Gold Cyanide Research Articles

Study on recovery of copper and zinc from cyanide lean solution in a smelting company

In the process of cyanidation of gold concentrate from a smelting company, the content of copper and zinc in the liquid gradually increased. In production, acidizing process is used to treat the lean solution from high copper concentrate, and mixed products containing copper, zinc and other metals are produced. In this paper, the pH value of zinc precipitation is 6.0 and the pH value of copper precipitation is 3.0 through theoretical calculation and experiment. The separation of copper and zinc in the lean solution is realized successfully. The zinc product with grade of 42.97% and the copper product with grade of 58.33% are produced.

Mechanism of Gold Cyanidation in Bioleaching of Precious Metals from Waste Printed Circuit Boards

Biocyanidation is an environment-friendly technology for recovering precious metals from waste printed circuit boards (WPCBs). Although the leaching mechanism has been studied a lot, Au-release behavior still remains unknown. In this paper, density functional theory (DFT) was employed to investigate the electronic structure of the complex existing in the Au cyanidation process. Extended charge decomposition analysis (ECDA) showed that the adsorption of CN– to Au and the adsorption of O to the formed [AuCN]⁻ caused net electron transfer of 0.356 and 0.574 au, respectively. Dissociation of O from [AuCNO]⁻ had a Gibbs free energy change of −154.229 kcal/mol. Electron localization function (ELF) and localized orbital locator (LOL) confirmed that CN– covalent bonding led to a transformation of the orbit localization region of the adsorbed Au atom. It might cause electrostatic repulsion from the nondirectly contacted Au atom. This speculation was demonstrated by the Mulliken overlap population analysis, which showed that CN– bonding caused antibonding interaction. The repulsive interaction would be an important factor triggering the release of the adsorbed Au atom. This work presented a new interpretation of Au cyanidation, providing important insights into Au-release behavior. It might help construct the leaching kinetics of multimetal resources to facilitate the recovery of precious metals from waste printed circuit boards.

Development of a Sustainable Alternative for the Ammoniacal Cyanidation of Copper–Gold Ores Through a Biological Approach

Due to the problems arising from the presence of copper in the gold cyanidation process, including high cyanide consumption and occupation of the activated carbon surface, biological ammoniacal cyanidation was implemented as a resolution. Bacillus megaterium was implemented to produce cyanide and ammonia in nutrient broth and vinasse media. Maximum cyanide concentrations of 29.8 and 47.5 mg/L were produced using 3 g/L glycine in the mentioned media, respectively. Afterward, the Box-Behnken experiment design method was implemented to optimize ammonia biogenesis in vinasse culture, where 1974 mg/L ammonia was synthesized at 13.56 g/L calcium chloride, 7.2 g/L urea, and pH = 7.9. Three different strategies, namely: (1) bio-cyanidation, (2) bio-ammoniacal cyanidation, and (3) bio-ammonia pretreatment/bio-cyanidation, were employed to recover gold and copper from a 1% solid pulp. Afterward, using the nutrient broth medium, 49% gold was recovered by the first approach; the second approach extracted 9.2% gold and 33.5% copper, and 77% copper removal and 76% gold recovery were achieved through the third technique. Nutrient broth substitution with vinasse increased the gold recovery to 97% in the third approach. Hence, ammoniacal pretreatment, in combination with bio-cyanidation, is suggested to recover gold from copper–gold ores. In conclusion, the originality of the present work lies first in developing a bacterial culture procedure in which nutrient broth was replaced with vinasse as an industrial byproduct to make the process more eco-friendly. And secondly, in using the biogenic ammonia to leach out copper from the copper–gold ore and prepare it for gold biocyanidation.

