Desorption Of Gold Research Articles

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.

Development of complete hydrometallurgical processes for gold recovery from ICs and CPUs using ionic liquids

Integrated circuits (ICs) and central processing units (CPUs), essential components of electrical and electronic equipment (EEE), are complex composite materials rich in recyclable high-value strategic and critical metals, with many in concentrations higher than in their natural ores. With gold the most valuable metal present, increase in demand for gold for EEE and its limited availability have led to a steep rise in the market price of gold, making gold recycling a high priority to meet demand. To overcome the limitations associated with conventional technologies for recycling e-waste, the use of greener technologies (ionic liquids (ILs) as leaching agents), offers greater potential for the recovery of gold from e-waste components. While previous studies have demonstrated the efficiency and feasibility of using ILs for gold recovery, these works predominantly concentrate on the extraction stage and often utilise simulated solutions, lacking the implementation of a complete process validated with real samples to effectively assess its overall effectiveness. In this work, a simulated Model Test System was used to determine the optimal leaching and extraction conditions before application to real samples. With copper being the most abundant metal in the e-waste fractions, to access the gold necessitated a two-stage pre-treatment (nitric acid leaching followed by aqua regia leaching) to ensure complete removal of copper and deliver a gold-enriched leach liquor. Gold extraction from the leach liquor was achieved by liquid-liquid extraction using Cyphos 101 (0.1 M in toluene with an O:A = 1:1, 20 °C, 150 rpm, and 15 min) and as a second process by sorption extraction with loaded resins (Amberlite XAD-7 with 300 mg of Cyphos 101/g of resins at 20 °C, 150 rpm and 3 h). In both processes, complete stripping and desorption of gold was achieved (0.5 M thiourea in 0.5 M HCl) and gold recovered, as nanoparticles of purity ≥95%, via a reduction step using a sodium borohydride solution (0.1 M NaBH4 in 0.1 M NaOH). These two hydrometallurgical processes developed can achieve overall efficiencies of ≥95% for gold recovery from real e-waste components, permit the reuse of the IL and resins up to five consecutive times, and offer a promising approach for recovery from any e-waste stream rich in gold.

Energy-efficient electrochemical recovery of gold enabled by a thiourea-based electrolyte system

The application of non-cyanide baths in electroplating for gold recovery has drawn significant attention due to their clear benefits on the environment and human health. Among these alternatives, thiourea has emerged as a promising non-cyanide bath, and yet high energy and reagent consumption has impeded its widespread adoption. Herein, an energy-efficient gold recovery process via electroplating was developed to reduce bath depletion. The redox potentials of gold deposition using thiourea electrolyte were examined through linear sweep voltammetry, and the consumed energy during the electrochemical plating of gold was quantified. The gold deposition was achieved in the two-electrode system enabling a 97% recovery under 0.3 V of the cell voltage. The proposed system exhibited a significant reduction in energy consumption to 0.129 kWh∙kg−1, implying that the oxidation of free thiourea on the anode mainly contributed to the decrease in the applied voltage and energy. Furthermore, the suppression of the bath consumption was evaluated compared with electroless plating, another reliable deposition process, throughout monitoring gold desorption and deposition efficiencies during the cyclic use of thiourea. The retardation of the sorbent consumption was observed in the electroplating during the consecutive cycles, which inferred that the reduction of its oxidized form, formamidine disulfide, led to the regeneration of the agent on the cathode. Thus, the suggested electroplating process with a gold-thiourea bath shows great potential as a workable means of gold recovery from an economic standpoint with its low energy and sorbent consumption to realize the commercialization of urban mining in the electronic industry.

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.

