WO2024058441A1 - Process for recovering platinum-group metal from waste catalyst by using biocyanide and ionic liquid - Google Patents

Abstract

Disclosed in the content of the present disclosure is a process for recovering a platinum-group metal with a high yield by using an organic phosphorus-based ionic liquid as an extracting agent, following bio-leaching of the platinum-group metal contained in a waste catalyst by using biocyanide produced from microorganisms.

Description

Process for recovering platinum group metals from spent catalysts using biocyanide and ionic liquids

This disclosure relates to a process for recovering platinum group metals from spent catalysts using biocyanide and ionic liquids. More specifically, the present disclosure relates to a process of bioleaching platinum group metals contained in a spent catalyst using biocyanide produced from microorganisms and then recovering the platinum group metals with high purity using an organophosphorus ionic liquid as an extractant. It's about.

Due to the recently strengthened regulation of polluting gases, catalytic converters have become mandatory to treat exhaust gases emitted from various vehicles. To capture exhaust gases, precious metals, specifically platinum (Pt) and palladium, are used as catalyst components. (Pd) etc. are applied.

Traditionally, spent catalytic converters are processed through a pyrometallurgical process, where the precious metals are collected in alloy form using collector metals or collector metals such as Cu ⁰ and Fe ⁰ . However, this process is not only difficult to see as a direct extraction method, but is also energy-intensive and involves isolating relatively low weight precious metals after subsequent chemical leaching (or elution), as well as producing large amounts of 2 Tea waste is produced in the form of slag. The slag produced in this way exhibits high alkalinity and is therefore not suitable for landfill. In addition, the problem of emitting a large amount of carbon dioxide has been pointed out, and after the alloy is reprocessed and separated from the collected metal, it must be treated with individual precious metal salts. Moreover, for the dry smelting process, the platinum recovery rate is about 80 to 94%, and the palladium recovery rate is about 80 to 96%. Therefore, there is a problem that greatly increases the processing cost of the entire recycling process.

Alternatively, hydrometallurgical methods have been proposed, but because they use high concentrations of toxic acids, they release hazardous wastewater and gaseous pollutants that increase environmental stress. In addition, since wastewater treatment is involved as a post-treatment step, the cost required for this is large, and gas cleaning also requires the use of expensive and sophisticated equipment, which inevitably increases the overall treatment cost.

In response to this, a chemical cyanidation process has been proposed as a potential alternative for the purpose of suppressing the use of highly concentrated acids. However, due to the toxicity of free cyanide, there is a high risk during transportation and high costs are incurred in decomposing cyanide before discharging cyanide-containing wastewater.

Recently, as an alternative to inorganic metal extraction methods involving solution chemistry, environmentally friendly microorganism-based technologies have been developed, specifically biocyanide solutions produced from cyanide-producing bacteria, to recover platinum groups by leaching them from spent catalysts. The technology has been reported (Domestic Patent No. 1575582; Hydrometallurgy 158 (2015) 10-18).

However, the above-described bioleaching-based technology does not specifically mention a method of recovering platinum group metals from cyanide leachate. In order to separate and recover platinum group metals from leachate containing platinum group metals, a method of precipitating them through the addition of ion exchange resin and sulfide such as sodium sulfide (NaHS) is also known (for example, U.S. Patent No. 7544231). However, it costs a lot of money to decompose the cyanide remaining in the solution, and it is not easy to discharge due to its toxicity.

In one embodiment of the present disclosure, in order to recover platinum group metals from a spent catalyst containing platinum group metals (PGM), an environmentally friendly method is provided to effectively recover platinum group metals while minimizing the use of toxic substances at a lower cost compared to the prior art. We would like to provide

Another embodiment of the present disclosure seeks to provide a method for recycling the residue generated after recovering platinum group metals from a spent catalyst using microorganisms.

According to one embodiment of the present disclosure,

a) forming a platinum group-containing cyanide leachate by leaching platinum group metals from a platinum group-containing spent catalyst using a solution containing biocyanide produced by the metabolic action of cyanide-producing microorganisms;

b) subjecting the platinum group-containing cyanide leachate to a liquid-liquid extraction treatment using a water-insoluble organophosphorus ionic liquid as an extractant to form a platinum group-rich extract and a platinum group-depleted raffinate; and

c) recovering platinum group metal from the extract;

A method for recovering platinum group metals from a spent catalyst containing a is provided.

According to an exemplary embodiment, the platinum group-containing spent catalyst may contain at least one platinum group metal selected from the group consisting of platinum and palladium.

According to an exemplary embodiment, the platinum group-containing spent catalyst may not contain rhodium.

According to an exemplary embodiment, the platinum group-containing spent catalyst may be provided in step a) in the form of particles or pulverized material having a particle size range of 350 μm or less.

According to an exemplary embodiment, the total content of platinum group metal in the platinum group-containing spent catalyst may range from 0.005 to 0.4% by weight.

According to an exemplary embodiment, the platinum group-containing spent catalyst contains platinum and palladium, and the contents of platinum and palladium may be in the range of 0.003 to 0.15% by weight and 0.002 to 0.1% by weight, respectively.

According to an exemplary embodiment, the pH of the aqueous solution containing biocyanide in step a) may range from 9.5 to 14, and the concentration of cyanide (CN ^- ) may range from 2 to 6 g/L.

According to an exemplary embodiment, before leaching the platinum group metal in step a), the step of trapping or collecting the solution containing biocyanide into an alkaline solution and concentrating or accumulating it may be further included.

According to an exemplary embodiment, the pH of the platinum group-containing cyanide leachate formed in step a) may range from 9 to 12.5.

According to an exemplary embodiment, the organophosphorus ionic liquid used in step b) may include a phosphonium-based cationic group represented by the following general formula 1, and an anionic group selected from the group consisting of halide, sulfide, and nitrate. there is:

[General Formula 1]

In the above formula, R ¹ to R ⁴ are each an alkyl group having 35 to 56 carbon atoms.

According to an exemplary embodiment, the molecular weight (M _w ) of the organophosphorus-based ionic liquid used in step b) may range from 200 to 900.

According to an exemplary embodiment, step c) may be performed by stripping.

According to an exemplary embodiment, the step of separating the organophosphorus ionic liquid from the extract remaining after recovery of the platinum group metal in step c) and reusing it as an extractant in step b) may further be included.

The process for recovering platinum group metals from spent catalysts according to embodiments of the present disclosure uses a green biogenic cyanide solution based on bioleaching or biohydrometallurgical mechanisms, compared to conventional techniques (pyrometallurgical processes, chemical wet metals using acids). It can dramatically solve problems pointed out in the smelting process (in particular, emissions of harmful gases or toxic substances, slag production, high energy consumption, etc.). Furthermore, by performing a liquid-liquid extraction method using a specific extractant, platinum group metals can be easily separated from the platinum group-containing leachate produced through biocyanide-based leaching, and further, individual platinum group metals can be recovered with high purity. It provides advantages that can be done. In particular, because it is environmentally friendly, low energy-intensive, and highly efficient, it is consistent with the ESG strategies of related companies and is expected to be widely commercialized in the future.

