Thiosulfate Leaching Research Articles

Biooxidation-thiosulfate leaching of refractory gold concentrate

A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated. Mineralogical studies on the concentrate showed that very fine gold grains (<10 µm) were encapsulated in pyrite and arsenopyrite, while the proportion of monomer gold was only 21%. The gold-bearing sample was identified as a high-sulfur fine-sized wrapped-type refractory gold concentrate. The gold leaching efficiency obtained by direct cyanidation was only 59.86%. After biooxidation pretreatment, the sulfide minerals were almost completely decomposed, 92wt% of the mineral particles of the biooxidation residue were decreased to <38 µm, and the proportion of monomer gold in the biooxidation residue was over 86%. Meanwhile, the gold content in the biooxidation residue was enriched to 55.60 g/t, and the S, Fe, and As contents were reduced to approximately 19.8wt%, 6.97wt%, and 0.13wt%, respectively. Ammoniacal thiosulfate was used for gold extraction from the biooxidation residue of the refractory gold concentrate. The results showed that the optimal reagent conditions were 0.18 M thiosulfate, 0.02 M copper(II), 1.0 M ammonia, and 0.24 M sulfite. Under these conditions, a maximum gold leaching efficiency of 85.05% was obtained.

The ultrasound leaching kinetics of gold in the thiosulfate leaching process catalysed by cobalt ammonia

The effect of ultrasound on gold leaching rate and kinetics was investigated in the Co-NH3-S2O32− system. First, the effects of ultrasound power, temperature, the concentration of thiosulfate, cobalt and ammonia on gold leaching rate were studied under ultrasound. The optimized leaching parameters are 0.03 M Co2+, 0.2 M S2O32−, 1 M NH3, 323 K, and 750 W ultrasonic power. Moreover, the leaching rate of gold is 8 times faster, and the extraction percentage is approximately 25% higher, under ultrasound than under conventional conditions. The experimental results show that ultrasound can effectively enhance the leaching rate and the extraction percentage. The kinetic analysis indicates that the internal diffusion step controlled the ultrasound leaching process. The increase in the leaching rate under ultrasound is due to the decrease of activation energy from 22.65 kJ/mol to 13.86 kJ/mol. Therefore, ultrasound efficiently improved the leaching rate of gold in the Co-NH3-S2O32− leaching system.

Use of polyethylenimine functionalised magnetic nanoparticles for gold thiosulfate recovery

The use of calcium thiosulfate (CaS2O3) as an alternative lixiviant to cyanide to treat double refractory gold ores has become an industrial reality. In this study, a novel adsorbent, polyethylenimine coated iron oxide magnetic nanoparticles (PEI-MNPs), was evaluated for the adsorption of gold from thiosulfate leaching systems that contain gold, copper and calcium thiosulfate. Particles were characterised in terms of their size and morphology, zeta potential, crystalline structure, surface properties, functional groups, magnetic properties and thermal degradation properties. The effect of nanoparticle dosage, thiosulfate concentration, copper concentration, solution pH and solution temperature on gold loading in synthetic leaching solutions was examined. In addition, adsorption kinetics and adsorption isotherms were investigated. PEI-MNPs demonstrated a positive surface charge up to a pH of 11, which facilitated electrostatic attraction of anionic gold thiosulfate complex. A higher nanoparticle dosage, lower free thiosulfate concentrations and lower temperatures favoured gold adsorption, while copper concentration and solution pH did not show a considerable effect. Gold adsorption kinetics were fast, irrespective of the solution content and reached equilibrium in less than 30 min. The adsorption isotherm data could be fitted with both the Langmuir and the Freundlich isotherm models. The adsorbent was able to be reused after a selective metal elution process.

