Novel process for the selective extraction of gold

Abstract

The invention relates to a process for the selective extraction of gold. More particularly, the invention relates to a process for the selective extraction of gold from ore, mine wastewater, old mine dumps and e-waste wherein the yield of recovered gold exceeds 95%. The invention further provides a process for preparing an aerogel for use in the selective extraction gold process.

Description

[0001] NOVEL PROCESS FOR THE SELECTIVE EXTRACTION OF GOLD

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a process for the selective extraction of gold. More particularly, the invention relates to a process for the selective extraction of gold from ore, mine wastewater, old mine dumps and e-waste wherein the yield of recovered gold exceeds 95%.

[0004] BACKGROUND TO THE INVENTION

[0005] Gold is an extraordinary metal and is used extensively in a plethora of applications including electronics, aerospace, dentistry, medicine, jewellery and finance. Gold nanoparticles are expansively used in inter alia catalysis and drug delivery.

[0006] Historically, gold was mined from alluvial deposits. The expansion of gold mining to ores that are not on the surface has led to more complex extraction processes such as pit mining. Owing to its high affinity for gold, cyanide is able to selectively leach gold from ores.

[0007] Gold cyanidation is a hydrometallurgical technique for extracting gold from low- grade ore by converting gold to a water-soluble coordination complex. Gold cyanidation is the most commonly used leaching process for gold extraction. However, cyanide remains in tails streams from gold mining plants and due to its high toxicity, its use can lead to severe environmental contamination if not managed carefully. Accidental spills or leaks from mining operations can result in the contamination of water sources, soil, and ecosystems, impacting biodiversity and posing risks to human health through exposure to contaminated water or food. This has incentivized alternative methods for extracting gold. Other extractants have been used including thiosulfate (S2O32"), thiourea (SC(NH2)2), iodine / iodide, ammonia, liquid mercury, and alpha-cyclodextrin. However, these reagents all present challenges including high reagent cost as well as inferior efficiency of gold recovery.

[0008] Electronic waste (e-waste) has been reported as the fastest growing solid waste stream in the world, which according to some reports, is increasing three times faster than the world’s population. Less than a quarter of e-waste, which includes discarded electronic devices such as smartphones, tablets, and computers, produced globally in 2019 was known to be formally recycled; however, e-waste streams contain valuable and finite resources that can be reused if they are recycled appropriately.

[0009] Electrical and electronic items contain many different toxic substances. While users are unlikely to have contact with any of these substances when the items are in use, when they become waste, these toxicants can be released into the environment if the devices are heated or burned; manually disassembled, stripped or shred which may lead to the release of toxic pollutants contaminating the air, soil, and water. E-waste contains small amounts of gold and other precious metals, which are extracted using chemical processes. Acid leaching is commonly employed, where acids such as nitric acid or aqua regia are used to dissolve and recover the metals. These acids are corrosive and release toxic fumes when handled improperly. Furthermore, the process generates toxic sludge and wastewater contaminated with heavy metals and other hazardous substances, posing risks to both the environment and the health of workers involved in handling e-waste.

[0010] The extraction of gold from ore, mine wastewater, old mine dumps and e-waste thus represents significant environmental and economic challenges.

[0011] Recent advances in material science have led to the development of innovative materials, such as aerogels, that can be used to clean water by extracting certain elements or decomposing organic material.

[0012] Aerogels represent a diverse category of porous, solid materials renowned for their exceptional properties. Chief among these is their extraordinarily low density, ranging from 0.0011 to approximately 0.5 g cm’3. Notably, aerogels hold the distinction of being the lightest solid materials ever created; for instance, a silica aerogel has been fabricated to be just three times heavier than air, and through the removal of air from its pores, it can even become lighter than air.

[0013] Despite their minimal densities, most aerogels typically weigh around 0.020 g cm’3or higher, approximately 15 times denser than air. Even at these densities, it would require more than 40 brick-sized pieces of aerogel to match the weight of a single litre of water. Aerogels consist predominantly of air (or another gas), typically comprising 95-99% of their volume, with the least dense aerogels reaching up to 99.98% air volume. These materials are characterized by their open-porous structure, featuring pore diameters ranging from less than 1 to 100 nm, usually less than 20 nm. Technically defined, an aerogel is an open-celled, mesoporous solid foam composed of interconnected nanostructures, exhibiting a porosity of at least 50%. The term "mesoporous" denotes pores typically ranging from 2 to 50 nm in diameter, with most aerogels falling within this size range. In practice, aerogels often display porosities ranging from 90% to over 99.8%, and they also feature significant microporosity (pores less than 2 nm in diameter).

