WO2023175570A1 - System and method for controlling or removing hard deposits on electrowinning cathodes - Google Patents
System and method for controlling or removing hard deposits on electrowinning cathodes Download PDFInfo
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- WO2023175570A1 WO2023175570A1 PCT/IB2023/052604 IB2023052604W WO2023175570A1 WO 2023175570 A1 WO2023175570 A1 WO 2023175570A1 IB 2023052604 W IB2023052604 W IB 2023052604W WO 2023175570 A1 WO2023175570 A1 WO 2023175570A1
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- Prior art keywords
- electrowinning
- cathode
- cell
- precious metal
- anode
- Prior art date
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- 238000005363 electrowinning Methods 0.000 title claims abstract description 472
- 238000000034 method Methods 0.000 title claims abstract description 129
- 239000010970 precious metal Substances 0.000 claims abstract description 143
- 230000008569 process Effects 0.000 claims abstract description 40
- XFXPMWWXUTWYJX-UHFFFAOYSA-N Cyanide Chemical compound N#[C-] XFXPMWWXUTWYJX-UHFFFAOYSA-N 0.000 claims description 84
- 230000002441 reversible effect Effects 0.000 claims description 57
- KXZJHVJKXJLBKO-UHFFFAOYSA-N chembl1408157 Chemical compound N=1C2=CC=CC=C2C(C(=O)O)=CC=1C1=CC=C(O)C=C1 KXZJHVJKXJLBKO-UHFFFAOYSA-N 0.000 claims description 54
- 239000000654 additive Substances 0.000 claims description 50
- 230000000996 additive effect Effects 0.000 claims description 46
- 238000003860 storage Methods 0.000 claims description 38
- 230000001965 increasing effect Effects 0.000 claims description 30
- 230000015572 biosynthetic process Effects 0.000 claims description 27
- LFAGQMCIGQNPJG-UHFFFAOYSA-N silver cyanide Chemical compound [Ag+].N#[C-] LFAGQMCIGQNPJG-UHFFFAOYSA-N 0.000 claims description 25
- 229940098221 silver cyanide Drugs 0.000 claims description 25
- 239000003153 chemical reaction reagent Substances 0.000 claims description 24
- 229910052751 metal Inorganic materials 0.000 claims description 18
- 239000002184 metal Substances 0.000 claims description 18
- 239000003795 chemical substances by application Substances 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 16
- 239000003607 modifier Substances 0.000 claims description 15
- 239000004034 viscosity adjusting agent Substances 0.000 claims description 15
- 238000000151 deposition Methods 0.000 claims description 14
- 229910021645 metal ion Inorganic materials 0.000 claims description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 14
- 239000000080 wetting agent Substances 0.000 claims description 13
- 150000002739 metals Chemical class 0.000 claims description 12
- 150000002894 organic compounds Chemical class 0.000 claims description 12
- NNFCIKHAZHQZJG-UHFFFAOYSA-N potassium cyanide Chemical compound [K+].N#[C-] NNFCIKHAZHQZJG-UHFFFAOYSA-N 0.000 claims description 12
- 238000005406 washing Methods 0.000 claims description 12
- 239000007800 oxidant agent Substances 0.000 claims description 11
- 238000005507 spraying Methods 0.000 claims description 11
- 238000007790 scraping Methods 0.000 claims description 7
- 238000007664 blowing Methods 0.000 claims description 6
- 239000012530 fluid Substances 0.000 claims description 5
- 238000011010 flushing procedure Methods 0.000 claims description 5
- DOBRDRYODQBAMW-UHFFFAOYSA-N copper(i) cyanide Chemical compound [Cu+].N#[C-] DOBRDRYODQBAMW-UHFFFAOYSA-N 0.000 claims description 4
- 230000003247 decreasing effect Effects 0.000 claims description 3
- 230000008021 deposition Effects 0.000 claims description 2
- 238000003723 Smelting Methods 0.000 abstract description 5
- 230000008901 benefit Effects 0.000 abstract description 4
- 230000006378 damage Effects 0.000 abstract description 2
- 239000000243 solution Substances 0.000 description 106
- 238000004140 cleaning Methods 0.000 description 34
- 238000005755 formation reaction Methods 0.000 description 19
- MNWBNISUBARLIT-UHFFFAOYSA-N sodium cyanide Chemical compound [Na+].N#[C-] MNWBNISUBARLIT-UHFFFAOYSA-N 0.000 description 18
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 17
- 229910052709 silver Inorganic materials 0.000 description 17
- 239000004332 silver Substances 0.000 description 17
- 239000010931 gold Substances 0.000 description 15
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 13
- 229910052737 gold Inorganic materials 0.000 description 13
- 239000012527 feed solution Substances 0.000 description 10
- 238000007747 plating Methods 0.000 description 10
- LELOWRISYMNNSU-UHFFFAOYSA-N hydrogen cyanide Chemical compound N#C LELOWRISYMNNSU-UHFFFAOYSA-N 0.000 description 8
- 230000003466 anti-cipated effect Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 241000894007 species Species 0.000 description 7
- LEKPFOXEZRZPGW-UHFFFAOYSA-N copper;dicyanide Chemical compound [Cu+2].N#[C-].N#[C-] LEKPFOXEZRZPGW-UHFFFAOYSA-N 0.000 description 5
- 238000011065 in-situ storage Methods 0.000 description 5
- 238000011084 recovery Methods 0.000 description 5
- 238000011144 upstream manufacturing Methods 0.000 description 5
- -1 1 -4 wt.%) Chemical compound 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000005868 electrolysis reaction Methods 0.000 description 3
- 239000003517 fume Substances 0.000 description 3
- 239000010802 sludge Substances 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 125000004122 cyclic group Chemical group 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000011066 ex-situ storage Methods 0.000 description 2
- 230000002045 lasting effect Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000001473 noxious effect Effects 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 238000011536 re-plating Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 241001062472 Stokellia anisodon Species 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 238000010923 batch production Methods 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- RLJMLMKIBZAXJO-UHFFFAOYSA-N lead nitrate Chemical compound [O-][N+](=O)O[Pb]O[N+]([O-])=O RLJMLMKIBZAXJO-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 230000000153 supplemental effect Effects 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000004506 ultrasonic cleaning Methods 0.000 description 1
Classifications
-
- 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
- C25C1/12—Electrolytic production, recovery or refining of metals by electrolysis of solutions of copper
-
- 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
-
- 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
- C25C7/06—Operating or servicing
Definitions
- Embodiments of the present invention pertain to improvements to electrowinning apparatus and methods of electrowinning which are particularly useful for precious metals recovery, such as for gold and silver recovery processes.
- embodiments of the invention provide an electrowinning apparatus and method which overcomes or ameliorates one or more of the disadvantages or problems described above - or, which at least provides a useful alternative to conventional electrowinning apparatus and methods.
- a novel electrowinning apparatus and method is disclosed.
- a method of electrowinn ing a precious metal may comprise the step of providing an electrowinning solution containing dissolved metal ions of the precious metal therein, to an electrowinning cell having at least one cathode and at least one anode.
- the method may further comprise the step of depositing the precious metal onto the cathode by virtue of passing electrical current from the anode to the cathode.
- the method may further comprise the step of softening the deposited precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode.