Multi‐stage economic model predictive control for a gold cyanidation leaching process under uncertainty

ABSTRACTIn order to dynamically operate the gold cyanidation leaching process (GCLP) under uncertainty, a multi‐stage economic model predictive control (EMPC) is proposed for GCLP for the transient and steady‐state economic optimization. The proposed multi‐stage EMPC is composed of two steps. In the first step, the unmeasurable uncertain parameters are estimated by using Tikhonov regularization based method, so as to avoid amplification and propagation of the noise measurements into the estimation. Based on the estimated results, the scenario tree for multi‐stage EMPC is generated from the historical data using a data‐driven approach, and the control inputs are obtained from solving the resulting large nonlinear programming problem (NLP) at each sampling point. The resulting uncertainty model and the probability of each scenario are more consistent with the actual industrial GCLP, and the solutions are less conservative. The efficiency of the proposed multi‐stage EMPC is verified through a simulated industrial GCLP. Compared with other EMPC methods, including classic EMPC and multi‐stage EMPC with box uncertainty region, the proposed method can reduce the economic cost while accounting for the constraints at the same time.

Destabilisation of gold cyanide complex by sulphur species: A computational perspective

The interaction of gold cyanide complex with elemental sulphur and all metastable sulphur species has been studied using Density Functional Theory (DFT). The elemental sulphur and sulphide species formed during pre-treatment of refractory gold ores or dissolution of sulphide minerals form a series of metastable species including hydrosulphide, polysulphide, thionates, sulphite and finally sulphates which are known to have a detrimental effect on gold cyanidation. Previous researchers have attributed this effect mainly to passivation of the gold surface. However, interaction of dissolved aurocyanide with sulphur species has received almost no attention. Here, DFT molecular modelling has been used for the first time to describe the interaction of dissolved gold cyanide and sulphur species, and to explain the reduction and destabilisation potential of sulphur species in gold cyanidation.Computational modelling shows that sulphur species can have a significant negative effect on the stability of gold cyanide complex. Elemental sulphur and sulphide ion with −446.6 and − 198.4 kJ.mol−1 interaction energies have the most negative effect. S0 and S2− contribute to the destabilisation of gold cyanide via two different mechanisms of precipitation of AuCN and thiocyanate formation as well as reduction of gold by formation of sulphite and sulphates respectively. The effect of elemental sulphur can be neutralised by excess free cyanide in solution, while sulphide ion can still stay reactive toward gold cyanide in the presence of free cyanide. Addition of lead salt can decrease the inhibiting effect of sulphide ions by formation of lead sulphide. However, lead cannot eliminate the negative effect of elemental sulphur. It is concluded that oxidation of sulphur species can significantly overcome the adverse impact of sulphur species on the stability of gold cyanide complex. The destabilisation of gold cyanide complex by sulphur metastable species is introduced as one of the main mechanisms for loss of gold in sulphide gold ores.

Effect of hydrogen peroxide and lead(II) nitrate on gold cyanide leaching of Malaysian mesothermal deposit gold ore

Effect of hydrogen peroxide and lead(II) nitrate on gold cyanide leaching of Malaysian mesothermal deposit gold ore

Mechanistic Insights into C(sp2)−C(sp)N Reductive Elimination from Gold(III) Cyanide Complexes

AbstractA new family of phosphine‐ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary 12/13C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp2)−C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp3)−C(sp3), C(sp2)−C(sp2), and C(sp3)−C(sp2) bond formation processes taking place on gold(III) species.

Mechanistic Insights into C(sp2 )-C(sp)N Reductive Elimination from Gold(III) Cyanide Complexes.

A new family of phosphine-ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary 12/13 C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp2 )-C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp3 )-C(sp3 ), C(sp2 )-C(sp2 ), and C(sp3 )-C(sp2 ) bond formation processes taking place on gold(III) species.

