Method for treating platinum group metal materials

Abstract

The invention relates to a method for treating platinum group metal materials. In particular, a method of removing arsenic from an arsenic-containing platinum group metal material, the method comprising: heating the arsenic-containing platinum group metal material in the presence of a flux material to melt the platinum group metal material and produce a molten platinum group metal material and slag, wherein the flux material comprises a reducing agent to promote extraction of arsenic from the molten platinum group metal material into the slag; and separating the platinum group metal material from the arsenic-containing slag.

Description

Technical Field

[0001] The present description relates to a method for treating a platinum group metal material. The method is particularly useful for treating a platinum group metal material which is provided as feed to a platinum group metal refining process to recover one or more platinum group metals. Background Art

[0002] The platinum group metal refining process typically may include one or more pyrometallurgical processes, including smelting, for separating the platinum group metals from other materials in the feed, followed by acid dissolution of the platinum group metals, and a range of hydrometallurgical methods for separating and purifying the individual platinum group metals (platinum, palladium, rhodium, iridium and / or ruthenium). Such methods are known in the art.

[0003] The nature of the platinum group metal feed material used in the refining process may vary. For example, the input feed for smelting may be in the form of a platinum group metal alloy such as an iron, copper or nickel-based alloy, which contains 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 waste platinum group metal catalyst material. Such material may be input to the refining process in a powdered (particulate / granulated) form. The present specification relates to a method for pretreating such a platinum group metal feed material prior to refining, although it will be understood that the method may also be applied to an intermediate platinum group metal material as part of a multi-step refining process. Summary of the invention

[0004] It has been found that some platinum group metal alloy feed materials provided for refining platinum group metals contain arsenic brought over from the source materials as well as collector elements such as iron, copper or nickel. Arsenic may also be present in other types of platinum group metal feed materials such as spent catalysts. This is problematic because some environmental permits place restrictions on the amount of arsenic allowed at a platinum group metal refining site. Therefore, such platinum group metal feed materials cannot be sent to a platinum group metal refining site for this reason. Furthermore, the inventors are not aware of any previously disclosed methods in the platinum group metal recycling / refining art for removing arsenic from such platinum group metal feed materials.

[0005] It has been found that some arsenic can be removed by thermal processing of PGM feed materials, where arsenic and arsenic compounds are removed via sublimation. However, the removal rates are low, at least for some types of PGM feed materials, and do not reduce the arsenic content below environmentally acceptable limits.

[0006] For the above reasons, the present inventors have developed a more efficient method for removing arsenic from arsenic-containing platinum group metal materials. The method comprises: heating the arsenic-containing platinum group metal material in the presence of a flux material so as to melt the platinum group metal material and produce molten platinum group metal material and slag, wherein the flux material contains a reducing agent (optionally a plurality of different reducing agents) to facilitate the extraction of arsenic from the molten platinum group metal material into the slag; and separating the platinum group metal material from the arsenic-containing slag.

[0007] It has been found that this process provides a more efficient method of removing arsenic from a platinum group metal feed material, thereby reducing the arsenic concentration to below environmental limits and thereby allowing the feed material so treated to be refined to recover the platinum group metals. The process thus enables the safe recovery of platinum group metals from source materials that otherwise could not be processed due to environmental concerns. DETAILED DESCRIPTION

[0008] As indicated in the Summary of the Invention section, the present specification provides a method for removing arsenic from an arsenic-containing platinum group metal material, the method comprising: heating the arsenic-containing platinum group metal material in the presence of a flux material so as to melt the platinum group metal material and produce molten platinum group metal material and slag, wherein the flux material comprises a reducing agent (optionally / advantageously a plurality of different reducing agents) to facilitate extraction of arsenic from the molten platinum group metal material into the slag; and separating the platinum group metal material from the arsenic-containing slag. The platinum group metal material can then be provided as feed to a platinum group metal refining process to recover one or more platinum group metals.