- This may be accomplished, for instance, by virtue of at least temporarily, increasing a current density of the electrowinning cell and/or maintaining current density of the electrowinning cell above 5 A/m 2 or 10 A/m 2 of the total cathode area, for example to within a range of 40 to 500 A/m 2 of the total cathode area (e.g., 40 to 200 A/m 2 ); at least temporarily, increasing a free cyanide concentration of (pure) cyanide to ⁇ 0.5 wt.% to 4.5 wt.% (e.g., using sodium cyanide or equivalent) within the electrowinning solution and/or maintaining a concentration of sodium cyanide within the electrowinning solution to within a range of 1 -8 wt.% (for example, between 1 and 6 wt.%, or between 1 and 4 wt.%
- the method may comprise the step of providing a heat exchanger to increase or decrease a temperature of the electrowinning solution.
- the method may comprise the step of controlling the temperature of the electrowinning solution (e.g., using a solution heater or heat exchanger) such that it remains between approximately 60 and 212 degrees Fahrenheit, without limitation.
- the electrowinning solution should at all times comprise aqueous cyanide (CN _ ) having a pH above approximately 9.5 to avoid generation of gaseous hydrogen cyanide (HCN) below the equilibrium range of 9.3-9.5.
- a repeated cyclic changing of polarity may be employed to remove a hard deposit.
- a plurality of reverse polarity sequences may be employed.
- successive amounts of hard deposits may be able to be removed with each “run” by virtue of a change in polarity.
- a “run” may be a cycle of reverse polarity (i.e., “reverse polarity sequence”) wherein most of the hard deposit may be electroplated from one or more electrodes onto one or more target cathodes and/or vice versa.
- the method may comprise the steps of altering a composition of the electrowinning solution in a separate mixing or storage tank.
- the method may include the step of delivering at least some of the electrowinning solution from the mixing or storage tank to the electrowinning cell.
- the method may include the step of softening the deposited precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode.
- Embodiments of the method disclosed herein may comprise the steps of depositing the precious metal on a cathode in an electrowinning cell; subsequently removing the cathode from the electrowinning cell and placing it within a cathode wash cell; and removing the deposited precious metal from the cathode using the cathode wash cell by virtue of performing at least one of the following steps: maintaining a current density of the cathode wash cell which is above a current density used for the electrowinning cell and/or within a range of 40 to 500 A/m 2 (e.g., 40 to 200 A/m 2 ) of the total cathode area; maintaining a concentration of cyanide (e.g., sodium cyanide or equivalent) within the cathode wash cell which is higher than a concentration of cyanide used in the electrowinning cell and/or within a range of 1 -8% sodium cyanide (e.g., 1 -4%); introducing an additive or reagent to the cathode wash cell; the additive comprising
- Embodiments of an electrowinning circuit for recovering a precious metal from an electrowinning solution containing dissolved metal ions of the precious metal therein is also disclosed.
- the electrowinning circuit may comprise an electrowinning cell having at least one cathode and at least one anode; and an electrical current passing from the anode to the cathode.
- the electrowinning circuit may further comprise means for softening the precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode during electrowinning.
- Such means may comprise a rectifier configured to at least temporarily increase current density and/or configured for maintaining current density of the electrowinning cell within a range of 40 to 500 A/m 2 (e.g., 40 to 200 A/m 2 ) of the total cathode area; a pump and/or adjustable control valve configured for at least temporarily increasing a concentration of cyanide (e.g., sodium cyanide or equivalent) within the electrowinning solution and/or configured for maintaining a concentration of cyanide within the electrowinning solution to within a range of 1 -8 wt.% sodium cyanide (e.g., 1 -4 wt.%); a pump and/or adjustable control valve configured for at least temporarily adding silver cyanide to the electrowinning solution; a rectifier configured to reverse polarity of the anode and cathode for performing a reverse polarity sequence and at least temporarily changing the charge of the cathode in the electrowinning cell; and/or an energizable ultrasonic transducer provided to the electrowinning cell configured for
- the electrowinning circuit may comprise a pump and/or adjustable control valve configured for introducing an additive or reagent to solution to the mixing or storage tank;
- the additive or reagent may comprise a hard electrowinning deposit remover selected from one or more of the group consisting of: one or more soft metals, one or more wetting agents, one or more surface modifiers, one or more viscosity modifiers, one or more releasing agents, one or more oxidants, one or more organic compounds.
- the electrowinning circuit may comprise a mixing or storage tank configured for receiving the electrowinning solution from the electrowinning cell and being further configured to aid in the softening the precious metal upon its deposition onto the cathode or at least discourage the formation of hard deposits of the precious metal onto the cathode.
- the electrowinning circuit may comprise a rectifier configured to at least temporarily increase current density and/or configured for maintaining current density of the electrowinning cell to within a range of 40 to 500 A/m 2 of the total cathode area, for example, to within a range of 40 to 200 A/m 2 , without limitation.
- the electrowinning circuit may comprise a pump and/or adjustable control valve configured for: at least temporarily increasing a concentration of cyanide (e.g., sodium cyanide or equivalent) within the mixing or storage tank, maintaining a concentration of cyanide within the mixing or storage tank to within a range of 1 -8 wt.% sodium cyanide (e.g., 1 -4 wt.%), and/or maintaining a concentration of cyanide within the mixing or storage tank to be higher than a concentration of cyanide used in the electrowinning cell.
- cyanide e.g., sodium cyanide or equivalent
- the electrowinning circuit may comprise a pump and/or adjustable control valve configured for introducing an additive or reagent to solution to the mixing or storage tank; the additive or reagent comprising a hard electrowinning deposit remover selected from one or more of the group consisting of: one or more soft metals, one or more wetting agents, one or more surface modifiers, one or more viscosity modifiers, one or more releasing agents, one or more oxidants, one or more organic compounds.
- a hard electrowinning deposit remover selected from one or more of the group consisting of: one or more soft metals, one or more wetting agents, one or more surface modifiers, one or more viscosity modifiers, one or more releasing agents, one or more oxidants, one or more organic compounds.
- the electrowinning circuit may comprise a pump and/or adjustable control valve configured for introducing process water to the mixing or storage tank.
- the electrowinning circuit may comprise a pump and/or adjustable control valve configured for at least temporarily adding silver cyanide to the electrowinning solution.
- the electrowinning circuit may comprise a rectifier configured to reverse polarity of the anode and cathode for performing a reverse polarity sequence and/or configured for at least temporarily changing the charge of the cathode in the electrowinning cell.
- the electrowinning circuit may comprise an energizable ultrasonic transducer provided to the electrowinning cell configured for mechanically removing the precious metal from the cathode using sound waves.
- the electrowinning circuit may comprise means for delivering the electrowinning solution from the mixing or storage tank to the electrowinning cell.
- the electrowinning circuit may further comprise a cathode wash cell and means for removing the cathode from the electrowinning cell and placing it within the cathode wash cell.
- the cathode wash cell may be configured for removing deposited precious metals from the cathode.
- the cathode wash cell may comprise a rectifier configured for maintaining a current density of the cathode wash cell above a current density used for the electrowinning cell and/or configured for maintaining current density of the cathode wash cell to within a range of 40 to 500 A/m 2 of the total cathode area (e.g., to within a range of 40 to 200 A/m 2 ).
