Gold Recovery Research Articles

Gold recovery from pregnant thiosulfate solution by ion exchange resin: Synergistic desorption behaviors and mechanisms

The behaviors and mechanisms of gold desorption from its loading resin with the mixed solution of Na2SO3 and NaCl were studied. The desorbent displayed evident “synergistic role” on the gold desorption and had good desorption performance over wide ranges of reagent concentration, flow rate and gold loading amount. Based on the thermodynamic analysis, a two-step desorption mechanism was proposed: (1) SO32– reacted with [Au(S2O3)2]3– to generate [Au(S2O3)(SO3)]3–; (2) The resin had weak affinity for the two-ligand gold complex which was thus replaced by Cl– readily. SEM-EDS, characteristic color of gold complex, Raman spectra and binding energy calculation results indicated SO32– could react with [Au(S2O3)2]3– to form [Au(S2O3)(SO3)]3–, and the affinity of the resin for the newly-generated complex was weaker than that for Cl–, which demonstrated the above mechanism. The mechanism model of gold recovery from pregnant thiosulfate solution by ion exchange resin was finally constructed.

UiO-66-NH2/chitosan with microalgae platform for gold valorization from waste microelectronics

The combination of UiO-66-NH2/chitosan (CTS) and microalgae was effective in precious metal recovery of electronic wastes (E-wastes) from discarded microchips. Herein, zirconium-based metal–organic frameworks were introduced to bind metal ions from the E-waste. Thus, UiO-66-NH2 was linked to CTS as examined by Fourier-transform infrared spectroscopy (FT-IR). Au(III) leachate solutions were prepared via acidic treatments from the microcomputer chips that were used to test metal binding using UV–Vis absorption spectroscopy. The prepared UiO-66-NH2/CTS was tested to recover Au(III) ions from the liquid phase waste, which exhibited higher adsorption capacity than UiO-66, UiO-66-CTS, and UiO-66-NH2. The inclusion of microalgae in UiO-66-NH2/CTS system enhanced gold adsorption efficiency and binding of Au(III) ions onto UiO-66-NH2/CTS and UiO-66-NH2/CTS/microalgae attained equilibrium within a few hours. UiO-66-NH2/CTS showed an adsorption capacity of ∼ 576 mg/g, which increased to ∼ 671 mg/g after the introduction of microalgae of Spirulina maxima. The pH effect on Au(III) binding revealed that electrostatic interactions between the negatively charged UiO-66 particles and gold anions decreased the adsorption capacities at higher pH values. The findings highlighted the potential use of UiO-66-NH2/CTS and microalgae for effective gold recovery from the E-waste.

Construction of Magnetic S‐Doped CoWO4 Composite for Efficient and Selective Recovery of Gold from Wastewater via Adsorption–Reduction Pathway

The design and synthesis of efficient adsorbents for the recovery of precious metals from secondary resources are of great environmental and economic significance. Herein, a magnetic sulfur‐doped composite CoFe2O4@S–CoWO4 (CF@S–CoWO4) is developed through a hydrothermal synthesis method, which is used to selectively recover gold in aqueous media. Significantly, CF@S–CoWO4 exhibits the best overall performance with gold ions adsorption capacity (Qmax) and distribution coefficient (Kd) are 1049 mg g−1 and 4.4 × 106 mL g−1, respectively, which are much higher than those of other gold adsorption materials. The selectivity coefficients (K) toward other metal ions (Pd2+, Ca2+, Mg2+, Cd2+, Al3+, Li+, Ni+) are also higher, which suggests that CF@S–CoWO4 had a preferential selectivity for Au3+ in coexisting ion solutions. Moreover, the antianion interference of the composite follows the order: SO42− > PO43− > NO3− > CO32−, and it also shows very good reusability with adsorption efficiency at 81.78% after four repeated cycles. Based on characterizations and calculation, it is found that Au(III) mainly undergoes chelation and reduction reactions in the S sites in CF@S–CoWO4, which indicates the important role of S sites. Hence the CF@S–CoWO4 composite demonstrates a promising application for the recycling of gold ions from electronic wastewater.

