The process of recovering metals from electronic waste

Abstract

SOLUTION: The invention relates to a method for recovering precious metal from electronic waste. Specifically, biometallurgical techniques are utilized during the process. In a first aspect, the invention provides a method of recovering one or more pieces of target metal from electronic waste, the method comprising (a) a pre-processing step comprising removing at least a portion of a non-target material from the electronic waste or grinding to a preselected size particle to give pre-processed electronic waste; (b) a dissolving step comprising contacting the pre-processed electronic waste with a leachant such that at least a portion of the pieces of target metal dissolve into the leachant to produce a pregnant solution; (c) a biosorption step comprising contacting a microorganism with the pregnant solution such that at least a portion of the target metal ions is biosorbed to the microorganism wherein the microorganism becomes metal laden and the pregnant solution becomes barren; (d) a separating step comprising substantially separating the metal laden microorganism from the barren solution; and (e) a recovery step comprising recovery of the pieces of target metal from the metal laden microorganism. In particular embodiments, the target metal is gold.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a process for recovering at least one precious metal from electronic waste, in particular during which biorefining techniques are used. [Background technology]

[0002] There are numerous materials throughout the world, including aqueous solutions and solid materials, that contain trace metals. However, due to the relative scarcity of metal constituents relative to non-metallic matrices, recovering these metals in an efficient and environmentally safe manner presents an enormous challenge. For example, the removal of toxic metal ions from aqueous waste streams presents a major challenge to a wide range of industries.

[0003] Similarly, as ore grades for virgin metal mining and refining decline, there is growing interest in obtaining metals from sources such as low-grade mining ores, smelter tailings, and electronic waste. However, recovering metals from these raw materials is often prohibitively expensive. Factors that affect the feasibility of any recovery process include the metal concentration of the raw material (and therefore the amount of raw material required for processing); the presence of impurities, such as other metals or refractory materials; and the volume of waste generated. Therefore, there is room for alternative solutions that target at least some of these problems and thereby improve the economics of recovering metals from low-grade or difficult-to-handle raw materials.

[0004] Conventional techniques for refining metals include pyrometallurgy and hydrometallurgy. In pyrometallurgy, raw materials are smelted at high temperatures (typically in the presence of suitable reducing agents and / or catalysts). This requires significant energy input (and associated emissions), and therefore a practical minimum metal concentration is required in the raw materials. In hydrometallurgy, the raw materials are treated with a leachant solution, which leaches the desired metals (specific or otherwise) into ionic or complexed soluble forms. Subsequent steps are required to recover the target metals from the solution (e.g., electrowinning). Depending on the temperature and pressure required for leaching, this approach may allow for processing of lower grade raw materials compared to pyrometallurgy. Considerations must be considered: the possible use of corrosive (e.g., acidic) or toxic (e.g., cyanide) solutions; any consumption of solution components during raw material processing; and the proper handling of waste effluents. Pyrometallurgical and hydrometallurgical techniques are not mutually exclusive and may be used sequentially over multiple steps to refine a particular metal.

[0005] The recovery of gold from gold-bearing ores is a prime example of a hydrometallurgical approach that presents multiple challenges. The amount of gold in gold-bearing ores has been declining for centuries as higher gold-content, more easily recoverable sources have been depleted through extensive mining. As such, hydrometallurgical techniques have been used to recover trace amounts of gold from large volumes of rock. Cyanide-based lixiviants have been successfully employed for many years, but toxicity issues and significant challenges associated with processing certain ore types remain.

[0006] Electronic waste, such as printed circuit boards from computers, mobile phones, notebooks, and LCD displays, is a major target for metal recovery systems. Approximately 41.8 million tons of electronic waste (e-waste) were generated worldwide in 2014, and this is expected to increase to 50 million tons by 2018 (Balde et al., The global e-waste monitor - 2014, United Nations University, IAS - SCYCLE, Bonn, Germany (2015)). On a per-unit-weight basis, this e-waste contains higher amounts of valuable base and precious metals (including gold) compared to virgin ore. Recovering metals from this raw material is attractive because the mining and refining processes used to obtain virgin metals consume energy and water resources (and generate associated carbon emissions); reuse means that these costs do not have to be incurred again. For example, recycling copper requires 85% less energy than producing virgin material from raw ore (Khaliq et al, Resources 3, pp 152-179 (2014)).

[0007] Electronic waste, such as printed circuit boards from computers, mobile phones, notebooks, and LCD displays, also contains significant amounts of precious metals (including gold). While much effort has been devoted to recovering gold and other metals from e-waste using pyrometallurgical or hydrometallurgical methods, sustainable success has yet to be achieved. Pyrometallurgical methods typically require incineration of circuit boards to liberate and fractionate the metals, which is energy- and capital-intensive and generates hazardous gases such as dioxins. Hydrometallurgical methods typically require the use of strong acids or cyanide-based solutions to leach metals, which are highly toxic, expensive, and non-recyclable. The heterogeneity of e-waste as a raw material also makes these existing technologies difficult to apply economically.

[0008] Biorefining is a more recent approach that uses microorganisms to expose, leach, bind, and / or recover metals from raw materials under ambient conditions (Zhuang et al, Current Opinion in Biotechnology 33, pp 327-335 (2015)). The use of microorganisms can further reduce the minimum grade required for raw materials or can make it possible to economically process raw materials that are complex mixtures or that are difficult to handle in pyrometallurgical and / or hydrometallurgical processes. However, a common trade-off is reaction time, with biorefining often requiring weeks to years to recover metals from raw materials (e.g., biooxidation of refractory copper ores using sulfur-reducing bacteria).

[0009] It is an object of the present invention to provide a method for recovering precious metals from e-waste using biorefining techniques that complement or replace traditional pyrometallurgical and hydrometallurgical approaches. This is expected to lead to the capture of valuable metals from currently ignored low-grade or waste streams, or at least provide the public with a useful option in this regard. It is an alternative object of the present invention to provide a method for recovering one or more target metals from e-waste, and / or the target metals recovered thereby, and / or a system for recovering the target metals, or at least provide the public with a useful option. Summary of the Invention [Means for solving the problem]

[0010] The present invention addresses the need in the art.The present invention provides a method for recovering at least one precious metal from electronic waste.

[0011] In a first aspect, the present invention provides a method for recovering one or more target metals from e-waste, the method comprising: (a) a pre-treatment step comprising removing at least a portion of non-target materials from the e-waste or grinding the e-waste into particles of a pre-selected size to provide pre-treated e-waste; (b) a dissolution step comprising contacting the pretreated e-waste with a leaching agent to dissolve at least a portion of the target metals in the leaching agent to produce a pregnant liquor; (c) a biosorption step comprising contacting a microorganism with the pregnant liquor such that at least a portion of the target metal ions are biosorbed by the microorganism, causing the microorganism to accumulate the metal and impoverish the pregnant liquor; (d) a separation step comprising substantially separating the metal-accumulating microorganisms from the barren solution; (e) a recovery step comprising recovering the target metal from the metal-accumulating microorganisms.

[0012] In certain embodiments, the target metal is gold.

[0013] In certain embodiments, the e-waste contains less than 5%, or less than 1%, or less than 0.1%, or less than 0.01%, or less than 0.001%, or less than 0.0001% of the target metal.

[0014] In certain embodiments, the pre-processing step comprises: Chip removal Grinding to a preselected size Removal of specific density fractions Removal of magnetic materials base metal leaching, The method includes one or more unit operations selected from the group consisting of:

[0015] In certain embodiments, the pre-processing step comprises at least one of these unit operations. In other embodiments, the pre-processing step comprises at least two of these unit operations. In other embodiments, the pre-processing step comprises at least three of these unit operations. In other embodiments, the pre-processing step comprises at least four of these unit operations.

[0016] In certain embodiments, the pre-treatment step removes at least a portion of the non-target materials from the e-waste to provide pre-treated e-waste.

[0017] In certain embodiments, the pretreatment step comprises base metal leaching.

[0018] In certain embodiments, the pretreatment step includes grinding and base metal leaching.

[0019] In certain embodiments, the pretreatment step removes at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the non-target material prior to recovery of the target metal. In certain preferred embodiments, the pretreatment step removes less than 20%, or less than 10%, or less than 5%, or less than 2%, or less than 1% of the target metal.

[0020] In certain embodiments, the non-target material comprises one or more non-target metals. In certain embodiments, the non-target metals are base metals. In certain embodiments, the pre-treatment step removes at least a portion of the non-target metals. In certain embodiments, the pre-treatment step removes at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the non-target metals prior to recovery of the target metals.

[0021] In certain embodiments, chip removal involves at least partially removing the solder used to secure the chip to the printed circuit board by raising the temperature of the solder above its melting point or by dissolving the solder in a suitable solvent. In certain embodiments, the solder comprises a non-target material. In certain embodiments, the solder comprises a non-target metal. In certain embodiments, the solder comprises a base metal.

[0022] In certain embodiments, a pre-processing step includes grinding to a pre-selected average size, wherein the pre-selected size is an average of about 10 to 0.05 mm diameter, hi certain embodiments, the pre-selected size is an average of about 5 to 0.1 mm diameter.

[0023] In certain embodiments, the grinding comprises the use of any one or more of a hammer mill, a ball mill, a ring mill, a shredder, and a cutter.

[0024] In certain embodiments, the pre-processing step includes grinding and separating particles that are substantially above a preselected maximum size, specifically less than about 10 cm, or less than 8 cm, or less than 5 cm, or less than 3 cm, or less than 1 cm.

[0025] In certain embodiments, base metal leaching involves treating the e-waste with a lixiviant comprising nitric acid, sulfuric acid, and / or hydrochloric acid. In certain embodiments, base metal leaching involves treating the e-waste with a lixiviant comprising sulfuric acid. In certain embodiments, the lixiviant comprises sulfuric acid and an oxidizing agent. In certain embodiments, the oxidizing agent is selected from hydrogen peroxide, potassium peroxymonosulfate, ozone, oxygen gas, or air (containing oxygen). In certain embodiments, the lixiviant comprises sulfuric acid and hydrogen peroxide.

[0026] In certain embodiments, removing the magnetic material comprises applying a magnetic field.

[0027] In certain embodiments, removing the density fraction comprises separating the e-waste into fractions using flotation, shaker tables, and / or electrostatic separation.

[0028] In certain embodiments, the pregnant liquor contains between about 0.1 ppm and 1500 ppm, or between about 0.1 ppm and 1000 ppm, or between about 0.1 ppm and 500 ppm, or between about 0.1 ppm and 200 ppm, or between about 0.1 ppm and 100 ppm, or between about 0.1 ppm and 50 ppm, or between about 0.1 ppm and 20 ppm of the target metal. Preferably, the pregnant liquor contains between about 0.5 ppm and 1500 ppm, or between about 0.5 ppm and 1000 ppm, or between about 0.5 ppm and 500 ppm, or between about 0.5 ppm and 200 ppm, or between about 0.5 ppm and 100 ppm, or between about 0.5 ppm and 50 ppm, or between about 0.5 ppm and 20 ppm of the target metal. Preferably, the pregnant liquor contains between about 1 ppm and 1500 ppm, or between about 1 ppm and 1000 ppm, or between about 1 ppm and 500 ppm, or between about 1 ppm and 200 ppm, or between about 1 ppm and 100 ppm, or between about 1 ppm and 50 ppm, or between about 1 ppm and 20 ppm of the target metal.

[0029] In certain embodiments, the leaching agent dissolves at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% of the target metals from the e-waste. In certain embodiments, the leaching agent dissolves 95-99.5% of the target metals.

[0030] Preferably, the electronic waste comprises printed circuit boards (PCBs). Preferably, the PCBs comprise at least 10 ppm, or at least 20 ppm, or at least 50 ppm, or at least 100 ppm, or at least 200 ppm, or at least 300 ppm, or at least 400 ppm, or at least 500 ppm of target metal. Because PCBs contain multiple metals, including base metals and target metals, it is recognized that there are substantial benefits in using a leaching agent that selectively dissolves target metals over other non-target metals. However, it is recognized that selectivity may be poor because precious metals (target metals) are typically less reactive than base metals.

[0031] In certain embodiments, the target metal and non-target materials are substantially selectively dissolved by the leaching agent, hi certain embodiments, the target metal and non-target materials are substantially selectively dissolved by the leaching agent at a ratio of greater than 1:1000 (target metal:non-target materials), or greater than 1:500, or greater than 1:200, or greater than 1:100, or greater than 1:50, or greater than 1:20, or greater than 1:10, or greater than 1:5, or greater than 1:2, or greater than 1:1.

[0032] In certain embodiments, the non-target material is a non-target metal. In certain embodiments, the non-target metal is a base metal. In certain embodiments, the target metal and the non-target metal are substantially selectively dissolved by the leaching agent. In certain embodiments, the target metal and the non-target metal are substantially selectively dissolved by the leaching agent at a ratio of greater than 1:1000 (target metal:non-target material), or greater than 1:500, or greater than 1:200, or greater than 1:100, or greater than 1:50, or greater than 1:20, or greater than 1:10, or greater than 1:5, or greater than 1:2, or greater than 1:1.

[0033] In certain embodiments, the leaching agent solution is a thiourea-based aqueous solution, or a thiosulfate-based aqueous solution, or a thiocyanate-based aqueous solution, or a cyanide-based aqueous solution, or a halogen-based aqueous solution, or an aqua regia-based solution. In certain embodiments, the leaching agent includes a chloride source. In certain embodiments, the leaching agent includes a chloride source and an oxidizing agent. In certain embodiments, the leaching agent includes an aqueous solvent, an oxidizing agent, and an acid, as specified by Foley et al. in International Publication No. WO 2016 / 168933 (incorporated herein by reference). In certain embodiments, the leaching agent includes a halogen solution, or acetic acid and chlorine, or hydrochloric acid and peroxide.

[0034] In certain embodiments of the biosorption step, the microorganisms are in contact with the pregnant liquor for between about 0.5 and 48 hours, or in certain embodiments, between about 0.5 and 24 hours, or between about 0.5 and 12 hours, or between about 0.5 and 4 hours, or between about 1 and 3 hours.

[0035] In certain embodiments, the barren solution contains less than 0.1 ppm, or less than 1 ppm, or less than 2 ppm, or less than 5 ppm, or less than 10 ppm, or less than 20 ppm, or less than 50 ppm, or less than 100 ppm of the target metal. In certain embodiments, the barren solution contains between about 0.001 ppm and 100 ppm, or between about 0.001 ppm and 50 ppm, or between about 0.001 ppm and 50 ppm, or between about 0.01 ppm and 50 ppm of the target metal.

[0036] In certain embodiments, the pregnant liquor contains at least 10 times more target metal than the barren liquor, hi certain embodiments, the pregnant liquor contains at least 20 times, or at least 40 times, or at least 45 times, or at least 50 times more target metal than the barren liquor.

[0037] In particular embodiments, the metal-accumulating microorganisms contain greater than 100 ppm, or greater than 200 ppm, or greater than 500 ppm, or greater than 1,000 ppm, or greater than 30,000 ppm of the target metal.

[0038] In certain embodiments, the enrichment factor of the target metal from the pregnant liquor to the microorganisms is greater than 5, or greater than 10, or greater than 20, or greater than 50, or greater than 100, or greater than 900.