In-situ reduction of gold thiosulfate complex on molybdenum disulfide nanosheets for a highly-efficient recovery of gold from thiosulfate solutions

Thiosulfate leaching is widely considered an alternative and nontoxic technique for cyanidation in gold hydrometallurgy; however, the main problem with this technique is the difficulty in recovering gold from pregnant solutions. Here, we report that a simple and accessible material, molybdenum disulfide nanosheets, can effectively in-situ reduce and recover gold from pregnant solution based on its semiconducting properties. The results of the in-situ reduction showed that the gold-thiosulfate complex([Au(S2O3)2]3−) can be reduced to elemental gold particles with a particle size of 130–320 nm. The origin of the in-situ reduction of gold might be derived from the photo generated electrons released by molybdenum disulfide. The 1866.762 mg∙g−1 recovery capacity of gold on molybdenum disulfide from a 100 mg∙L−1 initial gold solution, which is 1000 times the recovery capacity of modified activated carbon, further demonstrates that molybdenum disulfide is a superior gold recovery material. Moreover, the removal of ~99% gold from gold-loaded MoS2 indicates the recyclability of MoS2 in gold recovery. Based on these results, it is obvious that molybdenum disulfide nanosheets is an excellent material to recover gold from gold-thiosulfate complexes. Besides, the application of molybdenum disulfide to gold recovery can simplify the traditional thiosulfate leaching process.

Dissolution of Silver and Gold with Sodium Hypochlorite and Hydrochloric Acid in Refractory Minerals (Mangano-Argentiferous)

The present study examined a process for precious metal recovery (silver and gold) from difficult minerals which exhibit refractory characteristics to cyanidation and ammonium thiosulfate leaching (low extraction and high consumption of leaching agent). It is well known that mangano-argentiferous minerals are mainly composed of manganese, silver, gold, and iron. In this research, a mineral sample from Monte del Favor mine, located in Hostotipaquillo, Jalisco, Mexico, was physically and chemically characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fire assay, and atomic absorption spectroscopy (AAS). Two-stage leaching was carried out: first to eliminate manganese from the sample using sodium sulfite (Na2SO3) as a reductive reagent and sulfuric acid (H2SO4) and a second stage to dissolve silver and gold with sodium hypochlorite (NaClO) and hydrochloric acid (HCl); the results show extraction around 96% for Mn and 98.73% and 83% of Ag and Au, respectively. The usefulness of high acidity and Na2SO3 to obtain good results in Mn and Ag leaching is discussed along with the roles that HCl and NaClO play in the dissolution of Ag and Au values.

Construction of MoS2 nano-heterojunction via ZnS doping for enhancing in-situ photocatalytic reduction of gold thiosulfate complex

Recovery of gold thiosulfate complex ([Au(S2O3)2]3−) from leaching solutions has been recognized as a tough task, which limited the industrial promotion of eco-friendly thiosulfate leaching technique. In this work, MoS2/ZnS nano-heterojunction as a catalyst was proposed for the recovery of [Au(S2O3)2]3− from leaching solution. The results indicated that [Au(S2O3)2]3− could not only be efficiently recovered, but also in-situ reduced into Au0 when MoS2/ZnS nano-heterojunction being used in the leaching solution. Mo0.45Zn0.10S exhibited an extremely high reduction capacity (1120.56 mg/g), which was 4.52 and 1.72 times of ZnS and MoS2, respectively. The great improvement was resulted from the ZnS doping on MoS2, which brought stronger light absorption, higher transferred efficiency and lower recombination of photogenerated electron-hole pairs of MoS2. In addition, the Au0 could completely desorpt from MoS2/ZnS nano-heterojunctions in Na2S solution in less than 4 min, leading MoS2/ZnS nano-heterojunction to have remarkable cycling performances. This work provided a new insight for enhancing the recovery and in-situ reduction of gold thiosulfate complex from leaching solutions.

Study on Pre-oxidation of a High-Arsenic and High-Sulfur Refractory Gold Concentrate with Potassium Permanganate and Hydrogen Peroxide

For arsenic-containing refractory gold concentrate, gold recovery by leaching is extremely difficult due to the encapsulation of gold in arsenopyrite and pyrite. In this work, the pre-oxidation of a high-arsenic and high-sulfur refractory gold concentrate in the acidic potassium permanganate or hydrogen peroxide solutions has been investigated. The studied parameters include pre-oxidation time, acidity, pre-oxidation temperature, ethylene glycol addition and oxidant concentration. When potassium permanganate of 0.25 mol/L is used as oxidant, 61.4% of arsenic and 51.8% of iron can be removed, respectively. The results of kinetics analysis indicate that the oxidative dissolution of arsenopyrite during the pre-oxidation process is controlled by the product layer diffusion, with an activation energy of 7.92 kJ/mol. The stability of hydrogen peroxide can be significantly improved by increasing both sulfuric acid concentration and ethylene glycol addition when hydrogen peroxide is used as oxidant. Under optimum conditions, arsenic removal ratio of 57.2% and iron removal ratio of 51.9% have been achieved with hydrogen peroxide of 2.5 mol/L, sulfuric acid of 0.75 mol/L and ethylene glycol of 30 mL/L. The gold extraction of refractory concentrate is only 11.5% in the copper–ammonia–thiosulfate leaching solutions without pre-oxidation. A gold extraction of 71.8% and significant decrease in thiosulfate consumption from 28.2 to 5.7% have been observed for the concentrate after pre-oxidation.