Hydrometallurgical recovery of silver and gold from waste printed circuit boards and treatment of the wastewater in a biofilm reactor: An integrated pilot application

A hydrometallurgical process for the recovery of gold and silver from waste printed circuit boards (PCBs) was experimentally verified and tested at pilot scale. The process comprises four sequential leaching stages; the first two based on HCl, correspond to base metals (e.g. Sn, Cu) removal, while the third is based on HNO3 for Ag leaching and the final on aqua regia for Au leaching. After base metals leaching, the solid residue, enriched in silver and gold about 5 times, contained silver almost quantitively as insoluble AgCl and significant losses (Ag loss <8%) were avoided. The necessary reduction of Ag in the solid phase was achieved with a solution of 0.5 M N2H4 and 3 M NaOH, at 80 °C and S/L ratio 10%. Leaching of silver by 4 M HNO3 was followed by its recovery from nitrate solution by 0.08 Μ N2H4 at ambient temperature with an efficiency of 83%. Gold was leached by aqua regia and quantitively recovered by 0.13 M N2H4 at ambient temperature. Wastewater resulting from the process, rich in nitrate (5 g/L) and chloride (50 g/L), was treated by an effective and novel biological denitrification system tolerating metals at ppm level, to comply with zero nitrate and residual metals discharge guidelines. The overall process requires low reagents and energy input and has zero discharge for liquid effluents. The scheme is appropriate to be applied at local small to medium industrial units, complying with decentralized circular economy principles for metal recovery from electronic waste.

Current progress on gold recovery from refractory ore and waste electrical and electronic equipment

Current progress on gold recovery from refractory ore and waste electrical and electronic equipment

Aliquat-336 impregnated chitosan microspheres for Au(I) extraction from thiosulfate solution: Preparation, adsorption mechanism, and application

In this paper, Ionic liquid Aliquat-336 impregnated chitosan microspheres (CMA) was synthesized and applied for Au(I) recovery from thiosulfate solution, which possessed adjustable particle size, good hardness and good selectivity adsorption capacity. The synthesis parameters (Aliquat-336 dosage and size) of CMA were explored. And the effects of initial solution pH, initial gold concentration, thiosulfate concentration and temperature on the gold(I) adsorption performance by CMA were was investigated systematically. The results showed CMA performed well over a wide pH range, and maximum gold adsorption capacity of 20.3 mg/g. Additionally, the gold adsorption behavior on CMA was similar to pseudo-first-order kinetics and the Langmuir model. SEM-EDS, FT-IR and XPS analyses confirmed that the mechanism of [Au(S2O3)2]3- adsorb on the CMA may be anion exchange. Notably, CMA exhibited an excellent selectivity for Au(I) in a Cu-ethylenediamine (en)-S2O32- solution. Loaded gold on CMA was easily eluted using a sodium sulfite solution, achieving a gold recovery of 62.2 %, even after four adsorption–desorption cycles. Finally, in the actual gold ore leachate adsorption and slurry adsorption method, the adsorption of gold and copper by CMA is approximately 98 % and 7 %, respectively. This study makes significant progress towards gold selective recovery in thiosulfate system, which is useful for the gold thiosulfate hydrometallurgy field.

Core–Shell Structured Fe3O4@CuS for Effective Gold Capture and Recovery

Gold is a valuable commodity with numerous industrial and technological applications. Traditional adsorbents for gold adsorption using activated carbon or ion exchange adsorption resin are limited by low capacity and selectivity. To overcome these limitations, this study introduces a core–shell structured magnetic adsorbent, Fe3O4@CuS, which can capture and recover gold through in situ reduction. The resulting gold-loaded adsorbent can be easily separated using an external magnet, offering significant advantages such as high efficiency, ease of operation, low cost, low materials consumption, and low waste generation. Results show that this adsorbent has a gold loading capacity of 407 mg/g within 4 h, and the maximum capacity can reach up to 558.7 mg/g. Moreover, this magnetic adsorbent exhibited good selectivity for gold in the presence of other base metals. This research shows the feasibility of using Fe3O4@CuS for efficient gold recovery and provides insights into its adsorption behavior and mechanism.