[0039] In certain embodiments, the biosorption step is carried out at ambient temperature, for example, between about 15°C and 30°C.

[0040] In certain embodiments, the microorganism is an algae or a bacterium. In certain embodiments, the microorganism is a gram-negative or gram-positive bacterium. In certain embodiments, the microorganism is of the genus Pseudomonas, Escherichia, Bacillus, Desulfovibrio, Plectonema, Cupriavidus, Clostridium, or Delftia.

[0041] In certain embodiments where the target metal is gold, the microorganism is selected from Cupriavidus metallidurans, Delftia acidovorans, Pseudomonas aeruginosa, P. putida, Desulfovibrio desulfuricans, Bacillus subtilis, or Plectonema boryanum.

[0042] In certain embodiments where the target metal is gold, the microorganism is selected from an environment where gold is found in physiologically relevant concentrations, hi certain embodiments, the microorganism is selected from Capriavidus metallidurans or Delftia acidovorans.

[0043] In certain embodiments, the bioabsorption step is at least partially selective.

[0044] In certain embodiments, the microorganisms selectively biosorb the target metal. In certain embodiments, the target metal and non-target material are biosorbed by the microorganisms in a ratio of at least 1:1 (target metal:non-target material), or at least 5:1, or at least 10:1, or at least 20:1, or at least 50:1, or at least 100:1, or at least 200:1, or at least 500:1, or at least 1000:1, or at least 5000:1, or at least 10000:1. In certain embodiments, the microorganisms biosorb the target metal and do not substantially biosorb the non-target material.

[0045] In certain embodiments, where the non-target material includes one or more non-target metals, the microorganisms selectively biosorb the target metal over the non-target material. In certain embodiments, the pregnant liquor includes at least one additional metal (non-target metal) in addition to the target metal. In certain embodiments, the microorganisms specifically biosorb the target metal over the additional metals (non-target metals) during the biosorption step, and the additional metals (non-target metals) remain in the barren liquor during the separation step. In certain embodiments, the microorganisms specifically biosorb the target metal over the additional metals (non-target metals) during the biosorption step, increasing the mass ratio of the target metal to the additional metals (non-target metals) in the microorganisms by at least two-fold compared to the mass ratio in the pregnant liquor. In certain embodiments, the mass ratio increases by at least 3, or at least 5, or at least 8, or at least 10, or at least 20, or at least 50, or at least 100, or at least 200-fold. In certain embodiments, the target metal is gold. In certain embodiments, the additional metal (non-target metal) is selected from one or more of copper and nickel.

[0046] In certain embodiments, the target metal and non-target metal are biosorbed by the microorganisms in a ratio of at least 1:1 (target metal:non-target metal), or at least 5:1, or at least 10:1, or at least 20:1, or at least 50:1, or at least 100:1, or at least 200:1, or at least 500:1, or at least 1000:1, or at least 5000:1, or at least 10000:1. In certain embodiments, the microorganisms biosorb the target metal and do not substantially biosorb the non-target metal.

[0047] In certain embodiments, the present invention comprises at least a partially selective dissolution step and at least a partially selective bioabsorption step.

[0048] In certain embodiments, the dissolution step and the bioabsorption step may occur in the same vessel.

[0049] In certain embodiments, the separating step comprises: Gravitational separation of metal-accumulating microorganisms from the barren solution and removal of the barren solution; Centrifugation and removal of barren fluid; Filtration of metal-accumulating microorganisms from barren solutions, It includes at least one of the following.

[0050] In certain embodiments, the separation step involves gravity separation of the metal-accumulating microorganisms from the barren liquor, where at least 50% of the barren liquor is removed, or in certain embodiments, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the barren liquor is removed.

[0051] In certain embodiments, the separation step comprises separating the metal-accumulating microorganisms by centrifugation, wherein at least 50% of the barren fluid is removed from the metal-accumulating microorganisms during centrifugation, hi certain embodiments, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the barren fluid is removed during centrifugation.

[0052] In certain embodiments, the separating step comprises separating the metal-accumulating microorganisms by filtration, wherein at least 50% of the barren solution is removed from the metal-accumulating microorganisms during filtration, hi certain embodiments, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the barren solution is removed during filtration.

[0053] In certain embodiments, the separating step comprises drying the microorganisms.

[0054] In another embodiment, the invention includes a recycling step, in which case at least a portion of the barren solution can be used as a leaching agent, or can be partially used as a leaching agent, in the dissolution step.

[0055] It is understood that the barren solution may contain metal ions, and in some instances may even include target metal ions. In some embodiments, the barren solution may be treated to remove excess metal ions or other compounds prior to returning to the lysis step. In some embodiments, at least a portion of the barren solution is mixed with makeup water prior to returning to the lysis step.

[0056] It is further recognized that additional components may need to be added to the barren solution to enable it to act as a liquor and dissolve the target metal. For example, in certain embodiments where the liquor is thiosulfate, or cyanide, or thiourea, or chlorine, the active liquor may need to be at least partially recharged to allow further dissolution of the target metal. In certain embodiments, these additional components are added to the barren solution prior to returning to the dissolution step. As non-limiting examples, it may be necessary to add additional oxidizing agent, and / or additional acid or base, and / or additional counterions. Additionally or alternatively, the barren solution may need to be treated to adjust pH, ORP, temperature, or any other physical property that may be known to those skilled in the art in order to make it a suitable liquor.

[0057] In certain embodiments, at least 25% of the barren solution is returned to the lysis step, while in other embodiments, at least 35%, or at least 45%, or at least 55%, or at least 65%, or at least 75%, or at least 85%, or at least 95% of the barren solution is returned to the lysis step.

[0058] In alternative embodiments, the separated barren solution may be at least partially recycled for use in culturing microorganisms. In certain embodiments, additional components may need to be added to the barren solution to enable it to act as a suitable culture medium in a bioreactor. In certain embodiments, these additional components are added to the barren solution prior to passing to the bioreactor. In alternative embodiments, the additional components are added to the barren solution within the bioreactor. Additionally or alternatively, the barren solution may need to be treated to adjust pH, ORP, temperature, or any other physical property that may be known to one of skill in the art to make it a suitable culture medium.

[0059] In certain embodiments, at least 25% of the barren solution is transferred to the bioreactor, while in other embodiments, at least 35%, or at least 45%, or at least 55%, or at least 65%, or at least 75%, or at least 85%, or at least 95% of the barren solution is transferred to the bioreactor.

[0060] In certain embodiments, where the leaching agent includes a suitable carbon source as a growth medium for culturing microorganisms, the pregnant liquor may be delivered to a vessel configured to cultivate the microorganisms and contact the microorganisms with the pregnant liquor, whereby the microorganisms accumulate metals.

[0061] In certain embodiments, the leaching agent comprises acetic acid.

[0062] In certain embodiments, the recovering step comprises contacting the metal-accumulating microorganisms with conditions that induce the microorganisms to substantially desorb the target metal.

[0063] In certain embodiments, the conditions are a solution containing a compound that triggers desorption of the target metal. In certain embodiments, the desorption solution contains one or more compounds that desorb the target metal. In certain embodiments, the desorption solution contains cysteine, thiosulfate, or thiourea. Additionally or alternatively, the conditions trigger desorption of the target metal (either metallic or ionic form). By way of example, the desorption solution includes conditions that trigger desorption of the target metal or metal ions. By way of example, the conditions may be a pH of less than 5, or less than 4, or less than 3, or less than 2. Alternatively, the conditions may be a pH of less than 5, or less than 4, or less than 3, or less than 2. Alternatively, the conditions may be a pH between 1 and 5, or between 2 and 5, or between 2 and 4. As a further example, the conditions may be a pH of greater than 8, or greater than 9, or greater than 10, or greater than 11, or greater than 12. Alternatively, the pH may be between 8 and 13, or between 9 and 13, or between 10 and 13. Additionally or alternatively, the conditions may be a redox potential suitable for desorption of the target metal.

[0064] Alternatively, the recovery step involves incineration or chemical dissolution of the metal-accumulating microorganisms to desorb the target metal.

[0065] In certain embodiments, the method includes a filtration step following the dissolution step to remove at least a portion of the undissolved non-target material from the pregnant liquor.

[0066] In a second aspect, there is provided a target metal recovered by the method of the first aspect. In certain embodiments, the metal is gold.

[0067] In a third aspect, a system for recovering target metals from e-waste is provided, the system comprising: (a) a pre-processing means configured to remove or break down at least a portion of non-target materials from the e-waste into particles of a pre-selected size to provide pre-processed e-waste; (b) a vessel configured to contact the pretreated e-waste with a leaching agent to dissolve at least a portion of the one or more target metals and produce a pregnant liquor; (c) a vessel configured to contact the microorganisms with the pregnant liquor such that at least a portion of the target metal is biosorbed by the microorganisms, causing the microorganisms to accumulate the metal and the pregnant liquor to become depleted; (d) a separator configured to substantially separate the metal-accumulating microorganisms from the barren solution; (e) optionally, a recovery means configured to recover the target metal from the metal-accumulating microorganism; Includes:

[0068] In certain embodiments, the system includes a means for transferring the pretreated e-waste to a container in (b). In certain embodiments, the means in (a) is the container in (b). In certain embodiments, the system includes a means for transferring the pregnant liquor from the container in (b) to a container in (c). In certain embodiments, the container in (b) is the same as or part of the container in (c). In another embodiment, the system includes a means for transferring the barren liquor containing the metal-accumulating microorganisms from the container in (c) to a separator (d). In certain embodiments, the system includes a means for transferring the separated metal-accumulating microorganisms in (d) to a recovery means in (e).

[0069] In certain embodiments, the separator comprises means for gravity separation of the metal-accumulating microorganisms from the barren liquid, wherein at least a portion of the barren liquid is removed from the metal-accumulating microorganisms.

[0070] In certain embodiments, the separator comprises means for separating the metal-accumulating microorganisms by centrifugation, in which case at least a portion of the barren solution is removed from the metal-accumulating microorganisms.

[0071] In certain embodiments, the separator comprises means for separating the metal-accumulating microorganisms by filtration, in which case at least a portion of the barren solution is removed from the metal-accumulating microorganisms.

[0072] In certain embodiments, the separator includes means for gravity separation of the metal-accumulating microorganisms from the barren solution and removal of at least a portion of the barren solution.

[0073] In certain embodiments, the separator comprises means for separating the metal-accumulating microorganisms by centrifugation, in which case at least a portion of the barren solution is removed from the metal-accumulating microorganisms.

[0074] In certain embodiments, the separator comprises means for separating the metal-accumulating microorganisms by filtration, in which case at least a portion of the barren solution is removed from the metal-accumulating microorganisms.

[0075] In certain embodiments, the recovery means includes a component that contacts the metal-accumulating microorganisms with a solution.

[0076] In certain embodiments, the recovery means includes a component that incinerates the metal-accumulating microorganisms to release the target metal.

[0077] In certain embodiments, the pre-treatment means comprises: ● Chip removal Grinding to a preselected size Removal of specific density fractions Removal of magnetic substances ●Base metal leaching, The apparatus includes means for performing one or more unit operations, including but not limited to:

[0078] In certain embodiments, the pre-processing means comprises at least one of these unit operations. In other embodiments, the pre-processing step comprises at least two of these unit operations. In other embodiments, the pre-processing step comprises at least three of these unit operations. In other embodiments, the pre-processing step comprises at least four of the above unit operations.

[0079] In certain embodiments, the pretreatment step removes at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the non-target material prior to recovery of the target metal. In certain preferred embodiments, the pretreatment step removes less than 20%, or less than 10%, or less than 5%, or less than 2%, or less than 1% of the target metal.

[0080] In certain embodiments of various aspects of the present invention, the microorganism is a bacterium, algae, or fungus. Those skilled in the art will recognize that multiple microorganisms are capable of biosorbing metal ions. In certain embodiments, the microorganism is a gram-negative or gram-positive bacterium. Examples include the gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, the gram-positive bacteria Bacillus subtilis, and the fungus Saccharomyces cerevisiae. Nancharaiah et al. (Trends in Biotechnology 34, pp. 137-155 (2016)) identify a wide range of microorganisms that may be employed to biosorb target metals in accordance with the methods of the present invention, all of which are incorporated by reference.

[0081] In certain embodiments in which the target metal ion is gold, the microorganism may be selected from the Gram-negative bacteria Pseudomonas aeruginosa, P. putida, and Desulfovibrio desulfuricans, the Gram-positive Bacillus subtilis, and the algae Plectonema borianum. In certain preferred embodiments, the microorganism is selected from an environment in which gold is found in physiologically relevant concentrations, such as the Gram-negative bacteria Capriavidus metallidurans and Delftia acidovorans.

[0082] Additionally or alternatively, a mixture of microbial species may be used.

[0083] In certain embodiments, the microorganism is selected from an environment in which the target metal is found in physiologically relevant amounts.

[0084] The present invention may also be generally said to reside in the parts, components, or features referred to or displayed in the specification of this application, individually or collectively, in any or all combinations of two or more of said parts, components, and features, and where specific wholes having known equivalents in the art to which the present invention pertains are referred to herein, such known equivalents are claimed to be incorporated by reference herein as if individually set forth. [Brief explanation of the drawings]

[0085] The present invention is preferably considered in all its novel aspects and these and other aspects of the invention will become apparent from the following description, which description is given by way of example only with reference to the accompanying drawings, in which: [Figure 1] 1 depicts a method for recovering one or more target metals from e-waste in accordance with a first aspect of the present invention, or a system configured to recover target metals from e-waste in accordance with a third aspect of the present invention. [Figure 2] 1 depicts a method for recovering one or more target metals from e-waste according to the first aspect of the present invention, or a system configured to recover target metals from e-waste according to the third aspect, comprising multiple pre-treatment steps. [Figure 3]

[0013] Figure 1 depicts a method for recovering one or more target metals from e-waste according to the first aspect of the present invention, or a system configured to recover target metals from pregnant liquor according to the fourth third aspect of the present invention, including a recycling step. [Figure 4]

[0023] The present invention relates to a method for recovering one or more target metals from electronic waste according to the first aspect of the present invention, or a system for recovering target metals from electronic waste according to the fourth third aspect of the present invention, configured to recover target metals from pregnant liquor, wherein microorganisms may be cultured in a separate container. DETAILED DESCRIPTION OF THE INVENTION

[0086] definition The term "target metal" includes both elemental metal and ions of a particular target metal or metals. It is recognized that a particular target metal may exist in different ionic states (including elemental form), or in multiple ionic states, in different parts of the methods or systems of the present invention. The target metal may be dissolved or partially dissolved in the aqueous solutions of the present invention, either as ions, salts, or complexes, or elemental form, or combinations thereof. Similarly, the target metal may exist in solid form, as ions, salts, or complexes, or elemental form, or combinations thereof, as the context dictates.

[0087] The term "non-target material" refers to materials from e-waste that are not immediately desired for recovery. Non-target material may contain metals and / or non-metals that are not target metals, and may include epoxy, fiberglass, and base metals.

[0088] The term "base metal" refers to a metal in a similar state of matter as the term "target metal" above, but is not a precious metal. An illustrative list of examples of base metals includes copper, tin, nickel, lead, iron, and zinc. Other base metals known to those skilled in the art may include aluminum, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium, and thallium.

