Mechano-chemical dissolution of a noble metal in an aqueous solution and recovery therefrom

Abstract

A mechano-chemical process for separating at least one noble metal from a solid metal-containing component including forming a reaction mixture comprising the metal-containing component, an oxidizing agent of Formula (AE)zCnHmNpOqXa, and a reaction media comprising a protic solvent. The reaction mixture is subjected to mixing under a mechanical force being applied by acoustic waves providing an acceleration between 1 g and 100 g to the reaction mixture, thereby facilitating oxidative dissolution of the at least one noble metal from the metal-containing component. A product mixture is formed comprising an aqueous phase and an insoluble by-product being suspended in the aqueous phase. The aqueous phase includes the at least one noble metal having an oxidation state of at least 1 being present in dissolved form as a metal halide salt, a metal hydroxide salt, a metal hydroxide halide salt, a metal halide acid, or any combination thereof.

Description

MECHANO-CHEMICAL DISSOLUTION OF A NOBLEMETAL IN AN AQUEOUS SOLUTIONAND RECOVERY THEREFROMTECHNICAL FIELD

[0001] The present invention generally relates to metal purification and more particularly to a mechano-chemical process involving oxidative dissolution of a noble metal from a solid metal-containing component in an aqueous solution and recovery of the noble metal.BACKGROUND

[0002] Known processes to recover purified gold can include a chlorination step, being referred to as the Miller chlorination, in which chlorine gas (Cl2) is injected into a molten mixture of metals at elevated temperatures (>1100 ºC). At these elevated temperatures, gold is the most difficult metal to oxidize, and impurities are first oxidized to their chloride salts, facilitating their separation by either distillation or physical removal of a slag layer that floats on top of a molten gold layer. Gold remains unoxidized as the denser liquid and can be recovered with a purity of at most about 99.6%.

[0003] However, Cl2 gas is known to be corrosive which creates an acute environmental risk that also endangers workers and its use requires regular equipment maintenance and strict safety measures. In addition, the generated waste streams are difficult and expensive to treat.

[0004] Other known processes may include the use of aqua regia refining systems, particularly for refining gold alloys that are rich in platinum group metals. While these systems are less expensive to maintain, they still present a number of challenges for larger scale implementation, including the use of corrosive nitric (HNO3) and hydrochloric (HCl) acids, which leads to the production of environmentally hazardous waste streams that include NOx gases and acidic wastewater.

[0005] In cases where a purity higher than 99.5% is required, the molten gold can be poured into anodes and then purified according to the Wohlwill process, to provide gold in its highest purity, i.e., of about 99.999%. However, the Wohlwill process is relatively slow, and has the disadvantage of requiring a large, permanent inventory of gold that remains in the producing facility in the form of a chloroauric acid (HAuCl4) electrolyte. Chloroauric acid is also acidic and corrosive, creating similar issues for equipment upkeep, health and safety, and the processing of waste streams.

[0006] Because the oxidation of metal alloys plays such a critical role in the purification of gold, there have been efforts to develop less corrosive and toxic oxidant alternatives to Cl2 or HNO3. Amongst those oxidants, trichlorocyanuric acid (TCCA), and its closely related derivatives (e.g., TXYCA, where X= Cl or Br; Y = H or Na, K) have been tested. TCCA has already been adopted by a number of industries seeking more environmentally friendly oxidants, including as a disinfectant, sanitizer, and bleaching agent in water treatment, textile, pulp and paper, and food processing contexts. Because of their ability to prevent the growth of algae, fungi, and other waterborne pathogens, TCCA and its derivatives are used to treat water in municipal drinking and wastewater facilities, and in pools or spas. In the textile industry, TCCA is used as a disinfectant of processing equipment and as a bleaching agent for cotton and other natural fibers. Likewise, in the paper industry, TCCA and its derivatives are used as a bleach and disinfectant to produce large-volume products, including cardboard. It is also used in the food processing industry as a sanitizer and disinfectant for equipment, containers, and surfaces. TCCA is particularly effective against Escherichia coli and Salmonella, making it a component of many food safety protocols.7

[0007] TCCA and its derivatives have also found use in organic chemistry as a mild source of electrophilic chlorine or chlorine radicals. In inorganic chemistry, it has been used to oxidize a range of metals into their halide salts, including oxidations of gold, silver, platinum, palladium, zinc, iron, vanadium, and copper. TCCA and its derivatives have also seen some exploratory use in the mining industry to help extract gold and silver from sulfide-rich ores, as well as the recovery of gold from electronic waste. Their addition to slurries of ores with hydroxide or cyanide can help to solubilize metal sulphides by oxidizing sulfur, facilitating the release of metal ions that are readily leached by cyanide. However, long reaction times needed to dissolve the metal alloy under industrial conditions appear to have prevented further industrial development.

[0008] There is still a need for a technology that overcomes at least some of the drawbacks of what is known in the field, such as the above-mentioned drawbacks that may result from the use of specific oxidants at high temperatures. SUMMARY

[0009] In one aspect, there is provided a mechano-chemical process for separating at least one noble metal from a solid metal-containing component comprising the at least one noble metal and at least one metal impurity, the process comprising:forming a reaction mixture comprising the metal-containing component, an oxidizing agent of Formula (AE)zCnHmNpOqXa , and a reaction media comprising a protic solvent;subjecting the reaction mixture to mixing under an applied mechanical force to perform oxidative dissolution of the at least one noble metal from the metal-containing component, thereby forming a product mixture that comprises:an aqueous phase comprising the at least one noble metal having an oxidation state of at least 1 being present in dissolved form as a metal halide salt, a metal hydroxide salt, a metal hydroxide halide salt, a metal halide acid, or any combination thereof, andan insoluble by-product being suspended in the aqueous phase, the insoluble by-product comprising metal coordination complexes of at least one of a metal halide salt, a metal hydroxide salt and a metal hydroxide halide salt, wherein the metal from the metal coordination complexes is from the at least one metal impurity;separating the product mixture into the aqueous phase and a solid component comprising the organic by-product; andrecovering the at least one noble metal from the aqueous phase,wherein z, n, m, p, q, a are integers varying from 0 to 10, AE is an alkali metal, X is an halogen, andthe mechanical force is applied by acoustic waves providing an acceleration between 1 g and 100 g.

[0010] In some implementations, the at least one noble metal of the metal-containing component is selected among Ag, Au, Pd, Pt, Ru, Rh, Os, Ir or any combinations thereof, and optionally the at least one noble metal of the metal-containing component is Au.

[0011] In some implementations, the metal-containing component is in the form of coarse grains or powder having an average particle size of at most 20 mm.

[0012] In some implementations, the oxidizing agent is:, , , , , , , , , or an alkali salt thereof.

[0013] In some implementations, the oxidizing agent is:,wherein each X2 is independently from one another: X1, H or an alkali metal, and wherein X1 is Cl, Br or I, and optionally wherein X1 is Cl.

[0014] In some implementations, z + m = 3 – a.

[0015] In some implementations, the oxidizing agent is selected among MCCA, DCCA or TCCA, or an alkali salt thereof, and optionally the oxidizing agent is TCCA.

[0016] In some implementations, the oxidizing agent is HOCl or NaOCl.

[0017] In some implementations, the reaction media is a chloride solution and the at least one noble metal in metal halide salt form dissolved in the aqueous phase is at least one of a mono-, di- or tri-chloride salt.

[0018] In some implementations, the metal-containing component is a gold-containing alloy comprising gold, copper and nickel, the at least one noble metal is gold, the reaction media is a sodium, potassium or calcium chloride solution, and the at least one noble metal in metal halide form is at least one of a mono- or tri-chloride salt.

[0019] In some implementations, a molar ratio of gold to oxidizing agent is from 0.0001 to 600; a molar ratio of gold to water is from 0.0001 to 750; and a molar ratio of gold to halide salt in reaction media is from 0.0001 to 650.

[0020] In some implementations, a molar ratio of the oxidizing agent to the at least one noble metal is a limiting ration being between 0.25 and 1.