Optimization of selective gold recovery from electronic wastes through hydrometallurgy and adsorption

The feasibility of hydrometallurgy for metal extraction from electronic wastes was investigated in the current work. Samples were ground and preliminary extracted by nitric acid and aqua regia. The gold concentrations in nitric acid and aqua regia were measured as 1.82 mg L1 and 29.45 mg L1, respectively. In addition, extraction performances using Cl2 (oxidizer) were studied. Experiments were conducted by connecting an extraction reactor to an oxidizing electro-generator. It was found that copper and gold were mostly extracted by adjusting different extraction conditions, such as extraction time, HCl concentration, extraction temperature, current density, particle size range, sample mass (solution density), and stirring speed. Two specific extraction steps were employed to selectively extract copper and gold. It was detected that 98.1 % of copper was extracted using the first extraction step twice, whereas, in the final step, 95.1 % of gold was extracted from the residue sample of the first step. The gold recovery performances of five different resins were investigated, and IRA402 Cl and HPR9700 resins manifested the highest adsorption ability and selectivity. The adsorption mechanism was found to be a monolayer adsorption process, and the adsorption capacities of IRA402 Cl and HPR9700 resins reached 303.8 mg g1 and 295.4 mg g1, respectively. Finally, gold desorption from these resins was successfully performed using an acetone-HCl mixture as the eluent. Reusability tests revealed that these two resins could be reused at least 6–7 times with an adsorption capacity loss of less than 10 %.

Making untreated carbon effective in cleaner thiosulfate system: A new and high-efficiency method including gold adsorption and desorption

Compared with the cyanide method, the thiosulfate method is a green and clean gold production method, while gold recovery from thiosulfate solution is pending. Although the activated carbon adsorption method has been highlighted, current studies cannot avoid the complexity of activated carbon modification. This study used thiosemicarbazide (TSC) as the additive of the gold solution, investigating the gold recovery performance of pristine activated carbon and its adsorption mechanism. As a result, even for containing gold 100 mg/L, gold adsorption percentage close to 100% could be achieved on original carbon within 12 h when adding 0.02 g TSC. Next, under the optimal conditions, gold loading amount of 42.6 kg/t was attained after five-stage adsorption. Characterization via XPS, FT-IR, BET, and UV–vis verified the gold adsorption mechanism was related to TSC's decomposition into SCN− under activated carbon's catalysis, the formation of Au(SCN)2- and whose adsorption on the surface of original carbon. Furthermore, it was found that this method exhibited well gold recovery ability (99%) for gold in both Cu2+-en-S2O32− and Cu2+-NH3-S2O32− solutions; Additionally, well gold recovery performance (99%) was also achieved for two leaching solutions (Au: 35 and 42 mg/L, Cu2+: 3178 mg/L) of an actual ore. Last, gold desorption studies indicated that a good gold desorption rate of 95.3% was achieved within 24 h for carbon containing 5 kg/t of gold when using N, N-dimethylformamide (DMF) as desorbent. This paper gifted untreated activated carbon with excellent adsorption ability towards gold in thiosulfate system for the first time, which is meaningful for the cleaner production gold.

Kazmekhanobr's technologies in the field of processing of low-grade gold-bearing ores and technogenic raw materials

The Republic of Kazakhstan has been increasing gold production annually for the last 10–15 years. According to the results of 2019, Kazakhstan ranks 13th in the world in terms of gold production (77 tons), in terms of reserves — 16th in the world (377.5 tons). The article presents information about the innovative developments of Kazmekhanobr in the field of processing of poor goldbearing ores and man-made raw materials. Information on implemented technologies and projects in Kazakhstan for recent years is given. Kazmekhanobr’s deve lopments cover the whole complex of technological stages of processing of poor gold-bearing ores and man-made raw materials by heap leaching technology: ore preparation, leaching process, sor ption extraction of gold from productive solutions, desorption of gold from saturated sorbents and electrolytic extraction of gold from rich eluates. In particular, the company for the first time in Kazakhstan in 1998 developed and implemented pre-pelleting of ore and laying it in a pile leaching stack using a stacker at the mines “Suzdal”, “Mukur”, “Mizek”, “Komarovsky”, etc. It was also developed the highly efficient innovative technology of gold heap leaching from poor gold-bearing ores, complex gold-copper ores and technogenic wastes, which is characterized by low consumption of water and reagents and accordingly low negative load on the environment at the mines “Zhanan”, “Mukur”, “Miyali” “Balazhal”, “Aksu”,“Bestyube”,“Uzboy”, etc. Patents were obtained and a three-stage cascade scheme of sorption extraction of gold by ion exchange resin, original design of sorption columns and binding of columns were introduced, which allowed to maximize the heap leaching process and increase its efficiency, minimize processes of resin pumping processes and, accordingly, the mechanical impact on them, will increase saturation of the resin with gold and reduce the turnover of gold with working solutions at the Zhaltyrbulak, Uzboy, Vasilyevskoye deposits. Innovative processes of highefficiency technology of gold desorption and ion exchange resin regeneration, electrolytic extraction of gold from commodity regenerates have been introduced, in which the duration of gold desorption and resin regeneration together with gold electrolysis does not exceed 18–24 h. According to the projects developed by Kazmekhanobr with the use of innovative technologies, plants for the production of Dore alloy in Ust-Kamenogorsk, Semey and Stepnogorsk, Makmala (Kyrgyzstan) and the Asi gold mining plant (China) were built and successfully operate.