[0089] The term "pregnant liquor" refers to an aqueous solution containing dissolved target metals. In some extreme instances, the pregnant liquor may also contain at least some undissolved target metals and / or non-target metals.

[0090] The term "barren solution" refers to an aqueous solution that contains depleted amounts of dissolved target metals compared to the pregnant solution. It is recognized that in extreme cases, the target metals may be completely absent from the barren solution.

[0091] The term "contacting" refers to the mixing and interaction between two or more solutions or substances. An example of this is contact between a pregnant liquor and a microorganism. A further example of this is contact between a leaching agent and a solid raw material material.

[0092] The terms "biobsorb" and "biosorbent" and "biosorption," and the like, when used in connection with the methods and systems of the present invention, refer to microorganisms used to adsorb, adsorp, or absorb metals, or the process of adsorbing, adsorping, or absorbing metals onto microorganisms.

[0093] The term "microorganism" refers to algae, bacteria, fungi, protists, or archaea. The term may be used in multiple senses to refer to a mixture of microorganisms.

[0094] The term "metal-accumulating microorganism" refers to a microorganism that has biosorbed one or more target metals.

[0095] The term "ppm" refers to parts per million and relates to the concentration of one substance relative to another. It refers to the weight:weight ratio between the two substances. For aqueous solutions, ppm and mg / L are approximately equivalent.

[0096] The term "rcf" means relative centrifugal force.

[0097] The terms "decanted" or "decanting" or the like refer to the removal of the top portion of an aqueous solution from a solid / liquid mixture after the solid fraction has been allowed to settle.

[0098] The term "leaching agent" refers to an aqueous solution capable of dissolving the target metal into an aqueous form.

[0099] The terms "e-waste" and "electronic waste" refer to electronic waste, or waste electrical and electronic equipment (commonly referred to as WEEE).

[0100] The term "PCB" refers to printed circuit boards, a form of electronic waste.

[0101] The term "selectivity" refers to the ability of the leaching agent and / or microorganism to dissolve and / or biosorb one or more metals over other metals or non-target substances present in the sample and / or solution.

[0102] The "system" includes piping and other features that may typically be employed to extract metals from raw materials. By way of example, the "system" may include vessels, conduits, pumps, pressure valves, heat exchangers, filters, instrumentation (pressure sensors, flow sensors, pH sensors), and mixing tees (static mixers).

[0103] Consideration While the following description focuses on a particular embodiment of the invention, namely the recovery of gold from pregnant liquor or solid raw material, it should be appreciated that the invention may also be applicable to the production of alternative target metals as would be known by one skilled in the art to which the invention pertains.

[0104] As discussed previously herein, the present inventors have devised a method for recovering metals from aqueous solutions containing metal ions and / or solid raw material. Specifically, the present invention provides a method for recovering metals from aqueous solutions in a manner that has several cost and environmental advantages over existing methods.

[0105] In certain aspects of the present invention, there is provided a method for recovering one or more target metals from e-waste, the method comprising: (a) a pre-treatment step including removing at least a portion of non-target materials from the e-waste to provide pre-treated e-waste; (b) a dissolution step comprising contacting the pretreated e-waste with a leaching agent to dissolve at least a portion of the target metals in the leaching agent to produce a pregnant liquor; (c) a biosorption step including contacting a microorganism with the pregnant liquor such that at least a portion of the target metal ions are biosorbed by the microorganism, causing the microorganism to accumulate the metal and rendering the pregnant liquor barren; (d) a separation step comprising substantially separating the metal-accumulating microorganisms from the barren solution; (e) optionally, a recovery step comprising recovering the target metal from the metal-accumulating microorganism; Includes:

[0106] Referring to FIGS. 1 and 2, a method for recovering one or more precious metals from e-waste is provided, including a pre-treatment step, the method comprising: ● Chip removal Grind to preselected maximum size Removal of specific density fractions Removal of magnetic substances • one or more base metal leaching; The method includes a pre-processing step which may include one or more unit operations, including but not limited to:

[0107] There are several benefits to carrying out one or more of these pre-treatment steps prior to precious metal recovery, including reducing the volume of material to be processed in the target metal recovery step, removing certain fractions that may interfere with precious metal recovery or reduce the efficiency of the target metal leaching agent, and allowing for the selective capture of certain valuable fractions.

[0108] It is well known that e-waste contains a wide variety of non-target materials, including elements and compounds. However, some of these non-target materials may have detrimental effects during the recovery of target metals. The present inventors have surprisingly discovered that there are significant benefits to pre-treating e-waste to remove certain non-target materials, such as certain constituents, elements, metals, and / or compounds, prior to dissolving the target metals in a leaching agent.

[0109] In certain embodiments, the pretreatment step removes at least 50% of the non-target metals, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the non-target materials prior to precious metal recovery. In certain preferred embodiments, the pretreatment step removes less than 20%, or less than 10%, or less than 5%, or less than 2%, or less than 1% of the target metals.

[0110] 1, in certain embodiments, the method includes a pre-treatment step 8 configured to remove or recover at least a portion of the non-target materials prior to delivery to target metal leaching 1 (dissolution step) via conduit means 9. Those skilled in the art will recognize that the pre-treatment step may include multiple unit operations targeted at recovering or removing different fractions of non-precious metal materials.

[0111] For example, in accordance with one embodiment of the present invention illustrated in FIG. 2, a pre-treatment step is provided that includes several unit operations, including chip removal (10), grinding to a specified particle size (12), followed by base metal leaching (14).

[0112] Chip removal In certain embodiments of the present invention, the method includes one or more steps configured to remove chips and other surface-mounted components from the printed circuit board prior to precious metal recovery. Those skilled in the art will recognize that chips and other components are typically secured to the printed circuit board by solder. Soldering on the printed circuit board typically includes tin and lead, tin and silver, or a combination thereof. As such, the chip removal process typically involves removing the solder by raising the temperature of the solder above its melting point or by dissolving the solder in a suitable solvent. The chips and other components can then be easily removed by shaking, vibrating, disassembling, or banging the PCB, causing the chips and other components to break free and fall off.

[0113] Those skilled in the art will recognize suitable means for heating and removing chips and other components from printed circuit boards. However, as a non-limiting example, chips and other components may be heated in a trommel device configured to desolder multiple printed circuit boards at high temperatures. For example, Wang et al. (Waste Management, Vol. 53, July 2016, pp. 218-224) provide an automated system for disassembling PCBs using heated air at 265°C, capable of removing solder in 8 minutes.

[0114] Additionally or alternatively, chips and other surface-mounted components may be removed or recovered by immersing the printed circuit board in a solvent system suitable for selectively dissolving the solder. Those skilled in the art will recognize that there are multiple solvent systems suitable for selectively dissolving solder. For example, Yang Jian-Guang et al. (Journal of Hazardous Material, Vol. 304, March 2016, pp. 409-416) provide a 1:1 mixture of SnCl4 and HCl that can remove up to 99% of tin at 60-90°C. Additionally or alternatively, Manis Kuma Jha et al. (Hydrometallurgy, Vol 121-124, June 2012, 28-34) provide a nitric acid solution containing 0.2M HNO3 for dissolving lead-tin solder, with a solid-liquid ratio of 1g / 100ml, recovering 99.99% of the lead in 120 minutes at 90°C.

[0115] During the chip removal process, it may be beneficial to recover the solder, solder components, chips, and other surface mounted components once removed from the printed circuit board. Those skilled in the art will recognize that there are several methods for recovering such material, for example, the chips and other surface mounted components may be collected in trays and sorted through size exclusion screens.

[0116] crushing Due to the heterogeneous nature of e-waste, specifically PCBs, it may be desirable to grind the PCB material to a specific average size prior to precious metal recovery. Additionally, it is recognized that significant amounts of precious metals are embedded in chips or other components that can only be utilized if the PCB material is first ground to a specific size fraction. The inventors have also found that grinding e-waste can be beneficial for subsequent process steps, such as pumping or otherwise transporting the ground e-waste and / or e-waste in a leachant to a subsequent step. Those skilled in the art will recognize that grinding any material typically results in a size distribution, and that the resulting size distribution may be separated through known size exclusion or size separation techniques, such as size exclusion screens that provide particles with the largest size. Those skilled in the art will recognize that PCBs can be ground to a specific average size through a variety of well-known crushers or grinders, such as hammer mills, ball mills, ring mills, and shredders, or a combination of two or more of such implementations. For example, the comminution step could include a cutting stage followed by a two-step crushing and crushing stage. In the first stage, particle size may be reduced to an average of 3 mm. This may be followed by sieving of the particles to reduce the average size to below 1 mm, ideally in the range of 0.1-0.9 mm, prior to the second stage of comminution. Larger particles may be sieved and returned to the previous crushing stage for further comminution (Silvas et al. Waste Management, Vol 46, December 2015, 503-510).

[0117] For example, grinding to particle sizes smaller than 1 mm improves the extraction rate of copper and other base metals, however, no significant improvement is observed below 0.5 mm. When grinding to particle sizes below 0.075 mm, the extraction rates of copper and lead are adversely affected (Chen et al. Journal of Cleaner Production, Vol 95, May 2015, 142-147). Because shredding, grinding, and pulverization are energy-intensive processes, there is a desire to maximize extraction efficiency while minimizing energy consumption.

[0118] In certain embodiments of the present invention, the pre-processing step involves grinding the printed circuit board to a diameter of less than about 10 cm, or less than 8 cm, or less than 5 cm, or less than 3 cm, or less than 1 cm, or less than 5000 microns, or less than 2000 microns, or less than 1000 microns, or less than 500 microns, or less than 200 microns, or less than 100 microns, or less than 50 microns, or less than 20 microns. In preferred embodiments, the pre-processing step involves grinding the PCB to an average size of about 10 to 0.05 mm diameter. In certain embodiments, the pre-processing step involves grinding to a pre-selected average size, having an average diameter of about 10 to 0.05 mm diameter. In certain embodiments, the pre-selected size is an average diameter of about 5 to 0.1 mm diameter. While it is recognized that the particles need not be spherical, one skilled in the art will recognize that the size of non-spherical particles can be approximated by a sphere.

[0119] Removal of density fractions Once the printed circuit board material is pulverized to a smaller particle size, the particles in the pulverized material may vary in weight and density. As a non-limiting example, particles containing a significant amount of metal will have a higher density than particles that are substantially free of metal. As such, it may be beneficial to separate particles that are substantially free of metal from particles that contain metal. Those skilled in the art will recognize that there are several well-known techniques for completely separating pulverized material based on density. However, as a non-limiting example, such particles may be separated using flotation separation, a shaker table, and / or electrostatic separation. In certain embodiments of the present invention in which the printed circuit board is pulverized to less than 200 microns, the method includes removing substantially metal-free particles by electrostatic separation.

[0120] For example, according to Kaya (Waste Management, Vol 57, Nov 2016, 64-90), there are three main types of electrostatic separation: 1 - Corona Electrostatic Separation (most useful for producing metallic and non-metallic mixtures with little or no cross-contamination, works best for industrial applications with PCB sizes between 0.6 and 1.2 mm) 2 - Eddy current separation (useful for recovering aluminum) 3 - Triboelectric separation, there is.

[0121] Removal of magnetic materials Once the PCB material has been pulverized to a smaller particle size, it may be beneficial to separate the magnetic material from the non-magnetic material. Because precious metals and many base metals are non-magnetic, it may be beneficial to separate the magnetic material prior to further processing. The magnetic material may be removed using a magnetic field to physically remove the magnetic material from the pulverized PCB. For example, the metallic and non-metallic components may be completely dissociated from each other, resulting in a particle size of less than 0.6 mm (e.g., Guo Chao Wang Hui et al. Waste Management Vol 31, Sep-Oct 2011, 2161-2166). A two-step crushing process may be used, with particles larger than 1.25 mm recycled into a feed loop followed by electrostatic and magnetic separation.

[0122] base metal leaching Because printed circuit boards typically contain multiple different metals and alloys, it may be beneficial to completely separate some metals prior to recovering the precious metals. Those skilled in the art will recognize that most metals have solubility characteristics based on their electron configuration, position on the periodic table, size, hardness / flexibility, as well as other factors. As such, it is possible to substantially dissolve certain metals while leaving others substantially undissolved based on their solubility characteristics. For example, base metals, such as copper, zinc, aluminum, iron, and tin, tend to be at least partially soluble in sulfuric acid, while precious metals, such as gold, platinum, and silver, are substantially less soluble. As such, selective dissolution may be used to separate some metals from printed circuit board materials.

[0123] By way of non-limiting example, specific base metals include: Kell process (oxidative pyrolysis) Sulfuric acid leaching Hydrochloric acid leaching Nitric acid leaching Ammonia leaching, The precious metal may be selectively separated and dissolved from the precious metal-loaded printed circuit board material using techniques including, but not limited to,

[0124] The Kell process involves hydrometallurgy instead of smelting to produce concentrates containing base and precious metals. The process has three main steps (generally at the time of mining the ore): 1 - Liquid-phase pressure oxidation in an acidic sulfide medium to dissolve base metals. 2 - Roasting of the previous material to improve the conditions for final leaching. 3 - Leaching of the previous precious metals in a chloride medium to dissolve the residual metal content; accompanied by.

[0125] A key feature of this process is the separation of base and precious metal chemicals (http: / / www.saimm.co.za / conferences / pt2010 / 181-186_liddell.pdf).

[0126] Sulfuric acid leaching, involving 2M sulfuric acid and 35% hydrogen peroxide in a 4:1 ratio, can be used in a two-step process to selectively dissolve base metals, with the most common metals being copper, iron, nickel, tin, zinc, and aluminum. A solid-liquid ratio of 1:10 has been found to be most suitable (Behnamfard et al. Waste Management, 33 (2013) 2345-2363). Furthermore, Kaya (Waste Management, Vol 57 (2016) 64-90), incorporated herein by reference, provides a detailed table of base metal leaching agents.

[0127] It has also been reported that 1-6M nitric acid can be used to dissolve base metals, specifically copper, lead, and tin (as well as other common base metals in shredded e-waste). When concentrations above 4M nitric acid are used, tin precipitates as metastannic acid. Mecucci et al. (Journal of Chemical Technology and Biotechnology, Vol 77 (2002) 449-457) claim that nitric acid has an advantage over sulfuric acid because it forms less precipitate. Furthermore, because nitric acid is itself oxidizing, less or no additional oxidizing agent is required, and the ore is likely to be easily reclaimed and / or reused.

[0128] Fazhul et al. (http: / / dspace.unimap.edu.my / dspace / bitstream / 123456789 / 7476 / 1 / selective%20leaching%20for%20the%20recovery%20of%20copper.pdf) provide a leaching agent containing ammonia that selectively leaches certain base metals (specifically copper) in the presence of other common base metals. Additionally or alternatively, Sun et al. (Environmental Science and Technology Letters, 49 (2015) 7981-7988) provide a process using ammonium (7.55 wt%), 196 g / L ammonium carbonate, room temperature air, and a solid-liquid ratio of 1 g / 5 ml, which is capable of leaching copper while removing low amounts of other base metals, primarily zinc (less than 5% total).