- the cathode wash cell may comprise a pump and/or adjustable control valve configured for maintaining a higher concentration of cyanide (e.g., sodium cyanide or equivalent) within the cathode wash cell than a concentration of cyanide used in the electrowinning cell, and/or which is configured for maintaining a concentration of cyanide within the mixing or storage tank to within a range of 1 -8 wt.% sodium cyanide (e.g. ,1 -4 wt.%).
- cyanide e.g., sodium cyanide or equivalent
- the cathode wash cell may comprise a pump and/or adjustable control valve configured for introducing an additive or reagent to solution to the cathode wash cell; the additive comprising a hard electrowinning deposit remover selected from one or more of the group consisting of: one or more soft metals, one or more wetting agents, one or more surface modifiers, one or more viscosity modifiers, one or more releasing agents, one or more oxidants, one or more organic compounds.
- the electrowinning circuit may comprise a pump and/or adjustable control valve configured for at least temporarily adding silver cyanide to the electrowinning solution.
- the cathode wash cell may comprise a rectifier configured to at least temporarily reverse polarity of the cathode in the cathode wash cell.
- the cathode wash cell may comprise an energizable ultrasonic transducer provided to the cathode wash cell configured for mechanically removing the precious metal from the cathode using sound waves.
- an electrowinning circuit may comprise a heat exchanger to increase or decrease a temperature of the electrowinning solution.
- the solution heater or heat exchanger may be configured to control the temperature of the electrowinning solution such that it remains between approximately 60 and 212 degrees Fahrenheit, without limitation.
- the electrowinning solution should at all times comprise aqueous cyanide (CN _ ) having a pH above approximately 9.5 to avoid generation of gaseous hydrogen cyanide (HCN) below the equilibrium range of 9.3-9.5.
- an electrowinning circuit may be configured to perform a repeated cyclic changing of polarity to remove a hard deposit.
- the electrowinning circuit may be configured to perform a plurality of reverse polarity sequences or a combination of reverse polarity sequences, without limitation.
- successive amounts of hard deposits may be able to be removed with each “run” by virtue of a change in polarity.
- a “run” may be a cycle of reverse polarity (i.e., “reverse polarity sequence”) wherein some to all of the hard deposit may be electroplated from one or more electrodes onto one or more target cathodes and/or vice versa followed by a removal of some to all of the deposit from the source or target electrode by a wash sequence.
- a method of electrowinning a precious metal may comprise the steps of providing an electrowinning solution containing dissolved metal ions of the precious metal therein, to an electrowinning cell having at least one cathode and at least one anode; and depositing the precious metal onto the cathode during a first electrowinning cycle for a first cycle duration by virtue of passing electrical current from the anode to the cathode, wherein the method may be characterized in that it further comprises the step of softening the precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode by virtue of performing the following steps: i.
- a fluid such as water
- a ratio of the second cycle duration to the first cycle duration may be less than 0.5.
- a ratio of the second cycle duration to the first cycle duration may be less than 0.33.
- a ratio of the second cycle duration to the first cycle duration may be less than 0.25.
- a method of electrowinning a precious metal may comprise the steps of providing an electrowinning solution containing dissolved metal ions of the precious metal therein, to an electrowinning cell having at least one cathode and at least one anode; and depositing the precious metal onto the cathode during a first electrowinning cycle for a first cycle duration by virtue of passing electrical current from the anode to the cathode; wherein the method may be characterized in that it further comprises the step of softening the precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode by virtue of performing the following steps: i.
- the first and second cycle durations may be approximately the same.
- the second cycle duration may be greater than the first cycle duration.
- the second cycle duration may be less than the first cycle duration.
- the third cycle duration may be substantially shorter than the first cycle duration and/or shorter than the second cycle duration, without limitation.
- a method of electrowinning a precious metal may comprise the steps of: providing an electrowinning solution containing dissolved metal ions of the precious metal therein, to an electrowinning cell having at least one cathode and at least one anode; and depositing the precious metal onto the cathode by virtue of passing electrical current from the anode to the cathode.
- the method may be characterized in that it further comprises the step of softening the deposited precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode by virtue of performing the following two steps: i.) at least temporarily, increasing a current density of the electrowinning cell and/or maintaining current density of the electrowinning cell to within a range of 10 to 500 A/m 2 of the total cathode area; and ii.) at least temporarily, increasing a concentration of free cyanide within the electrowinning solution between approximately 0.5 and 4.5 wt.% and/or maintaining a target concentration of sodium cyanide within the electrowinning solution to within a range of 1 -8 wt.%, without limitation.
- the electrowinning cell described herein may comprise a plurality of said anode and cathode collectively forming “electrodes”. Accordingly, in any of the embodiments proposed, the method may further comprise the step of removing portions of the precious metal from all of the electrodes by virtue of rinsing, washing, pressure-washing, spraying, water-jetting, scraping, vibrating, generating a mechanical wave using an ultrasonic transducer or sound generator, air blowing, mechanical shaking, or flexing the electrodes. This may be done ex situ or in situ in relation to the tank of the electrowinning cell. If performed in situ, electrowinning solution may be present or absent from the electrowinning cell.
- the method may be characterised in that it may comprise the step of softening the deposited precious metal deposited on the cathode or at least discouraging the formation of hard deposits of the precious metal onto the cathode by virtue of performing the following two steps: i.) at least temporarily, increasing a current density of the electrowinning cell and/or maintaining current density of the electrowinning cell to within a range of 40 to 500 A/m 2 of the total cathode area; and ii.) at least temporarily, increasing a concentration of free cyanide within the electrowinning solution between approximately 0.05 and 4.5 wt.% and/or maintaining a target concentration of sodium cyanide within the electrowinning solution to within a range of 0.1 -8%, without limitation.
- the method may further comprise the step of removing portions of the precious metal from the cathode and/or the anode by virtue of rinsing, washing, pressure-washing, spraying, water-jetting, scraping, vibrating, generating a mechanical wave using an ultrasonic transducer or sound generator, air blowing, mechanical shaking, flexing the cathode and/or anode, or any combination thereof.
- the step of removing the precious metal from the cathode and/or anode may be performed outside of the electrowinning cell and/or performed inside of the electrowinning cell, without limitation.
- the method may further comprise the step of removing the anode and/or cathode, and subjecting the removed anode and/or cathode to a warm bath of solution held between 60 and 212 degrees Fahrenheit at a pH above 9.5, the solution comprising 1 -8 wt.% sodium cyanide.
- the cyanide may be provided in the form of sodium cyanide, potassium cyanide, copper cyanide, silver cyanide, equivalents thereof, or a combination thereof, without limitation.
- the method may further comprise the step of replacing the removed anode and/or cathode to the electrowinning cell.
- the step of subjecting the removed anode and/or cathode to a warm bath of solution may be performed for a period greater than 30 minutes.
- the step of subjecting the removed anode and/or cathode to a warm bath of solution may be performed for a period less than 5 days.
- the step of replacing the removed anode and/or cathode to the electrowinning cell may be performed for a substantially longer period of time than an electrowinning cycle (e.g., first cycle duration, second cycle duration, or third cycle duration), without limitation.
- the anode and/or cathode may not necessarily need to be removed from the electrowinning cell, and the above warm bath soak for the anode and/or cathode may be accomplished by draining the electrowinning solution from the tank of the electrowinning cell, and the fresh warm solution mentioned above pumped into the tank of the electrowinning cell to effect cleaning of the anode and/or cathode.