1 is a process diagram showing a schematic process sequence for recovering platinum group metals from spent catalysts;

2 is a process diagram showing an exemplary process for recovering platinum group metals from spent catalyst;

Figure 3 is a diagram showing an example of an apparatus for performing a cyanide production experiment using bacteria;

Figure 4 is a graph showing the results of measuring the number of C. violaceum cells in YP medium supplemented with 2.0 g/L glycine in biocyanide over time in batch mode;

Figure 5 shows the time course of the preparation of biocyanide solution using a NaOH trapping solution of 4.0 mol/L and YP medium with a glycine concentration of 2.0 g/L in (a) batch mode and (b) continuous mode, respectively. This is a graph showing the accumulation and pH change of biogenic cyanide;

Figure 6 is a graph showing the effect of temperature on the pressurized biocyanation reaction of Pt and Pd from a spent catalytic converter at conditions of CN ^- concentration of 2.9 g/L, pO ₂ of 10.5 bar, initial pH of 11.2 and 60 minutes;

Figure 7 shows the effect of oxygen partial pressure (pO ₂ ) on the pressurized biocyanation reaction of Pt and Pd from a spent catalytic converter at a temperature of 150 °C, ^CN concentration of 2.9 g/L, initial pH of 11.2, and 60 min. It is a graph representing;

Figure 8 is a graph showing the effect of biocyanide concentration on the pressurized biocyanation reaction of Pt and Pd from a spent catalytic converter under conditions of temperature of 150 °C, pO ₂ of 14 bar, initial pH of 11.2 and 60 minutes;

Figure 9 shows the effect of ionic liquid concentration on the extraction of Pt and Pd from (a) cyanide leachate under certain conditions (O:A, 1; pH, 10.8; contact time, 10 min; and temperature, 25°C). Graph showing the impact, and (b) D vs. It is a log plot of P-IL;

Figure 10 shows the platinum group metal-containing solution (leaching solution) for Pt-Pd extraction under given conditions (O:A, 1; P-IL concentration, 0.15 mol/L; contact time, 10 min; and temperature, 25 °C). This is a graph showing the effect of pH;

Figure 11 shows the effect of temperature on (a) Pt-Pd extraction under given conditions (O:A, 1; P-IL concentration, 0.15 mol/L; solution pH, 10.4; and contact time, 10 min). Graph, and (b) logK _ex vs. is the Van't Hoff plot for 1/T;

Figure 12 is a graph showing the effect of the concentration of NH ₄ SCN on the stripping behavior of Pt and Pd in the ionic liquid phase under certain conditions (O:A, 1; contact time, 10 min; and temperature, 25 °C). ;

Figure 13 shows the concentration of S(CH ₂ CH ₂ OH) ₂ for Pt-stripping in the Pd-depleted ionic liquid phase under given conditions (O:A, 1; contact time, 10 min; and temperature, 25 °C). This is a graph showing the impact of;

Figure 14 is (a) a graph showing the behavior of leaching Pt and Pd from a spent catalytic converter using the biocyanide solution accumulated in the recycled raffinate after performing the (Pt, Pd) extraction process using P-IL, and (b) a graph showing the results of evaluating the reusability of ionic liquid in a (Pt,Pd) extraction cycle from a cyanide leaching solution; and

Figure 15 is a graph showing the results of an experiment on biodegradation of cyanide in a bleed solution using C. violaceum drained from the bioreactor after being used to produce biocyanide.

The present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. In addition, the attached drawings are intended to aid understanding, and the present invention is not limited thereto, and details regarding individual configurations can be appropriately understood based on the specific purpose of the related description described later.

Terms used in this specification may be defined as follows.

“Platinum group metal” broadly includes the six metal elements belonging to the platinum group: platinum, palladium, rhodium, ruthenium, iridium, and osmium. It can be understood as referring to platinum and/or palladium in a narrow sense.

“Bioleaching” may generally refer to a process of dissolving a metal from a mineral source by microorganisms, and specifically to a process of converting a solid metal to a water-soluble form.

“Culture medium” may refer to an aqueous solution of nutrients available for cell growth.

“Extraction” can mean transferring a particular component, specifically a metal, from one phase to another.

“Stripping” may refer to a process of separating or removing a specific metal from a liquid medium or solvent, and selective stripping may refer to a process of separating or removing a specific metal from a liquid medium or solvent containing a plurality of metals. can do.

In this specification, when a numerical range is specified as a lower limit and/or an upper limit, it can be understood that any subcombination within the numerical range is also disclosed. For example, when written as “1 to 5,” it can include 1, 2, 3, 4, and 5, as well as any sub-combinations therebetween.

When any component or member is described herein as being “connected to” another component or member, unless otherwise stated, it refers not only to being directly connected to said other component or member, but also to the other component or member. Alternatively, it may be understood that cases of being connected through the intervention of a member are also included.

Similarly, the term “contact” may also be understood to include not only direct contact, but also contact through the intervention of other components or members.

When it is said to “include” a certain component, this means that it may further include other components, unless otherwise specified.

According to one embodiment of the present disclosure, a process of bioleaching and solvo-chemical extraction using microorganisms is provided to separate and recover platinum group metals from a spent catalyst containing platinum group metals, The schematic process is as shown in Figure 1.

Referring to the drawing, a solid platinum group-containing spent catalyst can be used as a starting material. In this regard, platinum group-containing spent catalysts are available from various fields such as the automotive and chemical industries, and may typically be derived from catalytic converters (e.g., catalytic converters of automobiles).

According to an exemplary embodiment, the content of the platinum group metal in the spent catalyst is not particularly limited, but the content (based on element) of the platinum group metal in the spent catalyst is, for example, about 0.005 to 0.4% by weight, specifically about 0.01 to 0.01% by weight. It may range from 0.3% by weight, more specifically about 0.011 to 0.15% by weight.

In an exemplary embodiment, the spent catalyst may contain platinum and/or palladium among the platinum group metals. According to a specific embodiment, the spent catalyst may simultaneously contain platinum and palladium, where the content (based on element) of platinum (Pt) is, for example, about 0.003 to 0.15% by weight, specifically about 0.005 to 0.1% by weight. %, more specifically, it may be around 0.08% by weight, and the content of palladium (Pd) (based on element) is, for example, about 0.002 to 0.1% by weight, specifically about 0.004 to 0.05% by weight, more specifically about It may be in the range of around 0.04% by weight. Illustratively, the weight ratio of platinum/palladium may range, for example, from about 0.1 to 3, specifically from about 0.3 to 2.5, and more specifically from about 0.5 to 2.1.