Recovery of valuable metals from mining and mineral processing waste

Ammonia-thiosulfate-copper leaching, aided by a direct current electrochemical impact, is proposed to extract gold (Au), silver (Ag) and copper (Cu) from old flotation tailings mixed with waste rock. Over 80 % of Au available in the waste material and over 75 % of Cu and Ag were extracted into the pregnant leach solution (PLS) at room temperature. Electrowinning from that PLS recovered around 92 % of Au and Cu, and about 87 % of Ag in the cathode deposit that is suitable for further metallurgical refining. The results are better, compared to leaching in the same system but without electrochemical impact and at air addition. The proposed direct current aided method is promising and more environmentally friendly compared to cyanide and even to sodium thiosulfate leaching.

The effect of tetrathionate on the anodic process of gold thiosulfate leaching

AbstractThe mechanism that tetrathionates retarded gold dissolution during the anodic process of gold thiosulfate leaching was studied with the help of electrochemical and spectroscopic techniques. The results show that the reduction in gold dissolution did not originate from the increase of a passive layer on the surface. When the gold electrode was controlled at 0.25 V, the topography of the gold surface and element composition in the tetrathionate‐supplemented solution is not easily distinguishable from that in the thiosulfate solution. The addition of tetrathionate in the thiosulfate solution reduces gold dissolution. This phenomenon is caused by the decrease in thiosulfate concentration at the gold interface. And the gold interface composition was also changed due to the presence of tetrathionate.

Effect of an additive TEA on thiosulfate leaching of low sulfur gold concentrate

The environmentally friendly and non-cyanide thiosulfate gold leaching technology was used to extract gold from a low-sulfur gold concentrate. The effect of TEA on leaching of pure gold under the condition of adding quartz indicated that TEA could significant increase the dissolution rates of gold and the mixed solution potentials and decrease the consumption of thiosulfate. Quartz has little effect on the gold leaching process. Moreover, the effect of additive Triethanolamine (TEA) on the gold extraction was further studied. The chemical analysis and process mineralogy analysis of the concentrate indicated that the concentrate contained 59 g/t Au, 64.49% SiO2, 19.55% Al and 5.76% Fe. The concentrate was composed of quartz, muscovite and chlorite as major minerals. Quartz was the main gold-bearing mineral in concentrate. The gold particles of less than 20 μm in the concentrate reached 50.56%. Traditional thiosulfate leaching technology was used to extract gold from the concentrate, and the gold leaching rate was only 44.49% after 48 hours. When 0.024 M (MTEA:Mcopper=2:1) TEA was added in the thiosulfate leaching gold system, the thiosulfate consumption significantly reduced by about 32% and the leaching rate of gold increased to 73.40%.

Ammonium thiosulfate extraction of gold from printed circuit boards (PCBs) of end-of-life mobile phones and its recovery from pregnant leach solution by cementation

In this study, the ammonium thiosulfate leaching of gold (Au) from printed circuit boards (PCBs) of end-of-life mobile phones and the subsequent recovery of dissolved metals from pregnant leach solution via cementation were elucidated under various conditions. Over 99% of Au was extracted from crushed PCBs (D50 = 85 μm) under the following conditions: 1 M of Na2S2O3, 10 mM of CuSO4, 1 M of ammonia/ammonium concentration, 0.1 g/10 ml of solid-to-liquid ratio, and a 24-h of leaching time in the presence of oxygen. In contrast, the recovery of Au ions via cementation was more favorable in the absence of oxygen. Among the various cementation agents evaluated, copper (Cu) was the most selective and recovered around 95% of extracted Au from the pregnant leach solution even in the presence of various coexisting metal ions. The cementation of Au exhibited two distinct kinetic regions: (1) an initially rapid rate, and (2) a more gradual and constant rate. Finally, the use of Cu plates to recover Au ions from ammonium thiosulfate pregnant solution of crushed PCBs is proposed, which could selectively recover about 80% of dissolved Au and is easier to handle and reuse compared with Cu powder.