The first effective utilization of activated carbon in gold thiosulfate system: A more eco-friendly, easier method for gold recovery and material regeneration

Employing activated carbon in the thiosulfate process has high potential applications for extracting gold. However, formidable challenges must be overcome to achieve such an application in an efficient and eco-friendly manner. Accordingly, this study aimed to develop a simple and environmentally friendly method for gold extraction. To this end, activated carbon with good gold capacity (15.9 kg/t) was synthesised for the first time by impregnating green reagent 1-methyl-5-mercapto-1,2,3,4-tetrazole (MMT), which can thermally decompose into a gas completely, and the mechanisms of adsorption and desorption process were studied. Acceptable desorption efficiency (nearly 100% in 12 h) was achieved for gold on activated carbon using environmentally safe and low-cost thiosulfate salt. More importantly, after gold desorption, the good gold adsorption performance (gold capacity of 13.8 kg/t) of activated carbon could be restored by treating it again with MMT. Additionally, green thiosulfate could be used not only as a leaching agent but as a desorbent for gold. Moreover, the results suggest that gold adsorption on MMT-AC takes place through a ligand exchange mechanism. Overall, the method reported herein exhibits good gold adsorption-desorption performance, while offering environmental friendliness and simplicity. With these achievements, this study is expected to accelerate the development of the expected potentially more environmentally friendly technology.

Gold recovery using porphyrin-based polymer from electronic wastes: Gold desorption and adsorbent regeneration

Electronic wastes containing precious metals have great potential as a sustainable source of such metals. Separation and refining, however, remain complicated, and none of the existing technologies have yet experienced commercialization. A novel porphyrin-based porous polymer, named COP-180, was recently introduced as a powerful adsorbent option, especially for gold, and in this study, aspects of desorption and recovery of adsorbed gold and regeneration of the polymer were investigated. A hydrometallurgical method using non-cyanide leaching agents was developed, and an acid thiourea-based solution was found to be particularly suited for the method based on COP-180 with gold desorption efficiency of 97%. Fourier-transform infrared spectroscopy spectra demonstrated the unaffected structure of COP-180 after desorption, implying the potential of its reuse. This high desorption efficiency was achieved even without typical aiding agents by means of a formamidine disulfide-mediated route that prevented thiourea consumption, which is considered a major drawback of the otherwise promising reagent. Using this method, the polymer was able to maintain more than 94% desorption efficiency after five times of regeneration. The results suggest that acid thiourea can offer a workable means of recovering gold particularly from the excellent gold-adsorbent of COP-180, and that repeated regeneration is also possible.

Development and identification of a mathematical model of the process of continuous autoclave desorption of noble metals in moving-bed apparatus

The process of continuous autoclave desorption is the most promising for the intensification of coal-sorption technology for extracting noble metals by active carbons from solutions and pulps. The article presents a mathematical model of continuous autoclave desorption of gold from active carbons, which is based on the physicochemical regularities of the process and describes its dynamics. The developed mathematical model of the dynamics of the continuous desorption process allows analyzing the influence of the main parameters on the degree of extraction of gold and silver from activated carbons. It has been established that such parameters as temperature, phase ratio, processing time and pH of the elution solution have the greatest influence. Identification of the mathematical model showed satisfactory agreement between the experimental and the data obtained as a result of the simulation, which confirms the possibility of using it for analyzing and optimizing the process.

Understanding the mechanism behind high-temperature desorption of gold from activated carbon using the process model

Understanding the mechanism behind high-temperature desorption of gold from activated carbon using the process model

Mesoporous Silica-gold Films for Straightforward, Highly Reproducible Monitoring of Mercury Traces in Water.