According to an exemplary embodiment, the spent catalyst may further contain other components in addition to platinum group metals, such as alumina, magnesia, silica, zirconia, titania, calcium oxide, etc., and the content of additional components or metals (element Standard) may be, for example, in the range of about 60% by weight or less, specifically about 40% by weight or less, and more specifically about 20% by weight or less.

On the other hand, the spent catalyst may be substantially free of rhodium. As such, platinum group-containing catalysts that do not contain rhodium are typically available from old generation catalysts of automobile vehicles, more specifically second generation catalysts of automobile vehicles, etc. These composition characteristics can affect the Pt and Pd extraction process using ionic liquid, the reuse process of cyanide leachate remaining after use, and the biodegradation process of cyanide remaining in the solution, which is discharged in a certain amount prior to the cyanide leachate reuse process. there is. However, it does not exclude the presence of trace amounts of rhodium in the form of impurities, for example, it may be contained in less than about 0.0004% by weight, specifically less than about 0.0001% by weight. However, rhodium may act as an impurity during the extraction of Pt and Pd, lowering the purity of Pt and Pd to be recovered, and as the recycling process of raffinate generated during the extraction process is repeated, rhodium may accumulate in the solution. , it may be advantageous to contain as little rhodium as possible. The content of platinum group components in the above-described spent catalyst may be understood as illustrative, and may vary depending on the source.

According to an exemplary embodiment, the spent catalyst may be provided in the form of particles or pulverized material. In this case, the particle size or size of the pulverized material or particles determines effective contact with the biocyanide solution described later, flow characteristics in the reactor, etc. It can be determined by taking into account, for example, about 350 ㎛ or less, specifically about 250 ㎛ or less, more specifically about 100 to 200 ㎛, and particularly specifically about 120 to 180 ㎛. Meanwhile, in the case of waste catalyst derived from a waste catalyst converter for automobiles, it may be provided in a pulverized form after the catalyst layer has been peeled off. At this time, for grinding, means known in the art can be used. As an example, the grinding means may be a roller grinder, vibrating mill, ball mill, pot mill, hammer mill, pulverizer, gyratory grinder, gyratory mill, etc., but is not limited thereto, and may be two or more of the listed types. It can also be pulverized by combining.

Pretreatment of spent catalyst (optional)

Referring to FIG. 1, the platinum group-containing spent catalyst may optionally undergo an alkali pretreatment step. This alkaline pretreatment can be performed to remove carbonaceous substances in the spent catalyst (or spent catalyst particles) and various impurities that may inhibit subsequent biocyanation. Illustratively, the alkaline treatment may be performed by contacting the spent catalyst with an alkali-containing solution (specifically, an aqueous solution), wherein the alkaline component is at least one selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. You can. Additionally, the concentration of the alkaline solution may be adjusted, for example, in the range of about 1 to 5 mol/L, specifically about 1.5 to 4 mol/L, and more specifically about 2 to 3 mol/L. Additionally, the pretreatment temperature may be adjusted, for example, to at least about 60°C, specifically about 70 to 98°C, and more specifically about 80 to 95°C. In addition, the pretreatment time is not particularly limited, but may be adjusted, for example, in the range of about 30 to 200 minutes, specifically about 40 to 100 minutes, and more specifically about 50 to 80 minutes.

Production of biocyanide

According to one embodiment, in addition to providing the above-described spent catalyst, a step of synthesizing cyanide, that is, biocyanide (HCN), is performed while growing and culturing cyanide-producing microorganisms, and accordingly, a step of synthesizing cyanide, that is, biocyanide (HCN), is performed. A solution (specifically an aqueous solution) may be formed.

In this regard, microorganisms can be selected from species capable of producing cyanide by metabolic action. As an example, the cyanide-producing microorganism may be at least one selected from species belonging to Betaproteobacteria, Gammaproteobacteria, etc., such as Chromobacterium violaceum , Pseudomonas fluorescens , It may be at least one selected from Pseudomonas plecoglossicida , Bacillus megaterium, etc., and in particular, it may be a type that can produce cyanide through oxidative decarboxylation of glycine. According to a specific embodiment, Chromobacterium violaceum , which belongs to Gram-negative beta-probacteria and promotes oxidase reaction, can be used as the spoilage bacteria. However, the types listed above may be understood as illustrative purposes.

According to an exemplary embodiment, for culturing cyanide-producing microorganisms, the medium may be a growth medium, specifically YP medium supplemented with glycine. At this time, the concentration of glycine in the medium may be, for example, in the range of about 0.5 to 5 g/L, specifically about 1.5 to 3.5 g/L, and more specifically about 2 to 2.5 g/L. Since the components of the medium used for microbial growth in this embodiment are known in the art, separate detailed description will be omitted.

Exemplarily, the pH of the growth medium can be adjusted in consideration of microbial characteristics, and may be, for example, at least about 7, specifically about 8 to 9, and more specifically about 8.5. Additionally, the culture temperature is not particularly limited, but may be typically adjusted in the range of about 20 to 40°C, more typically about 25 to 35°C.

Additionally, the concentration of microorganisms in the initial growth medium may range, for example, from at least about 10 ⁵ CFU/mL, specifically about 10 ⁶ to 10 ⁹ CFU/mL, and more specifically about 10 ⁷ to 10 ⁸ CFU/mL. However, this can be understood as an example.

According to an exemplary embodiment, the culture of microorganisms may be performed under the supply of an oxygen-containing gas, for example, air, and the culture may be performed using a bioreactor illustratively equipped with an aeration facility. The concentration of cyanide after culturing may range, for example, from about 900 to 1200 mg/L, specifically from about 950 to 1100 mg/L, and more specifically from about 1000 to 1100 mg/L.

According to an exemplary embodiment, a concentration or accumulation step may be performed to increase the concentration of biocyanide produced by microbial culture. For this purpose, cyanide (HCN) produced using an alkaline solution (specifically, an aqueous solution) can be trapped or collected into the alkaline solution.

As an example, the alkaline component in the alkaline solution (trapping or collection solution) may be at least one selected from, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc., and its concentration may be, for example, about 1 to 8 mol. /L, specifically, can be adjusted in the range of about 1.5 to 6 mol/L, more specifically about 3 to 5 mol/L, but this can be understood as an example. In this way, the principle of cyanide trapping is to utilize the phenomenon that the vapor density of cyanide (HCN) (0.94) is lower than the vapor density of air (1.0). To achieve this, aeration is applied as much as possible to push the HCN toward the alkaline solution. It is desirable to have it done. Illustratively, cyanide trapping may be performed according to Scheme 1 below.

[Scheme 1]

As an example, the trapping time is, for example, about 20 to 120 hours, specifically about 40 to 110 hours, more specifically about 60 to 105 hours, more specifically about 90 to 100 hours, considering the desired concentration of biocyanide. It can be adjusted appropriately within the time range.

