A method of treating rhodium materials

Abstract

A method of treating a rhodium material comprising both rhodium and base metal (e.g., prior to refining of the rhodium material to recover the rhodium), the method comprising: locating the rhodium material in water; passing chlorine through the water to chlorinate the water; adding hydrochloric acid to the chlorinated water and heating to dissolve the base metal forming a leach liquor comprising the base metal; separating the leach liquor comprising the base metal from the rhodium material comprising the rhodium.

Description

[0001] A METHOD OF TREATING RHODIUM MATERIALS

[0002] Field

[0003] The present specification relates to a method of treating a rhodium material comprising both rhodium and base metal. The methodology is particularly useful for treating rhodium material prior to refining of the rhodium material to recover the rhodium.

[0004] Background

[0005] Platinum group metal refining processes can typically involve one or more pyrometallurgical processes, including smelting, to separate platinum group metals from other materials in the feed, followed by acid dissolution of the platinum group metals and a series of hydrometallurgical processes in a refining circuit to separate and purify the individual platinum group metals (platinum, palladium, rhodium, iridium, and / or ruthenium). Such processes are known in the art.

[0006] Platinum group metal feed materials for the refining processes can vary in nature. For example, input feeds for smelting can be in the form of platinum group metal alloys such as iron, copper or nickel- based alloys comprising one or more of iron, copper and nickel and one or more platinum group metals. Alternatively, the input feed may be another type of platinum group metal material such as a spent platinum group metal catalyst material. Such materials can be input to the refining processes in powdered (particulate / granulated) form.

[0007] Pyrometallurgical processes tend to be energy intensive, costly to run, involve large capital investment to set up and maintain, involve process losses, and can produce greenhouse gas emissions. Furthermore, the requirement to perform pyrometallurgical processing prior to hydrometallurgical processing increases the lead time required to recover the platinum group metals. While such recycling processes are more environmentally friendly than obtaining platinum group metals from primary mining sources, there is a need to make platinum group metal refining processes more environmentally friendly and less energy intensive as well as reducing cost, process losses, and lead times for recovery of the platinum group metals.

[0008] One approach to achieving this goal is to avoid pyrometallurgical processing and only use hydrometallurgical process to separate and recover the platinum group metals. However, as previously indicated, platinum group metal feed materials for the refining processes can vary in nature and at least some of these feed materials are not suitable for hydrometallurgical processing without first passing through pyrometallurgical processing. For example, hydrometallurgical processing generally begins with a step of dissolving the platinum group metal in a concentrated acid, such as concentrated hydrochloric acid, followed by a number of further processing steps to separate, purify, and recover the platinum group metals from the acidic leach liquor. However, certain platinum group metal feed materials, such as rhodium materials, contain high concentrations of base metal. Addition of some base metals to concentrated HCI will result in the generation of hydrogen gas, and this poses an explosion risk. As such, for safe processing of high base metal containing rhodium materials, these have been pyrometallurgically processed first to remove base metals prior to hydrometallurgical processing to recover the rhodium. However, there is a significant increase in lead time, process losses, and expense through processing rhodium materials through the pyrometallurgical route. As such, there is a need to improve the methodology for processing of such rhodium materials to safely recover rhodium with lower lead times, process losses and expense in addition to improving the environmental impact of such rhodium recovery processes.

[0009] It is an aim of the present specification to address this problem.

[0010] Summary

[0011] The present specification provides a method of treating a rhodium material comprising both rhodium and base metal (e.g., prior to refining of the rhodium material to recover the rhodium), the method comprising: locating the rhodium material in water; passing chlorine through the water to chlorinate the water; adding hydrochloric acid to the chlorinated water and heating to dissolve the base metal forming a leach liquor comprising the base metal; separating the leach liquor comprising the base metal from the rhodium material comprising the rhodium.

[0012] The rhodium material is referred to herein as a rhodium residue which is a solid rhodium containing material typically recovered from an end application or process. Since rhodium is a precious metal, it is desirable to recover the rhodium from such materials for re-use by refining such rhodium materials / residues.

[0013] A key feature of the method is that chlorine is passed through the water to pre-chlorinate the water prior to addition of hydrochloric acid and heating to dissolve the base metal. Pre-chlorination of the water in this manner suppresses hydrogen generation during the subsequent addition of hydrochloric acid and heating to dissolve the base metal. Base metals, and any non-rhodium platinum group metals present in the residue, can thus be safely dissolved into solution with the pre-chlorination of the water suppressing hydrogen generation. The resulting leached rhodium containing residue, with base metal removed, can safely be subjected to a concentrated acid dissolve, and processed through known hydrometallurgical steps in a platinum group metal refinery to recover the rhodium without requiring pyrometallurgical processing. Any non-rhodium PGM's dissolved into the leach liquor can also be separated and recovered safely from the leach liquor via conventional hydrometallurgical refining processes.