Enhanced and selective gold recovery from phone waste: Use of thiosulfate, dissolved oxygen, and an agriculture-based, low-cost adsorbent

Efficient methods were proposed to improve the gold recovery from printed circuit boards (PCBs) in mobile phones. Gold was selectively extracted in the form of Au(S2O3)23− using Na2S2O3-CuSO4-NH3-O2/N2 system. Under optimal conditions (temperature: 25 °C; stirring: 200 rpm; O2/N2: 3.0/0.5 L/min; time: 3 h; Na2S2O3: 160 mmol/L; CuSO4: 120 mmol/L; NH3: 0.7 mol/L (pH 9.9); solid/liquid: 4 g/L), 98% of gold was extracted. The extracted gold was adsorbed by corncob-based activated carbon (CACw), which was prepared using pyrolyzed wood vinegar. The modification of CACw with mercaptobenzothiazole (MBT), forming MBT-CACw, which displayed maximum adsorption efficiency of 49.9 mg/g. The optimal pH for adsorption was found to be 7.5 at 40 °C with 0.2 mol/L (NH4)2S2O3. The adsorption was described by the pseudo-second-order model and the Freundlich isotherm, owing to the high affinity of MBT-CACw for the sulfur donor. Copper was eluted from the loaded MBT-CACw using 0.7 mol/L (NH4)2S2O3 followed by the gold elution with 40% v/v CH3OH. The two-step elution recovered 98.7% of copper and 97.6% of gold. These findings suggest that the oxygen-assisted extraction, combined with the adsorption conducted using low-cost, agriculture-based adsorbent and selective elution, is an eco-friendly approach to efficiently recovering gold from e-waste.

Comprehensive Recovery of a High-sulfur Copper-gold Ore in Shandong

The raw gold grade of a mine in Shandong is 1.42 g/t, and it is accompanied by copper and sulfur minerals, and the embedding is closely related, so it is difficult to obtain the ideal index using the original flotation process. In order to realize the effective recovery of gold, copper, and sulfur, the test study of mixing-separation flotation and priority flotation is carried out. The results show that the mineral is more suitable for the beneficiation process of mixing-separation flotation. The recovery rate of gold, copper, and sulfur is 70.42%, 93.58%, and 68.85%, and the recovery rate is 22.89% higher than the priority flotation. The produced copper and gold mixed concentrate and sulfur concentrate can be directly sold to realize the effective recovery of gold, copper, and sulfur.

New insights into selective flotation recovery of gold using dye-derived thermo-responsive polymeric surfactant: DFT calculation and adsorption mechanism

The selective flotation recovery of gold from secondary resources is a sustainable strategy to fill the ever-increasing demand for gold resources, and reduce the environmental pollution. In the present work, a novel method to realize the selective and fast recovery of Au(III) in the flotation process involving the use of thermo-responsive amphiphilic polymer poly(ethylene glycol)-b-poly(N-isopropylacrylamide-co-glycidyl methacrylate) (PEG113-b-P(NIPAM108-co-GMA62)) integrated with rhodamine B thiohydrazide (RBS) affinity ligand was studied. The polymer possessed the selective capture property toward Au(III) salt and excellent adsorption performance on bubble surfaces, driven by specific coordination interactions between Au(III) salt and RBS ligand, and hydrophobic interactions between GMA moieties and bubbles. Flotation using the thermo-responsive polymeric surfactant displayed a high separation efficiency and fast flotation kinetics, achieving a separation efficiency of 85% for Au(III) salt at 28 min, which was comparable with sulfur-functionalized mesoporous materials. This flotation process followed pseudo-second-order kinetics and Freundlich isotherm adsorption model. Furthermore, in flotation recovery of Au(III) salt form actual e-waste leaching solution, separation efficiency of 81% was achieved, while Au grade was improved from 1.55 % to 34.76%. This polymeric surfactant was easily regenerated by the reduction-induced release the bound Au(III) salt and thermal precipitation, leading to retain 81% of separation efficiency after five cycles. This work provides an effective way to fabricate flotation surfactant, which can meet the urgent demand for performance improvement and chemical consumption reduction in practical applications.

