Gold Recovery Research Articles

Complete gold extraction and recovery from double refractory gold ores by thiourea after bio-oxidation

Cyanidation, a conventional process to extract gold from gold ores, has been used for over 130 years in industrial mining because of the high efficiency and rate of formation of Au(CN)2− and the high recovery efficiency by adsorption of Au(CN)2− on activated carbon. However, carbonaceous refractory gold ores are not targeted because Au(CN)2− is easily adsorbed on carbonaceous matter in the ores, resulting in high recovery loss. In this study, the flotation concentrates of a carbonaceous refractory gold ores was subjected to biooxidation at 45 °C using a mixed culture containing iron-oxidizing and sulfur-oxidizing bacteria, followed by gold extraction using thiourea under strongly acidic conditions. The gold extraction efficiency reached ∼100% in 12 h without re-adsorption. Finally, the quantitative recovery of the Au(CS(NH2)2)2+ complex was confirmed by adsorption on strongly cationic exchange resin. Biooxidation reduced the amount of Fe-containing metal sulfides, which minimized the decomposition of thiourea, and the Au(CS(NH2)2)2+ complex had a low affinity toward carbonaceous matter, different to Au(CN)2−. Since the process described in this study does not require roasting to remove carbonaceous materials in pretreatment and does not use cyanide for gold extraction, it is environmentally friendly and should be considered for practical applications in carbonaceous gold ore-producing mines.

Biomass-Based N, S Co-Doped Hierarchical Porous Carbon for Selective Adsorption of Au(III): Facile Gold Recovery from Secondary Wastes

Biomass-Based N, S Co-Doped Hierarchical Porous Carbon for Selective Adsorption of Au(III): Facile Gold Recovery from Secondary Wastes

The Recovery of Gold from a Copper-Rich Zimbabwean Gold Ore by Cold Stripping

The Recovery of Gold from a Copper-Rich Zimbabwean Gold Ore by Cold Stripping

Evaluation of the Efficiency of Using an Oxidizer in the Leaching Process of Gold-Containing Concentrate

This article presents the results of cyanide leaching of gold-containing concentrate using the trichlorocyanuric acid (TCCA) oxidizer. Gold-containing concentrate was obtained from a gold tailings sample from a gold recovery factory (GRF) in one of the deposits of Kazakhstan that have not previously been studied for concentrability. According to X-ray phase analysis and energy dispersive spectrometry (DSM) data, the main compounds in the tailings sample under study are pyrite FeS2, quartz SiO2, calcite CaCO3, albite NaAlSi3O8, muscovite KAl2Si3AlO10(OH)8, dolomite CaMg(CO3)2, and oxidized iron compounds. Microscopic studies of the concentrate have established the presence of ultrafine gold with sizes from Au 0.9 to 10.2 μm in pyrite. Obtaining the gold-containing concentrate with a gold content of 15.95 g/t is possible according to the enrichment scheme, which includes centrifugal separation, classification according to the fineness class −0.05 mm, additional grinding of hydrocyclone sands to a fineness of 90.0–95.0% of the class finer than 0.050 mm, and control centrifugal separation. Since pyrite in technogenic raw materials is the main gold-containing mineral, this paper presents studies on the oxidizability of pyrite with the TCCA oxidizer. The results of studies on the oxidation of pyrite using the TCCA oxidizer show the products of its hydrolysis oxidize pyrite with the formation of various iron compounds on its surface. Pretreatment of gold-containing concentrate with oxidizer TCCA for 3 h before the cyanidation process (20 h) allows for an increase in the recovery of gold in the solution by 5.8%.