[0014] Aerogels can be fabricated from a wide array of substances, not limited to silica and including transition metal oxides, lanthanide and actinide metal oxides, main group metal oxides, organic polymers like resorcinol-formaldehyde and phenolformaldehyde, biological polymers such as gelatin and agar, semiconductor nanostructures like cadmium selenide quantum dots, carbon materials including carbon nanotubes, and metals such as copper and gold.

[0015] Recently, researchers from ETH in Zurich have produced an aerogel from whey protein obtained from old milk which they report was able to extract gold from e-waste with high selectivity and efficacy. Most notably however is that a cross-linking agent, namely 1 ,2, 3, 4 butanetetracarboxylic acid, was used in the presence of sodium hypophosphite (as a catalyst) to form the aerogel wherein the aerogel was heated to a temperature of 175°C for purposes of preparing the aerogel.

[0016] Yang et al. teaches of preparing a membrane from bovine serum albumin using tris(2- carboxyethyl) phosphine as a cross-linking agent. Here, it was reported that gold was efficiently extracted and reduced from Au3+to Au° by the membrane. To reuse the membrane, same was dissolved in an iron solution to reduce the Au° to Au1 +again so that it could dissolve whereafter it was coordinated with thiourea and thiocyanate ions. The membrane was selective for gold in the presence of metal ions such as iron, but the authors claim that it could also be used for platinum and silver absorption, making the selective extraction of gold from e-waste difficult. In addition, the extraction is dependent on the thickness of the membrane and the solution pH. The absorption times was between 36 and 72 hours depending on the gold concentration. It is important to note that in the presence of anions (nitrate, chloride etc), the membrane efficacy was reported to be only 85%.

[0017] According to the teachings of Sharma et al. polymeric films have been prepared, using various acrylamide polymers. These are water soluble and can be recycled five times for gold recovery. It was reported that the polymeric films could extract 0.4 g Au / 1g polymer.

[0018] Quin et al. teaches of preparing a polyimide aerogel from biomass-derived metal- phenolic networks which revealed a gold extraction and separation of 97% from a 3.6 ppm Au solution.

[0019] Wang et al. reports the synthesis of a silsesquioxane-based hybrid luminescent porous polymer with a high surface area, which is crosslinked to a thiol-derivative of chitosan to form a hybrid aerogel. This aerogel can recover gold from e-waste in high purity and fast, however notably UV-light is required for the process. Reduced graphene oxide can also be used for the selective extraction and reduction of gold, but the preparation of rGO is tedious with low yields. Accordingly, there is a clear need in the art for a selective extraction process for gold which is cost-effective, environmentally friendly and simple; which affords high yields of gold recovery and which does not suffer from the shortcomings demonstrated by the prior art teachings.

[0020] OBJECT OF THE INVENTION

[0021] It is accordingly an object of the present invention to provide a novel process for the selective extraction of gold which overcomes, at least partially, the abovementioned disadvantages and limitations and / or which will provide a useful alternative to existing technology to afford high yields of gold recovery using a simple, environmentally friendly and cost-effective process.

[0022] SUMMARY OF THE INVENTION

[0023] According to a first aspect of the present invention, there is provided a process for the selective extraction of gold, the process including the steps of:

[0024] (i) providing a source of gold ions in solution;

[0025] (ii) contacting the source of gold ions in solution with an aerogel, wherein the aerogel includes a natural and / or synthetic source of albumin, at a pH of 5 or lower, to allow the gold ions from the source of gold ions to reduce to gold(O) and to deposit (adsorb) onto the aerogel to form a gold aerogel composite;

[0026] (iii) combusting the gold aerogel composite in air at a temperature of at least 500°C for a time period of at least 30 minutes to 5 hours; and

[0027] (iv) recovering at least 95% of gold(O) from the solution.

[0028] In terms of the present invention, the word “gold” and the periodic symbol “Au” may be used interchangeably in the present specification. In this manner, metals and their periodic symbol may also be used interchangeably.

