Gold Leaching Research Articles

Gold recovery from chloride leach solution of TCCA using D301 anion exchange resin and elution with thiourea

Trichloroisocyanuric acid (TCCA), which is used for gold leaching, is an alternative to cyanidation due to its lower toxicity and higher efficiency. This study investigated the gold recovery procedures from highly effective chloride leaching solution using the D301 resin. This approach prevented the inhibition of gold adsorption when using activated carbon. Herein, the optimal conditions for gold adsorption were discussed, including establishing adsorption kinetics and isotherms, and calculating adsorption activation energy. Additionally, SEM (Scanning Electron Microscope), FTIR (Fourier Transform Infrared Spectroscopy), and XPS (X-ray Photoelectron Spectroscopy) techniques were used to reveal the mechanism of gold adsorption using D301 resin. Under optimal conditions (pH 4.0, temperature 25 °C, time 120 min), an average adsorption percentage of 99.2% was achieved. Analysis of the adsorption data confirmed that gold adsorption followed the pseudo-second-order kinetic model and Freundlich adsorption isotherm. The calculated activation energy was 9.69 kJ mol−1, indicating a predominance of physical adsorption involving ion exchange reactions with protonated tertiary amine groups in the D301 resin beads. Furthermore, among various eluents tested in desorption experiments, a solution containing a mixture of thiourea and hydrochloric acid with 0.4 mol L−1 and 0.8 mol L−1, respectively, demonstrated superior efficiency, achieving a successful desorption percentage reaching 95.7 ± 0.3% within 80 min. After three cycles of resin regeneration, the regeneration efficiency reached 91.2% while maintaining an average adsorption percentage of 95.3%.

Development of a novel cobalt-glycine catalyzed thiosulfate system by DFT calculation for eco-friendly and efficient gold extraction

In this study, a novel thiosulfate leaching system, cobalt-glycine catalyzed system, was proposed. DFT calculations suggest that the coordination ability of organic ligands with metal ions conforms to the order: glycine > oxalic acid > citric acid > acetylacetone, and the reactivity and adsorption capacity of complexes on gold surface follow the order: cobalt-glycine > nickel-glycine > iron-glycine > copper-glycine > copper-ammonia. Cobalt-glycine complex is more likely to gain electrons from the gold surface and promote gold dissolution than copper-ammonia complex. During gold leaching, glycine catalyzes the coordination of Au+ with S2O32− and stabilizes cobalt ions under alkaline conditions, and Co(gly)x(2−x) catalyzes the reduction of O2. The gold leaching percentage and thiosulfate consumption of cobalt-glycine system are 94.85 % and 17.38 kg/t-ore, it has higher gold leaching percentage and lower thiosulfate consumption than copper-ammonia system. 99.27 % of gold in the leaching solution of cobalt-glycine system is adsorbed on resin, which could be recovered by one-step desorption because cobalt is hardly adsorbed on resin. However, copper in the leaching solution of copper-ammonia system competes with gold for adsorption on resin, so the gold adsorption percentage is low at 95.36 % and two-step desorption are required to separate copper and gold. The novel cobalt-glycine system is more environmentally friendly, simplified and efficient than traditional copper-ammonia system.

Research on Enhancing Copper-Ammonia-Thiosulfate Eco-Friendly Gold Leaching by Magnetization of Lixiviant Solution and Their Kinetic Mechanism

In thiosulfate leaching of gold, the copper-ammonia complex serves as an oxidant and catalyst. This study examined the impact of magnetizing the copper-ammonia thiosulphate lixiviant solution on gold leaching from refractory oxidized ores. Magnetization reduced surface tension, improved wettability and infiltration, and enhanced the diffusion of leaching agents. It also increased dissolved oxygen content and boosted the catalytic efficiency of copper-ammonia complexes. These changes led to more efficient gold extraction, with column leaching showing a 4.74% improvement in extraction rates compared to non-magnetized methods and a 3.67% improvement over cyanide processes. These findings suggest that magnetized copper-ammonia thiosulphate lixiviant is a promising, environmentally friendly alternative to cyanide for refractory oxidized gold ores.

