EP3788177A1 - Method for dissolving precious metals - Google Patents
Method for dissolving precious metalsInfo
- Publication number
- EP3788177A1 EP3788177A1 EP19721599.9A EP19721599A EP3788177A1 EP 3788177 A1 EP3788177 A1 EP 3788177A1 EP 19721599 A EP19721599 A EP 19721599A EP 3788177 A1 EP3788177 A1 EP 3788177A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- potential
- pms
- dissolution
- dissolving
- sss
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B11/00—Obtaining noble metals
- C22B11/04—Obtaining noble metals by wet processes
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B11/00—Obtaining noble metals
- C22B11/04—Obtaining noble metals by wet processes
- C22B11/042—Recovery of noble metals from waste materials
- C22B11/048—Recovery of noble metals from waste materials from spent catalysts
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
- C25C1/20—Electrolytic production, recovery or refining of metals by electrolysis of solutions of noble metals
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Definitions
- the present invention relates to a method for dissolving metals, such as precious metals (PMs).
- metals such as precious metals (PMs).
- PMs such as the platinum group metals (PGMs) are in general used as catalysts for fossil fuel powered vehicle or system exhaust gas purification, organic chemical reactions, as well as fuel cell and electrolyzer electrodes. PMs are also constituents of electronic components and microcircuits. Therefore, the recovery of PMs from used materials is of crucial importance, in particular, due to their rarity and costs.
- PGMs platinum group metals
- the recovery of PMs from spent catalyst and other materials is currently mainly based on physical separation using melting temperature and density difference, and/or chemical dissolution processes in an acidic bath.
- dissolution processes generally occurs in strong acid or in strong oxidizing acid mixture such as aqua regia and / or toxic complexing agent such as cyanide.
- the metals are then separated from the solution by addition of a reducing agent or cation resulting a salt of low solubility.
- Cyanides such as sodium cyanide, are effective for PMs dissolution, but need careful handling and adequate liquid waste treatment due to their high toxicity.
- Electrochemical dissolution may solve some of the disadvantage of the chemical dissolution. Electrochemical dissolution of PMs, such as through potential cycling, leads to the formation of oxides on the outer surface, followed by dissolution, is an effective method to dissolve PMs. However, redeposition of dissolved PM soluble species during potential cycling and hence growth of larger particles, due to Ostwald ripening on the surface, may reduce the efficiency of the
- an improved method for dissolving PMs would be advantageous, and in particular, a more efficient and/or reliable method or dissolving PMs would be advantageous.
- An object of the present invention may also be seen as to provide an alternative to the prior art.
- the invention relates to a method of producing a solution comprising metal ions, the method comprising, subjecting a source of metals, such as metals from catalytic structures, to potential cycling in an electrochemical cell, thereby producing a solution containing a desired concentration of metal ions.
- the method could be applied to the dissolution of several metals, such as transition metal elements, e.g. PMs or PGMs.
- PMs are precious metallic elements comprising Platinum (Pt), Palladium (Pd), Ruthenium (Ru), Iridium (Ir), Rhodium (Rh), Osmium (Os), Gold (Au) and Silver (Ag).
- the invention relates to a method of dissolving PMs by subjecting a source of PMs, such as PMs from catalytic structures, to potential cycling in an electrochemical cell.
- the electrochemical cell comprises a first working electrode (WEI), and a counter electrode (CE) and an electrolyte.
- WEI working electrode
- CE counter electrode
- the source of PMs may be the WEI.
- the WEI Upon operation, the WEI will thus dissolve leaving the desired metal ions within the electrolyte solution.
- the electrochemical cell used may have a simple two electrodes configuration comprising the WEI as anode and the CE as cathode.
- the electrochemical cell further comprise a reference electrode (RE), so as to ensure correct application of the desired potential values.
- RE reference electrode
- the RE employed may be the reversible hydrogen electrode (RHE).
- RHE reversible hydrogen electrode
- SCE saturated calomel electrode
- Ag/AgCI Silver chloride electrode
- the PMs are or comprise nanoparticles.