- FIG. 1 depicts a first non-limiting embodiment of an apparatus and method according to the invention.
- the figure depicts one way of softening precious metal deposits on cathodes within an electrowinning cell and/or producing a soft precious deposit(s) on cathodes, without limitation.
- FIG. 1 depicts a process stream with feed from a pregnant solution tank or strip/elution column, wherein the barren solution is sent to a barren tank downstream of the electrowinning cell.
- FIG. 2 depicts a second non-limiting embodiment of an apparatus and method according to the invention.
- the figure depicts a second way of softening precious metal deposits on cathodes within an electrowinning cell and/or producing a soft precious deposit(s) on cathodes, without limitation.
- FIG. 2 depicts a recirculation of barren solution which was been treated with the reagents in a recycle mode.
- the recycle mode utilizes a mix/storage tank which is separate from the electrowinning cell.
- FIG. 3 depicts a third non-limiting embodiment of an apparatus and method according to the invention.
- the figure depicts a way in which cathodes with hard deposits may be cleaned hydrometallurgically, rather than using traditional pyrometallurgical (e.g., “smelting”) processes.
- This cleaning step may be accomplished in a cathode wash cell.
- the cathode wash cell comprises a vessel which is separate from the electrolysis cell of the electrowinning cell.
- FIG. 4 depicts a method according to some non-limiting embodiments, and its steps, with optional steps being identified with dashed boxes.
- the method depicted in FIG. 4 suggests one way to continuously soften and/or reduce occurrences of hard cathode deposit formation in an electrowinning cell, during an electrowinning process.
- FIG. 5 depicts an alternative method according to some non-limiting embodiments, and its steps, with optional steps being identified with dashed boxes.
- the method depicted in FIG. 5 suggests one way to soften and/or remove hard cathode deposits using a cleaning cell, in which one or more cathodes/anodes comprising hard deposits are removed from an electrowinning cell and separately cleaned in a batch process.
- Figure 6 depicts an alternative embodiment to the one depicted in FIG. 1 , using a heat exchanger.
- Figure 7 depicts an alternative embodiment to the one depicted in FIG. 2, using an optional heat exchanger and/or submersion heater.
- Figure 7 depicts an alternative embodiment to the one depicted in FIG. 3, using a an optional submersion heater.
- Embodiments of an apparatus and method for controlling hard deposits on cathodes (and/or anodes) during the electrowinning of precious metals are disclosed.
- the step of temporarily increasing the current density may be utilized during the electrowinning process to produce a softer deposit and/or to soften an existing hard deposit.
- the current density and/or a duration of change in the current density may vary as function of time, rate of plating, softness of deposits, and/or concentration of precious metals in the electrowinning feed, without limitation.
- a step of increasing a concentration of cyanide may be utilized during the electrowinning process to achieve a softer deposit and/or to soften an existing hard deposit.
- concentration of cyanide may vary as function of time, rate of plating, softness of deposits, and/or concentration of precious metals in the electrowinning feed, without limitation.
- a lixiviant additive comprising an organic compound, a surface modifier, a viscosity modifier, a wetting agent, a releasing agent, or a soft metal (e.g., lead) may be utilized during the electrowinning process, to produce a softer deposit and/or to help soften hard precious metal deposits which may have already formed on electrowinning cathodes or anodes, without limitation.
- the composition of the additive may be adjusted during the electrowinning process.
- the amount of the additive added to the electrowinning cell (or a cleaning cell) may be varied over time.
- the additive may be introduced to the electrowinning process periodically.
- the amount, duration, and/or composition of the additive introduced may vary as function of concentration of precious metal content in the electrowinning feed, without limitation.
- Mechanical cleaning means may be optionally provided to an electrowinning cell or cathode wash cell (i.e., “cleaning tank”). The mechanical cleaning means may be periodically or continuously used during the electrowinning process.
- Such means may include an ultrasonic transducer, without limitation.
- the ultrasonic transducer may be continuously or periodically energized, without limitation.
- the ultrasonic transducer may be energized differently as a function of time and/or “pulsed” to provide waves of varying amplitude or intensity, without limitation.
- Such means may include a sprayer or high-pressure sprayer or water current or water jet to wash the softened deposit from either electrode.
- an ultrasonic cleaning step may be optionally employed in order to aid soft deposit formation and/or hard deposit removal from cathodes/anodes.
- the cleaning step may be achieved by activating (e.g., energizing) the mechanical cleaning means.
- reverse polarity switching of the anodes and cathodes may be used with the method steps depicted herein. If polarity switching is employed, the step of reversing the polarity of anodes and cathodes within the electrowinning cell is preferably done intermittently and/or periodically (e.g., between normal operation electrowinning plating cycles).
- Embodiments may incorporate one or a combination of process parameters with or without the addition or use of special reagents (i.e., “additives”) in the process to effect soft cathode deposits during electrowinning.
- Process parameters may include, without limitation: the use of high current density (i.e., greater than 40A/m 2 ) in the electrowinning cell; the use of lixiviant having high free cyanide concentrations (e.g., greater than 0.5%, for example between 1 and 8 % by weight sodium cyanide) in the electrowinning cell; the use of one or more lixiviant additives (e.g., a small amount of: one or more soft metals, organic compound(s), wetting agent(s), surface modifier(s), viscosity modifier(s), releasing agent(s)) in the electrowinning cell, the use of increased silver concentrations within the lixiviant by virtue of the addition of Ag(CN)2 or “silver” solution to the electrowinning cell; and/or the introduction of mechanical waves or vibrations to
- mechanical cleaning is preferably induced via ultrasonic methods
- other mechanical means such as cathode scraping mechanisms, air or fluid spraying, and cathode vibrating/shaking/flexing means may be employed, without limitation.
- the unique and novel and unobvious addition or use of special reagents i.e. , “additives” during the process may accompany other broader process parameters including, without limitation: the use of current densities greater than 10 A/m 2 in the electrowinning cell; and the use of lixiviant having free cyanide concentrations greater than 0.05% (e.g., 0.1 - 8% by weight as measured by sodium cyanide in the electrowinning cell, without limitation.
- the electrowinning cell comprises a pump for introducing electrowinning feed from an electrowinning feed tank, a rectifier, and an electrolytic cell comprising alternating anodes and cathodes.
- the electrowinning cell may comprise mechanical cleaning means, such as an ultrasonic transducer for assisting with cathode cleaning wire mesh cathodes. When energized, the ultrasonic transducer produces waves that can assist with removal of electroplated deposits from the wire mesh cathodes. Energizing of such mechanical cleaning means may be done continuously or periodically/intermittently, without limitation. Moreover, amplitude and/or frequency of the ultrasonic waves generated may be adjusted over time. Amplitude and/or frequency of the ultrasonic waves generated may differ during different electrowinning cycles or portions of the electrowinning process, without limitation.
- Cathodes used in embodiments may be of any type but are preferably wire mesh, such as stainless-steel wire mesh, without limitation.
- An exhaust fan may be used to remove noxious fumes and/or gasses produced by and/or accumulating around the electrowinning cell. Barren solution from the electrowinning cell may be removed and recycled as lixiviant or sent to the adsorption circuit, without limitation.