The concentration of cyanide or cyanide ions (i.e., CN ^- ) concentrated or accumulated into the alkaline solution as described above is, for example, about 2 to 6 g/L, specifically about 3 to 5 g/L, more specifically It can increase to a range of about 4 to 4.5 g/L. In this regard, if the concentration of cyanide is below a certain level, there is a limit to increasing the leaching rate during bioleaching in the downstream stage, and if it exceeds a certain level, the leaching rate will no longer increase, so concentration It may be advantageous to appropriately adjust the degree.

Additionally, the pH of the concentrated cyanide solution may range, for example, from about 9.5 to 14, specifically from about 10 to 12, and more specifically from about 10.5 to 11.5.

Meanwhile, according to an exemplary embodiment, the production of biocyanide and the concentration or accumulation of cyanide using an alkaline solution (trapping solution or alkaline collector) may be performed in a batch or continuous manner, but biocyanide is produced in a relatively short period of time. Considering that it is generated in a section, continuous mode may be advantageous.

Bioleaching using cyanide

According to one embodiment of the present disclosure, the obtained biocyanide-containing solution or concentrated (accumulated) biocyanide-containing solution is supplied to a lixiviant medium to remove platinum group metals from the platinum group-containing spent catalyst. A leaching step is performed. In this case, the platinum group metal in the spent catalyst may form a form combined with cyanide ions, for example, a complex.

According to an exemplary embodiment, the amount of spent catalyst in the biocyanide-containing solution (or concentrated (or accumulated) biocyanide-containing solution) is, for example, about 2 to 40 g/100 mL, specifically about It can be adjusted in the range of 5 to 25 g/100 mL, more specifically about 10 to 20 g/100 mL. At this time, the bioleaching process may be performed under stirring conditions. For example, the stirring speed may be adjusted in the range of about 100 to 400 rpm, specifically about 200 to 250 rpm, but this is for illustrative purposes. It can be understood as

In addition, the leaching time may be determined considering the maximum leaching of Pt and Pd, for example, about 30 to 360 minutes, specifically about 30 to 120 minutes, and more specifically about 60 to 90 minutes. You can.

Meanwhile, according to an exemplary embodiment, bioleaching may be set to elevated temperature conditions and increased oxygen pressure (pO ₂ ) conditions. In this regard, the leaching temperature may be adjusted, for example, in the range of about 100 to 200 °C, specifically about 120 to 180 °C, and more specifically about 140 to 160 °C. At this time, if the leaching temperature is too low or too high, it may act as a factor in reducing the leaching rate, so it may be advantageous to appropriately adjust it within the above-mentioned range. However, the above-described leaching temperature can be changed depending on other conditions, such as cyanide concentration, leaching time, oxygen pressure, etc.

In addition, according to an exemplary embodiment, the leaching rate may tend to increase as the pressure during bioleaching, specifically the oxygen pressure (or oxygen partial pressure) increases, for example, at least about 8 bar, specifically about 10 bar. It can be adjusted in the range of from about 18 bar to about 18 bar, more specifically about 12 to 16 bar. However, at excessively high oxygen pressure (or partial pressure), the increase in leaching rate is insignificant and may actually act as a factor in reducing the economic feasibility of the process, so it may be advantageous to adjust it appropriately within the above-mentioned range.

Through the above-described bioleaching process, most of the platinum group metals in the spent catalyst can be leached into the cyanide solution, and the leaching rate of the platinum group metals is, for example, at least about 90%, specifically at least about 92%, more specifically at least It may be about 95%. At this time, the cyanide solution from which the platinum group has been leached may exhibit basicity. Specifically, the pH of the platinum group-containing leachate is, for example, about 9 to 12.5, specifically about 10 to 12, more specifically about 10.2 to 11.5, In particular, it may range from about 10.5 to 11, and this can be understood as an example.

Separation and recovery of platinum group metals

- Separation (extraction) of platinum group metals

According to one embodiment of the present disclosure, the platinum group-containing cyanide leachate produced by bioleaching contains other components (for example, Al ₂ O ₃ , MgO, SiO ₂ , ZrO ₂ , CaO, TiO _{2 ,} etc.), a step of selectively separating and recovering the platinum group metal is performed using a solvo-chemical method. To this end, in this embodiment, platinum group metals in the leachate are selectively moved into the extract by liquid-liquid extraction, thereby forming a platinum group-rich extract and a platinum group-depleted raffinate.

According to an exemplary embodiment, a water-insoluble organophosphorous ionic liquid may be used as the extractant. In this regard, organophosphorus-based ionic liquids are environmentally friendly because they are not flammable, unlike existing extractants, and also have good mass transfer and loading capacity.

According to an exemplary embodiment, the phosphorus-based ionic liquid may contain a phosphonium-based cationic group represented by General Formula 1 below.

[General Formula 1]

In the above formula, R ¹ to R ⁴ are each an alkyl group having 35 to 56 carbon atoms, specifically 38 to 50 carbon atoms, and more specifically 40 to 48 carbon atoms.

Meanwhile, in the case of the anion constituting the phosphonium-based ionic liquid, it may be at least one selected from halide, sulfide, nitrate, etc. At this time, the halide may be at least one selected from fluoride, chloride, bromide, iodide, etc., and more specifically, may be chloride (Cl ^- ).

According to an exemplary embodiment, the molecular weight (M _w ) of the above-described phosphonium-based ionic liquid may range, for example, from about 200 to 900, specifically from about 300 to 800, and more specifically from about 400 to 700. . In this regard, considering that the molecular weight of the phosphonium-based ionic liquid affects the extraction efficiency and selectivity for the platinum group, it may be advantageous to use a type having a molecular weight in the above-mentioned range. According to a specific example, a representative phosphonium-based ionic liquid may be trihexyl(tetradecyl)phosphonium chloride, which exhibits anion exchange properties and is contained in the cyanide leachate. It can be particularly advantageous for extracting platinum group metals.

According to an exemplary embodiment, the organophosphorus ionic liquid may be applied to the extraction process in a mixed form with an aromatic solvent, taking into account the dielectric constant of the solvent, metal affinity, and affinity with the ionic liquid and aqueous solution. . The aromatic solvent that can be used is an aromatic solvent having 7 to 12 carbon atoms, specifically 8 to 11 carbon atoms, and more specifically, about 10 carbon atoms, for example, Solesso100. It may be commercially available as Solvesso150, Solvesso200, ExxolD80, etc. In this case, the concentration of the organophosphorus extractant is, for example, at least about 0.08 mol/L, specifically at least about 0.1 mol/L, more specifically about 0.12 to 0.3 mol/L, especially specifically about 0.14 to 0.2 mol/L. Can be adjusted in the range of L

As described above, as a result of using a phosphonium-based ionic liquid as an extractant, an organometallic complex is formed between the cyanide of a platinum group metal (specifically Pt and/or Pd) and the ionic liquid in the extract, specifically phosphonium-based ionic liquid. It is believed that the metal moves from the aqueous phase to the organic phase by ion exchange between the anion of the phonium-based ionic liquid and the metal ion (specifically, the anion combining platinum and cyanide group). For example, when trihexyl (tetradecyl) phosphonium chloride is used as an extractant as a phosphonium-based ionic liquid, the structure of the organometallic complex according to the ion exchange reaction may be expressed as Formula 1 below.

