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![Figure 1. Gold production amount (t) and corresponding gold price ($) [1].](profile/Bernd-Friedrich-2/publication/306311080/figure/fig1/AS:663064261173261@1535098247821/Gold-production-amount-t-and-corresponding-gold-price-1_Q320.jpg)
The importance of gold recovery from low grade ores and flotation tailings is continuously increasing due to raising gold demand and thereby high gold prices. However, due to raising social awareness of the ecological impacts of cyanidic gold extraction and environ-mental specifications, the development and the implementation of alternative hydrome...
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Raising social awareness and environmental specifications on cyanide application force gold industry to search for alternative leaching reagents. therefore, researchers worldwide investigate cyanide alternatives for gold recovery since several decades. often the research activities cannot be compared directly, since different input materials and ex...
This article presents the raw data of silver concentration ([Ag]) obtained as a function of time (t) from silver leaching experiments, which were conducted using a synthetic sodium-silver jarosite and different complexing agents: thiosulfate, thiocyanate, and cyanide. Leaching experiments were performed under different conditions of temperature, pH...
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... Usually, the leaching of precious metals is carried out using cyanide solutions, which is associated with a significant deterioration of the environmental situation. To replace them in the process of utilization of man-made placers, we propose to use thiocarbamide solutions [1,2]. ...
Generalization of the obtained materials leads to the conclusion that a significant amount of useful components has been accumulated in the man-made placers of Primorye (south of the Russian Far East), at the same time they pose a considerable threat to the environment. Using the example of the gold mining dumps of the Fadeevsky node, ways to solve this problem are outlined. The essence of the new approach is to implement a scheme of rational environmental management, which allows: 1- to recover precious metals (Au, platinum group elements) and demercurize man-made placers by liquid extraction from thiocarbamide leaching solutions; 2- to obtain raw materials for non-traditional industries in gold mining (powder metallurgy, titanium production, road and civil engineering). The involvement of manmade placers in the production sector will have a beneficial effect on the environmental situation in densely populated areas, and will also contribute to meeting the growing needs of the region for precious metals.
... However, the process is reported to impose environmental, health, and safety challenges due to the high toxicity of cyanide (Hilson and Monhemius, 2006). Alternative reagents for gold leaching, such as thiourea, thiosulfate, halide, and thiocyanate that are more environmentally benign have been investigated over the past few decades and have been reported in several reviews (Aylmore, 2016;Gökelma et al., 2016;Hilson and Monhemius, 2006;Prasad et al., 1991). The thiosulfate process is the most developed alternative method for gold leaching, albeit having its technical challenges. ...
The Southern African region contains abundant gold tailing heaps that are an environmental concern due to dust pollution and chemical contamination of nearby water bodies. Nevertheless, these heaps contain gold with potential to be extracted for financial gain. In this study, the feasibility of extraction of gold from a Witwatersrand gold tailings using glycine was investigated using a two-level full factorial design. Effects of variables such as glycine concentration at levels of 0.5-1.5 M with a solid-liquid ratio of 50-200 g/L were investigated. Although the solid-liquid ratio used in this study was below the industrial norm, it provides a starting point for investigating the applicability of this technology. To enhance the gold extraction, potassium permanganate pretreatment and copper ion addition were adopted. The results revealed that 91.4% gold extraction was achieved after 24 h pre-treatment of the tailings using 2 g/L potassium permanganate followed by subsequent leaching using 1.5 M glycine at pH 12, with 50 g/L solid-liquid ratio and 2 g/L copper ions. Statistically, the solid-liquid ratio and potassium permanganate pre-treatment of the tailings were found to be significant at 95% confidence interval, whilst interactions of copper ions and glycine concentration were significant factors. The work demonstrates that potassium permanganate pre-treatment prior to glycine leaching of low-grade secondary gold resources, such as tailings, can be beneficial. Furthermore, the methodology developed in this work provides an opportunity for further investigation of the recovery of gold hosted in complex mineralogical matrices.