Connection between gold dissolution in thiosulfate leaching and Cu(II) complexes during the cathodic process

The effect of the reduction half reaction of Cu(II) complexes on passivation and gold dissolution in the copper-ammonia-thiosulfate system were studied using electrochemistry and density functional theory (DFT). The results show that the cathodic process accounts for the surface passivation, aside from contributions made by thiosulfate decomposition during the anodic process. Copper sulfide and polysulfide are formed in the passivation layer during the reduction half reaction of Cu(II) complexes. The addition of common additives, such as ethylenediamine (EN) and ethylenediamine tetraacetic acid (EDTA), are able to not only remove the passive layer but also change the Cu(II) reduction half reaction. Tafel curves show that the gold leaching current in the EDTA-supplemented solution is higher than that in the EN-supplemented solution. Linear sweep voltammetry demonstrated that the reduction half reaction of Cu(II) complexes is controlled by the diffusion process, and the diffusion coefficient of the Cu(II) complex in the EN-supplemented solution and EDTA-supplemented solution is 0.64 × 10−6 cm2/s and 1.44 × 10−6 cm2/s, respectively. Density functional theory (DFT) studies showed that the lowest unoccupied molecular orbital (LUMO) of the mixed Cu(II)-ammonia-EDTA complex has lower energy than that of the mixed Cu(II)-ammonia-EN complex. Additionally, gold atoms on the surface that adsorbed the Cu(II)-ammonia-EDTA complex have higher relaxation degrees than those in the Cu(II)-ammonia-EN complex system. This explains why the gold concentration in the EDTA-supplemented solution is higher than that in the EN- supplemented solution. This study provides insight into the differences in gold dissolution during the cathodic process.

Thermodynamic analysis of the copper (I) homogeneous and heterogeneous speciation in ammonium thiosulfate leaching systems

The paper presents a new thermodynamic approach to studying mixed ligand complex formation reactions in the multi-component two-phase system “cuprous oxide-ammoniacal copper (I) thiosulfate aqueous solution” under real conditions. The quintessence of the developed approach consists in the thermodynamic analysis of concurrent reactions in the heterogeneous system Cu(I) – NH3 – S2O32− – H2O on the basis of the introduced notion of generalized reaction equations. A detailed thermodynamic analysis in ammonium thiosulfate leaching systems has considered the formation of mixed ligand complex species Cu(OH)i(NH3)j(S2O3)k. The new feature is to focus on the chemical description of the overall process of complex formation consisting of a series of concurrent reactions, where the nature and ratio of the concentrations of chemical species, formed in such reactions, depend on the ratio of the concentrations of the metal Cu+ and ligands, temperature, and other thermodynamic parameters. On the basis of the selected thermodynamic data for involved species, the thermodynamic stability areas of solid phase and the repartition of soluble and insoluble chemical species towards the solution pH and a number of total reagent concentrations in heterogeneous mixtures have been investigated. The diagrams of heterogeneous and homogeneous chemical equilibria are used for the graphical representation of complex equilibria and distribution of soluble and insoluble species in examined systems. The used approach utilizes thermodynamic relationships coupled with original mass balance constraints, where the solid phases are explicitly expressed. The obtained results are useful for optimization of the overall scheme of thiosulfate leaching in gold hydrometallurgy to minimize reagent consumption and maximize gold extraction.

Effect of activated carbon on the thiosulfate leaching of gold

The catalyzed thiosulfate leach of gold from oxide ores has been evaluated. The addition of fine activated carbon resulted in increased dissolution rates and gold recoveries. It was hypothesized that activated carbon and gold form galvanic couples, and that the rate of oxygen reduction increased due to the increased surface area available on activated carbon. The use of activated carbon as catalyst in the thiosulfate leach of gold is a process alternative that may not require the addition of surrogate oxidants (like copper), can work at temperatures as low as 30 °C, and thiosulfate degradations of 2.1 kg per ton of ore or lower, making it an attractive alternative for the leaching of gold.