Efficient gold recovery from low concentrated Au(S2O3)23− solution through enhanced photocatalysis via photothermal and surface plasmon resonance assistance on MoS2/MXene/Ag

Thiosulfate technique is the most promising method to recover gold from electronic waste (e-waste) and natural ores due to its non-toxicity and high leaching efficiency. However, the bad affinity between Au(S2O3)23− and traditional adsorbents leads to unsatisfied gold recovery performance from leaching solution. In this work, highly efficient recovery of gold from low concentrated Au(S2O3)23− solution was achieved through enhanced photocatalysis process on a novel MoS2/MXene/Ag adsorbent. During recovery procedure, Au(S2O3)23− was in-situ reduced to Au0 by photogenerated electrons and then anchored on MoS2/MXene/Ag. Under Au(S2O3)23− concentration <10 ppm, over 99 % gold recovery performance could achieve within 2 h. Experimental tests have proved that MXene made fully use of near infrared (NIR) light energy to exhibit better photothermal effect, and surface plasmon resonance (SPR) effect of Ag can simultaneously facilitate the separation of electron-hole pairs on MoS2. By means of external temperature input and rapid charge carrier transmission, plenty of electrons were excited from MoS2/MXene/Ag for Au(S2O3)23− recovery. This work paved a pathway for efficient Au(S2O3)23− recovery, which catered to the demand for green production of gold in the future.

Comparative life cycle assessment of copper and gold recovery from waste printed circuit boards: Pyrometallurgy, chemical leaching and bioleaching

Printed circuit boards (PCBs) make up a substantial amount of electronic waste (e-waste) generated annually. Waste PCBs contain high quantities of copper and gold in comparison to natural ores. As such, “urban mining” of waste PCBs to recover these metals is of commercial interest. In this work, we used life cycle assessment to compare the environmental impact of four copper and gold recovery processes. We evaluated pyrometallurgy, chemical leaching, and bioleaching, as well as a hybrid leaching process that uses bioleaching to recover copper and chemical leaching to recover gold. Furthermore, we considered differences in environmental impact based on differences in electricity sources. If electricity comes from fossil fuels, the pyrometallurgical process results in the lowest environmental impact in all impact categories studied. If electricity comes from carbon-free sources, the pyrometallurgical process results in the lowest environmental impact in all categories studied except global warming, where the hybrid leaching process results in the lowest impact. In all cases, metal recovery from waste PCBs leads to lower environmental impact than primary metal production. Our goal is to guide e-waste recyclers towards more environmentally sustainable metal recovery processes and to provide knowledge gaps in the field to guide future research.

Role of Semiconductive Property on Selective Cementation Mechanism of Iron Oxides to Gold in Galvanic Interaction with Zero-Valent Aluminum from Gold–Copper Ammoniacal Thiosulfate Solutions

Iron oxides (hematite, Fe2O3, and magnetite, Fe3O4), previously used as electron mediators in the galvanic system with zero-valent aluminum (ZVAl), have been shown to recover Au upon cementation in Au–Cu ammoniacal thiosulfate media selectively, and this warrants further investigation. This research is focused on investigating the role of the semiconductive properties of metal oxides by performing a cementation experiment by mixing 0.15 g of electron mediators (Fe3O4, Fe2O3, TiO2 (anatase and rutile)) and 0.15 g of zero-valent aluminum powder as an electron donor in various electrochemical experiments. The results revealed that upon the cementation experiment, synthetic Fe2O3 and Fe3O4 were consistently able to selectively recover Au at around 90% and Cu at around 20%. Compared to activated carbon (AC), TiO2, in anatase and rutile forms, obtained selective recovery of gold, but the recovery was utterly insignificant compared to that of iron oxides, obtaining an average of 93% Au and 63% Cu recovery. The electrochemical and surface analysis supports the results obtained upon the cementation process, where TiO2, upon cyclic voltammetry (CV), obtained two reduction peaks centered at −1.0 V and −0.5 V assigned to reducing Au and Cu ions, respectively. Furthermore, various electrochemical impedance spectroscopic analyses revealed that the flat band potential obtained in the Mott–Schottky plot is around −1.0 V and −0.2 V for iron oxides and titanium oxides, respectively, suggesting that the electrons travel from semiconductor interface to electrolyte interface, and electrons are accessible only to Au ions in the electrolyte interface (reduction band edge around −1.0 V). The determination of this selective cementation mechanism is one of a kind. It has been proposed that the semiconductive properties of Fe2O3, Fe3O4, and, by configuring their relative energy band diagram, the travel of electrons from the iron oxide–electrolyte interface facilitate the selective cementation towards Au(S2O3)23+ ions in gold–copper ammoniacal thiosulfate solutions.