[0021] In some implementations, separating the product mixture into the aqueous phase and the solid component comprises:cooling the product mixture to trigger precipitation of the insoluble by-product and produce a cooled mixture comprising the solid component and the aqueous phase; andfiltering the cooled mixture to separate the solid component and recover the aqueous phase as a filtrate.

[0022] In some implementations, the metal-containing component comprises multiple metals as metal impurities and the aqueous phase further comprises the multiple metals in dissolved form as metal halide salt, metal halide acid, metal hydroxide salt, metal halide hydroxide salt, alkali salt of a metal hydroxide, or any combinations thereof.

[0023] In some implementations, the solid component of the product mixture further comprises undissolved / unreacted material from the metal-containing component.

[0024] In some implementations, recovering the at least one noble metal from the aqueous phase comprises adding a reducing agent to the aqueous phase to perform reductive precipitation of the at least one noble metal.

[0025] In some implementations, the recovery of the at least one noble metal from the aqueous phase comprises reduction of all metals into an insoluble metallic form using at least one of hydrides, chemical reductants, transition metal salts and low-valent elements.

[0026] In some implementations, the recovering of the at least one noble metal component from the aqueous phase comprises subjecting the recovered aqueous phase to electrolysis or electrowinning for reduction of the at least one noble metal into an insoluble metallic form.

[0027] In some implementations, the frequency of the applied acoustic waves is between 10 and 100 Hz.

[0028] In some implementations, the application of the mechanical force includes subjecting the reaction mixture to resonance acoustic mixing.

[0029] In some implementations, the resonance acoustic mixing is performed under conditions comprising a mixing time between 1 s to 24 h.

[0030] In some implementations, the process further comprises varying the acceleration of the resonance acoustic mixing according to different acceleration levels during the mixing time.

[0031] In some implementations, the process further comprises adjusting a temperature of the reaction mixture during mixing.

[0032] In some implementations, the process further comprises applying additional mechanical force during mixing via at least one of ultrasonication or mechanical grinding.

[0033] In some implementations, the at least one noble metal of the metal-containing component is gold, and the recovered gold has a purity of at least 99 %.

[0034] In some implementations, the protic solvent is water.

[0035] In some implementations, the reaction media is an aqueous solution of at least one halide salt of an alkali metal or an alkaline earth metal.

[0036] In another aspect, there is provided a dissolving system for recovering at least one noble metal from a solid metal-containing component, the dissolving system consisting of:an oxidizing agent of Formula (AE)zCnHmNpOqXa, wherein z, n, m, p, q, a are integers varying from 0 to 10, AE is an alkali metal, and X is a halogen,a reaction media being water or an aqueous solution of at least one halide salt of an alkali metal or an alkaline earth metal, andmechanical energy provided by resonant acoustic waves.

[0037] In some implementations, the system further comprises at least one additional feature as defined herein.

[0038] In another aspect, there is provided a mechano-chemical process for separating at least one noble metal from a solid metal-containing component, the process comprising:forming a reaction mixture comprising the metal-containing component, an oxidizing agent of Formula R1R2N-X1, a reaction media being an aqueous solution of at least one halide salt;subjecting the reaction mixture to mixing under an applied mechanical force to perform oxidative dissolution of the at least one noble metal from the metal-containing component by oxidation thereof into a metal halide, thereby forming a product mixture that comprises:an aqueous phase comprising the at least one noble metal in metal halide form, andan insoluble organic by-product being suspended in the aqueous phase;separating the product mixture into the aqueous phase and a solid component comprising the organic by-product; andrecovering the at least one noble metal from the aqueous phase,wherein X1 is Cl, Br or I; andwherein: R1 and R2 are each independently an organic moiety; or R1 = X1 and R2 is an organic moiety; orR1 and R2, together with the nitrogen atom to which they are attached, form a 5- to 10-member heterocyclic ring.

[0039] In some implementations, the process further comprises at least one additional feature as defined herein.

[0040] While the invention will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the invention to such embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the present description. The objects, advantages and other features of the present invention will become more apparent and be better understood upon reading of the following non-restrictive description of the invention, given with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Implementations of a mechano-chemical process for purification of a metal component by oxidative dissolution of at least one metal of interest and related techniques / systems are represented in and will be further understood in connection with the following figures.

[0042] Figure 1 is a schematic process flow diagram of the main steps of the proposed mechano-chemical process for the recovery of a purified metal component from a metal-containing component.

[0043] Figure 2 provides a flow chart of the general steps of a conventional Miller-Wohlwill process in comparison to the general steps of the metal recovery process proposed herein.

[0044] Figure 3 is a graph showing X-Ray Diffractograms (XRDs) of a Au-rich alloy, pure Au shavings, pure Cu powder and pure Ni powder.

[0045] Figure 4 provides scanning electron microscope (SEM) images of a gold-rich alloy particle being for example used as the metal component as defined herein, with magnifications of 640 (100 µm scale), 6000 (10 µm scale) and 30000 (1 µm scale).

[0046] Figure 5 is a graph showing an amount of dissolved gold (quantified by ICP-OES for 20 µL aliquots being diluted to 10 mL with deionized water) from a gold-rich alloy of the present process using water and alkali salts for the reaction media, TCCA (at least 3 equivalents) as oxidizing agent and resonance acoustic mixing (with a RAM instrument) at three different accelerations (30 g, 60 g and 90 g where g = 9.81 m.s-2).

[0047] Figure 6 is a graph showing a percentage of gold dissolved versus time of reaction in minutes (speed of alloy dissolution) for three initial reaction temperatures (25, 60 and 95oC) using the optimized conditions determined from Figure 5 and the conventional aqua regia system.

[0048] Figure 7 is a graph of the fitting of a Shrinkage kinetic model applied to the dissolution of gold, copper and nickel under the present mechano-chemical process versus dissolution time.

[0049] Figure 8 is a graph providing an analysis of TCCA as oxidizing agent and main organic by-product CA by Fourier-Transform Infrared Spectroscopy (FT-IR).

[0050] Figure 9 is a graph of applied current (mA) versus time during electrowinning to recover a purified gold component from an aqueous phase produced by the present mechano-chemical process at a fixed potential of 0.2V vs SCE for 10 min using (a) a post RAM solution (aqueous phase of multiphasic product mixture), (b) a blank of 0.1M NaCl, (c) a blank of 0.01M TCCA / CA in 0.1M NaCl.DETAILED DESCRIPTION

[0051] The proposed technology relates to separation of at least one noble metal from a metal-containing component by oxidative dissolution of the at least one noble metal, e.g., gold, in a reaction media due to the presence of an oxidizing agent, and further recovery therefrom. The oxidative dissolution is facilitated by the application of a mechanical force during mixing of the reagents, e.g., by imposing resonant acoustic mixing conditions. There is provided a process including a mechano-chemical dissolution of at least one metal of interest and further recovery of this metal in purified form.

[0052] The metal-containing component as encompassed herein is provided in solid form and includes at least one noble metal. The metal-containing component can include a mixture of metals. The metal-containing component can thus include at least one noble metal being considered as the metal of interest for separation and purification, while other metals from the metal-containing component can be considered as metal impurities. The metal impurities can also be dissolved along with the metal of interest and further selectively recovered by the presently proposed process.

[0053] A noble metal as referred to herein pertains to but is not limited to gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). For example, the noble metal of interest can be Au.

[0054] For example, the metal-containing component can be an alloy containing a noble metal including, but not being limited to, manufacturing alloys, dental alloys, jewelry alloys, and electronic waste alloys. For example, the metal-containing component can for example be a gold-containing alloy comprising gold, copper and nickel, with the copper and nickel being considered as metal impurities to be removed for recovering purified gold (having an increased purity with respect to the metal component). For example, the metal-containing component can be a mixture of different alloys comprising each at least one noble metal. For example, the metal-containing component can be a gold-containing alloy being a doré comprising gold and silver. For example, the metal-containing component is a gold-containing alloy that can further include metals from groups 4 to 6 or main group elements, all considered impurities. In another example, the metal-containing component can include anode slimes from noble metal refining.