- silver cyanide solution may be temporarily introduced in sufficient concentration to help soften early deposits on the wire mesh cathodes.
- Cyanide concentration e.g., sodium cyanide concentration
- current density may also remain elevated to promote keeping precious metal deposits soft.
- the ultrasonic transducer can be energized to discourage hard plating. It is anticipated that introduction of silver solution (e.g., Ag(CN)2) may help weaken or soften initially-deposited precious metal deposits to aid in precious metal deposit removal from the wire cathodes.
- the addition and elevated concentration of silver solution may be maintained throughout the electrowinning process, or its addition to the electrowinning cell may be gradually reduced to lower silver concentration within the electrowinning cell. At any time during electrowinning, silver solution may be intermittently added to the electrowinning cell (e.g., if it is determined that deposits formations are becoming too hard).
- an electrowinning cell may be accompanied by a mix/storage tank as shown.
- the electrowinn ing cell may operate normally, i.e., consistent with traditional prior art methods, in the sense that electrowinning feed may be pumped to the electrowinning cell from an electrowinning feed tank, and fumes evacuated by an exhaust fan. Barren solution may be removed from the electrowinning cell as depicted and as done for the embodiment shown in FIG. 1 . However, as depicted in FIG.
- some of the barren solution removed from the electrowinning cell may be transferred to the mix/storage tank, where additional process water, reagent/additive(s), and/or cyanide solution can be introduced to and/or mixed with the barren solution leaving the electrowinning cell via respective pumps and/or control valves.
- the composition of the barren solution changes in the mix/storage tank such that it may comprise an increased concentration of reagent/additive(s) and/or cyanide.
- the resulting solution may be pumped from the mix/storage tank back to the electrowinning cell, and may, as shown, be combined with the electrowinning feed upstream of a feed inlet to the electrowinning cell.
- a control valve may be employed to the circuit to allow adjustment of the ratio of electrowinning feed to recycled solution combined therewith.
- the electrowinning cell may comprise an electrolytic cell and a rectifier for adjusting a current applied to spaced electrodes (e.g., anodes and cathodes) which may be energized with a negative (cathode) or positive (anode) charge in alternating fashion.
- spaced electrodes e.g., anodes and cathodes
- the rectifier may be configured for continuously or intermittently increasing current density.
- the rectifier may be configured to enable reverse-polarity sequences.
- the mix/storage tank may comprise a pump and/or valve for introducing and/or controlling an amount of process water delivered thereto.
- the mix/storage tank may comprise a pump and/or valve for introducing and/or controlling an amount of cyanide (e.g., NaCN, KCN, Cu(CN)2, Ag(CN)2, an equivalent thereof, or a combination thereof) delivered thereto.
- the mix/storage tank may further comprise a pump and/or valve for introducing and/or controlling an amount of a cleaning reagent or additive delivered thereto.
- the cleaning reagent or additive may comprise a hard electrowinning deposit remover configured for promoting softening and/or removal of electrowinning hard deposits from the wire cathodes/anodes, without limitation.
- the process water, cleaning reagent/additive, and/or added free cyanide (e.g., by virtue of addition of one or more cyanide species such as NaCN, KCN, etc.) - or, a solution containing one or more of the aforementioned, may be pumped into the electrolytic cell at controlled process conditions which promote releasing of hard deposits and/or softening of the deposits.
- the deposit-laden anode/cathode may be energized with a charge which is opposite in the electrowinning cell.
- the rectifier may be used to allow the electrowinning cell to undergo a reverse polarity sequence in which a cathode or anode plated with precious metal deposits may be freed of its deposits through electrolysis.
- an electrowinning cell as described above may be provided.
- the electrowinning cell is provided without mechanical cleaning means, although the same may be provided to the electrowinning cell as an option.
- a hoist may be used to remove one or more cathodes and/or anodes comprising hard-deposits containing one or more precious metals (i.e., gold and/or silver) and re-locate them to a separate cathode wash cell (i.e., “cleaning tank”), instead of to a smelting operation typically used for destruction and recovery.
- a separate cathode wash cell i.e., “cleaning tank”
- the cathode wash cell may comprise a pump and/or valve for introducing and/or controlling an amount of process water delivered thereto.
- the cathode wash cell may further comprise a pump and/or valve for introducing and/or controlling an amount of a cleaning reagent or additive delivered thereto.
- the cleaning reagent or additive may comprise a hard electrowinning deposit remover configured for promoting softening and/or removal of electrowinning hard deposits from the wire cathodes/anodes, without limitation.
- the cathode wash cell may further comprise a rectifier, and an electrolytic cell comprising spaced plates which may be energized with a negative or positive charge in alternating fashion.
- the process water, the cleaning reagent/additive, and cyanide (e.g., NaCN) - or, a solution containing the same, may be pumped into the electrolytic cell at controlled process conditions which promote releasing of hard deposits and/or softening of the deposits.
- the laden anode/cathode may be energized with a charge which is opposite of the spaced plates in the electrolytic cell.
- the cathode wash cell may be used as a reverse polarity tank in which a cathode or anode plated with precious metal deposits may be freed of its deposits through electrolysis.
- the concentration of cyanide (e.g., NaCN or equivalent) in the cathode wash cell is preferably higher than the cyanide concentration within the upstream electrowinning cell from which the cathodes and/or anodes comprising hard- deposits was taken from.
- the rectifier may be configured such that current density in the cathode wash cell may be higher than what is used in the upstream electrowinning cell from which the cathodes and/or anodes comprising hard-deposits was taken from.
- the combination of higher cyanide concentration and higher current density in the cathode wash cell may present synergistic effects which foster the loosening hard deposits from the cathode(s)/anode(s) therein, and/or softening the plated precious metals. Accordingly, the cathode(s)/anode(s) placed therein may be cleaned and then hoisted from the cathode wash cell and placed back into the upstream electrowinning cell for recycle/reuse - without the need to sacrificially smelt them in order to recover precious metals entrained therein.
- the cathode wash cell may, as shown, comprise mechanical cleaning means, such as an ultrasonic transducer for assisting with the cathode cleaning wire mesh cathodes.
- mechanical cleaning means such as an ultrasonic transducer for assisting with the cathode cleaning wire mesh cathodes.
- the ultrasonic transducer when energized, will produce waves that can assist the removal of hard and/or soft electroplated deposits from the wire mesh cathodes.
- Energizing of such mechanical cleaning means may be done continuously or periodically/intermittently, without limitation.
- the amplitude and/or frequency of the ultrasonic waves generated may be adjusted (e.g., increased or decreased) over time. Amplitude and/or frequency of the ultrasonic waves generated may differ during different electrowinning cycles or portions of the electrowinning process, without limitation.
- Other mechanical means for cleaning such as scrapers or mechanical vibration means may be applied, without limitation.
- an exhaust fan may be used to remove noxious fumes and/or gasses produced by and/or accumulating around the cathode wash cell, without limitation.
- Solution may be removed from the cathode wash cell by a pump, and controlled via a control valve as shown. The solution may be recycled directly to the electrowinning cell, or to an electrowinning feed tank as shown, without limitation. While not expressly depicted in FIG. 3, some or all of the solution from the mix/storage tank may be removed and sent to adsorption for recycling as lixiviant, without limitation. Moreover, while not expressly depicted in FIG. 3, at least some or all of the solution from the cathode wash cell may be combined with the electrowinning feed in a controlled manner upstream of a feed inlet to the electrowinning cell in a manner similar to what is suggested in FIG. 2.