Metal-phenolic networks-engineered polyimide aerogels for high-efficiency gold extraction and separation from e-waste mixture

Engineering adsorption materials that offer easy handling, efficient, and selective recovery of precious metals, such as gold, from electronic waste (e-waste) are of significant interest, especially given the escalating volume of discarded electronic devices. However, the harsh digested solvents (e.g., aqua regia), ultralow gold concentrations (several ppm), and competitive interference from various metals present significant challenges. Herein, we engineer a porous polyimide (PI) aerogel with chemically reductive, mechanically resilient, and environmentally recyclable capabilities, using biomass-derived metal-phenolic networks (MPNs), for highly selective and efficient gold extraction and separation. The resulting aerogels show a high adsorption efficiency (∼97.4 %), selective extraction of gold ions from 12 metal ions in simulated leached solutions, and superior purity (∼100 %) in the reduced gold particles. The gold ions are reduced, nucleate, and grow into large agglomeration (∼12 μm) as observed in experiments and confirmed by density functional theory (DFT) calculations, facilitating their separation from the aerogels without the need for complex processes (e.g., membrane separation). On application to a central processing unit (CPU), our aerogels effectively extracted > 96 % of gold ions even at ultralow concentrations of 3.6 ppm in aqua regia, generating at least 66 times more profit compared to the cost (profit/cost = ∼52.9/∼0.8 $⋅g−1). These results demonstrated that MPNs-engineered aerogels are promising economical and practical adsorbents for gold recovery in e-waste.

Gold Recovery from E‐Waste by Food‐Waste Amyloid Aerogels (Adv. Mater. 19/2024)

Gold Recovery from E‐Waste by Food‐Waste Amyloid Aerogels (Adv. Mater. 19/2024)

Fluorescent porous hybrid silsesquioxane-based semiconductor polymer for sunlight-driven gold recovery with high efficiency and selectivity

As an important precious metal, the recovery of gold can not only relieve the shortage of resources, but also has a high economic value. In this work, a novel silsesquioxane-based fluorescent porous hybrid polymer (PTSC) was prepared successfully by Heck coupling reaction of octavinylsilsesquioxane with a dibromated distyry-bithiophenes containing cyano groups. The structure of PTSC was fully investigated, which featured a high surface area of 455 m2 g−1, wide light adsorption band, narrow optical band gap (1.73 eV) and excellent semiconductor performance. As Au(III) adsorbent, the adsorption capacity of PTSC reached 3080 mg g−1 under light irradiation for 4 h at pH = 5, and the purity of the recovered gold in e-waste could reach 23.92 K. The adsorption mechanism showed that photoelectrons produced by PTSC could reduce all Au(III) adsorbed to Au(I) and Au(0). Moreover, a hybrid aerogel device based on PTSC and chitosan was fabricated to realize the enrichment and recovery of gold ions in wastewater. Besides, PTSC could also act as a probe to detect Au(III) with high selectivity and specificity. This study provided a new strategy for efficient recovery and detection of Au(III).

Gold recovery from waste fine carbon using acetone as solvent (Amesmessa gold mine, Algeria)

Purpose. The aim of this work at the first stage is to develop a new method to recover gold from waste fine loaded activated carbon. At the second stage, a new method is to be developed using less energy and less hazardous chemicals to recover gold from fine and coarse activated carbon in all the process of gold ore treatment. Methodology. The desorption of gold cyanide from the waste fine loaded activated carbon was processed by agitating the carbon on alkaline aqueous solution containing 20 % (v/v) of acetone (pH between 10 and 13) at room temperature. Findings. The application of the proposed method gave satisfactory results in terms of process efficiency, the time of operation and no use of hazardous chemicals such as cyanide. The efficiency is more than 96 %, the resident time – less than 3 h. As for the hazardous chemicals, there is no use of cyanide unlike in the conventional process. Originality. The use of acetone as an organic solvent makes the gold cyanide desorption from activated carbon operated at room temperature and in short time better than any other conventionel process. Practical value. This method allows to recover easily and economically the gold entrapped into waste activated carbon existing in a mining plant at room temperature in an agitating tank, pH = 10–13 with an efficiency over 96 %. This method can be a good alternative for all gold recovery processes from activated carbon used nowadays.