[0055] It is noted that the metal-containing component includes the at least one noble metal in its metallic form, i.e., a metal having an oxidation state of zero. For example, all metals of the metal-containing component have an oxidation state of zero.

[0056] Although aspects of the proposed process can be described herein in relation to separation of gold from a gold-containing component, such as a gold-containing alloy, it is noted that such aspects can be applied to the separation of any other noble metals.

[0057] In the context of the present process, the metal-containing component is a solid component that can be provided in particulate form, such as coarse grains, powder or a combination thereof. In some implementations, an average particle size of the metal component can be of at most about 20 mm, e.g., can range from about 0.1 µm to about 20 mm, or e.g., can range from about 10 mm to about 20 mm.

[0058] The process includes oxidative dissolution of the at least one noble metal, such as gold, in presence of an oxidizing agent in a reaction media. Referring to the embodiment of Figure 1, the process includes forming a reaction mixture 2 including the metal-containing component, the oxidizing agent and the reaction media. Further definition of the reaction mixture 2 is provided below.

[0059] In some implementations, the oxidizing agent can be in the form of (AE)zCnHmNpOqXa, wherein z, n, m, p, q, a are integers varying from 0 to 10, and AE is an alkali metal and X is a halogen. In some implementations, z + m = 3 – a.

[0060] In some implementations, the oxidizing agent can be of formula R1R2N-X1, wherein X1 is Cl, Br or I, and wherein:R1 and R2 are each independently an organic moiety; orR1 = X1and R2 is an organic moiety; orR1 and R2, together with the nitrogen atom to which they are attached, form a 5- to 10-member heterocyclic ring.

[0061] For example, the oxidizing agent can be:, , , , , , , , , or an alkali salt thereof.

[0062] For example, the oxidizing agent can be:, wherein each X2 is independently from one another: X1, H or an alkali metal.

[0063] In some implementations, X1 can be Cl and each X2 can be independently Cl, Na or K.

[0064] In some implementations, the oxidizing agent can be HOCl or NaOCl.

[0065] In some implementations, the oxidizing agent can be trichloroisocyanuric acid (Cl3C3N3O3), dichloroisocyanuric (HCl2C3N3O3) acid, or monochloroisocyanuric acid (H2ClC3N3O3) being referred to as TCCA, DCCA or MCCA, respectively. It is noted that the oxidizing agent can be an alkali salt of TCCA, DCCA or MCCA.

[0066] The use of an oxidizing agent as defined herein eliminates the need for special handling and disposal procedures, reducing the process's overall cost and environmental impact.

[0067] The reaction media is selected to be a low-to-non-toxic / non-corrosive reaction media (solvent). In some implementations, the oxidizing agent can be provided in the reaction media. In some implementations, the reaction media can be a protic solvent. For example, the reaction media can be water. Optionally, the reaction media can further include at least one alkali salt. In some implementations, the reaction media can be an aqueous solution of at least one halide salt. Optionally, the reaction media can be an aqueous solution of at least one halide salt of an alkali metal or an alkaline earth metal. Optionally, the reaction media can be an aqueous solution of a chloride salt of an alkali or alkaline earth metal. For example, the reaction media can be an aqueous solution of potassium chloride, sodium chloride, lithium chloride or any combination thereof.

[0068] It is noted that a dissolving solution can be referred to herein and results from the addition of the oxidizing agent to the reaction media to form the dissolving solution. The use of the reaction media described herein as a low-to-non-toxic and low-to-non-corrosive solvent, provides a safer and more environmentally friendly alternative to other organic and inorganic components that are used as solvents in conventional metal dissolution processes such as aqua-regia, thiosulphate, cyanide and ionic liquids (IL).

[0069] The proposed process is defined as a mechano-chemical process involving chemical reactions under application of mechanical force. Referring to Figure 1, the process further includes mixing 4 of the reaction mixture, the mixing being assisted by the tailored application of a mechanical force 5, including using mechanical waves such as acoustic waves, to enhance dissolution of the metals (including the at least one noble metal of interest) as ions of metal salts in aqueous phase, such as metal halides and metal hydroxides. Still referring to Figure 1, mixing of the reaction mixture 2 under applied mechanical force 5 leads to the formation of a product mixture 6, which composition depends on the stoichiometry of the chemical reactants as explained in further detail below.

[0070] The product mixture includes an aqueous phase comprising the at least one noble metal in an oxidation state of at least one and in dissolved form including a metal halide salt. It is noted that the metals contained in the metal-containing component, including the at least one noble metal of interest, are also found in the aqueous phase of the product mixture as at least metal halide salts. The metals, including the at least one noble metal, can also be found in the product mixture as a metal halide acid, a metal hydroxide salt, a metal halide hydroxide salt, an alkali salt of a metal hydroxide, or any combinations thereof.

[0071] For example, when the at least one noble metal comprises or is gold, the aqueous phase includes auric halide salts, such as AuX and / or AuX3. The aqueous phase can further include at least one of an auric halide acid HAuX4, an auric hydroxide salt, such as AuOH and / or Au(OH)3, an auric halide hydroxide salt, such as AuX(OH) and / or AuX2(OH), an alkali salt of an auric halide, such as ZAuX4, and an alkali salt of an auric hydroxide, such as X2Au-OZ, where X can be Cl, Br, I or any combinations thereof, and Z can be Li, Na, K or any combinations thereof.

[0072] In some implementations, the metals, including the at least one noble metal, can also form coordination complexes. Depending on an ionic strength of the aqueous phase of the product mixture, the coordination complexes can be found as soluble compounds being part of the aqueous phase, and / or as insoluble compounds being part of an insoluble by-product being suspended in the aqueous phase above an unreacted metal-containing component, if any. It is noted that the coordination complexes are metal coordination complexes of at least one of a metal halide salt, a metal hydroxide salt and a metal hydroxide halide salt, such as inorganic coordination polymers of metal hydroxide halide salts. The metal that is included in the coordination complexes can be the at least one noble metal and / or at least one additional metal from the metal-containing component. Preferably, the metal coordination complexes that include the at least one noble metal are soluble in the aqueous phase of the product mixture.

[0073] For example, when the at least one noble metal comprises or is gold, coordination complexes where O can be a bridging ligand between two Au atoms can be X2Au-O-AuX2, X(OH)Au-O-AuX(OH)2, [-XAu-O-Au(X2)-O-] with the brackets denoting a repetitive unit within a coordination polymer of an auric hydroxide halide salt, or any combinations thereof. For example, where X is Cl, atacamite can be found as a green solid in suspension in the aqueous phase upon cooling of the product mixture.

[0074] Optionally, the insoluble by-product of the product mixture can further include an organic by-product deriving from the oxidizing agent when in the reaction media. Optionally, the insoluble by-product of the product mixture can also include coordination complexes that are formed by combination of certain metals of the metal-containing component, when present, with the organic by-product. For example, when TCCA is used as the oxidizing agent, the organic by-product generated by reaction of TCCA is cyanuric acid (CA), which can then form coordination complexes with copper and / or nickel (when present in the metal-containing component), and which are referred to as CA-adducts.

[0075] In some implementations, depending on the completion of the dissolution reaction(s), the product mixture may further include the unreacted / undissolved material from the metal-containing component that is present as a bottom dense solid remainder in the product mixture.

[0076] The below equation (1) provides an example of the oxidative dissolution of metallic gold in an aqueous phase in presence of TCCA as the oxidizing agent:Gold component + TCCA + H2O Au(III) + Ma+Cla + CA (1) M = other metal(s) being considered as metal impurities from the metal-containing component (exemplified “gold component” that can be a gold-containing alloy); and CA = an organic by-product being cyanuric acid when TCCA, DCCA or MCCA are used as the oxidizing agent. Au(III) is to be understood as a water soluble form of gold having an oxidation state of +3 and being present at least as AuCl3.H2O. Au(III) can also be present as Au(OH)3, AuCl2(OH), HAuCl4, or any combinations thereof. Au(III) can also be present as coordination complexes as defined herein. Optionally, gold can be found in dissolved form with an oxidation state of 1, as Au(I).