Исследования по переработке измельченного золотомедного флотоконцентрата методом сернокислотного атмосферного окисления

The study is focused on the conditions of sulphuric acid atmospheric oxidation of crushed gold-copper flotation concentrate for obtaining a solid gold-containing product suitable for gold extraction by cyanidation. Additionally, the scope of the study includes the problem of maximising the transfer of copper into a sulphate solution for subsequent separation into a commercial product. The object of research consisted of a gold-copper concentrate with the main copper minerals represented by chalcopyrite and tennantite. Experiments on atmospheric oxidation of flotation concentrate were carried out in a laboratory reactor at a temperature of 90-95°C in a sulphuric acid medium using industrial oxygen and air as an oxidiser. In order to analyse the chemical composition of solutions, atomic absorption, inductively-coupled plasma atomic emission and titrimetric analysis methods were used. The composition of solid phases was studied by assay-gravimetric, assay-atomic absorption and chemical methods. In the course of research on the selection of optimal parameters for conditioning the flotation concentrate prior to cyanidation, the particle size of the material was revealed to be at least 80% of the class, i.e. -20 μm. This contributes to an increase in the subsequent gold cyanidation recovery by 56.0% and a decrease in reagent consumption by 21.0 kg/t (compared to direct cyanidation without pre-treatments). In order to reduce the oxygen consumption in the process of atmospheric oxidation, as well as to increase the extraction of copper, a three-stage scheme of the process was proposed including air bubbling for 8 h, oxygen oxidation for 2 h and air oxidation for 8 h. In this case, the extraction of copper and gold (with subsequent cyanidation) into solution comprised 90.1 and 95.4%, respectively, with the consumption of NaCN decreased to 8.1 kg/t. Atmospheric oxidation of gold-copper flotation concentrate pre-crushed to a particle size of 20 μm in a sulphuric medium by bubbling the pulp with oxygen and air results in high recovery rates for copper into a sulphate solution and gold during cyanidation of solid product following atmospheric oxidation with simultaneous decrease in cyanide consumption.

A Review of the Cyanidation Treatment of Copper-Gold Ores and Concentrates

Globally, copper, silver, and gold orebody grades have been dropping, and the mineralogy surrounding them has become more diversified and complex. The cyanidation process for gold production has remained dominant for over 130 years because of its selectivity and feasibility in the mining industry. For this reason, the industry has been adjusting its methods for the extraction of gold, by utilizing more efficient processes and technologies. Often, gold may be found in conjunction with copper and silver in ores and concentrates. Hence, the application of cyanide to these types of ores can present some difficulty, as the diversity of minerals found within these ores can cause the application of cyanidation to become more complicated. This paper outlines the practices, processes, and reagents proposed for the effective treatment of these ores. The primary purpose of this review paper is to present the hydrometallurgical processes that currently exist in the mining industry for the treatment of silver, copper, and gold ores, as well as concentrate treatments. In addition, this paper aims to present the most important challenges that the industry currently faces, so that future processes that are both more efficient and feasible may be established.

Investigation of Au-Ag-Cu Alloy Electrodeposition to Electromechanical Systems

Electromechanical systems, which provide electrical power and data connection between moving terminals require high conduction and erosion resistant surfaces. Transfers of electrical power and data are accomplished by the contact of drum and brush wires. The simultaneous electrochemical deposition of desired Au-Ag-Cu alloy compositions, which can be used to coat the brush wires, was investigated in this study. In the scope of the study, the static potential and cyclic voltammetry behaviours of gold, silver and copper cyanide plating baths, as well as the mixtures of binary and ternary baths were investigated to obtain suitable amount of KCN and working potential values. SEM and EDS analyses were conducted in the characterization of coated samples.

Comparison of Adsorption Properties of Activated Carbons with Different Crops Residues as Precursors for Gold Cyanide Recovery: An Iranian Gold Industry Guide