[0009] The platinum group metal material can be an alloy, optionally an iron, copper or nickel-based alloy, which contains one or more of iron, copper and nickel and one or more platinum group metals. Iron, copper and / or nickel can constitute the main component of the alloy, such as>50% by weight. Alternatively, the platinum group metal material can be another type of material such as a waste platinum group metal catalyst material. The platinum group metal can include one or more of platinum, palladium, rhodium, iridium and ruthenium. The platinum group metal component can constitute a minor component of the platinum group metal material, such as at least 0.01% by weight, at least 0.05% by weight, at least 0.1% by weight, at least 0.15% by weight, at least 0.2% by weight, at least 0.5% by weight, at least 1% by weight, at least 2% by weight, at least 3% by weight, at least 4% by weight, at least 5% by weight, at least 10% by weight, at least 20% by weight, at least 30% by weight, at least 40% by weight or more. Typical platinum group metal collector alloys can contain 2-5% by weight of platinum group metals. The waste catalyst material can contain a lower amount of platinum group metals, such as 0.1-0.2% by weight. The refined feed may contain from 5% to 40% platinum group metals.

[0010] Such platinum group metal materials may contain at least 50 ppm, at least 80 ppm, at least 100 ppm, at least 200 ppm, at least 500 ppm, at least 1000 ppm, at least 2000 ppm, at least 1%, at least 2%, or at least 5% arsenic by weight. As previously mentioned, it has been found that collector elements for platinum group metals such as iron, copper and nickel can carry arsenic from the source material, and the method of the present invention has been found to effectively remove arsenic from such alloys, making them suitable for platinum group metal refining and recovery. The method can also be applied to other platinum group metal feeds such as spent catalysts that have been contaminated with arsenic.

[0011] The platinum group metal material (e.g., alloy) may be in granular or powder form and may optionally have a particle size of less than 2 mm, less than 1 mm, less than 0.5 mm, less than 0.3 mm, less than 0.2 mm, less than 0.15 mm, or less than 0.125 mm. It has been found that arsenic removal via sublimation is particularly problematic for small particle size platinum group metal feed powders (e.g., powders after 120 mesh processing or 0.125 mm diameter) because the feed material is more likely to sinter, thereby preventing arsenic and arsenic compounds from sublimating. In contrast, the process of the present invention has been found to effectively remove arsenic from such platinum group metal materials, making them amenable to platinum group metal refining and recovery.

[0012] The reducing agent in the flux material may comprise one or more of CaC, CaSi, Al and Ti in any combination. It has been found that these reducing agents are effective in promoting the extraction of arsenic from the PGM material into the slag when the PGM material is melted in the presence of the flux material. The flux material may additionally comprise one or both of FeSi and CaO. Metallic Fe may also be added to the platinum group metal material along with the flux material, for example when the platinum group metal material is a spent catalyst material that is not already in the form of a collector alloy.

[0013] The flux material may contain: at least 10 wt%, at least 20 wt%, at least 30 wt%, or at least 40 wt% reducing agent; no more than 100 wt%, no more than 80 wt%, no more than 70 wt%, no more than 60 wt%, or no more than 40 wt% reducing agent; or reducing agent in an amount within a range defined by any combination of these limits. The ratio of flux material to platinum group metal material may be: at least 1:5, at least 1:4, at least 1:3, or at least 1:2; no more than 1:1, no more than 1:1.3, no more than 1:1.6, or no more than 1:1.8; or within a range defined by any combination of these limits. Sufficient flux and reducing agent are required to facilitate the extraction of arsenic from the PGM material into the slag when melting the PGM material in the presence of the flux material. However, the composition and amount of the flux are advantageously selected to ensure that excess slag is not produced, thereby reducing waste.

[0014] In the melting process, the arsenic-containing platinum group metal material may be heated in the presence of a flux material to a temperature of at least 1400°C, at least 1500°C, or at least 1600°C; not more than 1800°C, not more than 1750°C, or not more than 1700°C; or within a range defined by any combination of these limits. The heating may be performed for a period of at least 15 minutes, at least 30 minutes, at least 45 minutes, at least 1 hour, at least 2 hours, at least 3 hours, or at least 4 hours. The heating may be performed under normal atmospheric conditions or under an inert atmosphere. The melting process may be performed in a furnace selected from an induction furnace, a rotary furnace, an electric arc furnace, a plasma furnace, a cupellation furnace, a muffle furnace, or other smelting equipment. Advantageously, the arsenic-containing platinum group metal material and the flux material are mixed before the materials are introduced into the furnace and / or mixed in the furnace during heating.