[0077] The oxidizing agent and the combined reaction media have a synergistic effect that enhances the dissolution process, resulting in faster and more complete dissolution of the various metals of the metal-containing component. The application of mechanical force during mixing via acoustic waves, for example through Resonant Acoustic Mixing (RAM), further enhances the dissolution of the metals (including gold) during the process.

[0078] It has been found that the process can dissolve gold-rich alloys in high yield (>99.5%), short time (within minutes), at mild temperatures (between 4-250oC) and with a low energy input using the RAM (green electricity). The dissolution process can thus be used as a substitution procedure for the conventional and energy-intensive Miller chlorination process, which is known to use an operationally challenging purification of gold alloys by chlorination according to the below equation:Alloy + Cl2 + >1100 oC  995Au + Ma+Cla M = metal impurities

[0079] Figure 2 shows the general schematic flow chart of two conventional gold refining processes being the high energy intensity, highly toxic, highly corrosive Aqua regia dissolution process and the Miller-Wohlwill chlorination process, and of the greener process as proposed herein (from left to right, respectively).

[0080] Referring to Figure 1, the proposed mechano-chemical process allows for the removal of impurities from the metal-containing component comprising the at least one noble metal. The process includes forming the reaction mixture 2 comprising the metal-containing component, the oxidizing agent and the reaction media (being an aqueous solution of at least one halide salt). The process further includes mixing 4 the reaction mixture under applied mechanical force 5, for example by subjecting the reaction mixture to resonant mixing (using resonance acoustic mixing (RAM) conditions), to perform the oxidative dissolution of the at least one noble metal from the metal-containing component by oxidation thereof into at least one metal halide salt that is soluble in aqueous phase. Other metals can be oxidized as metal halide salts being soluble in aqueous phase. All metals can also form coordination complexes which may be insoluble as further detailed below.

[0081] In some implementations, the process can further include controlling a stoichiometry of the dissolution reaction(s) to facilitate dissolution of the metal of interest in the aqueous phase. Controlling a stoichiometry of the dissolution reaction can include adjusting an amount of at least one of the oxidizing agent or the reaction media with respect to the metal to be dissolved. The stoichiometry of the dissolution reaction(s) can thereby be tailored to the metal of interest to be dissolved from the metal-containing component (alloy), and to a given dissolution rate.

[0082] For example, the stoichiometry can be controlled to force the dissolution of the metal impurities as dissolved halide salts in the aqueous phase of the product mixture. In another example, the stoichiometry can be controlled to allow dissolution of the metal of interest as dissolved halide salts in the aqueous phase of the product mixture while other metals (considered as the metal impurities) form insoluble coordination complexes with the organic by-product as suspended solids in the product mixture.

[0083] In some implementations, the stoichiometry of the dissolution reaction is controlled by gradually adding oxidizing agent to the reaction mixture so that the oxidizing agent is consumed and remains in a limiting ratio of oxidizing agent with respect to the noble metal of interest.

[0084] In some implementations, referring for example to Figure 1, forming the reaction mixture 2 can include combining a gold-containing alloy as the metal-containing component, TCCA as the oxidizing agent, and an aqueous solution of a halide salt as the reaction media. Exemplary implementations of the process are further described using a gold-containing alloy further comprising nickel (Ni) and copper (Cu).

[0085] In some implementations, the process can include providing the gold-containing alloy (comprising gold, copper and nickel) in the form of coarse grain or powder in presence of the oxidizing agent being TCCA in the reaction media comprising water (H2O) and sodium chloride (NaCl) to produce a reaction mixture within a reaction chamber of a reactor. The reaction mixture can be agitated by acoustic waves, for example by Resonance Acoustic Mixing (RAM) upon placing the reactor in a RAM instrument. The reaction stoichiometry can be controlled by varying a molar ratio of oxidizing agent (TCCA) with respect to the gold in the gold-containing alloy.

[0086] For example, the molar ratio of TCCA with respect to gold in the gold-containing component can be of at least the number of equivalents required to oxidize all metals of the gold-containing component to their +1, +2, +3 or +4 or +5 oxidation states to complete the dissolution of the gold from the gold-containing component into the aqueous phase of the resulting product mixture as dissolved metal halide salts or acid. For example, for a complete dissolution of the gold-containing component, the molar ratio of TCCA with respect to gold in the gold-containing component can be of at least 0.5 equivalents to complete the dissolution of the gold from the gold-containing component into the aqueous phase of the resulting product mixture as dissolved metal halide salts or acid (e.g., AuCl, AuCl3, HAuCl4, NaAuCl4, etc.).  If the gold-containing material contains gold and other metals (e.g. Cu, Ni, Ag), the molar ratio of TCCA to gold can be adjusted in order to have more oxidizing agent to oxidize all the Au to Au-(III), in addition to at least one of all Cu to Cu-(II), all Ni to Ni-(II), all Ag to Ag-(I) or Ag-(II), and all metals in their zero oxidation state to their oxidation state of at least 1. Depending on the level and nature of impurities in the gold-containing component, other dissolved salts and / or soluble / insoluble complexes can form including CuCl2, NiCl2, etc.

[0087] Thus, the gold-containing component, such as a gold-containing alloy, can be completely dissolved by oxidation of all metals to their halide salts and / or acid. The gold is oxidized and dissolved as Au(I) and Au(III) as defined herein. The formed product mixture further comprises a solid by-product including at least one metal coordination complexes poorly soluble organic by-product being cyanuric acid (CA) as solids in suspension in the aqueous phase. An equation, describing the oxidative dissolution under these conditions is provided below:(at least 0.5) TCCA(s) + Gold-containing alloy(s) + H2O(aq) + NaCl(aq)  CA(s) + Au(III) + CuCl2(aq), NiCl2(aq), etc.

[0088] In another example, the molar ratio of TCCA with respect to gold in the gold-containing alloy can be equal to or inferior to about 0.25, about 0.5 or about 1 to let only a fraction of the gold or fractions of the metals in the gold-containing alloy to be solubilized, thereby producing oxidized gold halide salts that are soluble in the aqueous phase. Optionally, limited amounts of TCCA of at least about 0.25 molar ratio and at most 1 molar ratio relative to the gold in the gold-containing alloy can be used. Under these conditions, metal impurities such as copper and nickel can form insoluble coordination complexes that are less dense than the unreacted alloy, thereby being suspended in the aqueous phase of the product mixture. The insoluble coordination complexes are as defined herein. An equation, describing the oxidative dissolution under these example conditions is provided below:1 / 4 TCCA(s) + Gold-containing alloy(s) + H2O(aq) + NaCl(aq)  Au(III) + Cu-based coordination complexes(s) + Ni- based coordination complexes(s), etc.

[0089] Thus, the product mixture that is produced with a limiting ratio of oxidizing agent includes a bottom phase being a dense solid phase of unreacted gold-rich alloy, metal impurities in the form of insoluble coordination complexes (including, for example, metal halide hydroxide coordination polymers and metal-CA adducts when TCCA is used as oxidizing agent) that are dispersed as a suspension in the aqueous phase, and an aqueous phase comprising at least an halide salt of the metal of interest in an oxidation state of at least 1, for example in an oxidation state of 3 in case of gold.