- Removed solids i.e., “soft” deposits
- Removed solids which are dislodged from the anode(s)/cathode(s) in the cathode wash cell may fall to the bottom of the electrolytic cell portion of the cathode wash cell.
- fallen solids may be pumped from the bottom of the electrolytic cell portion of the cathode wash cell and sent to another downstream refining process step.
- a reverse polarity step (e.g., within the electrowinning cell and/or cathode wash cell) may be employed, without limitation. Adding this step may further assist with dislodging hard- deposited materials containing precious metals from a cathode(s)/anode(s).
- current density is maintained above approximately 5 A/m 2 of cathode area, and even more particularly, above approximately 15 A/m 2 of cathode area.
- a high current density regime is used to soften cathode deposits and may be within the range of about 40-500 A/m 2 of cathode area, without limitation.
- target free cyanide concentration is maintained at all times above approximately Wo by weight of electrowinning solution, and preferably below approximately 4Wo by weight of electrowinning solution.
- free cyanide concentration may temporarily or continuously be elevated above approximately 0.65% by weight.
- target sodium cyanide concentration used to soften cathode deposits may be kept within the range of about 1 -8% by weight of electrowinning solution, without limitation.
- 1 -4% or approximately 1.5% to 3% by weight sodium cyanide concentration of the electrowinning solution may be maintained to clean hard-deposits of precious metals from cathodes (e.g., approximately 2% by weight sodium cyanide concentration of the electrowinning solution may be maintained).
- a lixiviant additive may be provided to improve softening of precious metals deposited onto cathodes and/or soften existing hard- deposits.
- the additive may comprise a soft metal, viscosity modifier, a surface modifier, and/or a release agent, without limitation.
- the additive may comprise a plurality of soft metals, viscosity modifiers, surface modifiers, and/or release agents, without limitation.
- the additive may comprise a combination of one or more soft metals, viscosity modifiers, surface modifiers, and/or release agents, without limitation.
- the additive may comprise 1 -10 ppm lead nitrate, without limitation.
- silver cyanide may be provided to improve softening of deposited precious metals onto cathodes.
- the application of the silver cyanide may be used during initial plating to effectively “pre-coat” wire mesh cathodes with a thin, soft layer of “silver- heavy” deposits prior to and/or during the plating of gold. In this regard, harder deposits of gold may become easier to dislodge from a cathode(s).
- silver cyanide may be added to an electrowinning solution intermittently. In some embodiments, 50-200 ppm of silver cyanide may be present in the electrowinning solution.
- the addition of silver cyanide to an electrowinning cell may be performed as a function of electrowinning feed composition.
- the electrowinning feed solution comprises gold and/or silver concentrations above 250 ppm, less or no silver cyanide may be added, since cathode deposits are anticipated to be softer and more easily removed.
- gold and/or silver concentrations in the electrowinning feed solution are measured to be below 100 ppm, harder cathode deposits may be anticipated - thus, necessitating the addition of a temporary addition or boosting of silver cyanide to the electrowinning solution to soften deposits.
- a composition of electrowinning feed solution may be monitored over time and periodically measured.
- a threshold for gold and/or silver concentration may be predetermined or set. If the % gold and/or silver in the electrowinning feed solution is measured to be below (or falls below) the threshold, a harder deposit may be expected and one or more of the following steps may be taken: the current density in the electrowinning cell may be increased, cyanide may be added to the electrowinning solution to increase cyanide concentration of the electrowinning solution in the electrowinning cell, silver cyanide may be added to the electrowinning cell to increase silver cyanide concentration of the electrowinning solution in the electrowinning cell, an amount of additive may be added to the electrowinning solution to help soften deposits or encourage releasability of deposits, and/or a reverse polarity step may be performed at any time during the electrowinning process, particularly in cases where there are hard-deposit occurrences.
- a softer deposit may be expected and one or more of the following steps may be taken: decrease current density in the electrowinning cell, remove cyanide from - or decrease cyanide concentration of the electrowinning solution in the electrowinning cell, remove silver cyanide from - or decrease silver cyanide concentration of the electrowinning solution in the electrowinning cell, remove an amount of additive from - or decrease an amount of an additive added to the electrowinning solution in the electrowinning cell, and/or omit, skip, or do not perform a reverse polarity step during electrowinning.
- an electrowinning cell may be provided.
- An electrowinning feed solution may be provided to the electrowinning cell.
- a concentration of precious metals in the electrowinning feed solution may be measured (e.g., ppm Au, ppm Ag).
- Cyanide e.g., sodium cyanide, potassium cyanide, copper cyanide, silver cyanide, or equivalent
- Cyanide may be added to boost the concentration of free cyanide in the electrowinning solution (e.g., to between 1 and 4 % sodium cyanide weight), in order to prevent the formation of hard cathode deposits.
- Current density may be maintained above 40 A/m 2 of cathode area, but preferably less than 200 A/m 2 of cathode area.
- steps may be further employed.
- silver cyanide solution may be added to the electrowinning feed solution or to the electrowinning cell.
- An additive as described above may be added to the electrowinning feed solution or to the electrowinning cell.
- One or more reverse polarity steps may be performed, e.g., by switching the polarity or charge of the anodes and cathodes in the electrowinning cell.
- Mechanical cleaning steps may be performed, e.g., by virtue of energizing an ultrasonic transducer, high pressure spray, mechanical cathode scraper, or mechanically vibrating one or more cathodes, without limitation. It will be appreciated by those skilled in the art that the above steps may be performed in any useable order, and that any one of the above steps may be performed in combination with other steps, as needed to effect soft cathode deposits.
- an electrowinning process may involve providing an electrowinning cell with an electrowinning solution comprising a cyanide concentration which is greater than or equal to 0.6 weight% to produce a soft deposit during electrowinning; and/or providing an electrowinn ing solution comprising a sodium cyanide concentration greater than or equal 1 .0 weight% to an electrowinning cell to soften a hard deposit already formed during electrowinning, without limitation.
- Sodium cyanide may be added to the elution solution to strip the carbon as conventionally done.
- an AARL circuit may utilize an approximately 5% sodium cyanide (NaCN) pre-soak with 10 BV rinse, which equates to an approximately 0.32% NaCN concentration in the final electrowinning solution.
- the AARL circuit may utilize an approximately 5% NaCN pre-soak with 6 BV rinse, which equates to an approximately 0.52% NaCN concentration in the final electrowinning solution.
- preferred embodiments employ the use of higher percent NaCN pre-soak concentrations and/or lesser BV of wash solution, in order to provide a final electrowinning solution having NaCN concentrations that are greater than or equal to 0.65 weight %.
- final NaCN concentrations are maintained above 1%, for example, between 1 and 4% by weight NaCN, without limitation.
- a 2% by weight NaCN solution may be employed to soften and remove a hard anode and/or cathode deposit during electrowinning.
- An additive may be present in the electrowinning solution, or added during electrowinning to soften cathode deposits and/or promote removal of cathode deposits.
- a lead-containing reagent may be added to produce a >1 ppm Pb concentration in an electrowinning feed to produce a softer deposit during electrowinning.