... The extraction of gold in Brazil began with the searches for precious metals in the time of colony, being initially in the region of Minas Gerais. At this time, gold was removed from superficial deposits and alluvion, being enriched and found in the form of large particles (Gökelma et al., 2016;Júnior, 2018;ANM, 2023). ...
Cyanide is used in several industries but is widely used for gold extraction due to its ability to complex and stabilize gold ions. The waste generated from this process is of great volume because of low ore grades that requires more processing areas. Also, it is highly toxic due to cyanide being a contaminant of animal life and the environment. The mining sector can recycle the effluents generated in their processes, however, this can affect the gold extraction and treatment methods. There are legal laws that define cyanide levels in effluents for disposal in water bodies. Methodologies for reaching these levels include oxidation degradation processes, physical-chemical, biological processes, adsorption, photocatalysis, among others. In this present review, the use of cyanide in gold mining and some of these methodologies for removing cyanide in effluents generated by gold processing are evaluated.
... The outstanding chemi cal resistance of gold is a disadvantage in hydrometallurgical processes due to the difficulties in f inding reagents which can easily dissolve gold. The reagents which can dissolve the gold, like cy anide, chloride or sulfur complexes, are mostly aggressive and very toxic ( Gökelma et al, 2016). ...
... The environmental impact is not the only problem which raises th e demand for new extraction technologies. There are other disadvantages of cyanide leaching, suc h as big losses in the processing of preg-robbing ores (Gökelma et al, 2016). ...
... from the literature that cyanide and oxygen work as ligand and oxidant respectively an d both play vital roles in the gold and silver extractions. Many theories have been proposed to ex plain the mechanism of gold dissolution in aqueous(Akcil, 2002;Xianwen et al., 2012; Xie, 200 9;Gökelma et al., 2016) from which the overall reaction was derived and confirmed by Elsner's as follows:4Au + 8NaCN + O2 + 2H2O = 4NaAu (CN) 2 + 4NaOH ………………………….(3)In this redox process, oxygen removes four electrons from the gold simultaneous with the transfe r of protons (H + ) from water.Hydrolysis of cyanide ions: CN + H2O = HCN + OH ……………………………...(4) ...
The recovery of gold concentrates has mainly been carried out by processes such as gravity concentration, amalgamation, and cyanidation. The latter processes use chemical reagents which pose extensive detrimental effects on the ecosystem; hence, the need to explore alternative methods of gold recovery while enhancing environmental sustainability. One such method is coal gold agglomeration (CGA) assisted flotation. This research employed the CGA assisted flotation method
to recover gold concentrates from the Iperindo-Ilesha lode gold deposit, Osun State, Nigeria. Five (5) kg crude gold ore was sourced, comminuted and characterized. About 3.2 kg of coal sourced from Onyeama-Enugu was subjected to proximate analysis. Coal-gold agglomeration (CGA) assisted flotation process was carried out using conventional reagents while varying oil-coal ratio and collector (potassium amyl xanthate – PAX) dosage at constant stirring speed and coal particle
size of 1600 rpm and 500 μm respectively. Chemical analysis results revealed that the run-of-mines assayed 4.10 ppm. The scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDX) analysis revealed that the surface of the bulk ore has a rough topography of mineral particles sparsely distributed abroad the ore matrix. The presence of gold within the ore matrix and high concentration of silica was confirmed. The X-ray diffractometry result also revealed that quartz
was predominant in the ore matrix alongside trace associated minerals such as dolomite (CaMg(CO3)2), sylvanite ((Au,Ag)Te4), and annite (KFe32+AlSi3O10(OH)2). The estimated work index of the ore was 10.78 kWh/ton. The proximate analysis of coal samples showed a volatile matter content of 27.34 wt. %, 1.95 % moisture content, 14.50 % ash content and 56.21 % fixed carbon. An optimal gold grade of 150 ppm and % gold recovery of 76.46 % was obtained at an oilcoal ratio of 0.1 by weight, PAX dosage of 0.3 g, stirring speed of 1600 rpm, and 500 μm coal particle size. At this optimal value, the enrichment and concentration ratios were 1.45 and 1.90 respectively which also attest to the optimal efficiency of the CGA process. Conclusively, the applicability of CGA to the processing of Iperindo-Ilesha gold deposit was viable.