[0129] Lysis step Figure 1 illustrates an embodiment of the present invention in which a vessel 1 is configured to dissolve target metals from e-waste. In certain embodiments, pre-treated e-waste is added to vessel 1, where a suitable leaching agent is applied to cause at least partial dissolution of one or more target metals to produce a pregnant solution containing target metal ions. Those skilled in the art will recognize suitable leaching agents and conditions necessary to at least partially dissolve the target metals.

[0130] In particular embodiments, the pregnant liquor contains greater than 1000 ppm, or greater than 500 ppm, or greater than 200 ppm, or greater than 100 ppm, or greater than 50 ppm, or greater than 20 ppm, or greater than 10 ppm, or greater than 5 ppm, or greater than 1 ppm. Preferably, the pregnant liquor contains between about 0.1 ppm and 1500 ppm, or between about 0.1 ppm and 1000 ppm, or between 0.1 ppm and 500 ppm, or between about 0.1 ppm and 200 ppm, or between 0.1 ppm and 100 ppm, or between about 0.1 ppm and 50 ppm, or between about 0.1 ppm and 20 ppm of the target metal. Preferably, the pregnant liquor contains between about 0.5 ppm and 1500 ppm, or between about 0.5 ppm and 1000 ppm, or between 0.5 ppm and 500 ppm, or between about 0.5 ppm and 200 ppm, or between 0.5 ppm and 100 ppm, or between about 0.5 ppm and 50 ppm, or between about 0.5 ppm and 20 ppm of the target metal. Preferably, the pregnant liquor contains between about 1 ppm and 1500 ppm, or between about 1 ppm and 1000 ppm, or between 1 ppm and 500 ppm, or between about 1 ppm and 200 ppm, or between 1 ppm and 100 ppm, or between about 1 ppm and 50 ppm, or between about 1 ppm and 20 ppm of the target metal.

[0131] In accordance with the methods of the present invention, in certain embodiments, the leaching agent solution used to dissolve the target metal ions serves as the pregnant solution. By way of non-limiting example, when gold is the target metal, the pregnant solution may be produced by dissolving the target metal in a leaching agent comprising a thiourea-based solution, or a thiosulfate-based solution, or a thiocyanate-based solution, or a cyanide-based solution, or a halogen-based solution, or an aqua regia-based solution; examples of suitable conditions can be found in Aylmore, Developments in Mineral Processing 15, pp 501-539 (2005), and references therein.

[0132] Suitable leaching agent systems for dissolving one or more target metals operate at different rates, pH, temperature, and ORP, and one skilled in the art will know how these conditions may be optimized to ensure efficient dissolution of the target metals. Examples of suitable leaching agent systems include:

[0133] Water and Chlorine A leaching system of water as a solvent plus chlorine gas can be used to dissolve gold, but this system is not selective and will dissolve most metal nanoparticles (A Straightforward Route to Tetrachloroauric Acid from Gold Metal and Molecular Chlorine for Nanoparticle Synthesis. doi:10.3390 / met5031454).

[0134] Aqueous solvents, oxidizing agents, and chlorides According to International Publication No. WO 2016 / 168933, which is incorporated herein by reference, a leaching agent system comprising glacial acetic acid as a solvent, an oxidizing agent, and a chloride source can be used to selectively dissolve gold. For example, acetic acid, hydrochloric acid, and chlorine gas have been shown to selectively dissolve gold from printed circuit boards. Similarly, a leaching agent system of glacial acetic acid as a solvent, plus hydrochloric acid, plus calcium hypochlorite, can be used to selectively dissolve gold. Additionally, a leaching agent system of glacial acetic acid as a solvent, plus hydrogen peroxide, plus hydrochloric acid, plus calcium chloride, can be used to selectively dissolve gold.

[0135] Potassium iodide and iodine A leaching agent system of water as the solvent plus iodine plus potassium iodide can be used to dissolve gold in accordance with US Pat. No. 3,957,505.

[0136] Thiourea A leaching system of thiourea plus ferric ions in an aqueous solvent, at a pH between 1 and 3, can be used to dissolve gold. (Alternative Lixiviants to Cyanide for Leaching Gold Ores, DOI: 10.1016 / S0167-4528(05)15021-2)

[0137] Thiosulfate A leaching system of thiosulfate plus ammonia plus copper(II) can be used to dissolve gold. (Alternative Lixiviants to Cyanide for Leaching Gold Ores, DOI: 10.1016 / S0167-4528(05)15021-2)

[0138] aqua regia A lixiviant system of nitric acid plus hydrochloric acid in a volume ratio of approximately 1:4 can be used to dissolve gold. (Cyanide and Other Lixiviant Leaching Systems for Gold with Some Practical Applications, DOI: 10.1080 / 08827509508914125)

[0139] cyanide

[0140] An air-saturated leaching system of sodium cyanide (0.02-0.1%) in a water solvent with a pH between 10 and 11 can be used to dissolve gold. (Cyanide and Other Lixiviant Leaching Systems for Gold with Some Practical Applications, DOI: 10.1080 / 08827509508914125)

[0141] In certain embodiments, a leaching agent system may be used to selectively dissolve target metals while leaving non-target metals substantially undissolved or to a lesser extent dissolved. Those skilled in the art will recognize that most target metals, such as gold, typically exhibit lower solubility in most leaching agents than non-target materials, such as base metals. However, in certain embodiments, at least a portion of the target noble metal dissolves in the leaching agent system, while the non-target materials dissolve at a slower rate. Additionally or alternatively, at least a portion of the target metal dissolves in the leaching agent system, while the non-target metals dissolve at a lower rate compared to the undissolved metals.

[0142] In certain embodiments, the target metals and non-target metals are substantially selectively dissolved by the leaching agent in a ratio of greater than 1:1000 (target metals:non-target metals), or greater than 1:500, or greater than 1:200, or greater than 1:100, or greater than 1:50, or greater than 1:20, or greater than 1:10, or greater than 1:5, or greater than 1:2, or greater than 1:1.

[0143] According to International Publication WO 2016 / 108933, systems using acetic acid exhibit greater selectivity for gold than systems using other solvents, such as water. One such system is glacial acetic acid, hydrochloric acid, and calcium hypochlorite. This leaching agent exhibits a molar ratio of 1 part gold to 1.32 parts copper and 0.87 parts nickel in 4 minutes, and in this case, all of the gold dissolves starting with an input of 133.6 parts copper and 38 parts nickel. Another system is glacial acetic acid plus hydrochloric acid plus chlorine, and in this system exhibits a molar ratio of 1 part gold to 2.4 parts copper and 0.6 parts nickel in 1 minute, and in this case, all of the gold dissolves starting with an input of 138.7 parts copper and 46.6 parts nickel.

[0144] In certain embodiments, the e-waste material / leaching agent mixture may require gentle heating to above 30° C., or above 40° C., or above 50° C. to aid in dissolution of the target metals. Similarly, the mixture may be agitated, sonicated, vibrated, or otherwise treated to aid in dissolution.

[0145] Bioabsorption step Following at least partial dissolution of the target metals in the leaching agent, the pregnant liquor is passed via conduit 2 to biosorption vessel 3. Biosorption vessel 3 is configured to allow contact of the pregnant liquor with microorganisms. Upon contact, at least a portion of the target metals is biosorbed by the microorganisms, such that the microorganisms become metal-laden and the pregnant liquor is lean. Consistent with embodiments of the present invention, the microorganisms are contacted with the pregnant liquor for at least 2 minutes, or at least 5 minutes, or at least 10 minutes, or at least 30 minutes, or at least 60 minutes, or at least 120 minutes, or for the time necessary to biosorb at least 50% of the target metal, or at least 60% of the target metal, or at least 70% of the target metal, or at least 80% of the target metal, or at least 90% of the target metal, or at least 95% of the target metal. This time is preferably between about 0.5 and 48 hours, or between about 0.5 and 24 hours, or between about 0.5 and 12 hours, or between about 0.5 and 4 hours, or between 1 and 3 hours.

[0146] In certain preferred embodiments of the present invention, the microorganisms specifically biosorb the target metal over additional metals (non-target metals) in the pregnant liquor. The additional metal is then separated from the target metal in a separation step, where the additional metal remains in the barren liquor. Examples 8 and 9 demonstrate the specific nature of the biosorption step. The coefficient of specific biosorption will depend in part on the ratio of the metals in the pregnant liquor; for example, if the metals are already in similar amounts, the mass ratio may not change as long as the additional metal is in significant excess. However, preferably, the microorganisms specifically biosorb the target metal over the additional metal in the biosorption step such that the mass ratio of the target metal to the additional metal in the pregnant liquor increases by at least 2, or at least 3, or at least 5, or at least 8, or at least 10, or at least 20, or at least 50, or at least 100, or at least 200 times compared to the ratio of the additional metal biosorbed by the microorganism to the target metal. The upper limit of the ratio increase will depend in part on the starting ratio, but can be 1,000 or more. Preferably the target metal is gold. Preferably the further metal is selected from one or more of copper and nickel.

[0147] The conditions necessary to biosorb the target metal will depend on several factors, including the pH, ORP, and concentration of the microorganism. However, in accordance with certain embodiments of the present invention, the microorganism is added to the pregnant liquor in a concentrate form at an acidic pH. In one embodiment, the microorganism is washed in a buffer solution, such as phosphate, Tris, saline, acetate, and / or perchlorate, prior to contact with the pregnant liquor. Similarly, the microorganism may be concentrated by volume prior to contact with the pregnant liquor. Such concentration may be at least 50%, or at least 10%, or at least 1%, or at least 0.1% of the original volume.

[0148] Several microorganisms are capable of biosorbing metal ions. The microorganisms are preferably algae or bacteria, preferably gram-negative or gram-positive bacteria, such as Pseudomonas, Escherichia, Bacillus, Desulfovibrio, Plectonema, Capriavidus, Clostridium, or Delftia. The microorganisms are preferably selected from environments where target metals are found in physiologically relevant amounts, e.g., less than 0.5 ppm. Examples of microorganisms capable of biosorbing metal ions include the gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, the gram-positive bacteria Bacillus subtilis, and the fungus Saccharomyces cerevisiae. Nancharaiah et al. (Trends in Biotechnology 34, pp. 137-155 (2016)), incorporated herein by reference, identify a wide range of microorganisms that may be employed for biosorbing target metals. The majority of biosorption processes are adsorptive in nature (i.e., metal ions are bound to the surface of the microorganism through passive interactions with cell wall or membrane moieties), but some are absorptive (i.e., metal ions are actively taken up by the microorganism into itself).

[0149] In certain embodiments where the target metal ion is gold, microorganisms such as the Gram-negative bacteria Pseudomonas aeruginosa, P. putida, and Desulfovibrio desulfuricans, the Gram-positive bacterium Bacillus subtilis, and / or the algae Plectonema borianum have been shown to biosorb gold (Reith et al., International Society for Microbial Ecology Journal 1, pp 567-584 (2007)). In certain preferred embodiments, the microorganisms are selected from environments where gold is found in physiologically relevant concentrations, such as the Gram-negative bacteria Capriavidus metallidurans and Delftia acidovorans (Rea et al., FEMS Microbiology Ecology 92, pp fiw082 (2016)). In other preferred embodiments, the microorganism is selected from those used in other industrial processes, such as the Gram-positive bacterium Clostridium autoethanogenum (Abrini et al., Arch Microbiol 161, pp 345-351 (1994)).

[0150] When used in the present invention, rather than in the environment, the microorganisms are generally a single culture or at least a limited mixture of two to five different microorganisms. Moreover, in natural environments, microorganisms are generally only exposed to low levels of target metals, e.g., less than 0.5 ppm. In preferred embodiments of the present invention, the pregnant liquor contains relatively high amounts of target metals, e.g., greater than 0.5 ppm or greater than 1 ppm. It is therefore surprising that the microorganisms still have the ability to biosorb even higher levels of target metals. Additionally or alternatively, it is surprising that the microorganisms can biosorb target metals in a relatively short time, e.g., less than 12 hours, and even when the target metals are at lower or higher concentrations.

[0151] The inventors have found that Capriavidus metallidurans (C. metallidurans) is particularly useful in the present invention where gold is the target metal. The inventors have found that C. metallidurans is relatively easy to grow, is adept at biosorbing gold, and / or biosorbs the target metal relatively quickly, and / or is effective at specifically biosorbing gold (see Examples 8 and 9), and / or is relatively tolerant of other metals present in the pregnant solution.

[0152] In certain embodiments where the target metal ion is gold and the pregnant solution is a thiosulfate-based solution, or a cyanide-based solution, or a chloride-based solution, C. metallidurans may be used to biosorb gold-thiosulfate complexes, or aurous cyanide, or chloroaurate, respectively (Reith et al, PNAS 106, pp 17757-17762 (2009); Etschmann et al, Chemical Geology 438, pp 103-111 (2016)).

[0153] Once the target metal ions have been at least partially biosorbed, the solution becomes a barren solution, which contains less target metal than the pregnant solution. In certain embodiments, the barren solution contains less than 0.1 ppm, or less than 1 ppm, or less than 2 ppm, or less than 5 ppm, or less than 10 ppm, or less than 20 ppm, or less than 50 ppm, or less than 100 ppm of target metal. Preferably, the barren solution contains between about 0.001 ppm and 100 ppm, or between about 0.001 ppm and 50 ppm, or between about 0.001 ppm and 50 ppm, or between about 0.01 ppm and 50 ppm. In certain embodiments, the pregnant solution contains at least 10 times more target metal than the barren solution. Preferably, the pregnant solution contains at least 20 times, or at least 40 times, or at least 45 times, or at least 50 times more target metal than the barren solution.

[0154] It will be appreciated that the microorganisms may be cultured in a separate vessel by any method familiar to those skilled in the art prior to contact with the pregnant liquor in biosorption vessel 3. By way of example, the microorganisms may be cultured in a bioreactor (e.g., vessel 20 of FIG. 4 ) containing a suitable growth medium and then transferred to biosorption vessel 3. The microorganisms may be transferred directly without further concentration, or may be concentrated prior to transfer. In certain embodiments, the microorganisms are concentrated through gravity separation and transferred to biosorption vessel 3 as a concentrated microbial slurry in a minimal volume of growth medium. In a related embodiment, the concentrated microbial slurry may be washed in another solution prior to being transferred to biosorption vessel 3.

[0155] In certain embodiments, microorganisms are cultured in a rich liquid medium (eg, nutrient broth or tryptic soy broth) until they reach mid-log or stationary phase of growth.

[0156] Separation step 1 , once at least a portion of the target metal has been biosorbed, the metal-accumulating microorganisms are separated from the barren solution in separation module 5. It is contemplated that the initial portion of the separation step may occur in the same vessel as the biosorption step, in which case the metal-accumulating microorganisms are simply left to concentrate via gravity separation. In other embodiments, the metal-accumulating microorganisms and barren solution are passed via conduit means 4 to separation module 5 for separation. Examples of means for separating microorganisms from barren solution will be familiar to those skilled in the art. However, by way of example, the metal-accumulating microorganisms may be separated by gravity separation, centrifugation, filtration, or a combination thereof, in each case removing the barren solution from the metal-accumulating microorganisms.

[0157] Substantially separated is preferably interpreted to mean physically separating at least a portion of the barren solution from the metal-accumulating microorganisms, which refers to having them in separate, non-contacting locations, for example, in separate containers rather than in contact layers within the same container.