A physical separation scheme to improve ammonium thiosulfate leaching of gold by separation of base metals in crushed mobile phones

As technology advances, consumers are looking to buy new phones. This phenomenon leads to decrease in life-cycle of mobile phones (ca. 2–3 years), resulting in increase of waste mobile phones. In waste mobile phones, it contains various components including display unit, battery, cases, and printed circuit boards (PCBs). PCBs alone contain variety of materials such as gold (Au), copper (Cu), and iron (Fe) as well as aluminum (Al) with plastics, which causes difficulty in recycling. The coexistence of Cu and Al in crushed mobile phones has been recently reported to cause very low Au extraction efficiency in ammonium thiosulfate medium due primarily to enhanced re-deposition of extracted Au ions via galvanically induced cementation. To limit this antagonistic effect of Cu and Al coexistence on Au extraction, Au-containing components were separated from Cu- and/or Al-bearing parts using a two-step crushing approach in tandem with various physical separation techniques (i.e. jig, hybrid jig, magnetic separation, flotation, and sink-float separation) that were applied on appropriate size fractions. The results showed that over 96% of PCBs, the primary Au-containing material in mobile phones, were recovered after jig separation. These concentrated PCBs were collected and further crushed to liberate Au-containing parts and then treated by diverse physical separation techniques such as magnetic separation, jig separation, hybrid jig separation, flotation, and sink-float separation depending on the crushed particle sizes. Ammonium thiosulfate leaching of the mixed Au-concentrated products from various physical pretreatment techniques showed that Au extraction improved by about 15-fold, indicating that the physical separation scheme proposed in this study is very promising.

Study on oxygen pressure thiosulfate leaching of gold without the catalysis of copper and ammonia

There are several limitations of thiosulfate leaching methods in its industrial application. The main limitation is the addition of copper and ammonia which act as catalysts in the thiosulfate leaching process. The introduction of cupric ions can accelerate the rate of gold leaching but cause massive oxidation of thiosulfate, and cupric ions in the leachates are also adverse to gold recovery. Moreover, the presence of ammonia must be taken into account due to the increasing environment concerns. In this paper, a systematic investigation was carried out during oxygen pressure thiosulfate leaching (OPTL) without adding copper and ammonia at elevated temperature and oxygen pressure. Thermodynamic calculations showed that the improvement of temperature and pressure was favorable to gold leaching by thiosulfate. However, high temperature and pressure also caused high thiosulfate consumption (55.3 kg/t-ore of sodium thiosulfate) and relatively low gold extraction (87.6%) without additives. Addition of ammonium alcohol polyvinyl phosphate (AAPP) in the tests could reduce thiosulfate consumption to 45.7 kg/t-ore, whilst 90.2% of gold extraction can be achieved. XPS and SEM studies indicated that AAPP could also hinder the deposition of some passivation species including FeOOH, Fe2O3, Al2O3, S0, etc. on the ore surface. The gold recovery from oxygen pressure thiosulfate leach solution was conducted by the method of resin adsorption. Over 98% of gold can be loaded at 1 g/L strong base anion exchange resin of Tulsion A-21S and almost 100% of gold on the loaded resin can be stripped with a two component eluent solution comprising chloride and sulfite.

An eco-friendly and efficient process of low potential thiosulfate leaching-resin adsorption recovery for extracting gold from a roasted gold concentrate