[0014] As such, the present specification provides an improved methodology for processing of base metal containing rhodium residues to safely recover the rhodium with lower lead times, process losses, and expense in addition to improving the environmental impact of such rhodium recovery processes. The methodology also has benefits for recovering any other PGM's leached from the rhodium residue.

[0015] Brief Description of the Drawings

[0016] For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a flow diagram of a method of treating a rhodium residue according to the present specification; and

[0017] Figure 2 shows another flow diagram of a method of treating a rhodium residue according to the present specification.

[0018] Detailed Description

[0019] As described in the summary section and illustrated in Figure 1, the present specification provides a method of treating a rhodium residue comprising both rhodium and base metal prior to refining of the rhodium residue to recover the rhodium, the method comprising: locating the rhodium residue in water; passing chlorine through the water to chlorinate the water; adding hydrochloric acid to the chlorinated water and heating to dissolve the base metal forming a leach liquor comprising the base metal; separating the leach liquor comprising the base metal from the rhodium residue comprising the rhodium.

[0020] The rhodium residue can than be safely processed via hydrometallurgical refining to recover the rhodium. The leach liquor can be processed via hydrometallurgical refining to separate and recover any other PGMs dissolved in the leach liquor.

[0021] The step of passing chlorine through the water to pre-chlorinate the water prior to addition of hydrochloric acid may comprise one or more of the following characteristics: chlorine can be passed through the water to chlorinate the water for a time period in a range 20 to 60 minutes; chlorine can be passed through the water to chlorinate the water at a flow rate in a range 1kg / hr to 5 kg / hr; and / or chlorine can be passed through the water to chlorinate the water at a temperature in a range 10 °C to 30°C.

[0022] In relation to the above, process parameters for this pre-chlorination step should be selected so that the water is sufficiently chlorinated in order to inhibit hydrogen production in the subsequent step of hydrochloric acid addition and heating.

[0023] The step of adding hydrochloric acid to the chlorinated water and heating may comprise one or more of the following characteristics: the hydrochloric acid added to the chlorinated water can have a concentration in a range 7M to 12M; the hydrochloric acid can be added to the chlorinated water until the concentration of HCI in the chlorinated water is in a range IM to 7M; the hydrochloric acid can be added to the chlorinated water and heated to a temperature in a range 40°C to 70°C; and / or the hydrochloric acid can be added to the chlorinated water at an addition rate in a range 300 to 1000 l / hr.

[0024] In relation to the above, process parameters for this hydrochloric acid addition and heating step should be selected so that the base metal (and potentially non-rhodium PGM if present in the residue) is dissolved without significantly dissolving the rhodium and without generating any significant quantities of hydrogen which could present an explosion risk. As previously indicated, the water is pre-chlorinated to a level at which during addition of hydrochloric acid substantially no hydrogen is generated. While examples of suitable parameter ranges for the present process are given above, it will be understood that for any given type of rhodium residue, operating parameters for the present method can be optimized via trials following the teachings of the present specification.

[0025] After leaching the base metal from the rhodium residue, the leach liquor comprising the base metal is separated from the rhodium residue comprising the rhodium, e.g., via filtration. After separating the leach liquor from the rhodium residue, the rhodium residue can then be safely refined to recover rhodium. For example, such a refining process can be initiated by subjecting the rhodium residue to a chlorine pressure dissolve to dissolve the rhodium into a solution which can then be processed to recover the rhodium using known methods. The chlorine pressure dissolve comprises reacting chlorine with rhodium at above ambient temperature and pressure in strong concentrations of hydrochloric acid.

[0026] The methodology as described above enables refining of rhodium residues using only hydrometallurgical processes without any pyrometallurgical processing required. As such, the present specification provides an improved methodology for processing of base metal containing rhodium residues to safely recover the rhodium with lower lead times, process losses, and expense in addition to improving the environmental impact of such rhodium recovery processes.