Trace-level detection of mercury in waters is connected with several complications including complex multistep analysis routines, applying additional, harmful reagents increasing the risk of contamination, and the need for expensive analysis equipment. Here, we present a straightforward reagent-free approach for mercury trace determination using a novel thin film sampling stick for passive sampling based on gold nanoparticles. The nanoparticles supported on a silicon wafer and further covered with a thin layer of mesoporous silica. The mesoporous silica layer is acting as a protection layer preventing gold desorption upon exposure to water. The gold nanoparticles are created by thermal treatment of a homogenous gold layer on silicon wafer prepared by vacuum evaporation. This gold-covered substrate is subsequently covered by a layer of mesoporous silica through dip-coating. Dissolved mercury ions are extracted from a water sample, e.g., river water, by incorporation into the gold matrix in a diffusion-controlled manner. Thus, the amount of mercury accumulated during sampling depends on the mercury concentration of the water sample, the accumulation time, as well as the size of the substrate. Therefore, the experimental conditions can be chosen to fit any given mercury concentration level without loss of sensitivity. Determination of the mercury amount collected on the stick is performed after thermal desorption of mercury in the gas phase using atomic fluorescence spectrometry. Furthermore, the substrates can be re-used several tens of times without any loss of performance, and the batch-to-batch variations are minimal. Therefore, the nanogold-mesoporous silica sampling substrates allow for highly sensitive, simple, and reagent-free determination of mercury trace concentrations in waters, which should also be applicable for on-site analysis. Successful validation of the method was shown by measurement of mercury concentration in the certified reference material ORMS-5, a river water.

Combined technology for gold desorption and ionite regeneration in the conical device

The principal technological scheme of desorption of gold and concomitant metal-impurities from the AM-2B resin phase used for the sorption processing of gold-bearing ores is considered. The proposed combined scheme, involving the use of two traditional, independent from each other methods (thiocyanate and acid-thiourea) for eluting gold, includes desorption of metal impurities from the resin with alkaline solutions of sodium thiocyanate, and gold with sulfuric acid solutions of thiourea. To shorten the duration of the process research of proposed technology was carried out the in a conical apparatus. The results of study of the elution of gold and impurity metals from anionite saturated with the following components, mg/g: Au – 2.6; Cu – 3.5; Zn – 1.3; Ni – 2.9; Co – 3.3, are given. It is shown that the main amount of impurity metals is desorbed from the resin upon its thiocyanate treatment, while the transition of gold into the eluate is negligible. The composition of the eluate in the thiocyanate treatment of saturated resin is, mg/l: Au – 1.7; Cu – 156.0; Zn – 53.0; Ni – 89.0; Co – 102.0. The subsequent treatment of the resin with sulfuric acid solutions of thiourea allows the conversion of 89.32 % of gold from the ion exchanger into the eluate. The resulting eluates containing ~113.0 mg/l gold and a small amount of impurities are target solutions for obtaining a valuable metal. The ion exchanger was regenerated by washing with water and treating with an alkaline solution of sodium to convert it to OH form, since gold sorption is carried out from alkaline cyanide solutions of heap leaching. Residual contents of components in the resin after regeneration were, mg/g: Au – 0.24; Cu – 0.23; Zn – 0.15; Ni – 0.07; Co – 1.29, which allows the successful use of the regenerated resin in the next stage of sorption.

Adsorption of gold ion from a solution using montmorillonite/alginate composite

Quaternary ammonium salt was added to enhance the layer separation of the montmorillonite. This montmorillonite was used to prepare montmorillonite/alginate composite, which were evaluated as an adsorbent of gold ion. The results revealed that the optimum conditions for the maximum gold ion remove with montmorillonite/alginate composite: montmorillonite concentration of 6 wt%, contact time of 90 min, pH of 3, and adsorbent dose of 5 g. The equilibrium data were fitted Langmuir and Freundlich isotherm models and adsorption capacity was 1.49 mg/g. The adsorption kinetic followed the pseudo second order model. The gold desorption that occurred at pH 3 was 18.6%.