... In general, the successful implementation of waste management strategies is contingent upon the existence of industrial methods for recovering materials from wastes. While significant progress has been made in recent years, many of these methods are not yet industrialized (Kumar and Yaashikaa, 2020;Abdelbasir et al., 2018), and some are restricted due to environmental regulations (Gökelma et al., 2016;Hao et al., 2020). Consequently, the development of appropriate methods that mitigate pollution remains crucial. ...
... Gold nanoparticles (AuNPs), due to their outstanding characteristics, such as low contact electrical resistance, excellent electrical conductivity, and exceptional corrosion resistance, have been widely used in optoelectronics, electrochemistry, catalysis, biosensors, antibacterial applications, etc. [1][2][3]. However, being one of the rarest elements on earth, the mining of gold (Au) is extremely costly. ...
A novel porous gold polymer composite was prepared by the functionalization of a glycidyl methacrylate-based copolymer (pGME) with ethylene diamine (pGME-en), and activation by gold (pGME-en/Au), in a simple batch adsorption procedure in an acid solution, at room temperature. Detailed characterization of the pGME-en before and after activation was performed. The main focuses of this research were the design of a method that can enable the recovery of gold and the reuse of this multipurpose sorbent as an antimicrobial agent. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis pointed out amine groups as the primary binding sites for Au activation, while hydroxyl groups also contributed to the chelation reaction. pGME-en exhibited fast gold adsorption with an adsorption half-time of 5 min and an equilibrium time of 30 min. The maximal adsorption capacity was about 187 mg/g. The analysis of sorption experimental data with a non-linear surface reaction and diffusion-based kinetic models revealed the pseudo-second-order and Avrami model as the best fit, with unambiguous control by liquid film and intra-particle diffusion. The biological activity studies against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Candida albicans revealed moderate activity of pGME-en/Au against different bacterial and fungal species. pGME-en/Au was stable in a saline solution, with a release of approximately 2.3 mg/g after 24 h.
... The pressure oxidation method requires a corrosion-resistant autoclave and is carried out at high pressure. The bio-oxidation process generally requires a relatively long time, which hinders achieving production capacity (Gökelma et al., 2016). Ultrasound pretreatment requires an external heat energy source and a reagent as an oxidizing agent. ...
... The hydrometallurgical process involves principally the dissolution of minerals in an acidic and/or basic aqueous medium, followed by extracting the target metals [46]. Typically, industrial leaching solutions environmentally benign (non-toxic), and compatible with sulfidic refractory gold ores/mine tailings [16,14]. ...
Environmental concerns about the traditional gold extraction process, and the potential volume of encapsulated
gold in sulfidic minerals i.e. pyrite, have motivated researchers to find effective, efficient and ecologically benign
ways to expose the enclosed gold for improved extraction. Neoteric deep eutectic solvents (DESs) are an analogue
of ionic liquids (ILs) which are gaining more attention as eco-friendly solvents. This study examined the viability
of pyrite dissolution in a DES comprised of choline chloride (ChCl) and ethylene glycol (EG), called Ethaline. The
pH of the ethaline solvent mixed with hydrogen peroxide oxidant, and different solid-to-liquid ratios were
examined. Ethaline solution with pH 8 provided the desired condition at which EG is deprotonated to
[C2H4O2]2 , a favourable ligand for Fe complexation and thus pyrite dissolution. A solid-to-liquid ratio of 1/20 was optimal and achieved 23.6% Fe extraction as an indication of pyrite dissolution. Density functional theory (DFT) was applied to determine which of the two ligands provided by ethaline (Cl– and/or [C2H4O2]2– ) can form the most stable complex with Fe2+ and/or Fe3+. As a result, the tetrahedral complex [Fe(C2H4O2)2]– with the ligand [C2H4O2]2– through O-donor chelating with Fe3+ was found to be the most probable and stable complex. However, the ethaline solvent did not deliver adequate Fe extraction compared to commonly used reagents/solvents like mineral acids, to fully break down pyrite and expose any encapsulated gold.