[Formula 1]

According to an exemplary embodiment, the extraction conditions are not particularly limited, but the volume ratio of organic phase to aqueous phase is about 1:5 to 5:1, specifically about 1:3 to 3:1, more specifically about 1:2. It can be adjusted in the range of 2:1. Meanwhile, the equilibration time may be, for example, in the range of about 2 to 30 minutes, specifically about 5 to 15 minutes, and more specifically about 5 to 10 minutes. In addition, the extraction temperature may be, for example, around 20 to 40°C, specifically around 22 to 35°C, more specifically around 24 to 30°C, particularly around 25°C.

Meanwhile, in the case of platinum group-depleted raffinate (aqueous phase) remaining during extraction using an organophosphorus ionic liquid, as it contains cyanide, it can be used to leach platinum group metals from the spent catalyst. As an example, it can be recycled as a solution containing biocyanide, and/or as a solution containing biocyanide concentrated (or accumulated) by an alkaline solution (trapping or collection solution).

Meanwhile, at least a portion of the platinum group-depleted raffinate can be treated in a manner to decompose (specifically, biodegrade) the cyanide contained therein. At this time, cyanide can be decomposed by microorganisms that can be used to produce the aforementioned biocyanide, and can be discharged outside the process or system after going through the decomposition process.

- Recovery of platinum group metals

According to one embodiment of the present disclosure, recovering platinum group metals from a platinum group-rich extract may be performed. At this time, the recovered platinum group metal may be a single platinum group metal or a combination of at least two types of platinum group metals.

Although this specific example does not exclude the recovery of a combination of two or more platinum group metals, for example, a combination of Pt and Pd, considering the usability, it is better to recover each platinum group metal contained in the spent catalyst with high purity. It can be advantageous. From this perspective, the following description will focus on methods for recovering a plurality of platinum group metals contained in the extract, specifically Pt and Pd.

According to an exemplary embodiment, selective stripping may be performed to recover a plurality of platinum group metals contained in the extract (i.e., organophosphorus-based ionic liquid). As an example, when the platinum group metals extracted in the extract (organic phase) are platinum (Pt) and palladium (Pd), a solution (specifically an aqueous solution) of a compound (i.e., stripping agent) that exhibits selectivity for the specific metal is used. Pt and Pd can each be recovered by contacting them with a platinum group-containing extract (oil phase), individually or sequentially.

According to an exemplary embodiment, in order to first selectively strip palladium from an extract containing platinum (Pt) and palladium (Pd), an aqueous solution of a stripping agent that has water miscibility and selectivity for palladium can be used. (First stripping step). These stripping agents may be selected from thiol compounds that have selectivity in forming Pd complexes. As an example, the Pd-selective stripping agent may be, for example, a thiocyanate compound. Such a thiocyanate compound may be, for example, at least one selected from ammonium thiocyanate (NH ₄ SCN), sodium thiocyanate (NaSCN), potassium thiocyanate (KSCN), etc., and specifically, ammonium thiocyanate (NaSCN). It may be a cyanate (NH ₄ SCN) compound.

In this regard, the concentration of the aqueous solution of the stripping agent selective for palladium can be adjusted so that the Pd stripping rate is maximum and at the same time the Pt stripping rate is minimum, for example at least about 0.7 mol/L, specifically at least about 0.8 mol/L. to 3 mol/L, more specifically about 1.2 to 2.6 mol/L, and particularly specifically about 1.8 to 2.3 mol/L.

According to an exemplary embodiment, the volume ratio of the organic phase to the water phase during palladium stripping is about 1:5 to 5:1, specifically about 1:3 to 3:1, more specifically about 1:2 to 2:1. It can be adjusted within a range. In addition, the stripping temperature may be, for example, about 20 to 40° C., specifically about 22 to 35° C., more specifically about 24 to 30° C., and particularly specifically about 25° C. In addition, the contact time is specifically limited. Although not guaranteed, it can be appropriately adjusted, for example, in the range of about 2 to 30 minutes, specifically about 5 to 15 minutes, and more specifically about 5 to 10 minutes.

According to exemplary embodiments, the stripping rate of palladium may be at least about 90%, specifically at least about 95%, and more specifically at least about 98%. On the other hand, the stripping rate of platinum may be, for example, less than about 3%, specifically less than about 2.5%, and more specifically less than about 2%. As such, through selective stripping for palladium, a palladium-rich fraction and a palladium-depleted fraction can be formed.

Next, the organic phase, i.e., the palladium-depleted fraction in which most of the platinum (Pt) is contained in the organophosphorus ionic liquid, can be subjected to additional stripping to recover platinum (second stripping step).

In this regard, as palladium was previously separated as a two-component system (Pd and Pt) separation step, the platinum stripping agent should be selected from types that are easy to form a Pt complex and have properties that can move Pt from the organic phase to the aqueous phase. You can. As such a platinum stripping agent, for example, thioalcohol can be used, specifically 2,2-thiodiethanol (S(CH ₂ CH ₂ OH) ₂ ), Beta-rhodinol, (S)-3,7- It may be at least one selected from dimethyl-6-often-1-ol, etc., and specifically may be 2,2-thiodiethanol (S(CH ₂ CH ₂ OH) ₂ ).

In this regard, the concentration of the aqueous solution of the stripping agent selective for platinum is determined taking into account the maximum stripping rate of Pt, for example at least about 0.8 mol/L, specifically at least about 1 to 3 mol/L, more specifically about It can be adjusted in the range of 1.2 to 2.2 mol/L, particularly about 1.4 to 2 mol/L.

According to an exemplary embodiment, the volume ratio of organic phase to aqueous phase during platinum stripping is about 1:5 to 5:1, specifically about 1:3 to 3:1, more specifically about 1:2 to 2:1. It can be adjusted within a range. In addition, the stripping temperature may be, for example, about 20 to 40° C., specifically about 22 to 35° C., more specifically about 24 to 30° C., and particularly specifically about 25° C. In addition, the contact time is specifically limited. Although not guaranteed, it can be appropriately adjusted, for example, in the range of about 2 to 30 minutes, specifically about 5 to 15 minutes, and more specifically about 5 to 10 minutes.

According to exemplary embodiments, the stripping rate of platinum may be at least about 90%, specifically at least about 95%, and more specifically at least about 98%.