[0090] In some implementations, a molar ratio of the noble metal to the oxidizing agent can be from about 0.0001 to about 600, optionally from about 0.001 to about 60, further optionally from about 0.01 to about 50, yet further optionally from about 0.05 to about 10. In some implementations, a molar ratio of the noble metal to the reaction media can be from about 0.0001 to about 750, optionally from about 0.001 to about 750, further optionally from about 0.01 to about 750, yet further optionally from about 0.1 to about 750. In some implementations, a molar ratio of the noble metal to the halide salt (when present in the reaction media) can be from about 0.0001 to about 650, optionally from about 0.001 to about 100, yet further optionally from about 0.1 to about 50. For example, the provided molar ratio can apply when the noble metal is gold and the metal-containing component is a gold-containing component. For example, a molar ratio of gold in the gold-containing alloy to TCCA can be from about 0.0001 to about 600; a molar ratio of the gold in the gold-containing alloy to water can be from about 0.0001 to about 750; and a molar ratio of the gold in the gold-containing alloy to sodium or potassium chloride can be from about 0.0001 to about 650. For example, the mixing can be performed using a limiting molar ratio of oxidizing agent to the at least one noble metal. For example, the molar ratio of oxidizing agent to the at least one noble metal can be between about 0.25 and about 1.

[0091] The dissolution process described herein can be carried out on a small, pilot or industrial scale, making it suitable for laboratory use, or on a larger scale, suitable for industrial applications (e.g., 0.001 to 1000 kg).

[0092] Further recovery steps of the noble metal of interest, such as gold, will depend on whether the other metals (metal impurities) have been obtained equally dissolved in the aqueous phase or undissolved as insoluble coordination complexes.

[0093] Referring to Figure 1, recovery of the noble metal generally includes separation 8 of the product mixture into the aqueous phase 10 and a solid component 12 including at least one of the unreacted material, coordination complexes and the organic by-product, if any. For example, the separation can include cooling the product mixture 6 and filtering the cooled product mixture to separate the cooled product mixture into the aqueous phase 10 and the solid component 12.Still referring to Figure 1, the process further includes mobilization 14 of the noble metal from the aqueous phase 10. Depending on the composition of the aqueous phase 10, for example depending on whether the aqueous phase 10 includes the noble metal of interest only or other metals considered as impurities, chemical or electrochemical reduction 14 of the noble metal of interest can include precipitation of the noble metal of interest in presence of a chemical reductant, or deposition of the noble metal of interest by electrolysis or electrowinning to produce a pure metal component provided in a slurry 16 or as layer of an electrode 16. Additional details regarding recovery implementations are provided further below. The process further includes separating 18 the pure metal component from the slurry / electrode, for example by filtration of the slurry or scraping of the electrode to recover the pure metal 20.Separation of the noblemetal of interest

[0094] Recovery of the noble metal, such as gold, is performed in two main steps which can be defined as a first separation of the metal impurities and organic by-products, and a second separation of the noble metal in purified form. For example, the noble metal can be recovered with a purity of at least 99%.

[0095] The product mixture can be separated into the aqueous phase and a solid component. In some implementations, recovering the aqueous phase from the product mixture can include cooling the product mixture to trigger precipitation of the organic by-product and produce a cooled mixture comprising a precipitated solid component and the aqueous phase. The cooled mixture is then filtered to separate the solid component and recover the aqueous phase as a filtrate. For example, the product mixture can be cooled to reach a temperature between 0.1 and 15 ºC, for example about 4 ºC. Then, the cooled product mixture can be further filtered through a fine to medium pore-size glass filter under vacuum to remove the precipitated solid component that can include insoluble and unreacted materials including the organic by-product.

[0096] For example, when the metal-containing component dissolution is complete and all metals are dissolved as halides in the aqueous phase, recovery of the aqueous phase can include precipitating the organic by-product and separating the precipitated organic by-product by filtration. For example, when TCCA, DCCA or MCCA is used as oxidizing agent, because CA is only sparingly soluble in H2O (0.27 g / 100 mL), the process can include precipitating the organic by-product CA and removing the precipitated organic by-product from the product mixture to recover the aqueous phase. The precipitated solid component is a reduced form of the oxidant TCCA, DCCA or MCCA that is recovered as the organic by-product, and can further be recycled and reused.

[0097] Then, the process includes recovering the noble metal from the separated aqueous phase (filtrate) including the noble metal in dissolved form. The aqueous solution, whether containing metal impurities as halides salts or not, can be thus further treated to allow recovery of the noble metal of interest, such as gold.

[0098] For example, gold (and optionally other metals in their reduced forms) can be recovered from the resultant aqueous phase by reduction into its insoluble metallic form using at least one of hydrides, chemical reductants, transition metal salts and low-valent elements, or by electrowinning. Although certain techniques are exemplified herein, it is noted that the recovery of the noble metal in its insoluble and purified form is not limited to those techniques.

[0099] In some implementations, the process can include recovering gold by adding a reducing agent to the aqueous phase to precipitate gold in its reduced form (metallic gold (Au)). For example, the reducing agent can be FeCl2or Cu, and is added to the recovered aqueous phase to reduce the gold halide KAuCl4or HAuCl4 into a solid powder of metallic gold, that is further recovered by filtration with a high purity.

[00100] An equation describing the precipitation of Au using FeCl2 as the reducing agent is provided below:HAuCl4(aq) + 3FeCl2(aq)  Au(s) + 3FeCl3(aq) + HCl(aq)

[00101] An equation describing the precipitation of Au using metallic Cu powder as the reducing agent is provided below:2 HAuCl4(aq) + 3 Cu(s)  2 Au(s) + 3 CuCl2(aq) + 2 HCl(aq)

[00102] In other implementations, the process can include recovering gold from the aqueous phase by electrowinning. For example, gold can be recovered from the aqueous phase by electrodeposition using an electrolytic cell, in a process known as electrowinning. The composition of the resulting aqueous phase impacts the performance of electrodeposition, including the rates of metal deposition, and its purity. Electrowinning has been investigated for recovering noble metals such as gold, silver, palladium, and platinum from dilute streams such as industrial wastewater or spent electrolytes from refineries, but it is not currently employed as part of a large-scale gold-refining process, as encompassed herein.

[00103] Additional example implementations of methods for recovering gold in purified form from the aqueous phase are provided in Examples 1 and 2.

[00104] It is noted that the recovery techniques allowing separation of the noble metal are not limited to the techniques described herein and encompass any techniques available to one skilled in the art for extraction of the noble metal from an aqueous phase.Mechanical assistance

[00105] The oxidative dissolution of the at least one noble metal is facilitated by the application of the mechanical force that enhances collisions of the various components of the reaction mixture by acceleration and favors dissolution of the metal(s) of the metal component, thereby leading to reduced energy, resource consumption and cost. The mechanical force is applied to provide a collision-based mixing to the mechanical system. The application of the mechanical force is tailored to allow displacement of the matter at an acceleration and a frequency being sufficient for maintaining the unreacted metal-containing component exposed to unreacted oxidizing agent, thereby allowing immediate consumption of the oxidation agent via oxidative dissolution of the at least one metal of interest into the reaction media.

[00106] It is noted that under insufficient mixing, the surface of the unreacted metal-containing component (e.g., gold-containing alloy) is not maintained in contact with fresh dissolving solution (unreacted oxidizing agent in reaction media), thereby allowing the oxidizing agent to react with itself and degrade which leads to a decrease in the oxidizing capacity of the dissolving solution. For example, in the implementation where TCCA is used as oxidizing agent, HOCl can be produced from TCCA when TCCA comes into contact with H2O. If the produced HOCl is not immediately consumed, HOCl will decompose, and the oxidizing capacity of the dissolving solution will decrease.

[00107] For example, application of the mechanical force during mixing includes exposing the reaction mixture to mechanical energy provided by acoustic waves having a frequency between 10 and 100 Hz, optionally between 40 and 70 Hz. The mechanical energy transmitted by the acoustic waves is tailored to provide an acceleration between 1 g to 100 g.

[00108] More particularly, as seen in Figure 1, the mechanical force 5 can be provided during mixing by subjecting the reaction mixture to resonance / resonant acoustic mixing, being referred to as RAM. Specific implementations regarding the application of the RAM in the context of the present process are provided further below.Resonance Acoustic Mixing (RAM) 15 mm

[00109] The application of a mechanical force during dissolution of the metal(s) from the metal-containing component allows for enhanced mixing and agitation of the reaction mixture, facilitating the process of oxidation and reducing the time and energy required for metal dissolution.