... The presence of nitrates in the effluents should also be avoided, which might necessitate another post-leaching treatment. Several different approaches have been attempted in the literature to find an alternative to aqua regia: 13 organic solvents with SOCl 2 as complexing agent, 14 highly concentrated solutions of AlCl 3 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O, 15 or even the replacement of HNO 3 by another and stronger oxidant such as H 2 O 2 . The mix of HCl/H 2 O 2 was used as a leaching agent for a complete recycling process of the MEA. ...
Carbon-supported platinum nanoparticles (Pt/C) are widely used electrocatalysts in proton exchange membrane fuel cell and electrolyzer applications and represent a substantial part of the capital expenditure of these devices. Platinum being a critical raw material, its recovery is critical for the deployment of these technologies. In this contribution, the first step of a recycling protocol, i.e. the leaching of Pt/C, is studied. To avoid the use of concentrated acids and oxidants, the focus of the present study is on the design of an efficient electrochemical protocol. In particular, the values of the upper and lower potential limits have an impact on Pt dissolution efficiency. The upper potential limit should avoid (or at least limit) Pt particles' detachment from the carbon support and the lower potential limit should take into account the competition between the platinum dissolution and the unwanted platinum redeposition. The evolution of the particle morphology and dissolution rate were monitored by coupling a statistical analysis of TEM images and ICP-MS concentration measurements. The cycling potential window was first optimized for a model commercial Pt/C catalyst in a low-chloride concentration electrolyte, leading to a full Pt leaching efficiency (99%). A similar protocol was transferred to more technological objects: MEA aged under realistic conditions. The MEAs were electrochemically treated without any prior GDL separation and the efficiency of the process was demonstrated.
Keywords: MEA recycling; Platinum electrodissolution; Platinum recovery.
... Another alternative method for processing gold ore is using more environmentally friendly reagents. Thiosulphate and thiourea are currently an alternative to cyanide reagents because they show the ability to extract gold and have a smaller negative impact on the environment and health [22][23][24][25][26]. The thiosulphate solution can form an anionic complex [Au(S 2 O 3 ) 2 ] 3− with gold under alkaline conditions, while thiourea solution can form cationic complex Au[CS (NH 2 )] 2 + in acidic conditions [27]. ...
... The thiosulphate solution can form an anionic complex [Au(S 2 O 3 ) 2 ] 3− with gold under alkaline conditions, while thiourea solution can form cationic complex Au[CS (NH 2 )] 2 + in acidic conditions [27]. The advantages of these two solutions are the high dissolution rate of gold compared to cyanide solutions and fewer environmental problems [23,28,29]. In this study, the leaching process using thiosulphate and thiourea solutions is expected to increase the recovery of gold from ore by varying the contact time, varying the concentration, and determining the effect of using variations of reagent for leaching. ...
... Furthermore, the gold leaching process is carried out for 10 min. The reaction that occurs in the process of leaching gold with the solvent of aqua regia is shown in equation (1) [23]. ...
Gold extraction from the rock is generally carried out using mercury. However, the high toxicity of mercury has a very dangerous impact on the environment and health. Various efforts have been made to reduce the use of mercury in gold extraction, one of which is the leaching method using thiosulphate and thiourea solution because they have low toxicity and are environmentally friendly. This study aimed to determine the results of gold extraction with thiosulphate and thiourea solution and determined the optimum concentration and time of extraction. The yield of the gold extract with thiosulphate solution was greater than that of thiourea solution. The thiosulphate solution had an optimum concentration of 0.3 M and an optimum time of 2 h. While the thiourea solution had an optimum concentration of 0.2 M and an optimum time of 3 h. The results of the Friedman test on the leaching time and concentration parameters show that leaching time has a significant effect on the Au leaching process, and the concentration parameter does not affect the Au leaching process from solid samples.