Risks to Human Health from Mercury in Gold Mining in the Coastal Region of Ecuador.

Artisanal and small-scale gold mining (ASGM) plays a crucial role in global gold production. However, the adoption of poor mining practices or the use of mercury (Hg) in gold recovery processes has generated serious environmental contamination events. The focus of this study is assessing the concentration of Hg in surface waters within the coastal region of Ecuador. The results are used to conduct a human health risk assessment applying deterministic and probabilistic methods, specifically targeting groups vulnerable to exposure in affected mining environments. Between April and June 2022, 54 water samples were collected from rivers and streams adjacent to mining areas to determine Hg levels. In the health risk assessment, exposure routes through water ingestion and dermal contact were considered for both adults and children, following the model structures outlined by the U.S. Environmental Protection Agency. The results indicate elevated Hg concentrations in two of the five provinces studied, El Oro and Esmeraldas, where at least 88% and 75% of the samples, respectively, exceeded the maximum permissible limit (MPL) set by Ecuadorian regulations for the preservation of aquatic life. Furthermore, in El Oro province, 28% of the samples exceeded the MPL established for drinking water quality. The high concentrations of Hg could be related to illegal mining activity that uses Hg for gold recovery. Regarding the human health risk assessment, risk values above the safe exposure limit were estimated. Children were identified as the most vulnerable receptor. Therefore, there is an urgent need to establish effective regulations that guarantee the protection of river users in potentially contaminated areas. Finally, it is important to continue investigating the contamination caused by human practices in the coastal region.

Highly Efficient Recovery of Au(I) from Gold Leaching Solution Using Sodium Dimethyldithiocarbamate.

As a sustainable, nontoxic and environmentally friendly cyanide-free gold leaching agent, thiosulfate has been applied to some extent in the field of hydrometallurgy. However, the difficult recovery of gold ions in gold leaching solutions limits further application of thiosulfate gold leaching technology. This study demonstrated the feasibility of gold recovery by sodium dimethyldithiocarbamate (SDD) precipitation and recycling of ammonia and a lixiviant in solution. SDD achieved the purpose of recovering gold by forming granular precipitates with gold ions in solution. It can almost completely recover gold ions in 2.5-17.34 mg/L of gold leaching solution within 1 min at 25 °C, in which a gold recovery capacity of 7.99 kg/t is achieved. The leaching rate of gold ore did not change significantly after recycling the residual ammonia and thiosulfate in the leaching solution after gold recovery by SDD, and its leaching rate basically remained at 81%. The mechanism of SDD recovering Au was determined to involve the ligand exchange of SDD- and Au[(S2O3)2]3-. Moreover, the interaction mechanism between SDD and Au(I) was further validated by density functional theory calculations. Considering its low cost, simple technology, and environmental friendliness, the SDD precipitation process has the potential for large-scale application in gold recovery from thiosulfate gold leaching solutions.

One-dimensional D-π-A conjugated polymers for photoenhanced gold recovery from e-waste

In principle, photocatalytic Au(III) reduction from e-waste using sunlight could provide a cleaner and more efficient alternative strategy to existing processes. Two-dimensional (2D) conjugated polymers are often employed for photocatalytic systems due to their structural diversity and stability. However, the efficiency of active site utilization in 2D materials still needs to be improved because the catalytic reduction centers are located in the basal layer and it is difficult for Au(III) to access them. Herein, we demonstrate the application of D-A and D-π-A type one-dimensional (1D) conjugated polymers for the photoenhanced gold recovery from electronic waste. The two synthesized 1D conjugated polymers, named BTP-DET (D-π-A type) and BTP-TDB (D-A type), exhibit a wide light absorption range and excellent chemical stability. Benefiting from the superior charge separation and migration efficiency of the D-π-A skeleton, BTP-DET exhibits a small optical band gap of 1.60 eV, which is significantly smaller than that of BTP-TDB (1.78 eV), and thus enables the extraction of the gold with a higher capacity of BTP-DET (2580.8 mg g−1) under visible light, than the BTP-TDB (2072.7 mg g−1). This work paves the way for exploring low dimensions of conjugated polymers for photocatalysis.