[00110] In some implementations, application of the mechanical force during oxidative dissolution of the metal(s) can be performed by Resonant Acoustic Mixing (RAM). By using RAM, the resulting metal dissolution rates are industrially relevant, and only small amounts of water can be used to allow a solid phase separation of the metal impurities.

[00111] Resonant acoustic mixing conditions advantageously provide the necessary mechanical force to facilitate the metal dissolution during mixing. To facilitate the oxidative dissolution of at least one noble metal of the metal-containing component in the reaction media, the reaction chamber containing the reaction mixture is subjected to the resonant acoustic mixing conditions. For example, the resonant acoustic mixing conditions can include an acceleration (g) (where g = 9.81 m.s-2) and a mixing time (minutes and hours).

[00112] In some implementations, the acceleration can be adjusted to different acceleration levels during the mixing time. For example, the acceleration can vary between 1 g and 100 g. For example, the mixing time can vary between 1 second to 24 hours.

[00113] A reaction vessel or reactor can be defined herein as including a reaction chamber for receiving the reaction mixture. The reactor is then placed in a RAM instrument that subjects the reaction chamber to the resonant acoustic mixing conditions. The use of the mechanical energy and the collisions that assist the chemical reaction using the RAM instrument improves the mixing and agitation of the reaction mixture within the reaction chamber and enhances the mass and heat transfer of the reactants, leading to more efficient and effective dissolution of the metal-containing component, such as a gold-containing alloy.

[00114] In some implementations, the RAM can be used in combination with other techniques, such as ultrasonication, mechanical grinding and heating or cooling, to enhance the dissolution process and achieve larger dissolution and conversion of the metal component. For example, the reaction mixture can be heated to a temperature of at most 250 ºC. For example, the RAM instrument can be integrated into automated systems, allowing for high-throughput dissolution of multiple samples with consistent results.

[00115] The use of the RAM as a source of mechanical force represents a significant advancement in the field of alloy dissolution, offering a versatile and effective tool for materials science and engineering research, as well as industrial applications for noble metal refinement.Electrowinning

[00116] Although various techniques can be used to recover metals of interest from the aqueous phase of the product mixture, electrowinning can be performed to precipitate the at least one noble metal when dissolved in the aqueous phase of the product mixture.

[00117] There is thus provided a process including dissolution of at least one noble metal from a metal-containing component (e.g., alloy) according to the steps described herein, recovery of the aqueous phase as a metal-bearing solution including the at least one noble metal in dissolved form, and then extraction of the at least one noble metal by subjecting the metal-bearing solution to electrowinning.

[00118] The electrowinning process for precipitating the at least one metal of interest (noble metal) includes providing the separated aqueous phase, being referred to as the metal-bearing solution, in an electrolytic cell including a cathode, an anode and an inlet to receive the metal-bearing solution for contacting the cathode and anode. The process further includes delivering a voltage across the electrolytic cell, and applying a current density, thereby facilitating the selective deposition of the metal of interest on the cathode.

[00119] As readily understood, the metals of the metal-bearing solution can be recovered successively or simultaneously by covering the cathode.

[00120] In some implementations, the metal-bearing solution includes gold ions (Au+, Au3+ or AuCl4-), and the delivered voltage is between 1.0 V and 1.5 V, while the current density is maintained between 10 A.m-2 and 600 A.m-2, resulting in an efficient electrowinning of gold onto the cathode. In some implementations, the metal-bearing solution further comprises a mixture of copper (Cu2+) and silver (Ag+) ions, and the power supply can be set to deliver a voltage range of 2 to 8 volts, while the current density in the range of 400 to 800 A.m-2, allowing for the simultaneous electrowinning of copper and silver.

[00121] In order to tailor the electrowinning conditions to the metal of interest to be precipitated, there is further provided a method for optimizing electrowinning parameters to precipitate the noble metal of interest. The method includes conducting a series of electrowinning experiments with varying voltage ranges and current densities, for example according to the electrowinning process described herein. The method further includes analyzing each noble metal's deposition efficiency and purity. Then, the method includes determining an optimal voltage range and an optimal current density range for each noble metal that can be used as specification. The electrowinning techniques as described herein can then be tailored to a given metal-bearing solution by adjusting the voltage and current density (e.g. by gradually increasing a reduction potential) to the pre-determined specification for each noble metal, thereby enabling selective and efficient electrowinning of noble metals, from a metal-bearing solution.

[00122] In some implementations, the method can further include varying at least one of a pH, a KCl or NaCl content and a water content of the metal-bearing solution and determining an optimal composition of the metal-bearing solution enabling selective and efficient electrowinning of multiple noble metals from a metal-bearing solution. Particularly, the pH was found to influence an oxygen evolution reaction at the anode and possibly gold deposition at the cathode. KCl content was found to influence a solution conductivity in order to minimize ohmic drop. Water content is preferably reduced to increase the concentration of the noble metal(s), for example the gold concentration in the metal-bearing solution.Purity

[00123] The process for dissolution of the metal of interest and recovery as a purified metal as described herein allows the recovery of the purified metal with a purity of at least 99%, preferably of at least 99.5%.

[00124] The techniques used herein to evaluate purity of the recovered purified metal component include Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) which is an analytical technique used to determine how much of certain elements are in a sample (being the recovered aqueous phase).

[00125] It is noted that standard analytical techniques, such as spectrometry or microscopy, are used to evaluate the properties of the dissolved metal component and its constituent elements.EXPERIMENTAL RESULTSExample 1

[00126] Performance of the present process was tested on an initial reaction mixture being provided in a 60 mL Nalgene® reaction vessel, and including 1 gram scale of a gold-rich alloy having an average particle size of at most 10 mm, 3 equivalents of TCCAas oxidizing agent, and a reaction media consisting of 40 mL of water and 0.2 grams of KCl as halide salt. As seen in Figure 5, application of RAM was performed at three different accelerations (30 g, 60 g and 90 g).

[00127] Comparative performance of the oxidative dissolution of gold from a gold-rich alloy is provided in Figure 6 using a conventional aqua regia process under mixing at 300 rpm using a stir plate and the present process upon application of RAM at 90 g of acceleration, at three different temperatures and under atmospheric pressure.Dissolution

[00128] More particularly, oxidative dissolution of a gold-rich alloy according to the present process was tested in a chloride aqueous solution in presence of TCCA as the oxidizing agent. A custom-made reactor with an inside volume of 60 mL was charged with 1 g of a gold-rich alloy powder, optionally 0.2 grams of alkali salts, 3.15 g of TCCA and 40 mL of water. The gold-rich alloy can include Au, Cu, Ag, Ni, Fe, Zn, Te, Cr, V, Ti, Pd, Pt, Rh, Ir and Co. Oxidative dissolution could also be performed at room temperature in different molar ratio compositions of the above reactants, i.e., from 0.0001 to 600 related to the ratio of gold to TCCA; from 0.1 to 700 of gold to water; and from 0.0001 to 650 of gold to sodium or potassium chloride. Upon addition of water as the final reagent to form the reaction mixture, the reactor is closed by tightening the lid. The reactor is then placed into a RAM instrument where a mechanical force is applied to the reactor according to a series of gradual increases in acceleration: e.g., 20 g for 10 seconds, 30 g for 10 seconds, 40 g for 10 seconds and so on until reaching an acceleration target.

[00129] For comparison purpose, gold dissolution based on a conventional aqua regia process was performed at 300 rpm at room temperature. More particularly, a 20 mL screw cap glass vial was charged with 1 gram of alloy, 4 mL of H2O (such as deionized water) and a mixture of aqua regia comprised of 3 mL of concentrated HCl and 1 mL of concentrated HNO3. The system was magnetically stirred and the vial tightly closed, and samples were taken over time until the alloy was completely dissolved.

[00130] The progress of the reaction was monitored by taking samples of the aqueous phase (20 µL diluted with H2O to 25 mL in a class A volumetric flask) and analyzed by ICP-OES by comparing concentrations of dissolved metals against standard calibration curves for the elements of interest. The Au dissolved over time is plotted in Figure 6.