[0015] Finally, as previously indicated, after separation of the platinum group metal material from the arsenic-containing slag, the platinum group metal material may be provided as feed to a platinum group metal refining process to recover one or more platinum group metals.

[0016] The present specification is therefore able to remove arsenic from molten iron (or copper or nickel) based PGM materials. The lower the oxygen content in the molten alloy, the better the arsenic removal rate from the PGM alloy. Therefore, it can be advantageous to add a variety of different reducing agents such as CaC, CaSi, Al and Ti. The method removes arsenic from the iron (or copper or nickel) based PGM alloy into the slag by adding a strong reducing agent to the system to promote the separation of arsenic from the PGM alloy into the slag. The method can be implemented in any furnace that can provide a sufficiently high temperature of about 1650°C. The oxidation potentials of oxygen, sulfur and arsenic are listed as: O>S>As. Therefore, it is advantageous to use, for example, Al to remove O first. Then Ca, Fe and / or Ti can remove S and As from the PGM alloy.

[0017] As will be discussed in the Examples section of this specification, several tests have been conducted using different PGM feed materials including a PGM smelter alloy and two automotive PGM catalyst materials. Different flux compositions were also tested. In addition, two induction furnaces with different mixing capabilities were used. It has been found that after furnace processing with less than good mixing, the arsenic content in the smelter alloy was reduced by 58%. In contrast, the arsenic content in the smelter alloy was reduced by 85% when processed in the furnace with enhanced mixing. The arsenic content in the two automotive PGM catalyst materials was reduced by 78% and 100%.

[0018] Related to the above, it is noted that when providing a method for removing arsenic from PGM materials, there is an economic driver to minimize capital investment. Previous methods required additional processing equipment such as box furnaces or equivalent, leaching vessels and filtering equipment to achieve good results. The method of the present invention is intended to use smelting equipment, induction furnaces, rotary furnaces, arc furnaces, or plasma furnaces that PGM material processing companies already have. In order to promote the extraction of arsenic into the slag phase so that the PGM alloy is clean for further refining, additional reducing agent flux additives are required. However, it has also been found that other flux components can be reduced to keep the slag chemical composition similar to the previous formulation, thereby minimizing any increase in slag treatment.

[0019] The method may be provided as a dedicated arsenic removal step or may be integrated into existing PGM metal processing steps for removing other impurities from PGM metals.

[0020] Three public papers on arsenic removal from other types of materials have been noted: (1) “Selective removal and leaching kinetics of arsenic from electric dust collection of silver furnace by alkaline roasting-water leaching”, WANG Xiaoyang, WANG Wenxiang, FANG Hongsheng, MA Chengrong, WU Kefu, China Academic Journal Electronic Publishing House, Vol. 41, No. 3 (Total No. 183), June 2022; (2) “Removal of arsenic from arsenic-bearing copper ore”, LI Huimeng, SHI Lihua, China Academic Journal Electronic Publishing House, Vol. 40, No. 4 (Total No. 178), August 2021; and (3) “Removal of Arsenic in Steel”, LUO Lin-gen, WANG Jian-jun, KONG Hui, ZHOU Li, China Academic Journal Electronic Publishing House, The Chinese Journal of Process Engineering, Vol. 11 No. 4, August 2011. However, these documents do not suggest the problems associated with arsenic in some PGM feeds, such as PGM alloys based on iron, copper or nickel, and do not suggest the solution claimed in the present invention, which enables the safe recovery of PGMs from source materials that would otherwise be unprocessable due to environmental concerns.

[0021] Example

[0022] Several different arsenic-containing platinum group metal (PGM) feed powders have been tested:

[0023]

[0024] A series of experiments have been conducted to remove arsenic. Four of these experiments are summarized in the following table:

[0025]

[0026] It has been noted in the above table that the weight of the PGM alloy after treatment is different from the weight of the PGM-containing feed material before treatment. The mass balance can be expressed as: feed + flux = ash (negligible) + slag + alloy. The removal rate in the table is calculated based on the absolute amount of arsenic in the PGM-containing material before and after treatment. The formula is as follows: %As removal rate = (As concentration before treatment × feed weight – As concentration after treatment × alloy weight / As concentration before treatment × feed weight) × 100.