Through the sequential stripping process described above, palladium and platinum contained in the extract (organophosphorus ionic liquid) can be separated, respectively. At this time, each stripping solution can recover high purity platinum group metals, specifically platinum and palladium, through methods known in the art, such as precipitation and salt formation. As an example, in order to recover platinum and palladium from a platinum group metal-containing stripping solution, specifically a platinum-containing solution and a palladium-containing solution, respectively, for example, ammonium salt, sulfide salt, etc. are added and reacted to remove platinum group metal (specifically, It is possible to form a precipitate of salt (specifically, (NH ₄ ) ₂ PtCl ₆ , (NH ₄ ) ₂ PdCl ₆ , etc.) of platinum and palladium. At this time, the concentration of the added component, for example, ammonium ion, may be determined depending on the amount of platinum group metal in the stripping solution, for example, about 0.01 to 0.05 mol/L, specifically about 0.02 to 0.04 mol/L, More specifically, it may range from about 0.02 to 0.03 mol/L. However, the above numerical range may be understood as illustrative.

In addition, the temperature conditions for forming the precipitate are not particularly limited, but may be adjusted, for example, to a range of about 20 to 100°C, specifically about 30 to 80°C, and more specifically about 40 to 50°C.

Meanwhile, the extract remaining after the stripping process, specifically the organophosphorus ionic liquid, can be recycled after the separation process and reused as an extractant in the extraction step before the stripping step. As an example, the ionic liquid can be separated by contacting it with an aqueous solution of at least one acid selected from strong acids, such as hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, etc. At this time, the concentration of the acid aqueous solution may be adjusted in the range of, for example, about 3 to 9 mol/L, specifically about 4 to 8 mol/L, and more specifically about 5 to 7 mol/L, but the acid used It can be changed depending on the type, etc.

The present invention can be more clearly understood by the following examples, which are for illustrative purposes only and are not intended to limit the scope of the invention.

Example

- In this example, a spent catalytic converter (5 kg) for a vehicle obtained from a domestic disposal company was used. The collected catalyst was finely ground to a size of approximately 150 ㎛ using a gyratory crusher and ball mill.

As a result of analyzing the composition of the pulverized spent catalyst by It was the same.

ingredient	Al 2 O 3	MgO	SiO 2	ZrO2	TiO 2
Furtherance	41.8	17.4	24.2	0.72	0.56

Additionally, as a result of the fire assay, the contents of platinum and palladium among the platinum group metals were 756 ppm and 367.5 ppm, respectively.

- Hydrochloric acid (Merck), nitric acid (Riedel-deHa¨en), NaOH pellets (Junsei Chemical Co. Ltd.), thiourea (Junsei Chemical Co. Ltd.), thioglycol (Sigma-Aldrich), P-IL (trihexyl) (tetradecyl)phosphonium chloride; Cyphos IL101; Cytec Industries Inc., Canada), and aromatic solvent C10 (SOLVENTIS) were each commercially available, and no additional purification was performed.

In this example, platinum group metals were recovered from spent catalyst by performing the critical steps of the process shown in FIG. 2.

Example 1

Biocyanide synthesis

In this example, biocyanide production and concentration (accumulation) experiments were performed using the setup device shown in FIG. 3.

12 mL (12 mL) of cyanide-producing bacteria ( C. violaceum DSM30191) pre-grown in YP medium (10 g peptone, 5 g yeast extract, and 1.0 L distilled water) supplemented with 2.0 g/L glycine at 30 °C and pH 8.5. Approximately 10 ⁶ CFU/mL) was inoculated. Cyanide synthesis was performed in a bioreactor (equipped with a stirrer to provide agitation at 300 rpm), and air was constantly supplied through an aerator at a flow rate of 3.0 mL/s. The bioreactor was maintained at 30°C over 120 hours. In addition, 4.0 mol/L NaOH solution was used as an alkali collection means for concentrating (accumulating) the synthesized biocyanide. The concentration of biocyanide was analyzed by titration against a standard AgNO ₃ solution, and cells were counted by the drop plate method on nutrient agar using plates incubated at 30°C for 24 hours.

For biocyanide over time in batch mode, the results of measuring the number of C. violaceum cells in YP medium supplemented with 2.0 g/L glycine are shown in Figure 4.

According to the figure, the cell number increased from 10 ⁶ CFU/mL to 10 ⁹ CFU/mL within 36 hours after incubation and was maintained until 12 hours thereafter. Then, as a result of 120 hours of incubation, it decreased to 10 ⁷ CFU/mL.

On the other hand, in (a) batch mode and (b) continuous mode, the time elapsed during the preparation of biocyanide solution using YP medium with a glycine concentration of 2.0 g/L and NaOH trapping solution with 4.0 mol/L. The accumulation and pH change of biogenic cyanide are shown in Figure 5.

Referring to Figure 5a, biocyanide accumulation into the alkaline solution (NaOH trapping solution) started after 12 hours (10 ⁶ mg/L CN ^- ) and progressed over 48 hours, with a maximum accumulation of 1.05 g/L CN ^- reached, and then began to decrease.

Meanwhile, cyanide (HCN) synthesis was performed using YP medium supplemented with 2.0 g/L glycine and through a continuous process capable of accumulating higher concentrations of cyanide ions under conditions with a retention time of 24 hours. As can be seen in Figure 5b, the highest concentration of 4.17 g/L CN ^- was reached after 96 hours in the alkaline collection solution with a pH of 10.7. Afterwards, the CN ^- ion concentration decreased to 3.8 g/L after 120 hours, which is believed to be because some of the CN ^- ions were converted to HCN as the pH decreased to about 10 (pKa, 9.3).

Example 2

Evaluation of the effect of temperature on bioleaching

Bioleaching under pressurized conditions in an autoclave ((Ni-Cr) alloy 600 reactor; 200 mL) using a biocyanide solution pre-adjusted to a CN ^- ion concentration of 2.9 g/L as a lixiviant medium. was carried out. 20 g of spent catalyst sample was added to 100 mL of biocyanide solution, and pressure leaching was performed while changing the temperature within the range of 100 to 200 ℃ with a stirring speed of 200 rpm (pO ₂ : 10.5 bar; 1 hour). .

Afterwards, the solution was collected by filtration using a 0.45 ㎛ membrane filter, and the collected filtrate was analyzed for Pt-Pd using ICP-plasma mass spectrometry (ICP-MS; MSS 01, SPECTRO Analytical Instruments GmbH, Germany). Analysis was performed.

The metal leaching rate was calculated according to Equation 1 below.

[Equation 1]

In the above equation, M _IS and M _LL are the metal content in the solid sample and the metal content in the leachate, respectively.

The effect of temperature on the pressure biocyanation reaction of Pt and Pd is shown in Figure 6.