[00131] The resulting aqueous phase of the product mixture was seen to turn from a clear solution to light yellow to finally green. It is noted that the resulting colour depends on the alloy composition and the extent of dissolution of one or several metals. The reaction is stopped, and the reactor is open in a well-ventilated fume hood for a few minutes while control samples are taken. Insoluble and unreacted alloy residues might be observed. The reactor is then closed again and put back into the RAM instrument to complete the dissolution, if necessary, for an additional 3 hours.

[00132] The optimized operation conditions determined from Figure 5 have been selected and maintained to evaluate the effect of temperature on dissolution of the gold-rich alloy, as shown in Figure 6. Based on the same protocol, gold being the primary noble metal of interest in the alloy, was identified and quantified using ICP-OES over time for temperatures varying from 25 oC to 95 oC using the optimized conditions for alloy dissolution. It can be seen that an increase in temperature from 25 oC to 95 oC generated a more than 7-fold gold dissolution increase at 1 minute of RAM mixing; a more than 11-fold gold dissolution increase at 2 minutes of reaction and a more than 7-fold gold dissolution increase at 4 minutes of mixing.

[00133] Figure 6 shows comparative alloy dissolution over time. Optimized operation conditions for the present process can for example be selected as 16 minutes of mixing where the gold dissolution reached 85% when an acceleration of 90 g is used at 60oC. In comparison to the aqua regia process, it can be said that 85% of the gold is dissolved at the same reaction time. The latter with the understanding of all downstream are unfavorable conditions mentioned which include the use of high toxic and corrosive oxidants. Increasing the reaction temperature to 95oC at 90 g of acceleration will ensure complete dissolution at 16 minutes of reaction.

[00134] Figure 7 represents the fitting of a Shrinkage kinetic model applied to the dissolution of gold, copper and nickel under the conditions of process described herein. The data can be calculated from the following equation:1-(1-x)1 / 3 = krtwhere x is the yield of dissolved gold, copper and nickel, kr is the reaction rate constant (minutes-1) and t is the reaction time (minutes).

[00135] The yield of dissolved gold and all other metal elements can then be calculated with the following equation: Separation of impurities and byproducts

[00136] Once the mixing time in the RAM instrument is complete, the product mixture that contains the dissolved metals and organic by-products is placed in an ice-cold bath until the temperature reaches 4 oC to induce the precipitation of the organic by-product being cyanuric acid (CA). CA is then recovered by vacuum filtration. Figure 8 shows the FTIR of the solid generated as a byproduct of alloy dissolution. The resultant aqueous solution is then reduced to ¼ of its original volume and placed in an ice bath. The aqueous solution is acidified to a pH < 1 by adding concentrated HCl dropwise. At this point, additional CA is recovered by filtration to reach >98% of the expected material. The remaining 2% of CA stays soluble in the aqueous solution as a possible adduct with metal impurities, including Cu, Ag, Au, Ni, Fe, Zn, Te, Cr, V, Ti and Co, and alkali salts.Separation of a purified gold componentMethod 1

[00137] A first method including precipitation of the recovered aqueous solution was tested. More particularly, the clear, homogenous aqueous solution produced upon removal of CA was then transferred to an Erlenmeyer flask for use as the metal-bearing solution. A freshly made aqueous reducing solution was prepared including a reducing agent being MX2 (MX salts including iron(II) chloride, iron(II) sulfate) or sodium hydrogen sulfite or sulfur dioxide gas, oxalic acid, metallic elements, gas compounds - with a reduction potential between 1 and 10 V, was then added to the metal-bearing solution (filtrate) to produce a brown-black precipitate of metallic gold. A 5% excess of MX2 was used to ensure complete reduction of all Au+ or Au3+ions. The stoichiometry of a representative reduction using FeCl2 as reducing agent can be described by the following equation:HAuCl4(aq) + 3 FeCl2(aq)  999Au(s) + 3 FeCl3(aq) + HCl(aq)

[00138] The resulting mixture was decanted and filtered using filter paper under vacuum to recover the purified gold (999Au). The recovered gold was then washed with hot water (>90 oC) to remove unwanted alkali salts or any residual organic byproducts. The recovered gold was then placed in a petri dish and dried in an oven at 100 oC for six hours to afford metallic 999Au confirmed by ICP-OES analysis.

[00139] For example, the gold-rich alloy (with an initial composition determined by ICP-OES corresponding to 89% Au, 8% Cu, 2% of Ni plus other impurities) and post-processing purified gold component are characterized by powder X-ray diffraction (PXRD) analysis as presented in Figure 3. 2 theta angles and their respective diffraction planes were recorded at 38.39o (111), 44.61o (200) and 64.80o (220) assigned to pure gold with no other impurities observed. A slightly symmetric shift in the diffraction planes for Cu was presented as the main impurity recorded for the Alloy at 39.19 o (111), 45.48 o (200) and 66.58 o (220). The results agree with the face-centered cubic (FCC) structure with a lattice distance of 4.078 Å for metallic gold and 3.615 Å for metallic copper. Due to their low concentration, nickel and silver's components are not observed in the XRD pattern. Purity of the recovered gold can thus be said to be of at least 99.9 % by ICP-OES. Figure 4 provides scanning electron microscope (SEM) images of the gold-rich alloy with magnifications of 640 (100 µm scale), 6000 (10 µm scale) and 30000 (1 µm scale) were employed to determine the nature of the material.Method 2, precipitation b:

[00140] A second method was tested.  The clear homogenous solution produced upon removal of the CA from the aqueous phase was then transferred to a glass vessel as the metal-bearing solution.  Fine copper powder was added to the metal-bearing solution until a specified oxidation-reduction potential is attained, indicating that all the gold has precipitated out of the solution.  The stoichiometry of the precipitation reaction can be described by the following equation: 2HAuCl4(aq)  +  3Cu(s)            2Au(s)  +  3CuCl2(aq)  +  2HCl(aq) 

[00141] The resulting mixture was then stirred and heated to a temperature between 50°C and 100°C until all non-gold salts and / or organic by products were dissolved into solution.  At this point the hot clear liquid is decanted and fresh hot water (50-100°C) is added to the gold and again is stirred and heated.  This rinsing procedure was repeated until the rinse water was no longer colored. The recovered gold was then placed in a petri dish and dried at 400°C for 1hr to afford a purified metallic gold confirmed by ICP and Spark Analysis.Method 3

[00142] Another gold recovery method was tested by subjecting the filtered aqueous solution (that is depleted in organic by-product CA and used as the metal-bearing solution) to electrowinning. The following reactions are expected at a surface of used electrodes of an electrolytic cell including a cathode and an anode.

[00143] Cathode:HAuX4 + 3 H+ + 3e-  9999Au(s) + 4HClCA + 3 Cl- + 3e-  TCCA + 3H+2H2O + 2e-  H2 + 2OH-

[00144] Anode:2H2O  O2 + 4H+ +4e-

[00145] More particularly, the metal-bearing solution was electrowon in a lab scale electrolytic cell using a three-electrode setup including a 2 mm diameter platinum disk electrode as the cathode, a platinum mesh as the anode and a saturated calomel reference electrode (SCE). Referring to Figure 10, the application of a potential of 0.2 V vs SCE to the metal-bearing solution led to a significant increase in reductive current in comparison to blank solutions of 0.1M NaCl and 0.01M TCCA / CA in 0.1M NaCl. After 10 minutes, a brown colored deposit was seen on the cathode which was confirmed to be 999Au by ICP-OES.Example 2Dissolution of gold-rich alloy using 0.25 equivalents of TCCA

[00146] Using the same reactor as in Example 1, 50 g of gold-rich alloy is added with 15 g of TCCA, 20 g of NaCl and 50 mL of water. The reactor is then put into the RAM at 60 g of acceleration for 1 hour. Once the time is complete, a green aqueous emulsion is observed in the top of the multiphasic product mixture.Separation of impurities and byproducts

[00147] After the alloy dissolution is complete, the product mixture is cooled to 4 oC and filtered in a fine to medium pore-size glass filter under vacuum to remove insoluble and unreacted materials as a green solid, thereby forming the metal-bearing solution (filtrate).