The choice of criterion and structure of the optimal control system for periodic process of high-temperature gold desorption from active coals

The choice of criterion and structure of the optimal control system for periodic process of high-temperature gold desorption from active coals

Desorption of gold and silver from activated carbon

Experiments of gold and silver elution were conducted using several parameters, either fixed or varying parameters. Ethanol volume, temperature and percent solid belonged to varying parameters while loaded carbon, stirring rate, concentrations of NaOH and NaCN served as fixed parameters. The experiment results showed that the optimum condition for such a process included 20% of ethanol volume, 80°C of temperature and solid fraction of 25%. Using such condition, the experiment was conducted for 10-hour contact time and yielded the highest desorption percentages for gold and silver, namely 80.10 and 70.73% respectively. The derived contents of gold and silver were 295.16 and 159.38 ppm while their achieved weights were 56.080 and 30.601 µ g. The fact that the achieved contents of gold and silver was close to the requirements for electrowinning process, it is suggested that the next process using a semi-continue one in terms of gaining a result that satisfies the requirement for electrowinning.

Developing a mathematical model of dynamics of high-temperature gold desorption from active coals on the basis of physiochemical conceptions about the process

Developing a mathematical model of dynamics of high-temperature gold desorption from active coals on the basis of physiochemical conceptions about the process

Activated carbons of varied nature in recovery of gold

Morphology and structure of activated carbons produced from a wide variety of carbon-containing vegetable and mineral raw materials were studied and their physicochemical characteristics were determined. The sorption of gold from industrial solutions with various pH values with activated carbons based on birch wood, coconut shells, and even shungite was examined. Results obtained in desorption of gold from activated carbons with a NaOH solution are presented.

2-Aminothiazole Functionalized Polystyrene for Selective Removal of Au(III) in Aqueous Solutions

A new chelating resin, polystyrene-2-aminothiazole (PS-AT), was synthesized via one-step reaction by grafting 2-aminothiazole in a chloromethylated polystyrene polymer. Its structure was characterized by elemental analysis and infrared spectroscopy. Batch experiments were applied to investigate the adsorption properties of PS-AT for Au(III) ions. The resin exhibits an excellent selectivity for Au(III) ions in the presence of Ni(II), Cu(II), Cd(II), and Co(II) ions. The maximum adsorption capacity obtained at 308 K was 733.8 mg/g. The adsorption kinetic and equilibrium data were well fitted to the pseudo-second-order model and the Langmuir isotherm model, respectively. Desorption of gold from the resin can be achieved using 60 mL of 2 mol/L HCl-10% thiourea solution with a desorption ratio of 93.8%. The XPS data, along with IR spectra, revealed that gold was adsorbed on the surface of PS-AT in the form of chloride, and nitrogen and sulfur were involved in the chelation of gold chloride.

Role of Surface-Bound Intermediates in the Oxygen-Assisted Synthesis of Amides by Metallic Silver and Gold

A general mechanism for the oxygen-assisted synthesis of amides over metallic gold and silver surfaces has been derived from the study of acetaldehyde and dimethylamine in combination with previous work, allowing detailed comparison of the two surfaces' reactivities. Facile acetylation of dimethylamine by acetaldehyde occurs with high selectivity on oxygen-covered silver and gold (111) crystals via a common overall mechanism with different rate-limiting steps on the two metals. Adsorbed atomic oxygen activates the N-H bond of the amine leading to the formation of an adsorbed amide, which attacks the carbonyl carbon of the aldehyde, forming an adsorbed hemiaminal. Because aldehydes are known to form readily from partial oxidation of alcohols, our mechanism also provides insight into the related catalytic coupling of alcohols and amines. The hemiaminal β-H eliminates to form the coupled amide product. On silver, β-H elimination from the hemiaminal is rate-limiting, whereas on gold desorption of the amide is the slow step. Silver exhibits high selectivity for the coupling reaction for adsorbed oxygen concentrations between 0.01 and 0.1 monolayer, whereas gold exhibits selectivity more strongly dependent on oxygen coverage, approaching 100% at 0.03 monolayer. The selectivity trends and difference in rate-limiting steps are likely due to the influence of the relative stability of the adsorbed hydroxyl groups on the two surfaces. Low surface coverages of oxygen lead to the highest selectivity. This study provides a general framework for the oxygen-assisted coupling of alcohols and aldehydes with amines over gold- and silver-based catalysts in either the vapor or the liquid phase.