Referring to the figure, the leaching rate of Pt and Pd in the cyanide-containing solution at a high temperature of 100°C was found to be 85% or less. However, at 150 °C, the leaching rate reached a maximum of 91% Pt and 94% Pd. Thereafter, as the temperature increased, the leaching rate decreased, reaching a maximum of 87% Pt and 81% Pd at 250°C. This decrease behavior is believed to be due to the decomposition of cyanide due to an increase in the hydrolysis rate at higher temperatures, as shown in Schemes 2 and 3 below.

[Scheme 2]

[Scheme 3]

Example 3

Evaluation of the effect of oxygen partial pressure on bioleaching

The bioleaching experiment was performed according to the experimental procedure according to Example 2, except that the bioleaching was performed while changing the partial pressure of oxygen (pO ₂ ) in the range of 3.5 to 17.5 bar (temperature of 150°C, 2.9 g/L). CN ^- concentration, initial pH of 11.2 and 60 min). The results are shown in Figure 7.

According to the figure, the leaching of platinum group metals (Pt and Pd) increased significantly as pO ₂ increased and reached more than 94% at a pO ₂ of 17.5 bar. The catalytic role of oxygen in cyanide can be confirmed by the behavior through the cyanidation reaction according to Schemes 4 and 5 below.

[Scheme 4]

[Scheme 5]

Example 4

Evaluation of the impact of biocyanide concentration during bioleaching

A bioleaching experiment was performed according to the experimental procedure according to Example 2, except that the bioleaching was performed while changing the biocyanide (CN ^- ) concentration in the range of 0.23 to 4.17 g/L (temperature of 150°C, pO ₂ of 14 bar, initial pH of 11.2 and 60 min). The results are shown in Figure 8.

Referring to the figure, as the CN ^- concentration increased, the Pt leaching rate (43% to >95%) and Pd leaching rate (52% to 96%) also increased. Additionally, the residual cyanide concentration increased from 0.032 g/L to >1.0 g/L. In particular, the maximum leaching rate was observed in the cyanide-containing solution at a concentration of 2.9 g/L CN ^- . The stock leachate (Pt, 157.5 mg/L and Pd, 77.6 mg/L) was used in the subsequent separation (liquid-liquid extraction) process.

Example 5

Evaluation of the effect of extractant concentration on extraction of platinum group metals from platinum group-containing cyanide leachate

Trihexyl(tetradecyl)phosphonium chloride, a phosphonium-based ionic liquid, was dissolved in an aromatic solvent (C10), and the cyanide leachate (pH 10.8) was added while changing the concentration of the ionic liquid in the range of 0.01 to 0.15 mol/L. The platinum group metals (Pt and Pd) were extracted. At this time, the organic to aqueous phase ratio (O:A) was 1, and the contact was made at 25°C for 10 minutes. The results are shown in Figure 9.

According to Figure 9a, as the number of active molecules of the ionic liquid in the organic phase increased, the extraction efficiency of Pt and Pd increased, and at 0.15 mol/L of the ionic liquid, 97% Pt and 94% Pd. reached.

According to Figure 9b, the logarithmic distributions Pt and Pd showed a relationship between log[P-IL] and a straight line with a slope value of about 2. At this time, the slope value indicates that 2 molecules of ionic liquid are involved per mole of Pt and Pd extraction complexes. Based on this relationship, the extraction reaction can be represented by Schemes 6 and 7 below.

[Scheme 6]

[Scheme 7]

Example 6

Evaluation of the effect of pH on extraction of platinum group metals from platinum group-containing cyanide leachate

The extraction experiment was performed according to the experimental procedure according to Example 5, except that the liquid-liquid extraction was performed while changing the pH of the platinum group metal-containing solution (leaching solution) in the range of 10.4 to 11.2 (O:A, 1 ; P-IL concentration, 0.15 mol/L; contact time, 10 min; and temperature, 25 °C). The results are shown in Figure 10. At this time, the extraction rate was calculated according to Equation 2 below.

[Equation 2]

In the above formula, V _org and V _aq are the volumes of the organic phase and the aqueous phase, respectively.

Referring to the figure, Pt and Pd extraction tended to increase as the pH of the leach liquor decreased from 11.2 (96.4% Pt and 92.7% Pd) to 10.4 (98.2% Pt and 97.6% Pd). In this way, it is believed that the reason for the low extraction rate at high pH is because hydroxide ions are extracted competitively. To prevent the toxicity of HCN formed at low pH (HCN: CN ^- = 1:1 (pKa 9.3)), extraction was optimized at pH 10.4 and used in subsequent experiments.

Example 7

Evaluation of the effect of temperature on extraction of platinum group metals from platinum group-containing cyanide leachate

The extraction experiment was performed according to the experimental procedure according to Example 5, except that liquid-liquid extraction was performed while changing the extraction temperature in the range of 20 to 60 ° C. (O:A, 1; P-IL concentration, 0.15 mol/L; solution pH, 10.4; and contact time, 10 min). The results are shown in Figure 11.

Referring to Figure 11a, the extraction rate decreased as the temperature increased (Pt: from 98% to <87%; Pd: from 97% to 86%). These results indicate that an exothermic reaction was involved and that the metal-binding ability of the ionic liquid decreased with increasing temperature.

Referring to Figure 11b, a straight line with a regression coefficient exceeding 0.99 was derived. Using the slope value of the straight line, the apparent enthalpy change (ΔH°) for Pt and Pd extraction is ΔH°(Pt), -39.8 kJ. /mol and ΔH°(Pd), was measured to be -34.9 kJ/mol. From the above-mentioned results, the exothermic characteristics of the metal-ion complex can be confirmed.

Example 8

Pt stripping from Pt-Pd loaded ionic liquid

The Pt-Pd loaded ionic liquid was contacted with various concentrations of NH ₄ SCN aqueous solution (0.25 to 2.0 mol/L) (O:A, 1; contact time, 10 min; and temperature, 25° C.). The results are shown in Figure 12. At this time, the stripping rate was calculated according to Equation 3 below.

[Equation 3]

In the above equation, CS _org and CS _aq are the metal concentrations after stripping in the organic phase and aqueous phase, respectively.

In the figure, the NH ₄ SCN solution showed the selective recovery ability of Pd over Pt. Specifically, as the NH ₄ SCN concentration increased from 0.25 mol/L to 1.0 mol/L, the Pd-stripping rate increased significantly from 68% to >94%. Afterwards, stripping hardly progressed, showing a stripping rate of over 98% in a 2.0 mol/L NH ₄ SCN solution, and at this time, Pt was less than 3%.

In this regard, the selectivity achieved in thiocyanate stripping comes from the fact that the Pd-compound has a larger charge density due to the larger size of Pt(CN) ₄ ^2- than that of Pd(CN) ₄ ^2- . It is believed to be caused by The reaction involved in Pd-stripping using NH ₄ SCN solution can be expressed in Scheme 8 below.