- the method and the electrochemical cell of the invention have, in particular, the advantage of improving dissolution of PMs that are in nano size, e.g. are in the form of nanoparticles, having a diameter of few nanometers, such as of diameter 2-3 nm.
- the method and the electrochemical cell of the invention may be also applied to WEI comprising PMs in a bulk form.
- the step of subjecting the source of PMs to potential cycling comprises sweeping a potential between two predefined voltage values applied between the WEI and the CE.
- the potential applied between the WEI and the CE is swept in time, i.e. changed, such as ramped vs time, cyclically, i.e. after reaching the second predefined voltage value, the potential of the WEI is ramped in the opposite direction so to return to the initial first predefined voltage value.
- a first value of the two predefined voltage values is a PM deposition potential at which the PM soluble species deposit as PM atom, such as in a range between 0.2 V and 0.6 V, such as 0.4 V.
- a second value of the two predefined voltage values is a PM dissolution potential at which the PM dissolves as PM soluble species, such as in a range between 1.0 V and 1.8 V, such as 1.6 V.
- the electrolyte comprises a dilute acid, such as 1 M or 0.1 M, or lower concentration of HCI or HNO3 or H2SO4 or HCIO4 or a mixture thereof.
- a dilute acid such as 1 M or 0.1 M, or lower concentration of HCI or HNO3 or H2SO4 or HCIO4 or a mixture thereof.
- the use of strong and corrosive acid is not suitable for the invention.
- the electrolyte may be a suitable liquid electrolyte in which the electrochemical cell can be operated in between the desired potential range and contains ions, molecules or compounds having the ability of forming complexes with the dissolved PM ions.
- the electrolyte may comprise inorganic ions, such as cyanide, halogen, ammonium or organic molecules or mixture thereof.
- the organic molecules may be molecules or compounds comprising organic groups.
- the inorganic ions used may be generated preferably from salts, for example, ammonium halide salts, such as NH4CI,.
- the invention relates to a method of dissolving a source of PMs, the method comprising : providing an electrolytic cell comprising an anode, a cathode and an electrolyte comprising ammonium ions and a complexing agent, wherein the anode is the source of PMs; imposing an opportune potential cycling between said anode and said cathode to dissolve the source of PMs.
- the invention addresses the issue of the recovery of PMs through the use of strong acids as being highly corrosive and thus not environmental friendly.
- the invention thus offers as a solution the use of electrochemical dissolution through potential cycling in diluted acid bath or ammonium salt solution that forms stable ammonium chloride complexes during the potential cycling.
- the invention provides a process of dissolution PMs from, e.g. spent catalysts, through electrochemical dissolution at pH>4.5.
- the presence of a complexing agent in the electrolyte improve the dissolution of the PM by forming a stable PM/complex solution.
- the advantage of ammonium chloride over any other halide salt is that both Pt-chloride (PtCU/PtCl 6 ) and Ammonium chloro platinum complexes ((NH 4 )x.PtCl y ) can be formed in presence of Ammonium halide salts.
- the electrolyte comprises one or several surface switch species (SSS).
- SSS surface switch species
- a SSS is defined as a species that can be transformed between a soluble and aprecipitaion, such as insoluble solid form, in the correspondent suitable electrolyte by controlling the potential applied.
- the SSS is a species having the function of blocking the surface of the PMs when the potential applied may cause redeposition of the PMs.
- the SSS is a species having the function of rendering the surface of the PMs available for dissolution, when the opportune dissolution potential of the PMs is applied.
- the SSS is able to switch the nature and composition of the PM surface being exposed to the electrolyte depending on the potential applied.
- the SSS is a species having the property of being dissolvable before the PM in the electrolyte solution while the potential applied is the one correspondent to the dissolution potential of the PM.
- the SSS is also a species having the property of being able to deposit, i.e. precipitate, before the PM while the potential applied is the deposition potential of the PM soluble species, such as ion or complexes, thus blocking the surface for redeposition of the PM soluble species.
- the one or several SSS have a dissolution potential lower than the PM dissolution potential and a deposition potential higher than the PM deposition potential.
- the dissolution potential of the one or several SSS is the potential at which the SSS transforms into a soluble form.