[0027] The methodology is particularly suited to rhodium residues that have a high base metal content which represent the largest safety risk if initial pyrometallurgical processing is circumvented. For example, prior to implementing the leaching of the base metal, the rhodium residue may have a concentration of base metal of at least (or more than) 2.5 wt%, 5 wt%, 10 wt% or 15 wt%. In certain rhodium residues, the concentration of base metal is in a range 2.5 wt% to 15 wt% or 5 wt% to 15 wt%. Base metals in rhodium residues may include one or more of nickel, iron, copper, tin and / or chromium. Such residues can be unsuitable for hydrometallurgical processing on safety grounds. Subsequently, after leaching of the base metal, the rhodium residue may have a concentration of base metal no more than (or less than) 5 wt%, 4 wt%, 3 wt%, or 2.5 wt%, e.g., in a range 0 wt% to 5 wt% or 2.5 wt% to 5 wt%. Such residues are suitable for safe hydrometallurgical processing to recover the rhodium.

[0028] In addition to the above, certain rhodium residues may also comprise one or more other platinum group metals, e.g., Pt or Pd. Such platinum group metals can also be dissolved in the leach liquor with the base metal. In that case, the leach liquor can be processed to separate and recover these platinum group metals which are dissolved in the leach liquor. As such, in addition to providing an improved process for recovering rhodium from rhodium containing residues, the present method can also provide benefits for recovering other PGMs present in such residues without requiring pyrometallurgical processing.

[0029] According to embodiments of the present specification, base metal containing rhodium rich residues are loaded in an atmospheric chlorine (CL) / hydrochloric acid (HCI) dissolver into a volume of water. Chlorine is passed through the water for a fixed time prior to HCI addition and heating of the solution. Base metals and some platinum group metals are dissolved into the solution with the pre-chlorination of the water suppressing hydrogen generation. The resulting leached residue can be processed through the present hydrometallurgical rhodium sidestream in the platinum group metal refinery via a chlorine pressure dissolve. Any PGM's dissolved into the leach liquor can be separated and used to create final product via conventional PGM refining processes.

[0030] It should be noted that while a key feature of the present invention is pre-chlorination to suppress hydrogen generation during subsequent addition of hydrochloric acid and heating, in embodiments of the present invention addition of chlorine is continued during / after addition of hydrochloric acid. For example, the pre-chlorination step may involve chlorine gas addition (e.g., at 1 - 5 kg / hr) to a vessel containing the rhodium residue and water for 20 - 60 minutes. Once the water is pre-chlorinated in this manner, addition of hydrochloric acid can commence while continuing to add chlorine. The acidified solution can be heated (e.g., between 40°C to 70°C) while maintaining chlorine addition up to a time period of, for example, 120 to 300 minutes from initiation of the chlorine addition, after which chlorine addition can be stopped.

[0031] It has also been found that it can be advantageous to increase the temperature of the acidified solution after stopping the chlorine addition and prior to filtration. This can aid in increasing the amount of base metal which is leached from the rhodium residue. For example, after stopping the addition of chlorine, the temperature of the acidified solution can be increased to above 70°C, e.g., to around 100°C (e.g., between 100°C to 105°C). The solution can then be cooled (e.g., to room temperature) and filtered to separate leach liquor comprising base metals from solid residue comprising rhodium. Such a methodology is shown in Figure 2 which includes the following steps:

[0032] Load Rh containing residue into process vessel.

[0033] Add water and set agitator running.

[0034] Initiate chlorine gas addition to vessel at 1 - 5 kg / hr for 20 - 60 minutes.

[0035] Add hydrochloric acid.

[0036] Heat vessel to 40 - 70°C.

[0037] Stop chlorine addition after 120 - 300 minutes.

[0038] Raise vessel temperature to 100 - 105°C.

[0039] Cool vessel temperature to <30°C.

[0040] Separate leach liquor and solid via filtration.

[0041] Examples

[0042] Three rhodium rich residues containing quantities of base metal that would prevent processing via standard hydrometallurgical processing were processed according to the methodology described above. Initial residue compositions were as follows:

[0043] 1. Rh = 23.56 Kg; Ni = 2.11 Kg; Fe = 0.84 Kg

[0044] 2. Rh = 20.32 Kg; Ni = 0.89 Kg; Fe = 0.43 Kg

[0045] 3. Rh = 16.30 Kg; Ni = 0.23 Kg; Fe = 0.16 Kg

[0046] Pre-chlorination was used to suppress hydrogen generation during the subsequent addition of hydrochloric acid and heating to dissolve the base metals safely.