- 5 ppm Pb may be added to 500 ppm of Ag/Au/Cu in the electrowinning feed solution to obtain a soft cathode deposit.
- the additive may be delivered to the electrowinning cell periodically, for example, it may be used/introduced to the electrowinning cell upon use of new or clean anodes/cathodes.
- the additive may assist with preconditioning fresh cathode/anode surfaces. Preconditioning of the fresh, clean cathode/anode surfaces using the additive in the lixiviant may help with the formation of weak, soft, plated cathode layers, thus facilitating the removal of subsequent deposits formed thereover.
- the additive may also be delivered continuously to the electrowinning cell and the amount of it added to the electrowinning cell optionally adjusted over time, for example, as a function of precious metal concentration in the electrowinning feed. In this regard, the small amount of lead present in solution may help soften newly- formed deposits of precious metals on wire cathodes/anodes.
- lixiviant comprising various amounts/concentrations of a wetting agent, oxidant, and/or organic may be added to the electrowinning cell solution to produce a soft(er) deposit during electrowinning and/or to soften already-present hard deposits which were formed during the electrowinning process, without limitation.
- Current density is normally limited to 5-15 A/m 2 for production cells, but according to some embodiments of the present invention, additional measures may be taken to soften deposits and/or loosen hard deposits by increasing the same.
- electrowinning may be performed at a current density which is greater than 40 A/m 2 of cathode area in order to achieve or encourage the formation of softer cathode deposits.
- an approximately 40 A/m 2 of cathode area current density condition was achieved using a 1 Amp setting on the rectifier.
- current density may be kept below 500 A/m 2 of cathode area (e.g., less than 200 A/m 2 of cathode area), without limitation.
- an electrowinning process may involve providing an electrowinning cell with an electrowinning solution comprising a cyanide concentration which is greater than or equal to 0.6 weight% for example, an electrowinning solution comprising a free cyanide concentration which is greater than or equal 0.65 weight% and less than or equal to 5.0 weight% (e.g., approximately 1.0 - 2.5 weight% or approximately 2 weight%), without limitation.
- Sodium cyanide may be used as a matter of preference, although other species of cyanide may be employed in addition to, or in lieu of sodium cyanide.
- Current density used within the electrowinning cell may substantially exceed the traditional 5-15 A/m 2 used for production cells.
- electrowinning in the electrowinning cell may be performed at a current density which is greater than 40 A/m 2 of cathode area, in order to achieve or encourage the formation of softer initial cathode deposits on cathodes.
- a current density which is greater than 40 A/m 2 of cathode area, in order to achieve or encourage the formation of softer initial cathode deposits on cathodes.
- an approximately 40 A/m 2 of cathode area current density condition was achieved using a 1 Amp setting on the electrowinning cell rectifier.
- current density may be kept below 500 A/m 2 of cathode area.
- a first electrowinning cycle may be performed using the electrowinning cell. Some of the electrodes within the cell are positively-charged anodes and some of the electrodes are negatively-charged cathodes during the first electrowinning cycle.
- the first electrowinning cycle may be performed for a first cycle duration lasting, for example, between 60 and 400 minutes. During the first cycle duration, initial plating of precious metals (from the electrowinning solution) onto the cathodes within the cell may be achieved.
- the first electrowinning cycle may be around 90 to 180 minutes long (or longer, e.g., 240 minutes), without limitation.
- a relatively short reverse polarity cycle may be subsequently performed after the first electrowinning cycle, wherein the charge of the previous anodes and cathodes within the electrowinning cell are at least temporarily switch ed/in verted, and one or more precious metal plated previously negatively-charged cathodes will temporarily become positively-charged “anodes” during the relatively short reverse polarity cycle.
- This relatively short reverse polarity cycle may be considered to be a second electrowinning cycle, wherein the previously positively-charged anodes from the first electrowinning cycle will temporarily become negatively-charged “cathodes”.
- This relatively short reverse polarity cycle (or “second” electrowinning cycle) may be performed between 1 and 60 minutes (i.e., for a second cycle duration), or otherwise for a shorter duration relative to the first cycle duration in this Example. It is anticipated that this relatively short reverse polarity cycle may be substantially less than the first cycle duration.
- a reverse polarity cycle may take 400 minutes or more to completely re-plate initially deposited precious metals (which remained lodged on or hard-plated to cathodes of the first electrowinning cycle) onto the reversed-polarity anodes of the first electrowinning cycle.
- preferred embodiments may involve a relatively short reverse polarity cycle after the first electrowinning cycle lasting between 1 and 60 minutes, and preferably less than about 30 or 45 minutes, (e.g., 1 -20 minutes, approximately 10 minutes or less, approximately 15 minutes or less, or approximately 20 minutes or less), without limitation.
- the ratio of the second cycle duration to the first cycle duration is preferably between 0.01 and 0.5, more preferably between 0.5 to 0.3, such as 0.1 to 0.25 or approximately 0.2, without limitation.
- the second cycle duration of the relatively short reverse polarity cycle is preferably substantially shorter than the first cycle duration.
- the second cycle duration may be at least twice as short as the first cycle duration.
- the second cycle duration may be less than 1 /3 rd of the first cycle duration.
- the cycle second cycle duration may be less than 14 of the first cycle duration.
- the cycle second cycle duration may be less than a fifth of the first cycle duration, of the first electrowinning cycle, without limitation.
- the inventors have unexpectedly discovered that at the abovementioned elevated free cyanide concentrations and higher current density regimes, a relatively short reverse polarity cycle following an electrowinning cycle is sufficient enough to substantially soften plated electrodes loaded with precious metals during the electrowinning cycle, thus, allowing for easy removal of precious metal deposits from the electrodes with nothing more than simple flushing of unpressurized or pressurized water. Accordingly, the technical effect provides the advantage of reducing reliance on energy-intensive smelting practices that consume electrodes and allowing for cathode (and/or anode) re-use within the electrowinning cell and/or method of electrowinning.
- one or more precious metal removal steps may take place between one, some, or all of the electrowinning cycles.
- cleaning of one or more electrodes may occur between a first and second electrowinning cycle (and/or between a second and third electrowinning cycle, between a third and fourth electrowinning cycle, between a fourth and fifth electrowinning cycle and so on and so forth).
- the cleaning cycles may include removal of precious metal deposits from one or more electrodes of the electrowinning cell (anode or cathode).
- one or more electrodes may be temporarily hoisted or substantially removed from an electrowinning cell and cleaned (e.g., by virtue of rinsing the one or more electrodes, washing the one or more electrodes, pressure-washing the one or more electrodes, spraying the one or more electrodes, water-jetting the one or more electrodes, mechanically or physically scraping the one or more electrodes, mechanically or physically vibrating or inducing vibrations into the one or more electrodes, generating a mechanical wave using an ultrasonic transducer or sound generator, air blowing the one or more electrodes, mechanically or physically shaking the one or more electrodes, and/or mechanically or physically flexing the one or more electrodes, without limitation). Any of the above steps may be taken in any order, and in any combination, without limitation.
- the one or more electrodes may be cleaned of precious metal deposits in situ, that is, while remaining in the electrowinning cell (full of electrowinning solution or not).
- In situ cleaning may include one or more of the same steps mentioned above, in any order, and in any combination, without limitation. It is preferred that during any intervening cleaning step between successive electrowinning cycles, both cathodes and anodes are washed after each electrowinning cycle (e.g., including after each reverse polarity cycle).