[0029] Similarly, in terms of the present invention, the word “gold(O)” the periodic symbol “Au(0)” and the term “elemental gold” may be used interchangeably.

[0030] The invention provides for the source of gold ions to include a source of Au(l) or Au(lll).

[0031] Non-limiting examples of a source of Au(l) include gold(l) chloride, chloro(triethylphosphine)gold(l), and chloro(tri-fe / Y-butylphosphine)gold(l). Non-limiting examples of a source of Au(lll) include gold(lll) chloride (and its different hydrates), gold(lll) bromide, potassium gold(lll) chloride, and sodium tetrachloroaurate(lll) dihydrate.

[0032] In an embodiment of the invention, there is provided for the source of gold ions to be derived from gold ore or any suitable gold-containing waste, including but not limited to, gold mine waste; gold-containing mine wastewater or gold-containing e-waste.

[0033] It will be appreciated that the source of gold ions may be provided in an aqueous solution. Alternatively, the source of gold ions may be provided in a highly concentrated acid solution, for instance aqua regia. It will be appreciated that any suitable, highly concentrated acid solution may be provided.

[0034] In an embodiment of the invention, the concentration of the source of gold ions is from and including 0.05 mM (10 ppm) up to and including 0.05 M (10 OOOppm).

[0035] In a preferred embodiment of the invention, a solution of 10 ml of 1000 ppm gold(lll) chloride trihydrate in distilled water is provided.

[0036] In terms of the present invention, the solution may include other metals, including but not limited to, iron; copper; cobalt; chromium; platinum; silver; and a combination thereof.

[0037] In terms of the present invention, the aerogel includes a natural source of albumin. The natural source of albumin may be selected from the group consisting of chicken egg albumin (egg-white albumin); bovine serum albumin; plant-based albumin (from algae, legumes, beans, nuts, peas, potatoes, corn, and recovered com proteins); globulin; and a combination of one or more thereof.

[0038] Alternatively, the source of albumin may be synthetic albumin manufactured by companies, including but not limited to Solar Foods, Bioceutica and JustEgg; recombinant DNA synthesised albumin manufactured by companies including but not limited to TwistBioscience; synthetic amino acid-containing polymers (peptide synthesis, peptide assembly, folding and refolding) manufactured by companies including but not limited to Alamanda; inexpensive polymers such as carbomer, polylactic acid and polyacrylates cross-linked with amino acids containing sulphur atoms; and a combination of one or more thereof.

[0039] In an embodiment of the invention, there is provided for the 95% gold(O) recovered from the solution to be in the form of bulk gold.

[0040] In a further embodiment of the invention, there is provided for the 95% gold(O) recovered from the solution to be in the form of gold nanoparticles (GNPs).

[0041] It will be appreciated that where the solution includes other metals such as iron, copper, cobalt, chromium, platinum, silver, or a combination thereof; less than 5% of said metal or combination thereof is removed from the solution. According to a second aspect of the present invention, there is provided an aerogel comprising a natural and / or synthetic source of albumin for use in the process described in accordance with the first aspect of the present invention.

[0042] According to a third aspect of the present invention, there is provided a process for preparing an aerogel for use in the selective extraction of gold wherein a yield of at least a 95% gold(O) is recovered, the process including the steps of;

[0043] (i) providing a fresh or freeze-dried natural and / or synthetic source of albumin;

[0044] (ii) pyrolyzing the source of albumin at a temperature of at least 300°C to 1400°C under an inert atmosphere for a time period of at least 2 hours to 24 hours; and

[0045] (iii) obtaining an aerogel for use in the selective extraction of gold wherein a yield of at least 95% gold(0) is recovered.

[0046] According to a fourth aspect of the present invention, there is provided an aerogel prepared according to the process set forth in the third aspect of the invention for use in a process described in accordance with the first aspect of the present invention.

[0047] The invention further provides for the bulk gold extracted and recovered from the process of the present invention to be used in applications, including but not limited to, jewellery, decorative gold products, electronics, space exploration and satellite applications, medicine, dentistry, aesthetic cosmetology, finance, architecture, and building material applications.

[0048] The invention further provides for the GNPs extracted and recovered from the process of the present invention to be used in applications, including but not limited to, biomedical applications including imaging, diagnostics for the detection of biomarkers in various diseases, sensory probes, therapeutic drug delivery, catalysis, cardioprotective nanomaterials, and chemotherapy.