მადნეულის სპილენძის მადნების მამდიდრებელი ფაბრიკების მიმდინარე კუდების კომბინირებული ტექნოლოგიით დამუშავების საკითხები

Madneuli copper enrichment plant works since 1975. This plant works on copper sulphide ores from Madneuli and Sakdrisi deposits. In some ores due to difficulties of blotting secondary copper sulphides, recovery of copper in commercial production is low – 60-65%. At the same time, concentration of copper in tails is 0.17-0.19% and concentration of gold in tails 0.3-0.6 gr/t. In this article we consider combine technology of processing rich flotation tiles: preinrichment by gravity (use centrifugal concentrator and/or short noise hydrocyclone). Gravity concentrate with au and cu 5.47 gr/t, and 0.93%, respectively proceed hydrometallurgicaly (cyanidation) this technology makes possible rise recovery of gold and copper in commercial product by 20-25% and 17-20%.

Modeling and simulation of a gold concentrator plant implementing a dissolution loop method

Mineral processing applications increasingly use recycled water to preserve freshwater natural resources and comply with environmental regulations. However, accumulating anions, cations, and reagents in the process water may affect plant flotation performance and production continuity. Therefore, many cost actions may be needed to mitigate the recycled water effects. Typically, the process water properties and their effects on flotation performance are unknown for a greenfield project. Often, the result is an over-scaling up of the process plant with an additional financial cost. The experimental methodology in the paper focuses on creating water for testing that is closer to the actual process water during the comminution and flotation process for any greenfield project. The scope of the study consists of creating possible process water, conducting flotation experiments, and simulation. In order to validate the dissolution loop method, refractory gold flotation plant conditions were selected in our Finland laboratory. The simulation results of dissolution loop flotation kinetics were compared with the actual plant mass balance. According to the comparative results, the process water created by the dissolution loop method has the same physical and chemical properties as the actual process water at the site except for SO4 -concentration. Moreover, comparing the simulation results of the experimental data and plant mass balance studies shows that the gold grade and recovery results in the simulation were lower than the actual plant mass balance.

Mechanism and kinetics of gold recovery and Au nanoparticle synthesis by Gas-Diffusion Electrocrystallization (GDEx)

Standing at the forefront of cutting-edge research, the electrochemical reduction of gases is not only driving the industrial shift towards electrification and decarbonization but also unlocking the immense potential to pioneer uncharted realms of electrochemical conversions, including metal transformations. Carbon monoxide issued from the electrochemical reduction of CO2 on gas-diffusion electrodes (GDEs), was used for the in-situ reduction of AuCl4− ions into elemental gold nanoparticles (NPs). A minimal extent of CO2 reduction on the uncatalyzed activated carbon of the GDEs was sufficient to fully remove the AuCl4− ions from the electrolyte bulk present in the aqueous electrolyte, while steering their complete precipitation as Au0. A maximum current efficiency of 19% towards CO formation was achieved, under a flow-through gas regime. The efficiency for Au0 precipitation was improved by manipulating the gas-flow regime and cathode polarization. The mechanism and kinetic description for gold recovery and nanoparticle synthesis are portrayed for the reactions underpinning the gas-diffusion electrocrystallization process (GDEx).

Sensitivity of Gold Lixiviants for Metal Impurities in Leaching of RAM Printed Circuit Boards

The importance of gold recovery from waste printed circuit boards is continuously increasing due to raising gold prices and demand as well as the need for innovative and flexible recycling methods for this complex waste stream. The state-of-the-art recycling process aims at the pyrometallurgical recovery of noble metals, mainly using a copper collector. Different technical limitations justify the application of a hydrometallurgical process alternative for recovering gold. The direct application of gold lixiviants on comminuted PCBs is hardly possible due to the high concentration of metal impurities. As a solution, most researchers propose hydrometallurgical separation of disturbing base metals prior to gold extraction. For this, different leaching systems with aggressive chemicals can be applied, often leaving residual base metal concentrations behind. Within this study, two different leaching parameter sets were investigated to separate base metals and determine the impact of residual base metals on subsequent gold recovery. The gold lixiviants that were applied for comparison were thiosulfate, thiourea, iodine-iodide, NBS, and cyanide. It was found that thiosulfate and thiourea are less sensitive than other lixiviants to metal impurities. When base metals are separated completely, gold recovery is strongly improved, and cyanide also achieves a good gold recovery.