[0027] In Experiment 1, the mass of the PGM alloy (2156 ppm As) was 800 g and the total mass of the flux material was 400 g. Thus, the mass ratio of the PGM alloy to the flux material was 2:1. The flux material contained the following reducing agents: Al (40 g), CaC (60 g), CaSi (80 g) and Ti (20 g). The flux material additionally contained FeSi (80 g) and CaO (120 g). Thus, 50 wt. % of the flux material consisted of reducing agents. Therefore, the mass ratio of the PGM alloy to the reducing agents was 4:1. The PGM alloy and the flux material were heated in an induction furnace at 1650° C. for 1 hour. The arsenic content of the PGM alloy was reduced from 2156 ppm by weight to 812 ppm by weight, which, taking into account the mass changes of the feed PGM material and the PGM alloy after treatment, was equivalent to an As removal rate of 58.6% in absolute value.

[0028] In Experiment 2, the mass of the PGM alloy was 300 g and the total mass of the flux material was 175 g. Thus, the mass ratio of the PGM alloy to the flux material was 1.7:1 (i.e. slightly more flux to PGM alloy than in Experiment 1). The flux material contained the following reducing agents: Al (15 g), CaC (30 g), CaSi (30 g) and Ti (10 g). The flux material additionally contained FeSi (30 g) and CaO (60 g). Thus, approximately 50 wt. % of the flux material consisted of reducing agents. The mass ratio of the PGM alloy to the reducing agents was 3.5:1 (i.e. slightly more reducing agent to PGM alloy than in Experiment 1). The PGM alloy and the flux material were heated in an induction furnace at 1650° C. for 1 hour. The induction furnace was of a different type than in Experiment 1, which facilitated better mixing. The arsenic content of the PGM alloy was reduced from 2156 ppm by weight to 203 ppm by weight, which, taking into account the mass changes of the feed PGM material and the PGM alloy after treatment, equates to an improved As removal of 85.7% in absolute terms.

[0029] In Experiment 3, the mass of the PGM autocatalyst material (96 ppm As) was 760 g, to which 175 g of iron and 442.5 g of flux material were added. Thus, the mass ratio of the PGM autocatalyst material plus iron to the flux material was approximately 2:1. The flux material contained the following reducing agents: Al (35 g), CaC (70 g), CaSi (70 g) and Ti (17.5 g). The flux material additionally contained FeSi (180 g) and CaO (70 g). Thus, 43 wt % of the flux material consisted of reducing agents. The mass ratio of the PGM autocatalyst plus iron to the reducing agent was approximately 5:1, while the mass ratio of the PGM autocatalyst to the reducing agent was approximately 4:1. The PGM material, iron and flux material were heated in an induction furnace at 1650° C. for 1 hour. The arsenic content of the PGM material was reduced from 96 ppm by weight to 76 ppm by weight, which, taking into account the mass changes of the feed PGM material and the PGM alloy after treatment, equals an As removal of 78.1% in absolute terms.

[0030] Experiment 4 was similar to Experiment 3 but used a different PGM catalyst material with a 60 ppm As content. The flux material was also similar to that of Experiment 3 but had a reduced amount of FeSi (140 g instead of 180 g used in Experiment 3). Thus, the flux material contained a slightly higher proportion of reducing agent in this example. The PGM material, iron and flux material were heated in an induction furnace at 1650° C. for 1 hour. The arsenic content of the PGM material was reduced from 60 ppm by weight to 0 ppm by weight, equaling a 100% As removal rate.

[0031] These experiments demonstrate that arsenic can be effectively removed from a platinum group metal material by melting the platinum group metal material with a flux containing a reducing agent to facilitate the extraction of arsenic into the slag, which can then be separated from the platinum group metal material. After the platinum group metal material is separated from the arsenic-containing slag, the platinum group metal material can then be provided as feed to a platinum group metal refining process to recover one or more platinum group metals in a more environmentally friendly manner.