[0049] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrates, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached figures.

[0050] BRIEF DESCRIPTION OF THE DIAGRAMS

[0051] The invention will now further be described, by way of example only, with reference to the accompanying figures wherein:

[0052] Figure 1 is a photograph of an egg-white albumin aerogel prepared and used in the process of the present invention, wherein the aerogel comprises freeze-dried albumin (shown at the bottom) and pyrolyzed albumin (shown at the top);

[0053] Figure 2 is a photograph demonstrating gold reduction (adsorption) on the pyrolyzed egg-white albumin aerogel of Figure 1 ; Figure 3 is a series of three photographs demonstrating the gold aerogel composite after filtration (Figure 3(a)); before (Figure 3(b)) combustion; and after combustion (Figure 3(c));

[0054] Figure 4 is a SEM image of the freeze-dried egg-white albumin aerogel used in the process of the present invention;

[0055] Figure 5 is an EDS of the freeze-dried egg-white albumin aerogel used in the process of the present invention;

[0056] Figure 6 is a SEM image of the pyrolyzed egg-white albumin aerogel used in the process of the present invention;

[0057] Figure 7 is an EDS of the pyrolyzed egg-white albumin aerogel used in the process of the present invention;

[0058] Figure 8 is a SEM image of gold reduction (adsorption) on the pyrolyzed eggwhite albumin aerogel;

[0059] Figure 9 is an EDS of gold reduction (adsorption) on the pyrolyzed egg-white albumin aerogel (indium was used to coat the aerogel to reduce charging); Figure 10 is a UV-Vis of a 500 ppm gold solution after 20 hours with either the pyrolyzed albumin aerogel or fresh egg-white albumin aerogel used in the process of the present invention;

[0060] Figure 11 is a SEM image of gold nanoparticles wherein a fresh egg-white albumin aerogel was employed in the process of the present invention;

[0061] Figure 12 is an EDS of gold nanoparticles wherein a fresh egg-white albumin aerogel was employed in the process of the present invention; and

[0062] Figure 13 is a TEM of gold nanoparticles wherein a fresh egg-white albumin aerogel was employed in the process of the present invention.

[0063] The presently disclosed subject matter will now be described more fully hereinafter with reference to the accompanying examples, in which representative embodiments are shown. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0064] The following non-limiting examples were performed in order to demonstrate the process of the present invention.

[0065] Preparation of aerogel

[0066] Albumin (egg-white) was used for purposes of preparing the aerogel. The egg-white was utilised as is, that is, no extraction or purification was performed.

[0067] 10 ml of albumin (egg-white) frozen and freeze-dried. The freeze-dried albumin was cut into smaller pieces and pyrolyzed at 700°C under flowing nitrogen for 16 hours (as shown in Figure 1 ). It will be appreciated by a skilled person that pyrolysis can also occur at different temperatures, such as 300-1400°C, and under other inert atmospheres such as flowing argon.

[0068] Flowing inert gas was required to remove the oxygen and synthetic bio-diesel (which occurs in very small quantities) formed during the process. It will be further appreciated that the time period may be varied from 2 to 24 hours.

[0069] Gold extraction from a known gold concentration

[0070] The aerogel (40 mg) was placed in a 25 ml beaker containing 10 ml of 1000 ppm gold(lll) chloride trihydrate in distilled water. The aerogel may be provided in bulk, however it is more effective when finely ground. It will be appreciated that the mass of the aerogel to volume of the solution ratio may also be adjusted.

[0071] After 1 hours, reduced gold could be observed on the aerogel (as shown in Figure 2). Here it can be clearly seen that the gold is reduced to elemental gold, which manifests as a yellow lustre coating the aerogel (as shown further in Figure 3(c)).

[0072] The solution was allowed to passively (no stirring) react for 24 hours. It was observed that when stirring takes place, the reaction takes place faster.

[0073] Isolation of gold from the aerogel

[0074] Referring to Figure 3(a), Figure 3(b) and Figure 3(c), the gold / aerogel composite was combusted in air at 500°C for 1 hour and then at 1000°C for 2 hours to sufficiently burn off carbon leaving the reduced gold. However, it was also found that after combustion at lower temperatures for shorter time periods, similar results were obtained.