A new strategy for extraction of copper cyanide complex ions from cyanide leach solutions by ionic liquids

Copper cyanide complexes in cyanide leach solutions deteriorate the recoveries of gold. Herein, five phosphonate-based [P204]− ionic liquids were synthesized, which were pioneered to apply to extraction of copper cyanide complex ions in cyanide leach solutions. In the extraction process, macroscopic layered solids rich in copper cyanide complex ions were formed at the aqueous-organic phase interface, which was driven by self-assembly of ionic liquids. Notably, the layered solids can be obtained by simple filtration. The extraction behaviors were systematically studied in the present work. The results show that the extraction efficiency in excess of 90 % can be achieved at higher pH (13.16) and enriched as self-assembly solids in the process of one-step extraction and solidification, based on the self-assembly extraction systems of [P4444][P204] IL. It is worthy of note that no self-assembly sample was observed when the extraction systems is applied to extraction zinc and iron cyanide complex ions. It indicates that the present self-assembly extraction systems could be applied in separation copper and zinc/iron cyanide complex ions. Meanwhile, the coordination mechanism was investigated detaily, and the covalent nature played a leading role in the binding interaction. Remarkably, [P4444][P204] can be repeatedly used without obvious loss in extraction capacity of copper cyanide complex ions after two cycles, indicating that the IL has a good recycling ability. In conclusion, it is possible to employ the self-assembly extraction systems to separate and recover various valuable metals from aqueous solutions by designing and developing ILs extractants in the future.

Gold recovery improvements in grinding and flash flotation circuit

Grinding and a flash flotation cell are frequently installed to recover fast floatability coarse particles avoiding their regrinding. However, the ore textural characteristics, such as grain size, change during mine operation and consequently the recovery of valuable particles in the flash flotation cell decreases. This article proposes and validates an interesting method of solving the problem of low gold recovery, making relevant and well thought out changes in a grinding and flash flotation circuit. This was done by optical ore characterisation (Leica DM2700 P microscope using 20X and 40X lens), mathematical modelling, and steady state process simulation (evaluating the original circuit (simulation I) and two proposed circuits (simulation II, and III)). The mineralogical characterisation indicates that, liberated gold (Au), electrum (Au-Ag), and acanthite (Ag2S) particles of less than 100 µm were the desired particles in the flash concentrate. Additionally, true flotation was identified as the predominant mechanism in gold and silver recovery, but mathematical model suggests that a small fraction of fine particles with gold could be recovered by entrainment. Both analyses led to the proposed installation of a re-grinding mill with recirculation to a flash cell (simulation III). After its commissioning, gold recovery in the flash cell increased 27.0%, reaching a maximum of 48.3%. This represents a clear improvement in gold recovery in a single stage. A significant increase in the global gold recovery was also observed (from 78.9% to 90.6%).

Investigating the selective flotation of auriferous arsenian pyrite from refractory ores using thionocarbamate

Thionocarbamate, specifically modified Isopropyl Ethyl Thionocarbamate (IPETC) is selective in the separation of pyrite from arsenopyrite, following copper activation. In this work, the flotation response of a refractory gold (Au) ore containing arsenic (As) mainly in the form of arsenian pyrite is investigated to reject gold-barren sulphidic phases. The recovery of Au increased with an increase in CuSO4 concentration to 0.3 kg/t, beyond which further increase in concentration yielded no significant recovery. Variations of IPETC concentration between 0.2 and 1.5 kg /t of ore influenced both gold and arsenic recovery. It was surmised that the high collector dosage may have resulted from competitive adsorption between arsenian pyrite and other gangue minerals in the ore. 0.3 kg/t CuSO4 and 1.2 kg/t IPETC concentration at pH 11 gave the best results of 86% Au and 83% As recovery at an Au and As grade of 8.14 g/t and 2436 ppm respectively. LA-ICP-MS analysis of the concentrate showed a positive correlation between gold and arsenic. The technique also revealed arsenic-rich zones in pyrite which was further confirmed by SEM/BSD imaging to be rims of arsenian pyrite encapsulating Au-barren pyrite. MLA mineral maps of concentrates obtained at different times also showed that there is no relationship between the arsenic content of pyrite and the flotation rate. The deportment of arsenic in the rims of pyrite presents a complex mineralogical association which results in a decrease in concentrate grade.