[0032] Although the present invention has been specifically shown and described with reference to some embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the present invention as defined in the appended claims. It should be noted that the claimed features may be combined in any manner, and multiple claim references may be contemplated where formally acceptable.

Claims

1. A method for removing arsenic from an arsenic-containing platinum group metal material, the method comprising: heating the arsenic-containing platinum group metal material in the presence of a flux material so as to melt the platinum group metal material and produce molten platinum group metal material and slag, wherein the flux material comprises a reducing agent to facilitate extraction of arsenic from the molten platinum group metal material into the slag; and Separation of platinum group metal materials from arsenic-containing slag.

2. The method according to claim 1, The platinum group metal material is a platinum group metal alloy.

3. The method according to claim 2, The platinum group metal alloy is an iron-, copper- or nickel-based alloy comprising one or more of iron, copper and nickel and one or more platinum group metals.

4. The method according to claim 1, The platinum group metal material is a spent catalyst material comprising one or more platinum group metals.

5. The method according to claim 1, wherein the platinum group metal material contains at least 0.01 weight percent, at least 0.05 weight percent, at least 0.1 weight percent, at least 0.15 weight percent, at least 0.2 weight percent, at least 0.5 weight percent, at least 1 weight percent, at least 2 weight percent, at least 3 weight percent, at least 4 weight percent, at least 5 weight percent, at least 10 weight percent, at least 20 weight percent, at least 30 weight percent, at least 40 weight percent or more of a platinum group metal.

6. The method according to claim 1, The platinum group metal material is in granular or powder form with a particle size of less than 2 mm, less than 1 mm, less than 0.5 mm, less than 0.3 mm, less than 0.2 mm, less than 0.15 mm or less than 0.125 mm.

7. The method according to claim 1, Wherein the platinum group metal material contains at least 50 ppm, at least 80 ppm, at least 100 ppm, at least 200 ppm, at least 500 ppm, at least 1000 ppm, at least 2000 ppm, at least 1%, at least 2%, or at least 5% arsenic by weight.

8. The method according to claim 1, The reducing agent in the flux material includes one or more of CaC, CaSi, Al and Ti.

9. The method according to claim 1, The flux material additionally contains one or both of FeSi and CaO.

10. The method according to claim 1, Together with the flux material, metallic Fe is also added to the platinum group metal material.

11. The method according to claim 1, The flux material comprises: at least 10 wt %, at least 20 wt %, at least 30 wt %, or at least 40 wt % of the reducing agent; no more than 100 wt %, no more than 80 wt %, no more than 70 wt %, no more than 60 wt %, or no more than 40 wt % of the reducing agent; or an amount of the reducing agent within a range defined by any combination of these limits.

12. The method according to claim 1, The ratio of the flux material to the platinum group metal material is: at least 1:5, at least 1:4, at least 1:3 or at least 1:2; not greater than 1:1, not greater than 1:1.3, not greater than 1:1.6, or not greater than 1:1.8; or within a range defined by any combination of these limits.

13. The method according to claim 1, wherein the arsenic-containing platinum group metal material is heated in the presence of the flux material to a temperature of at least 1400°C, at least 1500°C, or at least 1600°C; no greater than 1800°C, no greater than 1750°C, or no greater than 1700°C; or within a range defined by any combination of these limits.

14. The method according to claim 1, wherein the arsenic-containing platinum group metal material is heated in the presence of the flux material for a period of at least 15 minutes, at least 30 minutes, at least 45 minutes, at least 1 hour, at least 2 hours, at least 3 hours or at least 4 hours.

15. The method according to claim 1, The arsenic-containing platinum group metal material is heated in the presence of the flux material in a furnace selected from an induction furnace, a rotary furnace, an electric arc furnace, a plasma furnace, a soot blowing furnace, a muffle furnace or other smelting equipment.

16. The method according to claim 15, wherein the arsenic-containing platinum group metal material is mixed with the flux material in the furnace during heating.

17. The method according to claim 1, Wherein after separating the platinum group metal material from the arsenic-containing slag, the platinum group metal material is provided as a feed to a platinum group metal refining process to recover one or more platinum group metals.

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