Electrochemical Oxidation Mechanism of Pyrite in a Copper(II)-Citrate-Sodium Thiosulfate Composite System

Pyrite is an important gold carrier during gold leaching, but it is readily oxidized, which causes environmental problems such as acidic mine drainage. Thus, it is necessary to study the oxidation mechanism of pyrite in a gold-leaching electrolyte. The surface oxidation reaction of pyrite is a multi-electron transfer electrochemical oxidation process. Based on this, electrochemical technology was used to explore the electrochemical oxidation mechanism of pyrite in a Cu2+-Cit3−-S2O3 2− system. The surface oxidation products of the pyrite were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The experiments showed that the thiosulfate concentration did not change the oxidation mechanism of pyrite at 0.30 V under the conditions of this experiment. Increasing the concentration and potential of thiosulfate accelerated the oxidation rate of pyrite. The electrochemical oxidation of pyrite in the Cu2+-Cit3−-S2O3 2− system occurred in two stages. At low potentials in a passivated state, the process was diffusion-controlled, and the surface oxidation rate was slow. When the potential exceeded 0.50 V, the passivation film on the surface was penetrated, allowing the oxidation reaction on the surface of pyrite to continue. The results of this experiment are useful for deepening the understanding of the oxidation mechanism of pyrite in electrolytes.

Solution circulation for green and sustainable gold extraction with an integrated low potential thiosulfate leaching-resin adsorption recovery process

A systematic research of solution circulation for gold extraction from a gold ore with an integrated low potential thiosulfate leaching-resin adsorption recovery process was performed by using the analysis and detection methods of ICP-OES, SEM-EDS, HPLC, XPS, etc. The pulp potential was controlled at about 200 mV under low reagent concentration and closed condition where the gold leaching percentage achieved 89.02 % while the thiosulfate consumption was only 19.22 kg/t. 100 % of the gold and 32.61 % of the copper in the leaching solution were adsorbed by the resin, and their desorption percentages separately reached 98.59 % and 98.86 % after selective two-stage desorption. The leaching and adsorption percentages of gold first decreased and separately kept at about 91 % and 96 % after 10 solution circulations while the gold desorption percentage and thiosulfate consumption were basically unchanged with solution circulation. The sulfur-oxygen anions in the solution including S2O32–, S3O62–, S4O62–, SO32– and SO42–, and only SO42– was gradually accumulated with solution circulation. SO42–, S2O32– and S3O62– were the main sulfur-oxygen anions adsorbed on the resin, and they did not accumulate obviously on the resin with solution circulation. The novelty of this study is that gold was recovered as elemental gold product based on the the proposed process, and the effect of solution circulation on gold extraction and the accumulation and conversion rules of sulfur-oxygen ions during solution circulation were revealed for the first time.

Effective and selective recovery of Au(III) from WPCBs using quaternary phosphonium adsorbent synthesized by adjusting steric hindrance

With the gradual depletion of natural gold ore, waste printed circuit boards (WPCBs) have become one of the most attractive alternatives to gold ore. Here, a series of quaternary phosphonium adsorbents with a large size were successfully synthesized by adjusting the number of functional groups and carbon chain length of functional monomers, which can be used for selective recovery of gold(III) from WPCBs leaching solution. The quaternary phosphonium adsorbent (PS-TEP) prepared by the nucleophilic substitution reaction between triethyl phosphine with the smallest volume and chloromethylated polystyrene (PS-Cl) exhibited the best gold loading capacity (617.90 mg g−1). The adsorption mechanism of gold(III) on PS-TEP surface mainly involves anion exchange between AuCl4− and Cl− in the adsorbent. The charge level of the H atom closest to –CH2–P+ group directly determines the strength of the interaction between the adsorbent and the gold ion. Multiwfn and VMD programs visually confirm the weak interaction between PS-TEP+ and AuCl4−. After 5 adsorption-stripping cycles, the adsorption rate of gold(III) in solution remained at about 99 %. In addition, PS-TEP exhibited good gold(III) selectivity in both simulated and actual WPCBs gold leaching solutions. These results indicate that the large-particle PS-TEP with high capacity is suitable for selective gold recovery from WPCBs leaching solution.

