-containing recycled solution; as well as The iridium-containing recycled solution is treated using the method according to any of the preceding claims.

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