[00148] ICP-OES analysis of the resultant filtrate reveals that Au purity is of at least 99% and the green solid contains Ni and Cu complexes, along with all present impurities in the gold-rich alloy used for the initial dissolution.

[00149] ICP-OES analysis of the resultant green solid demonstrates that ~3% of gold, 85% of Cu and 11% of Ni plus other metal impurities were separated from the initial gold-rich alloy material in form of M-complexes. The remaining 3% of Au can be recovered with consecutive washes of the green solid with hot water. The CA by-product can also be precipitated and recovered when diluted HNO3 or HCl is added.

[00150] It is worth mentioning that throughout the description when the article “a” is used to introduce an element it does not have the meaning of “only one” it rather means of “one or more”. For instance, the reactor according to the invention can be provided with one or more reaction chambers without departing from the scope of the present invention. It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

[00151] In the following description, the term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. It is commonly accepted that a 10% precision measure is acceptable and encompasses the term “about”.

[00152] It should be understood that any one of the above-mentioned aspects / implementations of each process, method, reactor, system described herein may be combined with any other of the aspects thereof, unless two aspects clearly cannot be combined due to their mutual exclusivity. For example, the various operational steps of the mechano-chemical process described herein-above, herein-below and / or in the appended Figures, may be combined with any of the general aspects of the electrowinning process, method, or system as described herein.

Claims

1. A mechano-chemical process for separating at least one noble metal from a solid metal-containing component comprising the at least one noble metal and at least one metal impurity, the process comprising:forming a reaction mixture comprising the metal-containing component, an oxidizing agent of Formula (AE)zCnHmNpOqXa , and a reaction media comprising a protic solvent;subjecting the reaction mixture to mixing under an applied mechanical force to perform oxidative dissolution of the at least one noble metal from the metal-containing component, thereby forming a product mixture that comprises:an aqueous phase comprising the at least one noble metal having an oxidation state of at least 1 being present in dissolved form as a metal halide salt, a metal hydroxide salt, a metal hydroxide halide salt, a metal halide acid, or any combination thereof, andan insoluble by-product being suspended in the aqueous phase, the insoluble by-product comprising metal coordination complexes of at least one of a metal halide salt, a metal hydroxide salt and a metal hydroxide halide salt, wherein the metal from the metal coordination complexes is from the at least one metal impurity;separating the product mixture into the aqueous phase and a solid component comprising the organic by-product; andrecovering the at least one noble metal from the aqueous phase,wherein z, n, m, p, q, a are integers varying from 0 to 10, AE is an alkali metal, X is an halogen, andthe mechanical force is applied by acoustic waves providing an acceleration between 1 g and 100 g.

2. The process of claim 1, wherein the at least one noble metal of the metal-containing component is selected among Ag, Au, Pd, Pt, Ru, Rh, Os, Ir or any combinations thereof, and optionally the at least one noble metal of the metal-containing component is Au.

3. The process of claim 1 or 2, wherein the metal-containing component is in the form of coarse grains or powder having an average particle size of at most 20 mm.

4. The process of any one of claims 1 to 3, wherein the oxidizing agent is:, , , , , , , , , or an alkali salt thereof.

5. The process of any one of claims 1 to 3, wherein the oxidizing agent is:,wherein each X2 is independently from one another: X1, H or an alkali metal, and wherein X1 is Cl, Br or I, and optionally wherein X1 is Cl.

6. The process of any one of claims 1 to 5, wherein z + m = 3 – a.

7. The process of any one of claims 1 to 6, wherein the oxidizing agent is selected among MCCA, DCCA or TCCA, or an alkali salt thereof, and optionally the oxidizing agent is TCCA.

8. The process of any one of claims 1 to 6, wherein the oxidizing agent is HOCl or NaOCl.

9. The process of any one of claims 1 to 8, wherein the reaction media is a chloride solution and the at least one noble metal in metal halide salt form dissolved in the aqueous phase is at least one of a mono-, di- or tri-chloride salt.

10. The process of any one of claims 1 to 9, wherein the metal-containing component is a gold-containing alloy comprising gold, copper and nickel, the at least one noble metal is gold, the reaction media is a sodium, potassium or calcium chloride solution, and the at least one noble metal in metal halide form is at least one of a mono- or tri-chloride salt.

11. The process of claim 10, wherein a molar ratio of gold to oxidizing agent is from 0.0001 to 600; a molar ratio of gold to water is from 0.0001 to 750; and a molar ratio of gold to halide salt in reaction media is from 0.0001 to 650.

12. The process of any one of claims 1 to 11, wherein a molar ratio of the oxidizing agent to the at least one noble metal is a limiting ration being between 0.25 and 1.

13. The process of any one of claims 1 to 12, wherein separating the product mixture into the aqueous phase and the solid component comprises:cooling the product mixture to trigger precipitation of the insoluble by-product and produce a cooled mixture comprising the solid component and the aqueous phase; andfiltering the cooled mixture to separate the solid component and recover the aqueous phase as a filtrate.

14. The process of any one of claims 1 to 13, wherein the metal-containing component comprises multiple metals as metal impurities and the aqueous phase further comprises the multiple metals in dissolved form as metal halide salt, metal halide acid, metal hydroxide salt, metal halide hydroxide salt, alkali salt of a metal hydroxide, or any combinations thereof.

15. The process of any one of claims 1 to 14, wherein the solid component of the product mixture further comprises undissolved / unreacted material from the metal-containing component.

16. The process of any one of claims 1 to 15, wherein recovering the at least one noble metal from the aqueous phase comprises adding a reducing agent to the aqueous phase to perform reductive precipitation of the at least one noble metal.

17. The process of claim 16, wherein the recovery of the at least one noble metal from the aqueous phase comprises reduction of all metals into an insoluble metallic form using at least one of hydrides, chemical reductants, transition metal salts and low-valent elements.

18. The process of claim 16, wherein the recovering of the at least one noble metal component from the aqueous phase comprises subjecting the recovered aqueous phase to electrolysis or electrowinning for reduction of the at least one noble metal into an insoluble metallic form.

19. The process of any one of claims 1 to 18, wherein the frequency of the applied acoustic waves is between 10 Hz and 100 Hz.

20. The process of any one of claims 1 to 19, wherein the application of the mechanical force includes subjecting the reaction mixture to resonance acoustic mixing.

21. The process of claim 20, wherein the resonance acoustic mixing is performed under conditions comprising a mixing time between 1 s to 24 h.

22. The process of claim 21, comprising varying the acceleration of the resonance acoustic mixing according to different acceleration levels during the mixing time.

23. The process of any one of claims 1 to 22, further comprising adjusting a temperature of the reaction mixture during mixing.

24. The process of any one of claims 1 to 23, further comprising applying additional mechanical force during mixing via at least one of ultrasonication or mechanical grinding.

25. The process of any one of claims 1 to 24, wherein the at least one noble metal of the metal-containing component is gold, and the recovered gold has a purity of at least 99 %.

26. The process of any one of claims 1 to 25, wherein the protic solvent is water.

27. The process of any one of claims 1 to 26, wherein the reaction media is an aqueous solution of at least one halide salt of an alkali metal or an alkaline earth metal.

28. A dissolving system for recovering at least one noble metal from a solid metal-containing component, the dissolving system consisting of:an oxidizing agent of Formula (AE)zCnHmNpOqXa, wherein z, n, m, p, q, a are integers varying from 0 to 10, AE is an alkali metal, and X is a halogen,a reaction media being water or an aqueous solution of at least one halide salt of an alkali metal or an alkaline earth metal, andmechanical energy provided by resonant acoustic waves.

29. The system of claim 28, further having at least one feature as defined in any one of claims 1 to 27. 

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