[0158] In certain embodiments, the metal-accumulating microorganisms are gravity separated from the barren liquid over a period of time in biosorption vessel 3 or separation module 5. Following gravity separation, at least a portion of the barren liquid can be decanted, siphoned, or otherwise removed, leaving behind concentrated metal-accumulating microorganisms, which can be passed via conduit means 6 to optional recovery module 7 for carrying out a recovery step.

[0159] In certain embodiments, the separation step involves gravity separation of the metal-accumulating microorganisms from the barren liquor, wherein at least 50% of the barren liquor is removed. Preferably, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the barren liquor is removed. By way of example, the solution of microorganisms may be allowed to settle by gravity for up to 2 hours, or up to 6 hours, or up to 12 hours, or up to 24 hours, or up to 48 hours, or up to 72 hours before removing the barren liquor.

[0160] In an alternative embodiment, the metal-accumulating microorganisms can be separated from the barren solution in separation module 5 by centrifugation and removal of the barren solution. Those skilled in the art will recognize the appropriate conditions and equipment required to separate the barren solution from the metal-accumulating microorganisms, which can be passed via conduit means 6 to recovery module 7 following separation.

[0161] In certain embodiments, the separation step comprises separating the metal-accumulating microorganisms by centrifugation, wherein at least 50% of the barren solution is removed from the metal-accumulating microorganisms during centrifugation, preferably at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the barren solution is removed during centrifugation.

[0162] Those skilled in the art will recognize that the operation of the centrifuge will depend on the volume of liquid being handled and the speed of separation required. There are also several centrifuge systems that may be employed with the methods and systems of the present invention, including suitable continuous flow or decanter type centrifuges.

[0163] In a further embodiment, the metal-accumulating microorganisms may be separated from the barren solution in separation module 5 by filtration. Those skilled in the art will recognize the appropriate conditions and equipment required to separate the barren solution from the metal-accumulating microorganisms, which may be passed via conduit means 6 to recovery module 7 for subsequent separation.

[0164] In certain embodiments, the separation step comprises separating the metal-accumulating microorganisms by filtration, wherein at least 50% of the barren solution is removed from the metal-accumulating microorganisms during filtration. Preferably, at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% of the barren solution is removed during filtration. As an example, the solution containing the metal-accumulating microorganisms may be vacuum filtered through a filter having a pore size of approximately 0.45 μm, or approximately 0.65 μm, or approximately 0.8 μm, or approximately 1 μm to remove the barren solution. As another example, a cross-flow filtration device or a membrane bioreactor device may be used to filter the barren solution.

[0165] The separation step is important for several reasons. It removes the metal-accumulating microorganisms, and therefore the target metal, from other components in the pregnant liquor. These other components may be toxic or corrosive, such as cyanides or acids. The separation step also allows for enrichment of the target metal. Following the separation step, the dried metal-accumulating microorganisms preferably contain greater than 100 ppm, greater than 200 ppm, greater than 500 ppm, greater than 1000 ppm, or greater than 30,000 ppm of the target metal. Furthermore, the inventors have demonstrated large enrichment factors for the target metal from the pregnant liquor to the isolated microorganisms. The enrichment factor for the target metal from the pregnant liquor to the microorganisms (i.e., the number of times the target metal is enriched in the microorganisms relative to the pregnant liquor) can be greater than 5, greater than 10, greater than 20, greater than 50, greater than 100, or greater than 900. For example, Example 1 demonstrates an enrichment factor for the target metal from the pregnant liquor to the microorganisms of 990. Wet microbial biomass is commonly estimated to be five times its dry mass, i.e., the dry mass is about 20% of the wet mass (Luria, The Bacteria, vol. 1. Academic Press, Inc., New York, pp 1-34 (1960)). Therefore, the metal enrichment factors calculated for the wet microbial biomass used in Examples 1 and 6 can be multiplied by 5 to estimate the enrichment factor for the dried microorganisms. Drying of microorganisms is exemplified in Example 11A. This enrichment is important because, for example, although lixiviants are used in hydrometallurgy to extract metals, the metals must still be recovered from the lixiviants.

[0166] The separation step may in some cases also allow for selective separation and / or concentration of metals; for example, Example 8 demonstrates the specific biosorption of gold from copper, followed by separation and / or concentration. As a result of the selective biosorption of gold by microorganisms, in the separation step, the gold biosorbed by the microorganisms is separated from the copper in the barren solution.

[0167] Collection Step Those skilled in the art will recognize suitable recovery means for recovering the target metal from the metal-accumulating microorganisms in recovery module 7. However, as a non-limiting example, the metal may be desorbed from the metal-accumulating microorganisms by altering the conditions of the microorganisms. For example, in certain embodiments of the present invention, the metal may be desorbed from the metal-accumulating microorganisms by altering the pH of the microorganisms, for example, by contacting the microorganisms with a solution containing an acid or a base. In such embodiments, the microorganisms may be contacted with a liquid having a specific pH to induce desorption of the target metal into the liquid. In certain embodiments, the pH of the contacted liquid is higher than that of the barren liquid, while in other embodiments, the pH is lower, depending on the characteristics of the system. By way of example, the conditions may be a pH less than 5, or less than 4, or less than 3, or less than 2. By way of further example, the conditions may be a pH greater than 8, or greater than 9, or greater than 10, or greater than 11, or greater than 12.

[0168] In alternative embodiments, metal-accumulating microorganisms may be contacted with a liquid containing a compound to induce desorption of the target metal into the liquid. For example, aqueous cysteine ​​may be used in certain embodiments to induce desorption of the target metal. In certain embodiments where the target metal is gold, a cysteine ​​solution of approximately 0.3 mM, approximately 1 mM, approximately 10 mM, approximately 30 mM, or approximately 60 mM may be contacted with the metal-accumulating microorganism (Kenney et al., Geochimica et Cosmochimica Acta 82, pp 51-60 (2012)). In related embodiments, aqueous thiosulfate, thiourea, thiocyanate, cyanide, or other thiol ligands may be used to induce desorption of gold from the microorganisms. Additionally or alternatively, other conditions, such as changes in redox potential or temperature, may be used to promote desorption of the target metal.

[0169] The concentrated solution may then be subjected to separation and purification procedures, such as precipitation of impurities, solvent extraction, adsorption, and ion exchange, to isolate and / or further concentrate the target metal. The solution can then be treated by an electrorefining process, chemical reduction, or crystallization to recover the target metal, or other methods that will occur to those skilled in the art.

[0170] In alternative embodiments, the isolated metal-accumulating microorganisms may be dried and combusted and / or smelted to recover the target metals, which may be separated from the ash using conventional pyrometallurgical or hydrometallurgical techniques known to those skilled in the art (Hennebel et al, New Biotechnology 32, pp 121-127 (2015)).

[0171] It will be apparent that the recovery step may recover the target metal in metallic or ionic form, and therefore reference to recovering the target metal should be interpreted as including recovery of metallic metal or metal ions.

[0172] In certain embodiments of the methods and systems of the present invention, the target metal is gold. In such embodiments, the separated gold-accumulating microorganisms may be dried at ambient temperature or at 30°C or 50°C to minimize moisture content and then gently incinerated, for example with a gas torch, to minimize loss of the ash produced. This ash may then be treated with nitric acid to solubilize the base metals, filtered, and the gold-containing residue treated with aqua regia (3 parts hydrochloric acid to 1 part nitric acid) to produce a solution of chloroauric acid. In a related embodiment, the gold-accumulating microorganisms may be passed directly to the acid treatment mentioned above, without the need for prior incineration. Gold may be precipitated and refined from the chloroauric acid using methods known to those skilled in the art.

[0173] In certain embodiments of the methods and systems of the present invention, the target metal is gold. In such embodiments, the separated gold-accumulating microorganisms may be dried at ambient temperature or at 30°C or 50°C to minimize moisture content and then incinerated to minimize loss of the resulting ash, for example, gently with a gas torch or in a furnace at 1100°C. Both techniques utilize a borax flux, which helps bind the gold and minimize any loss, and which also thoroughly cleanses the gold of any oxide impurities. The ash may then be treated with nitric acid to solubilize the base metals, filtered, and the gold-containing residue treated with aqua regia (3 parts hydrochloric acid to 1 part nitric acid) to produce a solution of chloroauric acid. In a related embodiment, the gold-accumulating microorganisms may be passed directly to the acid treatment mentioned above, without the need for prior incineration. Gold may be precipitated and refined from the chloroauric acid using methods known to those skilled in the art.

[0174] Reuse of the solution The inventors recognize that recycling certain solutions used in the process may improve the efficiency of the process. For example, in certain embodiments, means are provided for recycling at least a portion of the barren solution separated from the metal-accumulating microorganisms back into dissolution vessel 1. In certain embodiments, this recycling step is expected to reduce the amount of water required throughout the system, thereby making it more cost-effective and / or environmentally efficient. Referring to Figure 3, in certain embodiments, means 18 are provided for transferring at least a portion of the barren solution from separation vessel 5 to dissolution vessel 1. In certain embodiments, the system includes a pump that transfers the solution from vessel 5 to vessel 1.

[0175] It will be appreciated that the barren solution may contain metal ions, and in some instances may even include target metal ions. However, one skilled in the art will understand the amount of barren solution that may be passed back to vessel 1 to dissolve the target metal. In some embodiments, the barren solution may be treated to remove excess metal ions or other compounds prior to passing to dissolution vessel 1. In some embodiments, at least a portion of the barren solution is mixed with makeup water or other suitable liquid prior to passing to dissolution vessel 1. Additionally or alternatively, at least a portion of the barren solution may be mixed with makeup liquid within dissolution vessel 1.

[0176] It is further recognized that additional components may need to be added to the barren liquor to enable it to act as a leaching agent in dissolution vessel 1. For example, in certain embodiments where the liquor is thiosulfate or cyanide or thiourea or chlorine, it may be necessary to at least partially recharge the active liquor to allow further dissolution of the target metal. In certain embodiments, these additional components are added to the barren liquor prior to passing it to dissolution vessel 1. In alternative embodiments, the additional components are added to the barren liquor in dissolution vessel 1. Additionally or alternatively, the barren liquor may need to be treated to adjust the pH, ORP, temperature, or any other physical property that may be known to one skilled in the art in order to make it a suitable liquor.

[0177] 4, in certain embodiments, means 19 are provided for transferring at least a portion of the barren solution from the separation vessel 5 to the bioreactor 20. In certain embodiments, the system includes a pump that transfers the solution from the vessel 5 to the bioreactor 20.

[0178] It is understood that the barren solution may contain metal ions, and in some instances may even include target metal ions. However, one of ordinary skill in the art will understand the amount of barren solution that may be passed back to bioreactor 20 to allow for the cultivation of microorganisms. In some embodiments, the barren solution may be treated to remove excess metal ions or other compounds prior to passing to bioreactor 20.

[0179] In some embodiments, at least a portion of the barren liquid is mixed with makeup water prior to delivery to bioreactor 20. Additionally or alternatively, at least a portion of the barren liquid may be mixed with makeup water within the bioreactor.

[0180] It is further recognized that additional components may need to be added to the barren solution to enable it to act as a suitable culture medium within bioreactor 20. In certain embodiments, these additional components are added to the barren solution prior to passing to bioreactor 20. In alternative embodiments, the additional components are added to the barren solution within bioreactor 20. Additionally or alternatively, the barren solution may need to be treated to adjust the pH, ORP, temperature, or any other physical properties that may be known to one of skill in the art to make it a suitable leaching agent.

[0181] In certain embodiments, at least a portion of the barren liquid is passed to a bioreactor 20 and at least a portion is passed to a dissolution vessel 1 according to any of the above embodiments described in connection with FIG.

[0182] In certain embodiments, at least 25% of the barren solution is delivered to the dissolution vessel 1. In other embodiments, at least 35%, or at least 45%, or at least 55%, or at least 65%, or at least 75%, or at least 85%, or at least 95% of the barren solution is delivered to the dissolution vessel 1.

[0183] Alternatively, at least 25% of the barren liquid is passed to the bioreactor 20. In other embodiments, at least 35%, or at least 45%, or at least 55%, or at least 65%, or at least 75%, or at least 85%, or at least 95% of the barren liquid is passed to the bioreactor 20.

[0184] Unless otherwise indicated, the order of steps set forth in the methods described herein is highly preferred and has been optimized through trials conducted by the inventors to ensure that the process provides efficient production and an economically viable recovery method. [Example]

[0185] Background Example 1 Biosorption of Gold Dissolved in Aqua Regia Materials and Methods: Microbial cultures were grown under sterile conditions, but subsequent processing was performed using non-sterile solutions and equipment.

[0186] 1. A culture of Capriavidus metallidurans strain CH34 (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH #2839) was grown in 25 mL of nutrient broth (0.5% peptone, 0.3% yeast extract) at 30°C and approximately 200 rpm for at least 16 hours until stationary phase. 2. The medium was washed by centrifuging at 3,100 rcf for 15 minutes, discarding the supernatant, and resuspending the pellet (approximately 0.1 g) in 30 mL of 0.1 M sodium perchlorate. This centrifugation / wash step was repeated again using a 10 mL volume. 3. The medium was centrifuged again as above, the supernatant discarded, and the pellet resuspended in 25 mL of 0.1 M sodium perchlorate, 25 μM chloroauric acid (approximately 5 ppm Au), pH 4 (adjusted with sodium hydroxide). The pH of the gold / microorganism mixture was checked and adjusted to 4.0–4.5 using sodium hydroxide or hydrochloric acid, as appropriate. 4. The gold / microorganism mixture was incubated at room temperature for 2 hours, with the mixture gently agitated on an orbital shaker throughout to keep the microorganisms in suspension. 5. The mixture was centrifuged as in step 2, the supernatant (barren fluid) was discarded and the pellet was stored at 4°C. 6. The pellet (biosorbent pellet) obtained from step 5 (approximately 100 μL volume) was resuspended in 100 mL of water, 1 mL of 70% nitric acid was added, and then analyzed for total gold content by inductively coupled plasma mass spectrometry (supported by Watercare Services Ltd, Auckland, New Zealand). result:

[0187] At the end of the biosorption phase (step 4), the pH of the mixture was checked and found to be between 4.5 and 5.0.

[0188] The total gold content was reported in mg / L based on the volume analyzed and was used to calculate the amount biosorbed and the biosorption yield (Table 1). The precision of the total gold content was estimated to be 15-20% variance.

[0189] [Table 1]

[0190] Based on the amount of gold biosorbed, the pregnant solution contained approximately four times more target metal (gold) than the barren solution.

[0191] Using the data in Table 1, the concentration of gold remaining in the lean supernatant was back-calculated to be approximately 1 ppm ([0.125 mg - 0.099 mg] / 0.025 L). The enrichment factor resulting from the biosorption process, i.e., the increase in Au concentration from pregnant solution to biosorbent pellet (wet microorganisms), was also calculated using the original biosorbent pellet volume of approximately 100 μL (Table 2). Wet microbial biomass is commonly estimated to be five times its dry mass, i.e., the dry mass is approximately 20% of the wet mass (Luria, The Bacteria, vol. 1. Academic Press, Inc., New York, pp 1-34 (1960)). This is therefore close to an enrichment factor for Au from pregnant solution to dry microorganisms of approximately 990. This example demonstrates that microorganisms can be used to biosorb gold from an "ideal" solution, i.e., the target metal, gold, in a solution free of other non-target metals or other non-target materials (e.g., glass fiber).