[0075] Figure 4 and Figure 5 show the SEM and EDS images of the freeze-dried egg-white albumin aerogel, respectively.

[0076] Figure 6 and Figure 7 show the SEM and EDS images of the pyrolyzed egg-white albumin aerogel, respectively. Figure 8 and Figure 9 show the SEM and EDS images of gold reduction (adsorption) on the pyrolyzed egg-white albumin aerogel, respectively.

[0077] According to UV-Vis measurements as shown in Figure 10, ca. 95% of the gold was removed from the solution.

[0078] Here, the pH of the solution was ca. 5; however, at lower a pH (for instance, where the solution of metals is in aqua regia) the reduction / adsorption is believed to be more effective.

[0079] Other metal extraction from a known concentration

[0080] The aerogel (10 mg), either in bulk or ground form, was placed in a 10 ml beaker containing 5 ml of a known concentration of either Fe, Cu, Co, Cr, Pt or Ag in distilled water. It was found that the mass of aerogel to volume of the solution ratio could also be adjusted. The solution was allowed to passively (no stirring) react for 24 hours. It was observed that when stirring takes place, the reaction takes place faster.

[0081] According to UV-Vis measurements, ca. less than 5% of the metal was removed from the solution. Gold extraction from dissolved e-waste or gold ore

[0082] Gold-containing e-waste or gold ore was dissolved in aqua regia (w / v 1 g / 20 ml) overnight. It will be appreciated by a skilled person that the ratio and time can be adjusted.

[0083] Finely ground aerogel was added to the e-waste or ore dissolved in aqua regia (aerogel / solution 10 mg / 20 ml). (Similarly, it will be appreciated by a skilled person that the ratio and time can be adjusted.)

[0084] The mixture was stirred for 24 hours. The time period may also be adjusted. It was observed that the reduced / adsorbed gold aerogel flakes sank to the bottom and were filtered off (Figure 3(a)). The gold was then recovered by combustion of the gold / aerogel composite as described previously.

[0085] Preparation of gold nanoparticles using fresh or freeze-dried albumin

[0086] Fresh or freeze-dried albumin (20 mg) was added to 20 ml of 1000 ppm gold(lll) chloride trihydrate in distilled water. It will be appreciated that the mass of albumin to volume of the solution ratio could also be adjusted.

[0087] The solution was allowed to passively (without stirring) react for 24 hours. It was observed that stirring speeds up the reaction.

[0088] In both cases the solution turned purple, which is an indication of gold nanoparticles. This was confirmed by the SEM, EDS and TEM images of gold nanoparticles shown in Figures 11 , 12 and 13, respectively.

[0089] Nanogold may then be collected from the solution and used in medical applications like chemotherapy etc.

[0090] In this regard, it will be appreciated that the process of the present invention affords a number of significant and surprising solutions to address the shortcomings of the prior art.

[0091] Notably, the process of the present invention employs an aerogel which is easier to synthesize than other known methods. Here, the use of membranes as taught by the prior art require multiple steps such that Au(0) must be oxidized and then complexed using ligands such as thiourea and thiocyanate after which the Au must be reduced again. In addition, the art teaches of exposing membranes for longer periods to the gold solution, a shortcoming which the present process surprisingly addresses. Furthermore, aerogels currently used require the need for cross-linking which, in turn, results in more synthesis steps. Here, it will be appreciated that a significant number of these cross-linkers are expensive and / or toxic / unsafe, underpinning the need to arrive at the improved process surprisingly afforded by the present invention. A further shortcoming associated with the current aerogels is the need to utilize UV-light in order to bring about the extraction process; this is negated with the process of the present invention. Importantly, the present process unexpectedly demonstrates a selectivity for gold when other metals are present. It is clear that the teachings of the prior art do not demonstrate such selectivity and in fact teach against the solution afforded by the present invention. In particular, the process of the present invention demonstrates exceptional selectivity for the extraction of gold from ore, mine wastewater, old mine dumps and e-waste of at least 95% to 99% of gold from a 1000 ppm solution within 24 hours, whilst simultaneously resulting in minimal extraction of other metals (for instance, iron and cobalt).

[0092] Moreover, the process of the present invention demonstrates remarkable stability in aqua regia and harsh chemical environments as well as enhanced performance at lower pH levels rendering the present process surprisingly versatile and suitable and robust for industrial applications in processes where gold from gold ore or e-waste is dissolved in aqua regia without resulting in the degradation of the aerogel.