[Scheme 8]

Example 8

Pt stripping from Pd-depleted ionic liquids

The Pd-depleted ionic liquid was contacted with various concentrations of S(CH ₂ CH ₂ OH) ₂ aqueous solution (0.25 to 2.0 mol/L) (O:A, 1; contact time, 10 min; and temperature, 25 °C. ). The results are shown in Figure 13.

According to the figure, the Pt stripping rate reached about 90% in a 1.0 mol/L S(CH ₂ CH ₂ OH) ₂ solution and about 96% in a 1.5 mol/L S(CH ₂ CH ₂ OH) ₂ solution. % has been reached. However, even if the S(CH ₂ CH ₂ OH) ₂ concentration was further increased, no significant increase in the stripping rate was observed. In this regard, the coordination substitution reaction of Pt-stripping using S(CH ₂ CH ₂ OH) ₂ can be represented by Scheme 9 below.

[Scheme 9]

Example 9

Evaluation of recyclability of cyanide-containing raffinate and reusability of organophosphorus ionic liquid

The recyclability of cyanide remaining in the raffinate formed after extraction of platinum group metals (Pt and Pd) in bio leachate was evaluated using an organophosphorus ionic liquid (trihexyl(tetradecyl)phosphonium chloride) as an extractant.

Specifically, as shown in ^Figure 2, raffinate containing ^3.8 Cyanide was concentrated (accumulated). Using this concentrated biocyanide, five consecutive leaching experiments were performed under optimized leaching conditions (temperature, 150 °C; pO ₂ , 14 bar; CN ^- concentration, 2.9 g/L). The results are shown in Figure 14a.

Referring to the figure, the leaching rates of Pt and Pd were both about 95%, confirming the recyclability of the residual cyanide solution.

Meanwhile, the reusability of the organic ionic liquid used in the extraction process was evaluated by contacting it with 6.0 mol/L HCl solution for 30 minutes to separate the ionic liquid and the acidic solution, and then regenerating the organic phase. did. At this time, the extraction, stripping, and regeneration cycles were repeatedly performed to separate the two types of platinum group metals. The results are shown in Figure 14b.

Referring to the figure, the extraction rates of Pt and Pd were both >97% from the results of a total of 5 consecutive cycles. This means that the ionic liquid is stable and also exhibits good regeneration and reusability, supporting that the process proposed in Figure 2 is sustainable.

Example 10

Evaluation of biodegradability of recycled cyanide-containing raffinate

After performing five sequential leaching-extraction-stripping cycles, 25% of the volume of the cyanide-containing raffinate was bleed out to evaluate the biodegradability of residual cyanide. The results are shown in Figure 15.

Referring to the figure, significant decomposition of residual cyanide began as soon as 8 hours after contact with drained C. violaceum , and exceeded 90% after 28 hours. Maximal detoxification (>99%) of CN ^- ions was achieved after 60 hours. The final concentration of CN ^- ions was 5.64 × 10 ^-11 μmol/L (the initial concentration in the bleed solution was 3.76 × 10 ^-8 μmol/L).

In this way, it can be seen that residual cyanide can be decomposed by microorganisms (enzymes) that can be used to produce biocyanide, and that it can be discharged with reduced toxicity after the decomposition process.

Simple modifications or changes of the present invention can be easily used by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (19)

1. a) forming a platinum group-containing cyanide leachate by leaching platinum group metals from a platinum group-containing spent catalyst using a solution containing biocyanide produced by the metabolic action of cyanide-producing microorganisms;

   b) subjecting the platinum group-containing cyanide leachate to a liquid-liquid extraction treatment using a water-insoluble organophosphorus ionic liquid as an extractant to form a platinum group-rich extract and a platinum group-depleted raffinate; and

   c) recovering platinum group metal from the extract;

   A method for recovering platinum group metals from a spent catalyst comprising a.
2. The method of claim 1, wherein the platinum group-containing spent catalyst contains at least one platinum group metal selected from the group consisting of platinum and palladium.
3. 3. The method of claim 2, wherein the platinum group-containing spent catalyst does not contain rhodium.
4. The method according to claim 1, wherein the platinum group-containing spent catalyst is provided to step a) in the form of particles or pulverized particles having a particle size range of 350 μm or less.
5. The method according to claim 1, wherein the total platinum group metal content in the platinum group-containing spent catalyst is in the range of 0.005 to 0.4% by weight.
6. The method according to claim 5, wherein the platinum group-containing spent catalyst contains platinum and palladium, and the contents of platinum and palladium are in the range of 0.003 to 0.15% by weight and 0.002 to 0.1% by weight, respectively.
7. The method of claim 1, further comprising the step of pretreating the platinum group-containing spent catalyst with an alkali-containing solution selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonium hydroxide prior to step a). How to do it.
8. The method of claim 1, wherein the cyanide-producing microorganism is selected from at least one species belonging to Betaproteobacteria and Gammaproteobacteria.
9. The method of claim 1, wherein the pH of the aqueous solution containing biocyanide in step a) is in the range of 9.5 to 14, and the concentration of cyanide (CN ^- ) is in the range of 2 to 6 g/L. method.
10. The method according to claim 1, further comprising trapping or collecting the solution containing biocyanide into an alkaline solution to concentrate or accumulate it before leaching the platinum group metal in step a).
11. The method according to claim 1, wherein the leaching is carried out at a temperature of 100 to 200° C. and an oxygen pressure of at least 8 bar.
12. The method according to claim 1, wherein the pH of the platinum group-containing cyanide leachate formed in step a) is in the range of 9 to 12.5.
13. The method of claim 1, wherein the water-insoluble organophosphorus ionic liquid used in step b) comprises a phosphonium-based cationic group represented by the following general formula 1, and an anionic group selected from the group consisting of halide, sulfide, and nitrate. Method characterized by:

    [General Formula 1]

    

    In the above formula, R ¹ to R ⁴ are each an alkyl group having 35 to 56 carbon atoms.
14. The method of claim 13, wherein the molecular weight (M _w ) of the organophosphorous ionic liquid used in step b) is in the range of 200 to 900.
15. The method according to claim 2, wherein step c) is performed by stripping.
16. 15. The method of claim 14, wherein to recover palladium from the extract, a stripping agent selected from at least one thiocyanate compound is used, and

    A method characterized by using at least one stripping agent selected from thioalcohols to recover platinum from the extract.
17. 11. The method of claim 10, further comprising the step of recycling the platinum group-depleted raffinate to the biocyanide-containing solution of step a) and/or to the concentrated or accumulated biocyanide-containing solution. How to.
18. The method of claim 1, further comprising decomposing cyanide in the platinum group-depleted raffinate by the cyanide-producing microorganism.
19. The method of claim 1, further comprising the step of separating the organophosphorus ionic liquid from the extract remaining after recovery of the platinum group metal in step c) and reusing it as an extractant in step b).

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