[0192] [Table 2]

[0193] Background Example 2: Biosorption and Desorption of Gold Chloride Materials and Methods: Microbial cultures were grown under sterile conditions, but subsequent processing was performed using non-sterile solutions and equipment.

[0194] 1. In 600 mL of tryptic soy broth (1.7% tryptone, 0.3% soytone, 0.25% glucose, 0.5% sodium chloride, 0.25% dipotassium phosphate), a culture of either Bacillus subtilis strain (Ehrenberg 1835) Cohn 1872 (Ehrenberg 1835) (Landcare Research New Zealand Ltd #20567) or Pseudomonas putida strain (Trevisan 1889) Migula (Trevisan 1889) (Landcare Research New Zealand Ltd #15057) was grown at 30°C and approximately 200 rpm for at least 16 hours to stationary phase. 2. Each culture was centrifuged at 2,500 rcf for 10 minutes, the supernatant discarded, and the pellet resuspended in 300 mL of water. This centrifugation / washing step was repeated twice. 3. Each culture was centrifuged again as above, the supernatant discarded, and the pellet resuspended in 20 mL of 0.1 M sodium perchlorate. This centrifugation / wash step was repeated twice. 4. Each culture was centrifuged again as above, the supernatant discarded, and the wet mass of the pellet weighed. Each pellet was resuspended in 0.1 M sodium perchlorate to a concentration of 250 g / L. 5. To 117.5 mL of 25 μM chloroauric acid (approximately 5 ppm Au), pH 4 (adjusted with sodium hydroxide) (pregnant solution), 2.4 mL of 250 g / L microbial solution was added to achieve a final concentration of approximately 5 g / L microbial in 120 mL. This was done separately for both B. subtilis and P. putida. The pH of the gold / microbial mixture was checked and adjusted to 3.0-4.0 using sodium hydroxide or hydrochloric acid, as appropriate. 6. Each gold / microorganism mixture was incubated for 2 hours at 30° C. The mixture was gently agitated on an orbital shaker throughout to keep the microorganisms in suspension. 7. Each mixture was centrifuged as in step 2 and the supernatant (barren fluid) was decanted and stored at 4°C. 8. Each pellet was resuspended in 7 mL of supernatant, 0.11 g of L-cysteine ​​hydrochloride monohydrate was added, and the pH was adjusted to 7.9-8.1 with 1 M NaOH. Each mixture was topped up with supernatant to a final volume of 10 mL, resulting in a cysteine ​​concentration of approximately 62 mM. 9. Each cysteine / gold / microorganism mixture was incubated as in step 6 at 30°C for 2 hours. 10. Each mixture was centrifuged as in step 2 and the supernatant was decanted. Both the supernatant and pellet were stored at 4°C. 11. The following B. subtilis and P. putida samples were analyzed for total gold content by inductively coupled plasma mass spectrometry (correspondence provided by Watercare Services, Auckland, New Zealand): a. Lean supernatant (step 7): 100 mL to which 1 mL of 70% nitric acid was added. b. Desorption supernatant (step 10): 7 mL to 100 mL with water (approximately 14.3-fold dilution) and 1 mL of 70% nitric acid added.

[0195] result: The wet mass of the washed pellet obtained from 600 mL of B. subtilis culture was 3 g and was therefore resuspended in 12 mL of 0.1 M sodium perchlorate to a concentration of 250 g / L; for P. putida the mass and resuspension were 2.6 g and 10.4 mL, respectively.

[0196] At the end of the biosorption phase (step 6), the pH of each mixture was checked and found to be between 3.0 and 4.0.

[0197] The total gold content was reported in mg / L based on the volume analyzed and was used to calculate the amount biosorbed or desorbed, and the biosorption yield relative to the gold input mass (Table 3). The precision of the total gold content was estimated to be 15-20% variance.

[0198] [Table 3]

[0199] For B. subtilis, the pregnant solution contained approximately 49 times more target metals than the barren solution. For P. putida, the pregnant solution contained approximately 16 times more target metals than the barren solution.

[0200] The results in Table 3 show that both B. subtilis and P. putida biosorbed over 90% of the gold from the pregnant solution. After the recovery steps (steps 8-10), P. putida was found to readily desorb gold using cysteine ​​conditions. B. subtilis did not release gold as readily using cysteine ​​conditions, although other conditions may be used to increase recovery rates if necessary.

[0201] Using these results, the enrichment factor from the biosorption step was calculated using a volume of 10 mL of desorption supernatant (Table 4). In this example, the enrichment factor is the change in concentration from the pregnant solution to the recovered Au (i.e., the desorption supernatant). The lower value for B. subtilis is due to the slower desorption rate as discussed above, and not to the biosorption step.

[0202] [Table 4]

[0203] Background Example 3: Leaching Agents for Dissolving Gold Materials and Methods: A sample of gold-bearing quartz ore (micronized to a particle size of less than 100 μm), containing approximately 16 ppm Au and approximately 260 ppm Ag, was obtained from a mining site in the Coromandel region of New Zealand. Printed circuit boards were collected from discarded desktop computers, and sections with gold-plated connector pins were cut from the boards to serve as model e-waste feedstock.

[0204] 1. A leaching solution for gold was prepared as follows: a. Thiosulfate leaching agent: 0.2 M sodium thiosulfate pentahydrate, 0.4 M ammonia, 12 mM copper sulfate pentahydrate; pH adjusted to 9.5-10.0 with 1 M sulfuric acid. b. Thiourea-based leaching agent: 0.13 M thiourea, 5 mM iron(III) chloride; pH adjusted to 1.0-1.5 using 1 M sulfuric acid. 2. In separate 500 mL flat-bottom glass bottles for each raw material / leaching agent combination, 100 mL of leaching agent was added to each of the following gold raw materials: a. 2 to 20 mg of gold powder b. 25 g of finely divided ore (containing approximately 0.4 mg of Au) c. Two gold-plated pin sections of e-waste approximately 0.5 cm 2 Things 3. The reaction was incubated at 30°C and approximately 100 rpm for 20 hours. The bottle was left loosely capped and ventilated. 4. The reaction was allowed to settle (to pulverize the ore solids sediment) and the pregnant leachant was decanted. The following samples were analyzed for total gold content by inductively coupled plasma mass spectrometry (courtesy of Watercare Services, Auckland, New Zealand): a. Gold powder (thiosulfate leaching agent): Dilute 20 mL with water to 100 mL (approximately 2x dilution) and add 1 mL of 70% nitric acid. b. Gold powder (thiourea-based leaching agent): Dilute 10 mL with water to 100 mL (approximately 2x dilution) and add 1 mL of 70% nitric acid. c. Finely divided ore (thiosulfate leaching agent): 50 mL to 100 mL with water (approximately 2x dilution) and 1 mL of 70% nitric acid added. d. Finely divided ore (thiourea leaching agent): Dilute 50 mL with water to 100 mL (approximately 2x dilution) and add 1 mL of 70% nitric acid. e. e-waste (thiosulfate leaching agent): 50 mL to 100 mL with water (approximately 2x dilution) and add 1 mL of 70% nitric acid.

[0205] result: For the thiosulfate-based leachants, the initial redox potential was measured to be between 230 mV and 260 mV (vs. the reference hydrogen electrode); at the end of leaching, it was between 160 mV and 180 mV. For the thiourea-based leachants, these values ​​were between 360 mV and 400 mV, and 340 mV and 370 mV, respectively. The initial color of the thiosulfate-based leachants was light blue, changing to dark blue by the end of leaching. The initial color of the thiourea-based leachants was pale orange, changing to colorless (with the formation of a white precipitate) by the end of leaching.

[0206] Dissolution of gold powder in the leaching agent could be observed; for the micronized ore, no apparent change was apparent; whereas for the e-waste, discoloration and dissolution of the gold plating could be observed. E-waste was not tested with thiourea-based leaching agents, but there is no reason to believe it would not give similar results to the other raw materials listed.

[0207] Total gold content was reported in mg / L based on the volume analyzed and was used to calculate the amount leached from the raw material and, where applicable, the yield relative to the gold input mass (Table 5). The precision of the total gold content was estimated to be 15-20% variance.

[0208] [Table 5]

[0209] Example 3B Leaching Agent for Dissolving Gold Materials and Methods: Printed circuit boards were collected from discarded desktop computers and sections with gold-plated connector pins were cut from the boards to serve as model e-waste feedstock.

[0210] 1. A leaching solution for gold was prepared as follows: a. Iodine-based leaching agent: 0.1 M iodine, 37.5 mM potassium iodide; prepared in water and allowed to stand for 2 hours prior to use. b. Acetic acid / peroxide leaching agent: 1.5 M hydrochloric acid, 0.6 M hydrogen peroxide, 0.6 M calcium chloride; prepared in glacial acetic acid and stirred for 30 minutes prior to use. This leaching agent is similar to that disclosed in International Publication No. WO 2016 / 168933 AI (Foley et al., 27 October 2016 (27-10-16)). c. Acetic acid / hypochlorite leaching agent: 0.7M hydrochloric acid, 0.25M calcium hypochlorite; prepared in glacial acetic acid. d. Acetic acid / chlorine leaching agent: 0.48M hydrochloric acid prepared in glacial acetic acid, then charged with chlorine gas for 30 minutes prior to use. e. Aqua regia leaching agent: 9.6M hydrochloric acid and 3.2M nitric acid. 2. In separate glass reaction vessels, each leaching agent was reacted with e-waste feedstock as follows: a. Iodine-based leachant: Five gold-plated connector pins, approximately 1.5 cm long (total weight approximately 0.85 g), were added to 10 mL of leachant and gently stirred at 22°C for 1 hour. b. Acetic acid / peroxide leaching solution: A whole RAM board (17.3 g) with gold-plated connector pins was added to 100 mL of leaching solution and stirred at 300 rpm using a stir bar at 22 °C for 2 hours. c. Acetic acid / hypochlorite leaching solution: Ten 500g portions of whole RAM boards with gold-plated connector pins were added sequentially to 2L of leaching solution every 30 minutes and stirred at 300 rpm with a stir bar at 22°C for a total of 24 hours. d. Acetic acid / chlorine leaching agent: 38.8 g of gold-plated connector pins were added to 100 mL of leaching agent and stirred at 500 rpm with a stir bar for 5 minutes at 22 °C. e. Aqua regia leaching agent: 11.98 g of RAM integrated circuit chips, crushed to a powder, were added to 51 mL of leaching agent and stirred at 300 rpm using a stir bar at 22°C for 16 hours. f. Aqua regia leaching solution: A quarter of a RAM board (5.1 g) with gold-plated connector pins was added to 50 mL of leaching solution and stirred at 300 rpm using a stir bar at 22 °C for 16 hours. 3. The reaction was filtered to separate the depleted e-waste raw material from the pregnant leachant solution. Samples were analyzed for total gold content by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions. a. Sample aliquots were diluted appropriately to achieve absorbances that fell within the dynamic range of the atomic absorption spectrometer, and the total gold content was back-calculated accordingly.

[0211] result: The following observations were made during each reaction: - Iodine-based leachant: After 1 hour, the connector pin had a dull gray powder covering the metal surface. When disassembled, the dull gray powder came off, leaving behind the copper-colored metal pin. No gold was observed on the connector pin. The dull gray powder was hypothesized to be insoluble copper iodide, formed when the copper lining from the pin was exposed to the iodine solution upon completion of gold dissolution. - Acetic acid / peroxide leaching agent: During the pre-contact stirring period (when the leaching agent was made), a deep yellow solution formed after 30 minutes, with a small amount of calcium chloride remaining undissolved. During leaching agent contact, the surface gold disappeared within minutes, revealing a tarnished underlying nickel and / or copper layer. - Acetic acid / hypochlorite leaching agent: The initial solution color was deep yellow with a small amount of undissolved calcium hypochlorite remaining. Upon addition of the e-waste feedstock, the solution turned deep green and the connector pins lost their gold surface, revealing a tarnished layer of nickel and / or copper. No visible precipitation was observed. - Acetic Acid / Chlorine Leachant: During the filling period, the solution turned deep yellow as it became saturated with chlorine. Upon adding the connector pin, the solution turned bright yellow and all visible metals were dissolving into the solution. No visible precipitate was observed. - Aqua regia leaching agent (circuit chips were crushed into powder): The initial color of the orange / yellow solution turned green after adding the connector pins. All visible metal dissolved in the solution and no visible precipitate was observed. - Aqua Regia Leachant (1 / 4 RAM substrate): The initial color of the orange / yellow solution turned green after adding the RAM components, and all visible metal was dissolving over time. No visible precipitate was observed.

[0212] Total gold content is reported in mg / L based on the volume analyzed and was used to calculate the amount leached from the raw material and, where applicable, the yield relative to the gold input mass (Table 6). The precision of the total gold content was estimated to be 20% variance.

[0213] The results for aqua regia-based leaching agents show an improvement when the e-waste is pretreated by grinding into a powder. The inventors believe this effect is even more pronounced when larger amounts of mixed e-waste are treated by the method of the present invention, particularly when the target metals are not on the surface of the e-waste.

[0214] [Table 6]

[0215] Example 4A. Dissolution of Gold from Crushed Printed Circuit Boards and Base Metal Leaching Materials and Methods: As a model e-waste raw material, printed circuit boards were collected from discarded desktop computers and ground to a particle size of less than 3 mm. This powder was then sieved to a particle size fraction of less than 1 mm, which was used in subsequent experiments.

[0216] 1. To pretreat the e-waste powder for the purpose of removing base metals, 1,200 g of sub-1 mm ground e-waste was treated as an approximately 30% w / v slurry with 5 M sulfuric acid in a reactor using a mechanical stirrer at 200 rpm for approximately 16 hours. 50% hydrogen peroxide was added dropwise until a final concentration of approximately 7.5% was achieved. a. This process was repeated and the resulting powder reduced in weight to 745g. b. An additional processing step was carried out on 125 g of this powder as an approximately 25% w / v slurry in 4 M nitric acid in a reactor using a mechanical stirrer at 200 rpm for approximately 48 hours. 2. The leaching solution for gold was prepared as follows: a. Hypochlorite Leachant #1: 0.26M calcium hypochlorite; prepared in 5% acetic acid. b. Hypochlorite Leachant #2: 0.26M calcium hypochlorite, 90 mM calcium chloride; prepared in 5% acetic acid. c. Chlorine Gas Leachant: Chlorine gas was slowly sparged into 100 mL of water. Chlorine gas was generated in a separate flask by adding 25 mL of 32% hydrochloric acid dropwise over 30 g of 65% calcium hypochlorite over a period of 1 hour. d. Acetic Acid / Chlorine Gas Leachant: Chlorine gas was slowly sparged into 100 mL of 5% acetic acid solution. Chlorine gas was generated as above. e. Thiourea Leaching Agent: 0.32 M thiourea, 0.11 M ferric chloride; prepared in water and adjusted to pH 1 with 98% sulfuric acid. 3. In separate glass reaction vessels, each leachant was reacted with the ground powder as follows: a. Hypochlorite Leachant #1: 16.1 g of untreated powder was placed in 100 mL of leaching agent in a flat-bottom reaction flask and stirred using a stir bar to keep the powder suspended for 1 hour at an initial temperature of 22 °C. b. Hypochlorite Leachant #2: 20 g of the pretreated powder from Step 1(a) was placed in 100 mL of leaching agent in a flat-bottom reaction flask and stirred using a stir bar to keep the powder suspended for 1 hour at an initial temperature of 22 °C. c. Thiourea Leaching Agent: 20 g of the pretreated powder from step 1(a) was placed in 100 mL of leaching agent and stirred using a stir bar to keep the powder suspended for approximately 16 hours at an initial temperature of 22 °C. d. Chlorine gas leaching agent, acetic acid / chlorine gas leaching agent: 10 g of the pretreated powder from step 1(a) was placed in 100 mL of leaching agent in a round-bottom reaction flask prior to sparging with chlorine gas and stirred using a stir bar to keep the powder suspended for 2 hours at an initial temperature of 22 °C. 4. Additionally, the nitric acid treated powder obtained from step 1(b) was treated as in steps 3(b) and 3(c) with the following modifications: a. Hypochlorite leaching agent: 2.5 hour reaction time. b. Thiourea leaching agent: 9 hours reaction time. 5. Samples were taken from each reaction and filtered to separate the e-waste powder from the pregnant leachant solution. Each clarified solution was then analyzed for total gold content by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions.