Study on high-efficiency sulfide removement using sulfate radical-based AOPs and its oxidation mechanism of refractory gold ore

Pyrite enclosure poses a significant challenge in refractory gold ore processing, inhibiting gold leaching. This study explores Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) as an effective alternative for pretreating such ores. The oxidation pretreatments were performed under heat and ultrasound activation methods, including heat and ultrasound, and the influences of pretreatment time, pH, ultrasound power, pretreatment temperature, and precursor (PDS) concentration were investigated. Both ultrasonic and heat activation effectively mitigate the negative impact of pyrite enclosure on gold leaching. Specifically, the gold leaching rate improved from 21.9 % to 46.1 % and 74.9 % with heat and ultrasound activation, respectively The and generated by PDS dominate the pyrite oxidation according to EPR and quenching tests. Meanwhile, the SR-AOPs treatment also promotes the interactions between pyrite enclosure and leaching agent, reducing the negative influences of pyrite. Kinetic studies indicated that the oxidation processes are different under heat and ultrasound activation. Heat activation is governed by an interfacial chemical reaction, with an activation energy of 25.57 kJ/mol. In contrast, ultrasound-induced cavitation and microjets remove the oxidation layer, disrupt the pyrite crystal structure, and expose encapsulated gold. These effects accelerate pyrite oxidation, shifting the kinetic control step from interfacial chemical reaction to internal diffusion, with a reduced activation energy of 35.06 kJ/mol.

Highly Efficient and Selective Extraction of Gold from Thiosulfate Leaching Solution Using Functionalized Dicationic Ionic Liquids.

Thiosulfate leaching has been regarded as a promising alternative to cyanidation, but it still faces the challenge of the recovery of low content of gold from high concentrations of thiosulfate solutions. Liquid-liquid extraction is a method to address this issue but is still limited by the use of volatile and toxic organic solvents. To overcome this limitation, this work synthesized some functionalized dicationic ionic liquids (DILs) to serve as extraction solvents for the recovery of the gold-thiosulfate complex, [Au(S2O3)2]3-, from thiosulfate solutions. Experimental results indicated that the DILs showed higher extraction rates toward [Au(S2O3)2]3- compared with their monocationic-based counterparts, likely due to the stronger electrostatic interaction between the dications of the ILs and [Au(S2O3)2]3-. The transfer of [Au(S2O3)2]3- from the water phase to the IL phase was identified as an anion exchange and endothermic process. The rate of extraction was limited by the anion exchange process occurring at the IL-water interface. The extraction ability of ILs highly depended on the type of anion; specifically, the ILs with anions that had strong hydrogen-bonding ability exhibited high extraction ability toward [Au(S2O3)2]3-. Finally, DILs proved effective in the recovery of [Au(S2O3)2]3- from an actual gold leaching solution and exhibited high selectivity toward coexisting ions, indicating their potential as environmentally friendly solvents for gold recovery.

Effectively adsorb Au(S2O3)23- using aminoguanidine as trapping group from thiosulfate solutions.

Thiosulfate gold leaching is one of the most promising green cyanide-free gold extraction processes; however, the difficulty of recovering Au(I) from the leaching system hinders its further development. This study prepared aminoguanidine-functionalized microspheres (AGMs) via a one-step reaction involving nucleophilic substitution between aminoguanidine hydrochloride and chloromethylated polystyrene microspheres and used AGMs to adsorb Au(I) from thiosulfate solutions. Scanning electron microscopy, Brunauer-Emmett-Teller analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the structure and properties of AGMs. Experiments were designed to investigate the effects of pH, temperature, initial Au(I), and thiosulfate concentrations on the gold adsorption performance of AGMs. Results demonstrated that AGMs can efficiently adsorb Au(I) from thiosulfate solutions in a wide pH range. The adsorption process conforms to the pseudo-second-order kinetic model and Langmuir isotherm model, with a maximum capacity of 22.03kg/t. Acidic thiourea is an effective desorbent, and after four adsorption-desorption cycles, the adsorption rate of Au(I) by AGMs is 78.63%, which shows AGMs have good cyclic application potential. Based on the results of characterization, experiments, and density functional theory calculations, the mechanism for the adsorption of [Au(S2O3)2]3- on AGMs involves anion exchange. Importantly, AGMs exhibited satisfactory adsorption property for Au(I) in practical Cu2+-NH3(en)-S2O32- systems. This study provided experimental reference for the recovery of Au(I) from thiosulfate solution.