[0047] After leaching the residues following the methodology as described herein, the rhodium rich residues, leach solutions, and final dissolve solutions were analysed for metal content. The average wt% of rhodium leached from the three samples was less than 3 wt%, indicating that the process does not significantly leach rhodium which remains in solid form as desired. In fact, for the first two samples less than 1 wt% rhodium was leached, and it is believed that the slightly increased value for the third sample is due to a measurement error. The average amount of nickel leached was 44 wt% and the average amount of iron leached was 99 wt%. This level of base metal removal is sufficient to enable the remaining solid rhodium residue to be safely subjected to a concentrated acid dissolve and processed through known hydrometallurgical steps in a platinum group metal refinery to recover the rhodium without requiring pyrometallurgical processing.

[0048] It was also found that in samples of rhodium residue which contained platinum and / or palladium in addition to rhodium and base metal, a significant proportion of the platinum and / or palladium could be leached with the base metal and the leach liquor then processed to recover the platinum and / or palladium via conventional hydrometallurgical refining processes.

[0049] To summarize, the present methodology solves the problem that addition of some base metals in rhodium residues to HCI will result in the generation of hydrogen gas, and this poses an explosion risk. As such, previously, high base metal containing rhodium residues would need to be processed via a pyrometallurgical plant for safe processing. There is a significant increase in lead time, process losses and expense through processing rhodium residues through a pyrometallurgical route. The present methodology enables safe processing of base metal containing rhodium residues wholly within a hydrometallurgical plant. This will most notably provide improvements to the metal position for rhodium and some benefit for any other PGMs leached from the rhodium residue.

[0050] While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art 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

Claims1. A method of treating a rhodium material comprising both rhodium and base metal, the method comprising: locating the rhodium material in water; passing chlorine through the water to chlorinate the water; adding hydrochloric acid to the chlorinated water and heating to dissolve the base metal forming a leach liquor comprising the base metal; separating the leach liquor comprising the base metal from the rhodium material comprising the rhodium.

2. A method according to claim 1, wherein the chlorine is passed through the water to chlorinate the water for a time period in a range 20 to 60 minutes.

3. A method according to claim 1 or 2, wherein the chlorine is passed through the water to chlorinate the water at a flow rate in a range 1kg / hr to 5 kg / hr.

4. A method according to any preceding claim, wherein the chlorine is passed through the water to chlorinate the water at a temperature in a range 10°C to 30°C.

5. A method according to any preceding claim, wherein the hydrochloric acid added to the chlorinated water has a concentration in a range 7M to 12M.

6. A method according to any preceding claim, wherein the hydrochloric acid is added to the chlorinated water until the concentration of HCI in the chlorinated water is in a range IM to 7M.

7. A method according to any preceding claim,wherein the hydrochloric acid is added to the chlorinated water and heated to a temperature in a range 40 °C to 70°C.

8. A method according to any preceding claim, wherein the hydrochloric acid is added to the chlorinated water at an addition rate in a range 300 to 1000 l / hr.

9. A method according to any preceding claim, wherein the water is chlorinated to a level at which during addition of hydrochloric acid no hydrogen is generated.

10. A method according to any preceding claim, wherein the leach liquor comprising the base metal is separated from the rhodium material comprising the rhodium via filtration.

11. A method according to any preceding claim, further comprising, after separating the leach liquor from the rhodium material, refining the rhodium material to recover rhodium.

12. A method according to claim 11, wherein the refining of the rhodium material comprises hydrometallurgical processes without any pyrometallurgical processing.

13. A method according to claim 11 or 12, wherein the refining of the rhodium material comprises reacting the rhodium material with chlorine in hydrochloric acid at above ambient temperature and pressure to dissolve the rhodium.

14. A method according to any preceding claim, wherein, prior to leaching of the base metal, the rhodium material has a concentration of base metal of at least 2.5 wt%, 5 wt%, 10 wt% or 15 wt%.

15. A method according to any preceding claim, wherein, after leaching of the base metal, the rhodium material has no more than 5 wt%, 4 wt%, 3 wt%, or 2.5 wt% of the base metal.

16. A method according to any preceding claim, wherein the base metal includes one or more of nickel, iron, copper, tin and / or chromium.

17. A method according to any preceding claim, wherein the rhodium material also comprises one or more other platinum group metals which are dissolved in the leach liquor with the base metal.

18. A method according to claim 17, wherein the leach liquor is processed to separate and recover the one or more other platinum group metals which are dissolved in the leach liquor.

19. A method according to any preceding claim, wherein during and / or after adding hydrochloric acid to the chlorinated water, chlorine addition through the water is continued.

20. A method according to any preceding claim, wherein after stopping chlorine addition, the chlorinated water is heated above 70°C prior to cooling and separating the leach liquor comprising the base metal from the rhodium material comprising the rhodium.

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