Thiazole-functionalized conjugated microporous polymers enable efficient gold recovery from e-waste

From the perspectives of environmental protection and efficiency, the use of clean and efficient photocatalytic reduction technology to recover gold from e-waste not only has a high economic value, but also reduces environmental pollution. However, it remains a challenge to construct adsorbents with simultaneously high photocatalytic activity, high stability, high capacity and high selectivity. Here, we demonstrate the application of D-π-A type thiazole-functionalized conjugated microporous polymer (termed BTD-TEA) for adsorption-photocatalytic recovery of gold from e-waste. The synthesized BTD-TEA not only have a narrow optical bandgap (1.75 eV) and excellent semiconductor properties, but also have ultra-high acid stability (stable in aqua regia). Surprisingly, BTD-TEA exhibits breakthrough gold adsorption capacity (4052.83 mg g−1), ultrafast adsorption kinetics, excellent selectivity and outstanding reusability under light conditions. This work provides a promising new adsorption-photocatalytic strategy for gold recovery from e-waste.

Solvothermal Preparation of Microporous Polyureas for Au(III) Adsorption.

The enrichment and recovery of gold from wastewater are an alternative method to obtain this noble metal, which benefits reducing hazardous emissions from the conventional ore mining process and reserving natural gold for sustainable development. Inspired by our previous work (Lei et al., Macromol. Rapid Comm. 2022, 2200712), four families of microporous polyureas (mPPUs) with a large surface area (690 m2 g-1) and abundant heteroatom sites have been prepared via the factor-optimized solvothermal protocol. The resultant sample NPU-A starting from 1,5-naphthalene diisocyanate (NDI) and tri(4-aminophenyl) amine (TAPA) exhibits the maximum Au(III) adsorption capacity of 1300 mg g-1 and high selectivity even when the Au(III) concentration is as low as 0.1 mg L-1. This study not only demonstrates the robustness of the high-throughput synthetic strategy but also promotes the investigation of the structure-activity correlation between the mPPU chemical structure and Au(III) adsorption performance.

Dibutylamide hydrophobic deep eutectic solvent used for selective extraction of Au(III) from hydrochloric acid medium

The effective and environmentally friendly recovery of gold from secondary resources has recently received increased attention. Hydrophobic deep eutectic solvent (HDES) composed of N,N-di-butylacetamide and 1-decanoic acid was used to construct the liquid-liquid extraction system to extract Au(III) from HCl medium. At first, DSC, TGA, FT-IR, and 1H NMR were used to describe the evidence of internal hydrogen bond interaction. The above evidence was verified in the molecular dynamics study of HDES. Then, a series of optimization experiments were carried out to investigate the extraction behaviors of HDES. Based on the results of optimization experiments, response surface method was used to explore the best experimental conditions and the results showed that HDES extracted 99% Au(III) under 0.56 mol/L HCl, 2.19 mol/L NaCl, and 5.83 mmol/L Au(III), and the maximum loading reached 77.0 mg/g. Further studies on the kinetics and thermodynamics of the extraction were used to propose an ion association mechanism. In addition, using 0.1 mol/L thiourea as the stripping agent, HDES displayed outstanding Au(III) selectivity and maintained the extraction efficiency in tests which involved 5-cycles. Overall, this study provides a green and efficient Au(III) recovery strategy for secondary resources.