Three-dimensional Ti3C2 MXene-POSS/V2O3@C nanocomposite aerogel for ultrafast and selective recovery of gold (III) at low temperatures

The scarcity and economic importance of gold has motivated the researchers to develop novel and efficient adsorbents to the increase of recycling from secondary waste streams. In this work, the three-dimensional (3D) Ti3C2 MXene-POSS/V2O3@C aerogel (MPVA) with orderly network structure was fabricated by the interfacial assembly of MXene and freezing-induced preassembly. The new MPVA hybrid exhibited ultrafast kinetics (only 10 min to reach equilibrium), selectivity, and excellent trapping capacity for Au(III), owing to the reductive capture mechanism. The Langmuir model was used to describe the capture of Au(III) delivered by MPVA, achieving the maximum capture capacity of 1425.4 mg g−1 at 298 K. Moreover, MPVA displayed extremely high trapping efficiency (>99.9%) at 273 K, which suggests that this composite is promising for capturing Au(III) in cold temperatures. MPVA also shows good reusability after ten cycles. The results indicate that MPVA has great potential for efficient capturing from complex and cold aqueous solutions.

Mercury Reduction on Gold Extraction in Artisanal and Small-Scale Gold Mining. A Case Study in Pelangan Village, West Nusa Tenggara Province, Indonesia

The most common method used for gold processing in artisanal and small-scale mining is amalgamation using mercury as a gold extracting agent. Indonesia is one of the countries that ratify the Minamata Convention, meaning that Indonesia has agreed to reduce or even eliminate the use of mercury. Some methods for replacing mercury as a gold-extracting agent are cyanidation and borax. The research aims to determine whether the miners in Pelangan still use mercury in gold processing. The method of this research is observation, interviews, and literature review. The data obtained were then analyzed descriptively. The result indicates that the miners in Pelangan Village use two methods of gold processing from ore: (1) amalgamation using mercury followed by cyanidation and (2) cyanidation. Most of the miners use the cyanidation method without going through amalgamation. The main reason they do not use mercury are amalgamation method yields low gold recovery and the price of mercury is high. This indirectly shows that the miners in Pelangan Village have contributed to efforts to reduce mercury use in Indonesia.

Highly efficient electroextraction of gold and simultaneous iodine regeneration using ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

The iodination method is a cyanide-free and efficient gold-leaching process, but a large amount of electric energy is consumed for hydrogen evolution during the process of gold recovery by electrodeposition in the iodide/H2O system. Herein, [C2MIM][N(CN)2] ionic liquids were developed as electrolytes to overcome the limitations of water-based solvents for higher current efficiency by extending the electrochemical window. And the three-dimensional carbon felt with a high surface area and abundant active sites was selected as the cathode material to enhance the deposition rate. Cyclic voltammetry test demonstrated that both Au+ reduction and I- oxidation are irreversible processes controlled by diffusion with the diffusion coefficients of 1.48 × 10-7 cm2/s and 2.91 × 10-7 cm2/s at 20 °C, respectively. The optimal current efficiency (88.03%), specific energy consumption (216.37 kWh/t) and recovery of gold (95.77%), and iodine (85.75%) were obtained by regulating the electrodeposition parameters, including applied potential, temperature, and stirring speed. Moreover, the gold leaching and deposition efficiency were stable at approximately 93% and 95% with 0.2% iodine supplement for four cyclic leaching-electrodeposition. SEM-EDS, XRD, and XPS analysis showed the deposits on the carbon fibers had good uniformity, and the deposit composition contained Au0, Cu0, and CuO. [C2MIM][N(CN)2] ionic liquid is an attractive alternative to non-concentrated aqueous electrolytes for high-efficiency and low-power electrodeposition applications.