[0217] a. Sample aliquots were diluted appropriately to achieve absorbances that fell within the dynamic range of the atomic absorption spectrometer, and the total gold content was back-calculated accordingly.

[0218] result: Total gold content is reported in mg / L based on the volume analyzed and was used to calculate the amount leached from the raw material and, where applicable, the yield relative to the gold input mass (Table X). The precision of the total gold content was estimated to be 20% variance.

[0219] Results showed that sulfuric acid pretreatment of the crushed e-waste powder to minimize base metal content (base metal leaching) significantly improved the leached gold yield. Various leaching agents tested on the pretreated powder gave yields ranging from 35 to 84%; an additional nitric acid treatment in step 1(b) increased the yield from the thiourea leaching agent from 70% to 76%.

[0220] [Table 7]

[0221] Example 4B. Dissolution of Gold from Crushed Printed Circuit Boards and Base Metal Leaching Materials and Methods: As a model e-waste feedstock, printed circuit boards were collected from discarded desktop computers and ground to a particle size of less than 3 mm. This powder was then sieved to a particle size fraction of less than 1 mm.

[0222] 1. To pretreat the e-waste powder for the purpose of removing base metals, the powder was slurried at approximately 20% w / v in 5M hydrochloric acid in a reactor using a mechanical stirrer at 200 rpm while sparging with air. Specifically: 200 g of ground e-waste (<3 mm) was treated for approximately 16 hours while sparging with air at approximately 14 L / min. The resulting powder was reduced in weight to 116.4 g. b. 300 g of ground e-waste <1 mm was treated for approximately 48 hours while sparging with air at approximately 20 L / min. The resulting powder was reduced in weight to 164 g. c. 10 kg of sub-3 mm ground e-waste was treated for approximately 48 hours while sparging with air at approximately 50 L / min. The resulting powder was reduced in weight to 5,405 g. 2. The leaching solution for gold was prepared as follows: a. Hypochlorite Leaching Agent: 0.26M calcium hypochlorite; prepared in 3% acetic acid. b. Thiourea Leaching Agent: 0.32 M thiourea, 0.11 M ferric chloride; prepared in water and adjusted to pH 1 with 98% sulfuric acid. c. Iodine leaching agent: 39 mM iodine, 241 mM potassium iodide; prepared in water. 3. Each leachant was reacted with the pretreated powder as follows: a. Hypochlorite Leaching Agent: 116.4 g of powder from Step 1(a) was placed in 1,100 mL of leaching agent and stirred in a reactor using a mechanical stirrer at 200 rpm for 2 hours at an initial temperature of 22°C. b. Thiourea Leaching Agent: 164 g of the powder from step 1(b) was placed in 820 mL of leaching agent and stirred in a reactor using a mechanical stirrer at 200 rpm at 22° C. for approximately 18 hours. c. Iodine leaching agent: 10 g of the powder from step 1(c) was placed in 100 mL of leaching agent in a flat-bottomed glass flask and stirred using a stirrer bar to keep the powder suspended for 16 hours at an initial temperature of 22 °C. 4. Samples were taken from each reaction and filtered to separate the e-waste powder from the pregnant leachant solution. Each clarified solution was then analyzed for total gold content by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions. a. Sample aliquots were diluted appropriately to achieve absorbances that fell within the dynamic range of the atomic absorption spectrometer, and the total gold content was back-calculated accordingly.

[0223] result: Total gold content is reported in mg / L based on the volume analyzed and was used to calculate the amount leached from the raw material and, where applicable, the yield relative to the gold input mass (Table 8). The precision of the total gold content was estimated to be 20% variance.

[0224] The results showed that hydrochloric acid pretreatment of the crushed e-waste powder to minimize base metal content significantly improved the yield of leached gold (vs. crushed e-waste without base metal leaching in Example 4A, Table 7, #1, i.e., 10% yield).

[0225] [Table 8]

[0226] Background Example 5 Chlorine Leaching Agent Materials and Methods: As a model e-waste raw material, printed circuit boards were collected from discarded desktop computers and sections with gold-plated connector pins were cut from the boards.

[0227] 1. Gold-plated pin section of e-waste (total mass of 1.21 g) approximately 1 cm 2 Five pieces of the 100 mL of water were placed in a flat-bottom reaction flask. The flask was placed on a magnetic stir plate and a stirring flare was added. The stirring was performed at a speed sufficient to keep the e-waste moving around in the flask. 2. Chlorine gas was slowly sparged into the reaction liquid to form a chlorine-based liquor. a. Chlorine gas was generated in a separate flask by adding 12 mL of 32% hydrochloric acid to 3 g of potassium permanganate dropwise at 9 mL / hr using a syringe pump. b. Excess chlorine gas leaving the e-waste reaction flask was allowed to escape via sparging into 50 mL of 7 mM sodium thiosulfate pentahydrate solution for neutralization. 3. After 7 hours, the reaction was observed to be complete and the pregnant leachate was decanted into a separate flask. 4. 5 mL of the precious leachate was sent for analysis for total gold content by inductively coupled plasma mass spectrometry (correspondence provided by University of Auckland Mass Spectrometry Centre, Auckland, New Zealand).

[0228] result: The total gold content is reported in mg / L based on the volume analyzed and was used to calculate the amount leached from the raw material (Table 7). The precision of the total gold content was estimated to be 15-20% variance.

[0229] [Table 9]

[0230] Background Example 6 Biosorption from Chlorine Solutions Materials and Methods: Microbial cultures were grown under sterile conditions, but subsequent processing was performed using non-sterile solutions and equipment.

[0231] A chlorine-based leachant nobled with gold from e-waste feedstock was produced as in Example 5.

[0232] 1. Culture Capriavidus metallidurans strain CH34 (Deutsche Sammlung von Mikroorganismen und Sellkulturen GmbH # 2839) in 25 mL of nutrient broth (0.5% peptone, 0.3% yeast extract) and grow at 30°C and approximately 200 rpm for at least 16 hours until stationary phase. 2. The medium was washed by centrifugation at 4,000 rcf for 12 minutes, discarding the supernatant, and resuspending the pellet (approximately 0.1 g) in 30 mL of 0.85% saline solution. This centrifugation / washing step was repeated twice. 3. The medium was centrifuged again as above and the supernatant discarded. 4. 30 mL of chlorine-based leachant enriched with gold from e-waste feedstock (approximately 95 ppm gold) was gently sparged with air for 45 minutes to drive off residual chlorine gas, and the pH was adjusted to 4.5-5.0 with sodium hydroxide. This solution was then used to resuspend the microbial pellet obtained from step 3. 5. The gold / microorganism mixture was incubated at room temperature for 22 hours, with the mixture gently agitated on an orbital shaker throughout to keep the microorganisms in suspension. 6. The mixture was centrifuged as in step 2, the supernatant (barren) discarded and the pellet stored at 4° C. The pellet was resuspended in 30 mL of water and centrifuged as in step 2. 7. The supernatant was discarded and the pellet was resuspended in 2 mL of water and stored at 4°C. 8. The following samples were analyzed for total gold content by inductively coupled plasma mass spectrometry (correspondence by Auckland, New Zealand): a. Lean supernatant (step 6): 5 mL. b. Bioabsorbent pellet (Step 7): 1 mL.

[0233] result: Total gold content was reported in mg / L based on the volume analyzed and was used to calculate the amount biosorbed and the biosorption yield (Table 10). The precision of the total gold content was estimated to be 15-20% variance.

[0234] [Table 10]

[0235] These results were used to calculate the concentration factors from the biosorption process (Table 11).

[0236] [Table 11]

[0237] Background Example 7 Recovery of Metal-Accumulating Microorganisms from Poorly Solution Materials and Methods: Microbial cultures were grown under sterile conditions, but subsequent processing was performed using non-sterile solutions and equipment.

[0238] As an example, a gold / microorganism mixture was prepared as in Example 6.

[0239] 1. To isolate gold-accumulating microorganisms from the lean leachant solution, samples were processed by either centrifugation or filtration: a. Centrifugation: The mixture was centrifuged at 3,000 to 8,000 rcf for at least 10 minutes, and the lean leachant supernatant was decanted from the gold-accumulating microorganism pellet. For washing, the pellet was resuspended in a large volume of washing solution and subsequently collected through another centrifugation step. b. Filtration: The mixture was applied to a 0.45 μm PVDF filter under a vacuum of approximately 20 cmHg for several minutes until all the liquid had passed through. The filtrate was a poor leachant, and the residue was the gold-accumulating microorganisms. For washing, a large amount of washing solution was added to the residue, which was then filtered under vacuum. The residue was recovered by washing the filter in a 50 mL Falcon tube with a large amount of washing solution, after which the gold-accumulating microorganisms were resuspended, and the filter was subsequently discarded.

[0240] result: Centrifugation or filtration both worked well to remove the lean leachant solution from the gold-accumulating microorganisms.

[0241] Background Example 8: Microbial Selectivity for Gold from Gold / Copper Solutions Materials and Methods: Microbial cultures were grown under sterile conditions, but subsequent processing was performed using non-sterile solutions and equipment.

[0242] 1. 120 mL of Capriavidus metallidurans strain CH34 was cultivated as in Example 1. 2. The medium was divided into six equal aliquots, centrifuged at 4,350 rcf for 10 minutes, the supernatant discarded, and the pellet washed by resuspending in 30 mL of 0.85% saline solution. This centrifugation / wash step was repeated a total of two times, and the final wash supernatant discarded. 3. The pellets (average 0.15 g wet weight) were resuspended in 30 mL of a two-fold dilution series of chloroauric acid, ranging from 325 μM (approximately 64 ppm) to 10 μM (approximately 2 ppm) chloroauric acid, prepared in 0.85% saline solution, the original pH of which had been adjusted to 5.5. 4. Copper chloride was also added to each diluted sample prior to resuspending the pellet to a final concentration of 32.5 mM (2,060 ppm). 5. The gold / copper / microorganism mixture was incubated at room temperature for 4 hours, with the mixture gently agitated on an orbital shaker throughout to keep the microorganisms in suspension. 6. The mixture was centrifuged as in step 2 and the supernatant was saved. The pellet was resuspended / washed with water as in step 2 and finally resuspended in 1.2 mL of water (total volume estimated to be 1.3 mL). 7. Half of each sample (0.65 ml) from step 5 was digested in 4 ml of an acid mixture (3 ml of 69% nitric acid, 1 ml of HCl) and then analyzed for total gold and copper content by inductively coupled plasma mass spectrometry (correspondence provided by the University of Auckland, Mass Spectroscopy Centre, Auckland, New Zealand).

[0243] result: Total metal content was reported in mg / L based on the volume analyzed and used to calculate the amount biosorbed and the biosorption yield (Table 10). The precision of the total gold content was estimated to be 15-20% variance.

[0244] [Table 12]

[0245] This demonstrates that microorganisms (in this case, C. metallidurans) can selectively biosorb metals. In this case, gold was biosorbed much more selectively than copper. This allows for selective separation of metals in a separation step, i.e., separation of metal-accumulating microorganisms from the barren solution. In this case, gold-accumulating microorganisms can be separated from the barren solution, which retains much of the copper.

[0246] It can be seen from Table 12 that the gold to copper mass ratio changes after biosorption. For example, for sample "325 μM Au," the gold to copper ratio at this metal loading was approximately 1:32; after biosorption, the ratio was found to be approximately 9:1, favoring gold. This resulted in a 288-fold increase in mass ratio. Similarly, for sample "10 μM Au," the gold to copper ratio increased from 1:1,000 to 1:3, a more than 300-fold enrichment of copper.

[0247] Example 9 Microbial selectivity for gold from e-waste leachate Materials and Methods: Microbial cultures were grown under sterile conditions as in Example 1, but subsequent processing was carried out using non-sterile solutions and equipment.

[0248] A gold-enriched element-based leachant from e-waste feedstock was produced as in Example 3B and gently sparged with air for at least 10 minutes to drive off residual chlorine gas.

[0249] 1. Three 20 mL aliquots of stationary-phase Capriavidus metallidurans strain CH34 were centrifuged at 4,350 rcf for 10 minutes and the supernatant was discarded. Two of the pellets were washed by resuspending in 20 mL of 0.85% saline solution and repelleting, while one pellet was left unwashed. 2. One of the washed pellets was resuspended in 1 mL of a chlorine-based noble leachant (approximately 1,100 ppm Au, approximately 25,100 ppm Cu, approximately 3,150 ppm Ni). The second washed pellet and the unwashed pellet were separately resuspended in 0.5 mL of the same leachant, and 4.5 mL of water was added. 3. The precious infusion / microorganism mixture was incubated at room temperature for 2 hours. The mixture was gently agitated on an orbital shaker throughout to keep the microorganisms in suspension. 4. The mixture was centrifuged as in step 1 and the supernatant was saved. The pellet was washed by resuspending in 30 mL of water, centrifuging as in step 1 and discarding the wash supernatant. 5. The supernatant was discarded and each pellet was digested in 4 mL of aqua regia (see Example 3B) for 2 hours at room temperature. 6. The samples were analyzed for total gold, copper, and nickel content by atomic absorption spectroscopy as in Example 3B.

[0250] result: Total metal content was reported in mg / L based on the volume analyzed and was used to calculate the amount of each metal biosorbed and the biosorption yield (Table 13). The precision of the total metal content was estimated to be 15-20% variance.

[0251] [Table 13]

[0252] Example 10: Leaching of base metals Materials and Methods: Printed circuit boards were collected from discarded desktop computers and crushed to a particle size of less than 3 mm. Samples of this powder were treated with three acids: nitric acid (HNO), sulfuric acid (HSO), and hydrochloric acid (HCl).

[0253] 1. 100 mL of each acid (0.5 M) was taken from the concentrate, mixed and placed in a glass reaction vessel. 2. To each acid, 10 g of ground powder was added and the solution was allowed to react for 48 hours with stirring to keep the powder suspended in the solution. 3. Samples were taken from each reaction and filtered to separate the e-waste powder from the base metal leach solution. Each clarified solution was then analyzed for total gold content by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions. Sample aliquots were diluted appropriately to achieve absorbances that fell within the dynamic range of the atomic absorption spectrometer, and the total gold content was back-calculated accordingly.