A highly efficient clean hydrometallurgy process for gold leaching in a Fenton oxidation assisted thiourea system

Clean hydrometallurgy processes, formed by “oxidant-ligand” systems, present promising strategies for gold leaching to mitigate the environmental impact of cyanidation. In this work, a Fenton oxidation-assisted thiourea system was proposed, employing reactive oxygen species (ROS, generated from Fenton reaction) as oxidant and thiourea as the ligand, respectively. By precise parameters control, 100% leaching of gold was rapidly achieved within 30 min from a roasted gold concentrate, highlighting extremely fast kinetics. Furthermore, this system was optimized by incorporating nitrilotriacetic acid (NTA) as an additive, which significantly reduced the thiourea consumption and produced the same gold leaching (100%, 60 min). Experimental results demonstrate that NTA lowers the solution potential (ORP) and eliminates the side reactions between iron ions and thiourea, thereby reducing thiourea decomposition. Surprisingly, the combination of Fenton oxidation and thiourea showed a high selectivity of the generation of ROS, with superoxide radical anion (•O2−) dominating, singlet oxygen (1O2) co-existing, but hydroxyl radical (•OH) absenting. Importantly, the moderate •O2− primarily contributes to gold leaching, which is generated through a chain reaction pathway between iron complex and H2O2 (Fe3+-Ligand+H2O2 → Ligand-Fe3+-OOH → Fe2+-Ligand+•O2−). Besides, the generation process of •O2− can be regulated by adding NTA. This work presented a prospective way in establishing the clean hydrometallurgy processes for efficient gold leaching.

Variations in structure and adsorption characteristics of humic acid during pressure oxidation process

Humic acid extraction from carbonaceous pressure-oxidized gold ore was carried out. The structure of humic acid was analyzed utilizing elemental analysis, FTIR, UV–Vis, Raman spectra and XPS. Also, the kinetic and isotherm models of the gold-adsorbing process were established to calculate the thermodynamic parameters and isosteric heat of adsorption. The results showed that affected by pressure oxidation, the aliphatic structure, C=O and other oxygen-containing groups were destroyed. Most importantly, new bonds, such as C—O—Clx, C—Clx and Me4N—Cl, were formed in the humic acid extracted from pressure-oxidized gold ore. The adsorption test results showed that, pressure oxidation made a profound impact on the gold-adsorbing performance of humic acid. The adsorption rate of humic acid decreased to (42.78±1.05)% for the pure gold solution and (28.63±1.11)% for the gold leaching solution after pressure oxidation. Adsorption findings conformed to the pseudo-second-order and Langmuir isotherm models. The isosteric adsorption heat of humic acid increased with the increase of the adsorption amount.

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.

Gold recovery from cyanidation residue by chloride leaching and carbon adsorption – Preliminary results from CICL process

There is a vast amount of globally underutilized low-grade mine tailings and leach residues, including those from primary processing of gold. In this research, the target is to recover the remaining gold (10.9 g/t) from weathered refractory iron-rich residue that had previously been subject to autoclave oxidation, subsequent cyanidation in a conventional carbon-in-leach (CIL) circuit as well as storage at tailings area. Chloride leaching has been considered as one of the most promising cyanide-free gold leaching methods and it has shown positive outcomes in treating primary gold ores, concentrates, and flotation tailings. Therefore, in the current study, the iron-rich residue investigated was subjected to chloride leaching combined with simultaneous carbon adsorption. The investigated parameters included leaching time (2–8 h), chloride concentration ([Cl−] = 0.2–5 M), type and concentration of oxidant ([Cu2+]/[Fe3+] = 0.1–1 M), as well as type and concentration of activated carbon (14–25 g/L), whereas S/L ratio (100 g/L), acidity (pH = 1), and temperature (90 °C) were kept constant. Leaching results indicate that up to 40% of the remaining gold could still be recovered from the investigated residue with optimized chloride leaching. According to the results, the most important parameter for gold recovery was the leaching time. Moreover, of the studied oxidants, cupric ions were shown to contribute more to gold recovery when compared to ferric ions (35% vs. 24% at [Cu2+]/[Fe3+] = 0.1 M). Nevertheless, an increase of cupric concentration from 0.1 M (low-concentrated) to 0.5 M, resulted in only a slight increase in gold recovery (from 36% to 40%), whereas no further improvement in gold recovery was achieved with a 1 M cupric concentration. Two studied activated carbon products showed equal effectiveness in gold adsorption. In-situ carbon adsorption was shown to occur effectively in chloride media, as all dissolved gold could be detected in the activated carbon, and the concentration of remaining gold in the pregnant leach solution was minimal (< 0.02 mg/L). These findings indicate that low-concentrated chloride leaching of leach residues from industrial gold processes can allow an enhanced recovery of gold from previously mined and treated raw materials.