- the inventors have discovered the advantage of periodically removing electrodes (anode or cathode) from the electrowinning cell and submersing them in a warm bath of solution comprising 1 -8% sodium cyanide solution (e.g., 1 -4% sodium cyanide).
- the cyanide solution may comprise any of the cyanide species mentioned herein.
- the cyanide solution may comprise one or more of the agents or lixiviant additives mentioned herein (e.g., a wetting agent, oxidant, organic compound, surface modifier, viscosity modifier, releasing agent, soft metal (e.g., lead), or any combination thereof).
- the temperature of the warm bath is maintained between approximately 60 and 212 degrees Fahrenheit above a pH value of approximately 9.5.
- the cyanide solution may comprise sodium cyanide (NaCN), potassium cyanide (KCN), copper cyanide (CU(CN)2), and/or silver cyanide (Ag(CN) 2), without limitation. Doing this completely removes or reduces precious metal buildup on electrodes (anode or cathode) and ensures fresh electrode surfaces for future electrowinning cycles within the electrowinning cell.
- the (second electrowinning) reverse polarity cycle described in Example 2 may alternatively be taken to a full term within the purview of traditional reverse polarity cycle times, such that the second cycle duration is substantially the same duration as the first cycle duration or longer.
- the ratio of the second cycle duration to the first cycle duration may be between 0.7 and 1.5, more preferably between 0.8 to 1.3, such as 0.9 - 1.1 , or 0.2, without limitation.
- the reverse polarity cycle may be much longer than the first cycle duration of the first electrowinning cycle as well.
- the second cycle duration in this example may be substantially similar to - or greater than the first cycle duration.
- precious metals are initially plated onto cathodes.
- a third electrowinning cycle may subsequently follow the reverse polarity cycle.
- the polarity of anodes and cathodes may yet again, be switched, such that the polarity of the same resets to the same conditions as the first electrowinning cycle.
- the anodes i.e., which were cathodes plating during the second electrowinning/reverse polarity cycle
- Deposit removal from the now-plated “anodes” of the third electrowinning cycle may further be accomplished via a supplemental spray or rinsing.
- electrowinning solution may be flushed or removed from the electrowinning cell and replaced with new electrowinning solution, and softened deposit or sludge may be washed from the electrodes and removed from the cell.
- adjectives such as first and second, and the like may be used solely to distinguish one element or action from another element or action without necessarily requiring or implying any actual such relationship or order.
- reference to an integer or a component or step (or the like) is not to be interpreted as being limited to only one of that integer, component, or step, but rather could be one or more of that integer, component, or step etc.
- cathode means an electrode that is negatively-charged. It should be understood to those skilled in the art, that at various points during electrowinning, polarity of electrodes within the electrowinning cell may be temporarily switched (e.g., in the case of a reverse polarity step), wherein anodes which were previously positively- charged may become negatively charged - in which case, a previous anode may also be construed as a cathode while it is negatively-charged during said reverse polarity step.
- sodium cyanide and/or “NaCN” has been used for convenience throughout this specification, drawings, and claims, in order to establish and suggest one possible best mode for practicing embodiments the invention and quantifying target free cyanide concentrations.
- alternative cyanide species may be practiced (in addition to, or in lieu of sodium cyanide (NaCN)) to increase free cyanide concentration.
- sodium cyanide and/or “NaCN” may be interpreted broadly to also include or comprise amounts of potassium cyanide (KCN), copper cyanide (CU(CN)2), silver cyanide (Ag(CN)2), or a combination thereof, without limitation.
- KCN potassium cyanide
- CU(CN)2 copper cyanide
- Ag(CN)2 silver cyanide
- cyanide used in conjunction with the term “concentration” suggests an increase in free cyanide concentration (such as an increase in free cyanide concentration by approximately ⁇ 0.5 to -4.5 wt.%) which may be accomplished by introducing one or more or several cyanide species. While this increase in free cyanide concentration may (in some preferred embodiments) be measured in relation to sodium cyanide concentration (e.g., a 1 -8 wt.% target sodium cyanide concentration), other cyanide species may be used to increase the free cyanide concentration to within approximately -0.5 to -4.5 wt.%.
- Cyanide species used to increase free cyanide concentration may comprise any one or more of the following, without limitation: “sodium cyanide”, “potassium cyanide”, “KCN”, “copper cyanide”, “Cu(CN)2”, “silver cyanide”, “Ag(CN)2”, “inorganic cyanide”, or a “cyanide compound” (e.g. cyanide solution comprising one or more of: NaCN, KCN, Cu(CN)2, Ag(CN)2, or equivalent).
- the terms ‘comprises’, ‘comprising’, ‘includes’, ‘including’, or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.
- certain method steps and/or apparatus features may be shown or discussed together, it is anticipated by the inventors that one or more features and/or steps may be combined or grouped without employing other mentioned features and/or steps.
- method steps may be performed in sequences other than what is expressly depicted or disclosed herein, such that the order of execution of the steps may be performed in various different orders.
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Abstract
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AU2023233936A AU2023233936A1 (en) | 2022-03-16 | 2023-03-16 | System and method for controlling or removing hard deposits on electrowinning cathodes |
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US202263320359P | 2022-03-16 | 2022-03-16 | |
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Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3063921A (en) * | 1957-08-06 | 1962-11-13 | Rand Mines Ltd | Method of and apparatus for the electrolytic extraction of gold from a gold-bearing solution |
DE1808471A1 (en) * | 1968-11-12 | 1970-10-15 | Laney Lab Inc | Recovery of gold from dragout or washing solutions |
EP0329275A1 (en) * | 1988-01-20 | 1989-08-23 | Konica Corporation | Method of recovering silver from photographic processing solution and apparatus therefor |
WO2001051685A2 (en) * | 2000-01-10 | 2001-07-19 | Michael John Sole | Removal of metals from solution |
WO2004031453A1 (en) * | 2002-10-04 | 2004-04-15 | Michael John Sole | Electowinning of metals |
WO2011150984A1 (en) * | 2010-06-01 | 2011-12-08 | Voldemars Belakovs | Method for recovering noble metals and other byproducts from ore |
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2023
- 2023-03-16 AU AU2023233936A patent/AU2023233936A1/en active Pending
- 2023-03-16 WO PCT/IB2023/052604 patent/WO2023175570A1/en active Application Filing
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3063921A (en) * | 1957-08-06 | 1962-11-13 | Rand Mines Ltd | Method of and apparatus for the electrolytic extraction of gold from a gold-bearing solution |
DE1808471A1 (en) * | 1968-11-12 | 1970-10-15 | Laney Lab Inc | Recovery of gold from dragout or washing solutions |
EP0329275A1 (en) * | 1988-01-20 | 1989-08-23 | Konica Corporation | Method of recovering silver from photographic processing solution and apparatus therefor |
WO2001051685A2 (en) * | 2000-01-10 | 2001-07-19 | Michael John Sole | Removal of metals from solution |
WO2004031453A1 (en) * | 2002-10-04 | 2004-04-15 | Michael John Sole | Electowinning of metals |
WO2011150984A1 (en) * | 2010-06-01 | 2011-12-08 | Voldemars Belakovs | Method for recovering noble metals and other byproducts from ore |
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