[0254] result: Total dissolved metals were calculated as a percentage of the total metals available for dissolution (Table 14). Although the original metal composition of the printed circuit board is unknown, it is clear from a comparison of the results for different acids (base metal leaching) in Table 14 that different base metal leaching agents (acids in this case) have different solubilities for different metals. Specifically, when base metals, such as copper, zinc, aluminum, iron, and / or tin, are non-target metals and gold is the target metal, the base metal leaching agent can be selected appropriately. The results indicate that sulfuric acid is preferable to nitric acid and hydrochloric acid as the base metal leaching agent, specifically when gold is the target metal.

[0255] [Table 14]

[0256] Example 11A Microbial Selectivity for Gold from E-Waste Leachate After Base Metal Leaching Materials and Methods: Capriavidus metallidurans strain CH34 was grown and harvested as in Example 1, except at a 20 L scale in a suitable bioreactor. Subsequent processing was performed using non-sterile solutions and equipment.

[0257] 1. For 7.14 kg RAM boards, the gold-plated connector pins were removed and treated with 1.7 L of 2 M sulfuric acid, and 0.3 L of 50% hydrogen peroxide was added in small aliquots over 1 hour (causing the solution temperature to rise from 22°C to approximately 80°C). After 3 hours, it was visually determined that most of the base metal present in the connector pins had been removed. 2. The solids from Step 1 were removed by filtration and treated with 725 mL of chlorine-based lixiviant (prepared as in Example 3B) at 22°C for 30 minutes to produce a gold-enriched lixiviant. 3. 250 mL of this precious leachant solution containing gold, copper, and nickel was gently sparged with air for 10 minutes to drive off any residual free chlorine, and then contacted with 84 g of wet C. metallidurans biomass under gentle agitation at 22°C for 2.25 hours. 4. The mixture was centrifuged in a centrifuge bottle at 4,000 rcf for 40 minutes and the supernatant was saved. The pellet was washed by resuspending in 1.1 L of water and centrifuging again. The wash supernatant was saved. 5. The pelleted metal-accumulating biomass was spread on trays and left to dry for 72 hours to obtain an approximate dry mass of 22 g. 6. 125 mg of this dried biomass was ground, digested in 4 mL of aqua regia, and analyzed for total gold, copper, and nickel content by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions.

[0258] result: Total metal content was reported in mg / L based on the volume analyzed and was used to calculate the amount of each metal biosorbed and the biosorption yield (Table 15). The precision of the total metal content was estimated to be 15-20% variance.

[0259] [Table 15]

[0260] Using the data in Table 15, the concentration factors obtained from the biosorption process from 250 mL of leachant and subsequent drying were calculated using 22 grams of dry metal-accumulating biomass (Table 16).

[0261] [Table 16]

[0262] It can be seen that gold increases in concentration by about 10-fold (to about 3.6% of the biomass weight), while copper increases in concentration only by about 3-fold, and nickel is found at similar levels.

[0263] Example 11B Microbial Selectivity for Gold from E-Waste Leachate After Base Metal Leaching Materials and Methods: Capriavidus metallidurans strain CH34 was grown and harvested as described in Example 1. Subsequent processing was performed using non-sterile solutions and equipment.

[0264] Leachants nobled with gold (and other base metals) from pulverized printed circuit board raw material were produced as in Examples 4A and 4B.

[0265] 1. Iodine noble leachate from HCl-pretreated powder: 6 mL of noble leachate containing 68 ppm gold, produced as in Example 4B, step 2c, was diluted with 20 mL of water to yield 20.5 ppm gold (0.41 mg total). 410 mg of wet C. metallidurans biomass (820 μL from approximately 500 mg / mL feedstock) was added to this solution to yield an Au:microorganism (cell wet weight) ratio of approximately 1:1,000. The gold / microorganism mixture was incubated for 2.75 hours at 22° C. The mixture was gently agitated on an orbital shaker throughout to maintain suspension. b. The mixture was centrifuged as in Example 1 and the post-biosorption supernatant was collected. 2. Hypochlorite Noble Leachate from HCl-Pretreated Powder: Approximately 600 mL of the noble leachate from Example 4B, Step 3a, was sparged with air for 1 hour at 4 L / min to remove excess free chlorine. 30 mL of this sparged leachate, containing 20.4 ppm gold (0.61 mg total), was contacted with 245 mg of wet C. metallidurans biomass (490 μL from approximately 500 mg / mL feedstock), yielding an Au:microorganism (cell wet weight) ratio of approximately 1:400. The gold / microorganism mixture was incubated for 2 hours at 22° C. The mixture was gently agitated on an orbital shaker throughout to maintain suspension. b. The mixture was centrifuged as in Example 1 and the post-biosorption supernatant was collected. 3. Hypochlorite Noble Leachate from H2SO4-Pretreated Powder: Approximately 3.3 L of the noble leachate from Example 4B, Step 3a, was sparged with air for 2.75 hours at 8 L / min to remove excess free chlorine. This 3 L of sparged leachate, containing 35.2 ppm gold (105.7 mg), was contacted with 20.4 g of wet C. metallidurans biomass (40.8 mL from approximately 500 mg / mL feedstock), yielding an Au:microorganism (cell wet weight) ratio of approximately 1:200. The gold / microorganism mixture was incubated for 3 hours at 22° C. The mixture was gently agitated on an orbital shaker throughout to maintain suspension. b. The mixture was centrifuged as in Example 1 and the post-biosorption supernatant was collected. 4. Samples of the post-biosorption supernatant obtained from the above step were analyzed by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions, and the biosorbed metals were calculated by subtracting the post-biosorption supernatant metal content from the measured metal input content of each reaction.

[0266] result: Total metal content was reported in mg / L based on the volume analyzed and was used to calculate the amount of each metal biosorbed and the biosorption yield (Table 17). The precision of the total metal content was estimated to be 15-20% variance.

[0267] [Table 17]

[0268] Gold and palladium biosorption proceeds well from noble hypochlorite leachants but does not favorably occur from noble iodine leachants.

[0269] Using the data in Table 17, the enrichment factor from the biosorption process was calculated by comparing the metal concentration of the input noble leachant to the metal concentration in the removed metal-loaded biomass. The metal-loaded biomass, measured as wet weight, was extrapolated to an estimated dry weight by dividing its mass by 5 (Luria, The Bacteria, vol. 1. Academic Press, Inc., New York, pp 1-34 (1960)).

[0270] [Table 18]

[0271] It can be seen that while all metals are concentrated by biosorption, gold and palladium increase in concentration more significantly than any other base metal.

[0272] Background Example 12: Recovery of metals from microorganisms by smelting Materials and Methods: A sample of metal-accumulating microorganisms (previously determined by atomic absorption spectroscopy to contain 36,250 mg / kg [ppm] gold, 1,686 mg / kg copper, and 82 mg / kg nickel; see Example 11A) was incinerated to remove organic matter and recover the biosorbed metals.

[0273] 1. 0.5 g of dried metal-accumulating microbial powder was mixed with an equal portion of sodium tetraborate flux and placed in a crucible. 2. The mixture was carefully heated with a methylacetylene, propadiene, or propane gas torch until the flux began to liquefy, then the flame intensity was gradually increased to slowly burn off the organic matter. 3. The residue of molten metal remaining in the crucible was allowed to solidify into a single mass, allowed to cool, and subsequently weighed. 4. The cooled metal buttons were digested in 4 mL of aqua regia, and the resulting solution was analyzed for total gold, copper, and nickel content by atomic absorption spectrometry using a Shimadzu AA-6300 (Shimadzu Corporation, Kyoto, Japan) according to the manufacturer's instructions. a. Sample aliquots were diluted appropriately to achieve absorbances that fell within the dynamic range of the atomic absorption spectrometer, and metal contents were back-calculated accordingly.

[0274] result: The mass of metal buttons achieved after smelting was 20.94 mg. The total metal content is reported in mg / L and used to calculate the metal yield (Table 19). The precision of the total metal content was estimated to be 15-20% variance.

[0275] [Table 19]

[0276] Background Example 13: Recovery of Gold from Microorganisms by Chemical Dissolution and Precipitation Materials and Methods: As in Example 12, biosorbed metals were recovered from the metal-accumulating microorganisms by using chlorine-based leachant extraction.

[0277] 1. 100 mL of water was placed in a reaction vessel and charged with gaseous chlorine for 45 minutes. 2. 0.3 g of dried metal-accumulating microbial powder (see Example 11A) was added to the leaching agent and left to react overnight with gentle stirring. 3. The solution was then sparged with air to remove excess chlorine and 0.5 g of sodium metabisulfite was added to precipitate metal ions, such as gold, from the solution.

[0278] result: The metal content of the metal-accumulating microbial powder was previously determined to be 36,250 ppm Au, 1,686 ppm Cu, and 82 ppm Ni (see Example 11A). After standing at 22°C for 24 hours, a visible precipitate formed in the solution, which was gold powder.

[0279] Background Example 14. Gold Dissolution Using Depleted Microbial Media Materials and Methods: Depleted nutrient broth medium was obtained from the discarded supernatant of pelleted microbial culture (eg, Example 1) and used to produce a chlorine-based leachant.

[0280] 1. 100 mL of depleted medium was filled with gaseous chlorine for 30 minutes prior to use. 2. Three RAM substrate pins (0.58 g) cut into 1 cm lengths were placed in the filled solution and stirred at 300 rpm at 22°C for 1 hour. 3. The leachant was analyzed for gold content by atomic absorption spectroscopy as in the previous example.

[0281] result: A precipitate formed during chlorination of the depleted medium, likely due to chlorination of organic compounds present in the solution. The total gold content was reported in mg / L and used to calculate the leachant yield (Table 20). The precision of the total gold content was estimated to be 15-20% variance.

[0282] [Table 20]

[0283] Background Example 15. Dissolution of Gold Using Recharged Leachant Materials and Methods: Depleted leachant was obtained from the discarded supernatant of a pelleted metal-accumulating microorganism culture (e.g., Example 6) and used to produce a chlorine-based leachant. The residual concentration of gold in the depleted leachant was 27.8 mg / L (ppm).

[0284] 1. 100 mL of depleted leachant was charged with gaseous chlorine for 30 minutes prior to use. 2. RAM substrate pins (0.44 g) cut to a length of 3.5 cm were placed in the filled solution and stirred at 300 rpm at 22° C. for 1 hour. 3. The leachant was analyzed for gold content by atomic absorption spectroscopy as in the previous example.

[0285] result: Upon completion of the reaction, no visible metal appeared to remain on the RAM pin. Total gold content was reported in mg / L and used to calculate leachant yield (Table 21). The precision of total gold content was estimated to be 15-20% variance.

[0286] [Table 21]

[0287] The present invention has been described herein with reference to certain preferred embodiments with the intent of enabling the reader to practice the invention without undue experimentation. However, those skilled in the art will readily recognize that many of the components and parameters may be changed or modified to a certain extent, or substituted with known equivalents, without departing from the scope of the present invention. Such modifications and equivalents should be understood to be incorporated herein by reference as if individually set forth. Titles, headings, or the like are provided to aid the reader in better understanding of this specification and should not be read as limiting the scope of the present invention.

[0288] The entire disclosures of all applications, patents, and publications, if any, cited above or below are incorporated by reference.

[0289] The reference herein to any prior art is not, and should not be construed as, an acknowledgment or in any way implying that the prior art is part of the common general knowledge in the United States or any country throughout the world.

[0290] Throughout this specification and any claims that follow, unless the context otherwise requires, the words "comprise," "comprising," and the like, shall be interpreted in their non-exclusive, as opposed to exclusive, sense, i.e., "including but not limited to."

Claims

1. 1. A method for recovering one or more target metals from e-waste, comprising: (a) a pre-treatment step comprising removing at least a portion of non-target materials from the e-waste to obtain pre-treated e-waste, the pre-treatment step comprising non-target metal leaching to remove one or more non-target metals; (b) a dissolution step comprising contacting the pretreated e-waste with a leaching agent to dissolve at least a portion of the target metals in the leaching agent to produce a pregnant liquor containing target metal ions; (c) a biosorption step comprising contacting microorganisms with the pregnant liquor such that at least a portion of the target metal ions are biosorbed and / or bioadsorbed by the microorganisms by biosorption, such that the microorganisms accumulate the metal and the pregnant liquor becomes barren containing less than 5 ppm of the target metal; (d) a separation step comprising substantially separating the metal-accumulating microorganisms from the barren solution; (e) a recovery step comprising recovering the target metal from the metal-accumulating microorganism; the non-target material comprises one or more non-target metals, the microorganisms selectively biosorb and / or biosorb the target metals over the non-target metals in the biosorption step, and the non-target metals remain in the barren solution in the separation step, at least a portion of the barren solution is returned to the dissolution step (b) to be used as a leaching agent, and the target metal is gold; the non-target metal leaching comprises treating the e-waste with a leaching reagent in which the one or more non-target metals are substantially dissolved while the one or more target metals remain substantially undissolved, the leaching reagent comprising nitric acid, sulfuric acid, and / or hydrochloric acid; the dissolving step selectively dissolves at least a portion of the target metal while leaving the non-target metal substantially undissolved or to a lesser extent dissolved; The leaching agent solution is a thiourea-based aqueous solution, a thiosulfate-based aqueous solution, a thiocyanate-based aqueous solution, a cyanide-based aqueous solution, a halogen-based aqueous solution, or an aqua regia-based solution; 10. The method of claim 9, wherein the concentration factor of the target metal from the pregnant liquor to the microorganism is greater than 5.

2. The method of claim 1 , wherein the electronic waste comprises less than 5% of the target metal.

3. The pre-processing step comprises: Chip removal Grinding to a preselected size Removal of a specific density fraction, and / or Removal of magnetic materials, 3. The method of claim 1, comprising one or more unit operations selected from:

4. 4. The method of claim 1, wherein the pre-treatment step comprises grinding.

5. 5. The method of claim 1, wherein the leaching agent selectively dissolves the target metal over the non-target material.

6. 6. The method of any one of claims 1 to 5, wherein the enrichment factor of the target metal from the pregnant liquor to the microorganisms is greater than 10.

7. 7. The method of claim 1, wherein the microorganism is a gram-negative or gram-positive bacterium.

8. the separating step gravity separation of the metal-accumulating microorganisms from the barren solution and removal of the barren solution; and / or centrifugation and removal of said barren fluid, and / or filtration of the metal-accumulating microorganisms from the barren solution; The method according to any one of claims 1 to 7, comprising at least one of:

9. 9. The method of claim 8, wherein at least 60% of the barren solution is removed.

10. The recovering step 10. The method of any one of claims 1 to 9, comprising contacting the metal-accumulating microorganisms with conditions that induce the microorganisms to substantially desorb the target metal, or incinerating or chemically dissolving the metal-accumulating microorganisms to desorb the target metal.

11. 11. The method of any one of claims 1 to 10, comprising, following the dissolution step, a filtration step to remove at least a portion of undissolved non-target material from the pregnant liquor.

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