[0093] The description is presented by way of example only in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention and / or the equipment utilized therein in more detail than is necessary for a fundamental understanding of the invention.

Claims

CLAIMS1 . A process for the selective extraction of gold, the process including the steps of:(i) providing a source of gold ions in solution;(ii) contacting the source of gold ions in solution with an aerogel, wherein the aerogel includes a natural and / or synthetic source of albumin, at a pH of 5 or lower, to allow the gold ions from the source of gold ions to reduce to gold(O) and to deposit (adsorb) onto the aerogel to form a gold aerogel composite;(iii) combusting the gold aerogel composite in air at a temperature of at least 500°C for a time period of at least 30 minutes to 5 hours; and(iv) recovering at least 95% of gold(O) from the solution.

2. The process according to claim 1 , wherein the source of gold ions includes a source of Au(l) or Au(lll).

3. The process according to claim 1 or claim 2, wherein the source of gold ions are derived from gold ore or any suitable gold-containing waste, gold mine waste; gold-containing mine wastewater or gold-containing e-waste.

4. The process according to claim 3, wherein the source of gold ions are provided in an aqueous solution.

5. The process according to claim 3, wherein the source of gold ions are providedin a highly concentrated acid solution, including aqua regia.

6. The process according to claim 3, wherein the concentration of the source of gold ions is from and including 0.05 mM (10 ppm) up to and including 0.05 M (10 OOOppm).

7. The process according to claim 3, wherein the solution includes other metals, such as iron; copper; cobalt; chromium; platinum; silver; and a combination thereof.

8. The process according to claim 1 , wherein the natural source of albumin is selected from the group consisting of chicken egg albumin (egg-white albumin); bovine serum albumin; plant-based albumin (from algae, legumes, beans, nuts, peas, potatoes, corn, and recovered corn proteins); globulin; and a combination of one or more thereof.

9. The process according to claim 1 , wherein the synthetic source of albumin is selected from the group consisting of synthetic albumin manufactured by companies, including but not limited to Solar Foods, Bioceutica and JustEgg; recombinant DNA synthesised albumin manufactured by companies including but not limited to TwistBioscience; synthetic amino acid-containing polymers (peptide synthesis, peptide assembly, folding and refolding) manufactured by companies including but not limited to Alamanda; inexpensive polymers such as carbomer, polylactic acid and polyacrylates cross-linked with amino acids containing sulphur atoms; and a combination of one or more thereof.

10. The process according to any one of the preceding claims, wherein 95% gold(O) in the form of bulk gold is recovered from the solution.11 . The process according to any one of the preceding claims, wherein 95% gold(O) in the form of gold nanoparticles (GNPs) is recovered from the solution.

12. The process according to any one of the preceding claims, wherein where the solution includes other metals such as iron, copper, cobalt, chromium, platinum, silver, or a combination thereof; less than 5% of said metal or combination thereof is removed from the solution.

13. An aerogel comprising a natural and / or synthetic source of albumin for use in the process according to any one of claims 1 to 12, wherein the albumin is fresh or freeze-dried and the aerogel is prepared without added cross-linkers, the aerogel being structurally stable in solutions having a pH lower or equal to 5 and capable of achieving 95% or more gold(O) extraction.

14. A process for preparing an aerogel for use in the selective extraction of gold wherein a yield of at least 95% gold(O) is recovered, the process including the steps of;(i) providing a fresh or freeze-dried natural and / or synthetic source of albumin, in the absence of added cross-linkers;(ii) pyrolyzing the source of albumin at a temperature of at least 300°C to 1400°C under an inert atmosphere for a time period of at least 2 hours to 24 hours to form a carbonaceous aerogel stable in solutions having a pH equal to or between 1 and 5; and(iii) obtaining an aerogel for use in the selective extraction of gold wherein a yield of at least 95% gold(O) is recovered while co-extracting less than 5% of any other metals present in the solution.

5. An aerogel prepared according to the process according to claim 14 for use in the process according to any one of claims 1 to 12, wherein the aerogel is structurally stable at a pH lower or equal to 5 and achieves at least 95% gold(O) recovery from a gold-containing acidic solution while removing less than 5% of any co-existing non-gold metals.

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