Renewable ammonium chloride-induced calcium leaching of gold and copper tailings and selective preparation of vaterite CaCO3 by CO2 mineralization

This study introduced a high-value green processing solution for copper tailings to prepare high-purity vaterite from gold-copper tailings. The active reaction components were determined through Gibbs free energy calculations. The study discusses the impact of different experimental parameters on the leaching rate of Ca2+ and the degree of mineralization in gold-copper tailings, and then considers the influence of different dispersants on improving the stability of vaterite. The results show that the optimal leaching efficiency of Ca2+ in the NH4Cl solution is 75%, and the optimal mineralization efficiency is 87%. Under appropriate mineralization conditions, vaterite CaCO3 with d50 < 12 μm, a purity of 98%, and a whiteness of 98.7% can be prepared. The precipitated vaterite is affected by the pH swing method connected with the neutralization reaction. The presence of excess NH3 and supersaturated CO2 are necessary for the formation of vaterite-type CaCO3. Morphological analysis results show that dispersants such as polyacrylamide and sodium tripolyphosphate can improve the dispersibility of vaterite, preventing agglomeration and enabling its stable existence in aqueous solutions. Nanoparticle aggregation and crystal growth are two possible mechanisms for the formation of vaterite. The leaching-mineralization cycle technology using NH4Cl as the leaching solution meets the requirements for CO2 removal and alkaline industrial waste residue treatment, while avoiding the significant consumption of chemical reagents in traditional mineralization. This method provides a pathway for producing vaterite using copper tailings and has a broad market prospect.

Gold cyanide leaching recovery prediction model based on neighbourhood component analysis and artificial intelligence technique

Gold cyanide leaching recovery prediction model based on neighbourhood component analysis and artificial intelligence technique

Поэтапная комбинированная разработка золоторудных месторождений

Introduction. It is noted that in the Russian gold mining industry, the profitability of gold production is associated with the development of technologies for leaching it from substandard ores and enrichment waste. It is shown that the priority aspect of the development of substandard raw materials is to increase the yield of more gold with acceptable additional investments, predicted based on the analysis of the production function in the models of economic growth of enterprises. The purpose of the study is to substantiate the possibility of increasing the completeness of subsurface use during the phased development of reserves with a combination of chemical and mechanical extraction processes. Methods of achieving the goal include the use of literary and patent sources, production experience, laboratory and field experiments, modeling and technical and economic calculations. Results. The relevance of the development of a new raw material base is shown by the example of the reserves of the Sadonsky poly-metallic deposit. The information on the operations of hydrometallurgical and heap leaching of gold with bringing to the final product is detailed. An algorithm is proposed for the selection of options for the development of gold bulls. A model is presented to calculate the efficiency of phased field development over time. An optimized scheme of heap leaching of gold and indicators of gold extraction are presented. The scheme of electrochemical leaching of gold from sulfur-containing ores is recommended. The factors of the impact of mining on the environment at three stages of development are systematized. A model is presented for determining the efficiency of utilization of enrichment tailings and profits from the extraction of gold from enrichment tailings and metallurgy, taking into account environmental damage. The results of calculating the efficiency of gold extraction at the factory and leaching in blocks and cubes are presented. It is shown that the end-to-end metal recovery coefficient by leaching is comparable to the traditional technology of processing balance reserves. It is proved that when combining technologies at the stages of field development, a larger amount of metal is extracted from the subsurface. Conclusion: with a small increase in infrastructure modernization costs, combining traditional technology and leaching technologies, more metal is extracted from the subsurface.