Adsorption of gold cyanide on three types of Activated Carbons (ACs) has been investigated in batch and column adsorption conditions. Applied ACs have been derived from different crops precursors i.e., coconut shell (CAC), peach stone (PAC), and walnut shell (WAC). As peach stone and walnut shells are abundant agricultural residues in Iran, the activated carbons produced from these precursors are economically preferable for the gold recovery process. The ACs were characterized using FTIR, SEM, BET, and Wet-Bed Compaction Hardness analyses. Batch equilibrium adsorption data were analyzed using the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models. Freundlich isotherm was in better agreement with the equilibrium data and the maximum adsorption capacity (40.8 mg/g) was tabulated for CAC. Adsorption kinetics was also modeled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The PAC recorded the highest removal rate in the light of better agreement of the pseudo-second-order model. Fixed-bed column experiments were carried out at different initial gold concentrations (30, 50 mg/L) to determine the characteristics of the breakthrough curves. The maximum bed capacity (37.55 mg/g) was obtained for CAC. Three dynamic adsorption models including, Thomas, Yoon–Nelson, and Adam–Bohart,were applied to describe the breakthrough curves. Both Thomas and Yoon–Nelson models were in appropriate agreement with the experimental column adsorption data. This research introduces peach stone as a promising precursor considering availability, technical features, and economical aspects for the production of AC for gold recovery from cyanide leach solutions. Results are also conducive for gold mining industries to select the appropriate activated carbon.

Flotation extraction of elemental sulfur from gold-bearing cakes

Currently, in the development of the raw materials base of the gold mining industry, there is a tendency to reduce the quality of the initial mineral raw materials due to the depletion of reserves of rich gold-bearing ores. The article discusses the technology of extraction of refractory gold-bearing concentrates based on low-temperature leaching of pyrite concentrate. A decrease in the parameters of the autoclave oxidation of sulfide minerals, such as pyrite and arsenopyrite, leads to the incomplete extraction of gold into the solution and, consequently, its losses during subsequent cyanidation. As a possible option for a more complete extraction of gold using low-temperature oxidation technology, a method of flotation separation of elemental sulfur from leaching cakes is proposed. According to the basic process flow chart, the flotation process designed for gold extraction is carried out after autoclave oxidation, but before cyanidation. A series of experiments were carried out with varying reagent conditions and the dependence of gold losses on the extraction of elemental sulfur in the flotation tailings was established. As determining factors, pH and solid content in the initial pulp were considered. The paper justifies the separation of elemental sulfur from autoclave cake to enriched sulfur concentrate. The cake flotation modes after autoclave oxidative leaching of pyrite concentrate are investigated. The distribution of elemental sulfur and gold by flotation products makes it possible to conduct the tailings cyanidation process with acceptable indicators.

Technology of Gold Extraction from Mature Dumps by Thiourea Leaching

Tajikistan has a large volume of gold-containing dumps, which on conversion to gold equals ~18 t. These dumps are products of amalgamation and cyanidation processes, resulting from treating the ores from Tarorskoe, one of the largest deposits in Tajikistan, and from a few other nearby deposits: Dzhilau, Khirskhon, and Olimpiiskoe. The mineralogical composition of the dumps is represented primarily by quartz, feldspar, and clay minerals. Their average content of gold is rather high, 2.4 g/t. Therefore, it is expedient to treat the dumps on the premises of JV Zerafshan plant (in the city of Pendzhikent, Tajikistan), which processes ores of the Tarorskoe deposit and has an unloaded technological cycle. The treatment of these dumps does not require an ore pretreatment stage, since, for the actual grain-size class (–0.074 mm, 58.11%), the content of cyanided gold is 89.7%. This work presents the results of studying the extraction of gold from the dumps by thiourea leaching. The purpose of this work is to find ways to decrease the consumption of expensive reagent thiourea. It is found that the sample of the dumps contains sorption-active minerals, which lead to the loss of gold with tails. Therefore, it is suggested that raw material should undergo a preliminary acid treatment to reduce the consumption of thiourea and sodium sulfite should be added to the pulp during carbon in thiourea leach. A high degree of extraction (~89%) is achieved when thiourea is loaded in the amount of 2 kg/t, ferric sulfate 7 kg/t, sodium sulfite 12 kg/t, and the initial concentration of sulfuric acid of 0.5% (at the stage of acid treatment). In this case, the consumption of thiourea is 0.8 kg/t. A process flow diagram for the dump treatment is proposed, which includes the following operations: preliminary acid treatment, carbon in thiourea leach, desorption, reactivation, electrolysis, and melting.