- the deposition potential of the one or several SSS is the potential at which the SSS transform into a precipitate, i.e. insoluble solid form.
- the specific properties of the SSS ensure that the one or several SSS are the first species to dissolve during potential increase, i.e. during anodic sweep, and the first species to deposit during potential decrease i.e. during cathodic sweep.
- the SSS when the SSS is precipitated on the surface of the source of PM, it will dissolve first when the potential is raised, i.e. during the anodic sweep.
- the SSS are compatible with the PMs in a way that the SSS form, when the SSS deposition potential is applied, a precipitate, i.e. a layer, such as a thin atomic layer, precipitated onto the top surface of the PMs.
- the SSS in its insoluble form, is not compatible with the PM soluble species, or the potential of the PM soluble species for depositing onto the SSS in its insoluble form is lower than the deposition potential of the PM soluble species onto PM itself, therefore the PM soluble species cannot deposit onto the precipitated SSS at the deposition potential of the SSS.
- Conversion between the two forms of the SSS i.e. in solution and precipitated form, may be caused by different means.
- conversion between the two forms, in solution or precipitated in its solid form occurs by applying a suitable potential value.
- precipitation of SSS can be controlled by light irradiation, such as UV/Vis/IR light irradiation or by temperature changes, acoustic waves or variation of the magnetic field.
- the SSS may be an additive, such as an inorganic ion or an organic molecule, i.e. molecules comprising organic groups.
- the one or several SSS are or comprise metal ions, such as transition metal ions, such as group 10, 11 or 12 metal ions.
- the transition metal ions are Cu or Ag ions.
- Cu salts such as Cu(NC>3)2, CuCb, CuCI or CuS0 4 , i.e. providing Cu + and Cu 2+ ions, may be dissolved into the electrolyte solution so as to obtain Cu ions in solution.
- the invention in this aspect, thus relates to a process of improving dissolution of PMs, such as Pt or Au, based on the electrochemical dissolution of the PMs by potential cycling in electrolyte using acid or ammonium salt and in presence of other SSS, such as metal ions, inhibiting the redeposition of the PM during cathodic sweep.
- the SSS in solutions form a thin layer, such as a monolayer, onto the PMs, during the cathodic sweep and thus inhibiting the redeposition of the PMs.
- Complexing agents may also be present so as to further increase the dissolution rate by stabilizing the PM soluble species in solution.
- the invention in this aspect, has the advantage of proving a faster dissolution, such as three time faster, and can be used efficiently at low acid concentrations.
- the SSS may be present in very low concentration, such as in trace, i.e. in amount of few ppm.
- the SSS may be easily recovered from the electrolyte solution and may be reused.
- the invention in a second aspect, relates to a method of dissolving PMs, such as PMs from catalytic structures, comprising : dissolving the PMs by subjecting a source of PMs to potential cycling in an electrochemical cell in an electrolyte, the dissolving according to the first aspect of the invention; depositing the dissolved PMs.
- the electrochemical cell further comprises a second working (WE2) and the depositing occurs on the WE2 located within the electrochemical cell.
- WE2 second working
- the method further comprises, alternating between the dissolving and the depositing by switching, such as changing, between applying a predefined potential between the WEI and the CE and applying a predefined potential between the WE2 and the CE.
- Alternating between dissolving and depositing occur by swopping the predefined or appropriate potential when the potential reaches a value below the deposition potential of the PM soluble species.
- the swopping occurs from dissolving, occurring at the WEI, to depositing, occurring at WE2, when a potential applied reaches a value below the PM deposition potential, i.e. the potential at which the PM soluble species deposit as PM, such as when the potential applied reaches a value below 0.4 V.
- the WE2 may be a Pt electrode.
- the swopping occurs from depositing, occurring at the WE2, to dissolving, occurring at the WEI, when a potential applied reaches a value above said PM deposition potential, at which the PM soluble species deposit as PM, such as 0.4 V.
- the invention relates to the recovery of PMs, such as Pt, from different structures, through a two-step electrochemical process.