Effect of metals on recovery of gold from ammoniacal thiosulphate leach solutions by precipitation using trimercapto-s-triazine (TMT)

There are significant technical challenges/shortcomings in recovering gold from thiosulphate leach solutions. This study presents a new approach for the recovery of gold from ammoniacal thiosulphate leach solutions using an environmentally friendly organo-sulphide reagent, trimercapto-s-triazine (TMT; C3N3S33−). Precipitation of gold by TMT was investigated using synthetic gold and multi-metal solutions (Au-Ag, Au-Cu, Au-Ag-Cu) to investigate the effect of the co-presence of metals commonly present in thiosulphate leach solution. The effect of TMT concentration (by up to 115 mM), temperature (25–60 °C) and ammonia (0.25–1 M NH3) on the precipitation of gold was also investigated. The results showed that gold precipitation with TMT was relatively low (i.e., limited to only 37.7% over 15 min) from the solution containing only gold. However, the presence of silver and/or copper significantly improved the precipitation of gold. Silver concentrations at ≥20 mg/L led to a complete recovery of gold in 15 min, producing stable gold precipitates. The results have also indicated that silver readily precipitates when compared to gold. The effectiveness of the TMT precipitation process was also tested on a real leach solution from which complete recovery of gold and silver was readily achieved. The findings demonstrated that gold could be readily but unselectively recovered by precipitation with TMT from ammoniacal thiosulphate leach solutions containing silver, in particular, at the expense of co-precipitation of other metals such as copper and zinc.

A green and low-cost preparation of polyacrylonitrile fibers with imine dioxime and amidoxime groups for efficient and selective gold recovery

The preparation of adsorbents with low cost, efficient adsorption and high profitability for gold recovery has important practical applications. In this work, synergistic poly (imine dioxime and amidoxime) (PDA) adsorbents were successfully prepared for gold recovery. An inexpensive engineering polyacrylonitrile (PAN) fiber is selected as the adsorbent substrate covalent binding with hydroxylamine hydrochloride to obtain PDA. The PDA surface with imine dioxime and amidoxime groups has a rich charge density and is more easily combined with gold ions through electrostatic interactions. The adsorption process of gold on PDA is a spontaneous endothermic process with monomolecular layer adsorption and the adsorption capacity increases with the increasing temperature under acidic conditions. The maximum adsorption capacity of PDA can reach 2937 mg g−1 at 25 °C and pH = 2 with an equilibrium time of 168 h. Meanwhile, excellent gold adsorption performance is also observed for PDA in simulated water treatment filler and water circulation reactor as well as interference conditions with other metal ions. Surprisingly, PDA has an ultra-low preparation cost ($ 2.54 × 102 kg−1), yet enables high-value gold (2.9 kg) for every kilogram of PDA with significant economic benefits. Therefore, this work will provide new ideas for the development of inexpensive, highly efficient, and specialized adsorbent preparation for gold recovery.

Fine and super-fine gold in mine waste from a coastal placer in southern New Zealand

ABSTRACT Reprocessing of mine wastes is a growing procedure around the world, in order to extract more resources from already-mined rocks. Mineralogical and geometallurgical investigations are useful for planned reprocessing, and in this study at Round Hill placer gold mine we characterise fine (<100 µm) and super-fine (micron-scale) particulate gold that has passed through the mine separation stages without being extracted. The gold was discharged with water and suspended sediments to settling ponds, separate from the more voluminous gravel and sand tailings. Authigenic clay and pyrite are abundant in the placer deposit and the settled suspension, and oxidised pyrite yielded gypsum and ferric oxyhydroxide. These minerals coat surfaces of gold particles and are locally intergrown with micron-scale authigenic gold. Most of the gold has toroidal shapes characteristic of beach derivation, and many of these are hollow or clay-filled. Minor super-fine cinnabar and mercury-bearing gold occur with clay. Annealing of gold has liberated silver, and micron-scale authigenic native silver occurs in the settled sediment. Reconcentration of fine and super-fine gold used abundant clean water and slow reprocessing and may be currently uneconomic at this site. The observations on suspended gold loss are relevant to gold recovery at placer mines around the world.