Investigation of Au-Ag-Cu Alloy Electrodeposition to Electromechanical Systems

Electromechanical systems, which provide electrical power and data connection between moving terminals, require high conduction and errosion resistant surfaces. Transference of electrical power and data are carried out by the contact of drum and brush wires. The electrochemical deposition of desired Au-Ag-Cu alloy compositions was investigated in this study. In the scope of the study, the static potential and cyclic voltammetry behaviours of gold, silver and copper cyanide plating baths, as well as the mixtures of binary and ternary baths were investigated to obtain suitable amount of KCN and working potential values. Beside SEM and EDS analyses, hardness and friction measurements were conducted in the characterization of coated samples.

Recovery of gold from mature dumps by thiourea leaching

Tajikistan has a large amount of gold-bearing dumps making up - 18 tons in gold equivalent. These dumps are tails of amalgamation and cyanidation processes obtained in the processing of ores from the largest deposit in Tajikistan - Tarorskoe and a number of adjacent deposits - Jilau, Khirskhon, Olimpiyskoe. In terms of their mineralogical composition, dumps consist primarily of quartz, feldspar, and clay minerals. Average gold content in them is quite high - 2.4 g/t. Therefore, it is feasible to involve them in processing based on the existing Joint Venture «Zarafshon» plant (Penjikent, Tajikistan) processing ores from the Tarorskoe deposit and having underutilized process capacity. These dumps require no ore preparation for processing as the cyanided gold content is 89.7 % at the existing grain size class (-0.074 mm, 58.11 %). This article presents the results of studies on gold extraction from dumps by thiourea leaching. The paper is aimed at searching for ways to reduce the consumption of an expensive component - thiourea. It was found that dump samples contain sorption-active minerals that lead to the loss of gold with tails. In this regard, it is proposed to conduct gold sorption leaching. It was established that thiourea consumption can be reduced by acid pretreatment of raw materials with Na 2 SO 4 added to pulp during the thiourea leaching process. A high degree of extraction (-89 %) is achieved when loading 2 kg/t of thiourea, 7 kg/t of ferrous sulfate (III), 12 kg/t Na 2 SO 4 and the initial concentration of sulfuric acid of 0.5 % (at the stage of acid pretreatment). Thus, the thiourea consumption is 0.8 kg/t. A dump processing flow chart is presented that includes the following operations: acid pretreatment, thiourea sorption leaching, desorption, reactivation, electrolysis, and melting.

HCN emission by a Polydesmid Millipede Detected Remotely by Reactive Adsorption on Gold Nanoparticles Followed by Laser Desorption/Ionization Mass Spectrometry (LDI-MS).

Hydrocyanic acid (HCN) is a well-known defensive allomone in the chemical arsenal of millipedes in the order Polydesmida. The presence of HCN in the headspace vapor of adult Xystocheir dissecta (Wood, 1867), a common millipede from the San Francisco Bay Area, was traced by laser desorption/ionization-mass spectrometry (LDI-MS). To accomplish this, the headspace vapor surrounding caged, live millipedes was allowed to diffuse passively over gold-nanoparticle (AuNP) deposits placed at various distances from the emitting source. The stainless steel plates with AuNP deposits were removed and irradiated by a 355-nm laser. The gaseous ions generated in this way were detected by time-of-flight mass spectrometry. The intensity of the mass spectrometric peak detected at m/z 249 for the Au(CN)2- complex anion was compared to that of the residual Au- signal (m/z 197). Using this procedure, HCN vapors produced by the live millipedes could be detected up to 50 cm away from the source. Furthermore, the addition of H2O2, as an internal oxygen source for the gold cyanidation reaction that takes place in the AuNP deposits, significantly increased the detection sensitivity. Using the modified H2O2 addition procedure, HCN could now be detected at 80 cm from the source. Moreover, we found a decreasing intensity ratio of the Au(CN)2-/Au- signals as the distance from the emitting source increased, following an exponential-decay distribution as predicted by Fick's law of diffusion. Graphical abstract.