- the first step comprises an electrochemical dissolution of the PM contained in a structure, such as a spent catalytic structure, used as a first working electrode in a three-electrode electrochemical cell, through potential cycling between given potential values.
- a structure such as a spent catalytic structure, used as a first working electrode in a three-electrode electrochemical cell
- the second step relates to an electrochemical deposition of the PMs on a second working electrode by reduction at a suitable potential value.
- Dissolution and deposition occur within the same container and are obtained by alternating the use of the first and the second working electrode respectively.
- the invention has particularly shown an increase in dissolution in electrolytic solution of ammonium chloride, nitric acid and ammonium nitrate.
- the invention in a third aspect, relates to a method of recovering PMs, such as PMs from catalytic structures, comprising : dissolving the PMs according to the first aspect of the invention; depositing, such as depositing on a substrate, the PMs by chemical or electrochemical means.
- Figure 1 is a schematic representation of the mechanism behind the use of SSS according to some embodiments of the invention.
- Figure 2 is a bar chart comparing the dissolution of Pt during potential cycling in an electrolyte having Cu ion vs an electrolyte in which Cu ions are absent.
- Figure 3 is a bar chart comparing the dissolution of Pt during potential cycling in an electrolyte having Cu ion vs an electrolyte in which Cu ions are absent with similar concentration of Cl ions.
- Figure 4A and 4B are bar charts showing the influence in the dissolution of Pt using different sources of Cu ions.
- Figure 5 is a graph comparing the dissolution of Pt during potential cycling in an electrolyte having Cu ion vs an electrolyte in which Cu ions are absent vs the number of cycles.
- Figure 6 is a bar chart showing the influence of different type of SSS, such as different metal ions, on the dissolution of Pt.
- Figure 7 is a bar chart comparing the dissolution of Au during potential cycling in an electrolyte having Cu ion vs an electrolyte in which Cu ions are absent.
- FIG 8, 9 and 10 are schematic representations of different potential
- Figure 11 shows a schematic representation according to one embodiment of the invention.
- Figure 12 is a bar chart comparing the dissolution of Pt during potential cycling in an electrochemical cell according to figure 11 in which a second working electrode is used and operates as described below.
- Figure 13 is a bar chart comparing the effect of lower potential during
- Figure 14 is a flow-chart of a method according to one aspect of the invention.
- Figure 1 is a schematic representation of the mechanism behind the use of SSS in the method of dissolving PMs according to some aspect of the invention.
- the invention in one of its aspects inhibits the particle growth and enhance dissolution efficiency by using a SSS, such as Cu ions, that precipitate onto the PMs surface.
- the deposition of SSS monolayer during cathodic scans blocks the PM from redeposition of Pt soluble species.
- Figure 2 is a bar chart showing the dissolution percentage of a Pt working electrode having platinum nanoparticles (2-3 nm) supported on high surface area carbon, when potential cycling between 0.4V and 1.6 V is applied in a three electrode chemical cell configuration having a carbon rod as CE and a RHE reference electrode in HCI 0.1M, room temperature (20°C) and pressure (1 atmosphere).
- Figure 3 shows that the increase of dissolution cannot be only due to an increased concentration of Cl ions as even at similar concentration of Cl ions, the presence of Cu ions shows an increase of dissolution in the area of 20%.
- Figure 4A shows the effect of Cu on Pt dissolution efficiency (potential cycling between 0.4 and 1.6 V at a rate of 100 mV/s for 25 cycles) in presence of (CUNC>3)2 as a source of Cu 2+ . While keeping the H + concentration constant, presence of NO3 increases the dissolution efficiency slightly. Again, effect of Cu ++ towards increasing the dissolution of PM was clear even at Cu 2+ concentration of 0.01 M.
- Fig. 4B shows the effect of presence of Cu 2+ on Pt dissolution rate in non- complexing electrolytes (1 M H2SO4).
- Figure 5 shows the effect of Cu on Pt dissolution efficiency in terms of the number of potential cycles (between 0.4 and 1.6 V at a rate of 100 mV/s) required to achieve >95% dissolution.
- required number of potential cycles is reduced significantly (from 350 to 150), as compared to that in absence of Cu (10).