Designing magnetic catalysts based on gold nanoparticles supported by ethylenediamine tetraacetic acid functionalized amino‐modified poly(N‐isopropyl acrylamide) for reduction of nitro compounds in water

AbstractA novel smart catalyst was developed with amino‐modified thermo‐responsive poly(N‐isopropyl acrylamide) (PNIPAM) grafts on silica‐coated magnetic nanoparticles using the conventional free radical polymerization process. By this methodology, the polymer was successfully grafted mainly onto silica‐modified iron oxide nanoparticles (Fe3O4@Si). The PNIPAM‐grafted Fe3O4@Si was then subjected to ethylenediamine treatment to produce the amino‐functionalized support (Fe3O4@Si@PNIPAM‐NH2), which was subsequently modified with carboxyl functional groups by using EDTA (ethylenediaminetetraacetic acid) to create Fe3O4@Si@PNIPAM‐NH2‐EDTA. Au nanoparticles were then decorated on this support through its two amines and four carboxylates. Different methods were used to study this novel catalyst, including inductively coupled plasma, Fourier transport infrared spectroscopy, TGA, dynamic light scattering, SEM, energy‐dispersive X‐ray analysis, vibrating sample magnetometry, XRD and elemental CHN analysis. The reduction of several aryl‐nitro derivatives demonstrated a significant catalytic activity for the as‐synthesized gold catalyst (Fe3O4@Si@PNIPAM‐NH2‐EDTA‐Au). The Au catalyst can be successfully removed from the reaction components using a magnetic field and used again in eight successive reduction reactions without significant gold leaching and loss of catalytic activity. © 2024 Society of Industrial Chemistry.

Exploring Non-ammoniacal Thiosulfate Gold Leaching and Limited Gold Recovery from a Refractory Gold Ore Oxidized in Alkaline Pressure Conditions

Exploring Non-ammoniacal Thiosulfate Gold Leaching and Limited Gold Recovery from a Refractory Gold Ore Oxidized in Alkaline Pressure Conditions

Thiocyanate facilitating thiosulfate extraction of gold via inhibiting formation of passive layer

Thiosulfate leaching is a feasible alternative for cyanidation. However, thiosulfate is easily decomposed and forms the passive layer on the ore surface, thus hindering gold extraction. In this paper, by adding thiocyanate to reduce the undesirable effect, copper-ammonia-thiosulfate leaching system is utilized to extract gold from the calcine. This research investigated the factors affecting gold extraction and kinetics of the leaching system, and the potential reason and reaction mechanism of the thiocyanate for improving gold leaching efficiency were discussed and analyzed. Gold leaching percentage is increased from 62.99% to 88.45% by adding thiocyanate that is close to that of cyanidation. By using X-ray photoelectron spectroscopy, gold in the leachate may be in the form of gold(I) thiosulfate complex. The leaching mechanism and the reason for improving gold extraction by adding thiocyanate were investigated via characterization and the leaching thermodynamic analysis. The possible reason for improving gold leaching percentage lied in that the thiocyanate reduced the decomposition of thiosulfate, thus inhibiting the form of passivation layer. According to the leaching mechanism, thiocyanate is used as an additive in the copper-ammonia-thiosulfate leaching system, which is of great significance for facilitating gold recovery, lessening thiosulfate consumption, and reducing ammonia dosage.

Evaluating the catalytic effect of pyrite on thiourea leaching of gold in the absence and presence of citrate

With the depletion of high-quality ore, the extraction of gold from refractory gold ores/concentrates is a promising endeavor. Pyrite is an important gold-bearing sulfide mineral. It is of great significance to study its influence on gold leaching to realize the maximum utilization of refractory sulfide gold ores/concentrates. In this paper, the effect of pyrite on thiourea leaching of gold was investigated through leaching experiment, surface characterization and density functional theory (DFT) calculation. Results showed that the presence of pyrite sharply decreased both gold dissolution and thiourea stability, and its adverse effect of pyrite is likely that pyrite catalyzes the oxidation of thiourea by Fe3+, resulting in the high thiourea consumption, which deteriorates the gold dissolution. The catalytic mechanism is believed to be that thiourea firstly adsorbs on the pyrite surface, and then electrons transfer from thiourea to the oxidant of Fe3+ through the conduction band of pyrite. Citrate was used as an additive to improve the thiourea stability and gold dissolution, and its mechanism was proposed as follows: citrate weakens the interaction between Fe3+ and thiourea by complexing with Fe3+, and competes with thiourea to adsorb on the surface of pyrite, reducing the adsorption of thiourea. Furthermore, the formation of Fe-citrate complexes, as terminal electron acceptor, has a lower oxidation capacity than Fe3+, thus relieving the catalytic effect of pyrite on thiourea oxidation by Fe3+.