EDTA-enhanced cyanidation of refractory bio-oxidised flotation gold concentrates

In this paper, ethylenediaminetetraacetic acid (EDTA) was used to activate refractory bio-oxidised flotation gold concentrate and improve gold extraction efficacy during alkaline cyanide leaching. The results showed that EDTA activation influences physico-chemical properties such as particle size distribution, surface area and mineralogy, rate and yield of gold leaching, and overall reagent (sodium cyanide and sodium hydroxide) consumption. Specifically, EDTA activation reduced the particle size and increased BET surface area by eliminating refractory secondary sulphate minerals such as gypsum and jarosite prior to /or during alkaline cyanide leaching. The proposed gold extraction enhancement mechanism included disintegration of gold-encapsulating gangue mineral agglomerates, and elimination of thin film refractory jarosite and gypsum coatings from gold surfaces, leading to easy cyanide access to gold. Lower sodium cyanide and sodium hydroxide consumption during alkaline cyanide leaching were also observed for leaching systems involving EDTA compared with the as-received bio-oxidised flotation concentrate leaching. The results show good promise for designing smarter processing routes targeting higher gold extraction from complex, refractory ore mineralogy.

Chitosan-polyacrylamide graft copolymers prepared with gamma irradiation for gold cyanide adsorption

ABSTRACT Cyanidation is one important process in gold mining industries that required proper methods for gold recovery. The present study aims to explore gold cyanide adsorption using chitosan-polyacrylamide graft copolymers synthesized by gamma irradiation. The effects of pH, gold cyanide concentration, and adsorption time were evaluated. The FTIR analysis shows that grafting of polyacrylamide onto chitosan has been obtained. The results indicated that pH value of 7 had the highest adsorption capacity. It was found that the adsorption capacity increases with increasing gold cyanide concentration and adsorption time. The maximum adsorption capacity was 10.18 mg/g at pH 7, gold cyanide concentration 100 ppm, and adsorption time 100 minutes. Adsorption kinetic studies were also carried out and the experimental data were highest fitted to a zero-order with the rate constant, i.e., 0.3327 ppm.min−1. The Freundlich isotherm model was best suitable for this experiment. Recovery studies had been done with cyanide-NaOH and desorption for gold cyanide released from the adsorbent was obtained up to 18.70%. This research represents a promising application of chitosan-polyacrylamide graft copolymers for the gold adsorbent.

A mechanism of metastable sulfur speciation and the adsorption on a gold surface in the presence of sulfidic ore and lead in cyanide medium

Metallic gold or gold minerals have high affinity towards aqueous sulfur species during gold leaching process in cyanide solutions, thus the gold surface can often become passivated by the reaction between the different sulfur species and gold. During the cyanide leaching of sulfidic gold ores, the sulfide minerals dissolve into the leach solution and produce metastable sulfur species, such as sulfide, bisulfide, polysulfide, elemental sulfur, and thiocyanate. Most of the above sulfur species can directly passivate the gold surface, and significantly reduce the gold leaching efficiency.This paper pertains to studying the sulfur species formation in cyanide solutions and their adsorption chemistry and mechanism on gold surface. It was found that the lead salts, often added to the cyanidation process to improve the gold leaching efficiency, act as a sulfide oxidant and accelerates its oxidation to different metastable sulfur species. It was shown by electrochemical linear sweep voltammetry (LSV) tests that the gold oxidation current density, i.e. oxidation kinetics, was decreased 32%, from 2.20 to 1.50 mA/cm2, in the presence of a high sulfide ore by increasing the amount of lead salt from 0 to 50 mg/L at 300 mg/L free cyanide (300 mg/L CN). Monosulfide, disulfide and polysulfide sulfur species were detected on the gold surface, by X-ray photoelectron spectroscopy (XPS) method, confirming the adsorption of different sulfur species on the gold surface. At high concentration of added lead, 50 mg/L Pb2+, even elemental sulfur was shown to adsorb on the gold surface. The formation of different sulfur species was explored by thermodynamic modeling, which showed very good agreement with the results of the XPS study. This study helps to develop a better insight on the mechanism of gold surface passivation caused by sulfur species and the findings help to reduce gold passivation by better control of the process condition.