Thiosulfate is a promising alternative lixiviant to cyanide for leaching gold from its ores/concentrates due to increased environmental and public concern over the use of poisonous cyanide. However, high thiosulfate consumption and high cost for gold recovery from pregnant solution have limited its industrial application. In this work, an innovative process for extracting gold from a roasted gold concentrate is proposed: firstly, gold leaching with thiosulfate under a low mixed potential; then, gold separation and enrichment with an ion-exchange resin to produce concentrated gold solution that can be refined to metallic gold by electrowinning. Compared with traditional thiosulfate leaching, the mixed potential of stable stage of low potential leaching decreased around 30 mV through using low concentrations of reagents and limiting oxygen supply, a slightly higher gold extraction was obtained, whilst thiosulfate consumption substantially reduced from 34.6 kg/t-concentrate to 15.8 kg/t-concentrate. The amount of undesirable anions particularly cuprous thiosulfate and polythionates in the pregnant solution significantly dropped owing to the mild leaching conditions. This considerably weakened their competitive adsorption with gold (I) thiosulfate onto the resin, contributing to the decrease of resin dosage used for gold recovery. The eluent dosage also declined because of the less interfering ions on resin surface. Based on these results, low potential thiosulfate leaching followed by resin adsorption recovery is put forward, providing an eco-friendly and efficient process for gold extraction from roasted gold concentrate.

Control system for thiosulfate leaching of intermediate industrial products in metallurgy

The efficiency of the process of thiosulfate leaching of intermediate industrial products depends on the composition of the incoming raw materials, the operational control of which is impossible. In this paper, we propose upgrading of the process control system which allows reducing the downtime of the process equipment.

Precious metals recovery from waste printed circuit boards using thiosulfate leaching and ion exchange resin

Precious metals recovery from secondary sources is a novel alternative since they hold higher contents of several metals than average ores. In this research gold and silver were recovered from Waste Printed Circuit Boards (WPCBs) with the use of ammonia-thiosulfate solutions and the MTA 5011 ion exchange resin. First, it was necessary to remove the excess of copper from WPCBs since it could be detrimental for precious metals dissolution during leaching with thiosulfate. Nitric acid was the best reagent for decreasing copper concentration within WPCBs from 27% to 1.5%. Then, precious metals were dissolved with ammonia-thiosulfate solutions during 6 h at room temperature. Since copper was still within WPCBs, there was no need to add copper salts in order to form the copper tetramine complex required for accelerating precious metals dissolution. MTA 5011 ion exchange resin was used for precious metals recovery from leachates. It was determined that at higher resin: solution ratios, gold and silver recovery on the resin increased whereas selectivity towards gold diminished. The 87% of the gold was recovered and only 29% of copper was adsorbed too. Afterwards, a pre-elution stage was performed with sodium thiosulfate for a selective elution of copper. The 83% of the copper was desorbed while 28% of gold was eluted as well. For precious metals elution, several reagents were tested and KSCN was the most efficient of all since it desorbed the 98% of gold and only the 15% of the remaining copper. A combined solution of NaCl and Na2SO3 was assessed as well since they can regenerate the resin during the elution process. Finally, electrodeposition was better with solutions coming from elution with NaCl and NaSO3 (82% of Au and 94% of Ag recovery on cathodes surface) compared to those from thiocyanate elution (62% of Au and 87% of Ag).

Environmentally friendly extraction of gold from refractory concentrate using a copper – ethylenediamine – thiosulfate solution

The growing environmental concerns associated with the use of cyanides and their toxicity have led to the prohibition of cyanidation-based gold leaching in many countries, necessitating the search for other extraction methods. Herein, we show that thiosulfate leaching presents an alternative green way of gold extraction from S- and As-rich refractory gold concentrates, revealing the importance of oxidative ore pretreatment. Prior to leaching, samples were oxidized by roasting, with the optimum roasting temperature (642 °C) and time (240 min) determined using the response surface method. Subsequently, the roasted residues were subjected to cyanidation, copper – ammonia – thiosulfate system, and copper – ethylenediamine – thiosulfate system treatment. As a result, 18-h cyanidation achieved a gold extraction efficiency of 80.6%, with the consumption of NaCN equaling 1.05 kg/t, whereas the corresponding values for 1.5 h copper – ammonia – thiosulfate treatment equaled 63.0% and 11.3 kg/t. Importantly, 4 h copper – ethylenediamine – thiosulfate system treatment (5 mM copper ion, 10 mM ethylenediamine, 0.1 M thiosulfate, pH = 8–11, liquid-to-solid ratio = 3, stirring speed = 250 rpm) achieved a gold extraction efficiency of 80.3%, with the corresponding thiosulfate consumption equaling only 4.14 kg/t. Thus, copper – ethylenediamine – thiosulfate leaching proved to be an efficient, environmentally friendly, and low-cost method, being well-suited for gold extraction from roasted residues.