- Figure 6 shows the effect of different metal ions on the dissolution efficiency.
- Ni and Zn improve it slightly.
- the mechanism affecting the dissolution process in presence of metals not appropriate for the aforesaid surface switching mechanism may be active participation in complex formation, alloying with Pt, etc.
- Figure 7 shows the effect of Cu on dissolution of gold (bulk gold in form of 0.1 mm wire) through potential cycling (between 0.4 and 1.6 V at a rate of 100 mV/s in 1 M HCI). Similar to platinum, gold also shows enhanced dissolution in presence of Cu 2+ (0.1 M CuCI 2 ).
- Figure 8 is schematic representation of an electrochemical cell 3 comprising a cathode or counter electrode 6 and an anode or working electrode 11 according to some embodiments of the invention.
- Figure 9 is a schematic representation of an electrochemical cell 4 comprising a cathode or counter electrode 7 and an anode or working electrode 12 and a reference electrode 9 according to some embodiments of the invention.
- FIG 10 is a schematic representation of an electrochemical cell 5 comprising a cathode or counter electrode 8, a reference electrode 16 and two anodes or working electrodes 13 and 14 according to some aspects of the invention.
- the electrochemical cell 5 comprises a controlling means, such as a switch 15, that can change the application of potential to working electrode 13 and working electrode 14.
- Figure 11 shows a schematic of a typical experimental setup used in one aspect of the present invention.
- the working electrode is switched between WEI (for potentials higher than, for example 0.4 V) and WE2 (for potentials lower than, for example 0.4 V).
- Figure 12 shows the effect of presence of WE2 for reduction and redeposition of dissolved PM soluble species on the percentage of dissolution.
- the lower potential limit for redeposition was set to 0.1 V while the dissolution was performed by potential cycling between 0.4 and 1.6 V at a scan rate of 100 mv/s for 100 cycles in 0.5 M NH4CI electrolyte kept at normal temperature and pressure.
- Figure 13 shows the effect different lower potential limits (0.2, 0.4 and 0.6 V; with a fixed upper potential limit of 1.6 V) on dissolution of platinum through potential cycling.
- 0.1 M HCI (1) electrolyte the percentage of dissolution decreases when decreasing the lower potential from 0.4 to 0.2 V due to redeposition of dissolved Pt species on the platinum nanoparticles of the WE.
- 0.1 M HCI+0.01M CuCb (2) electrolyte the % dissolution remains almost constant when decreasing the lower potential from 0.4 to 0.2 V due to inhibition of redeposition of dissolved Pt species through formation of Cu layer on the platinum nanoparticles of the WE.
- Figure 14 is a flow-chart of a method according to one aspect of the invention.
- the method 19 of dissolving PMs comprises the steps of: (17) dissolving the PMs by subjecting a source of PMs to potential cycling in an electrochemical cell in an electrolyte according to figures 10 or 11; (18) depositing the dissolved PMs onto a substrate, such as the second WE.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Electrolytic Production Of Metals (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP18170312 | 2018-05-02 | ||
PCT/EP2019/061137 WO2019211318A1 (en) | 2018-05-02 | 2019-05-01 | Method for dissolving precious metals |
Publications (1)
Publication Number | Publication Date |
---|---|
EP3788177A1 true EP3788177A1 (en) | 2021-03-10 |
Family
ID=62104170
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19721599.9A Withdrawn EP3788177A1 (en) | 2018-05-02 | 2019-05-01 | Method for dissolving precious metals |
Country Status (2)
Country | Link |
---|---|
EP (1) | EP3788177A1 (en) |
WO (1) | WO2019211318A1 (en) |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2014185366A (en) * | 2013-03-22 | 2014-10-02 | Nagaoka Univ Of Technology | Method and apparatus for platinum recovery |
-
2019
- 2019-05-01 WO PCT/EP2019/061137 patent/WO2019211318A1/en unknown
- 2019-05-01 EP EP19721599.9A patent/EP3788177A1/en not_active Withdrawn
Also Published As
Publication number | Publication date |
---|---|
WO2019211318A1 (en) | 2019-11-07 |
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