Development of Gold Dissolution and Recovery Process Using Iodine-Based Aqueous Solution with a Membrane-Free Electrolytic Cell

Comparative life cycle assessment of copper and gold recovery from waste printed circuit boards: Pyrometallurgy, chemical leaching and bioleaching

This study evaluates the preg-robbing effect on gold recovery through a carbon-in-leach process, comparing three reactor types: glass, stainless steel, and stainless steel coated with ceramic resin. Protonated activated carbon (PAcC) and anthracite carbon (PAnC) were used as adsorbents. The results show that PAcC achieved a significantly higher gold adsorption rate of up to 99.87%, compared to PAnC, which achieved a maximum of 66%, mitigating the preg-robbing effect. The stainless steel reactor performed best, with gold recovery rates exceeding 90%, as confirmed by a multi-criteria decision matrix evaluating factors like durability, mechanical strength, and corrosion resistance. A 24−1 fractional factorial design identified key variables for optimal recovery, with aeration of 9.31 L/min, a PAcC pulp density of 2.5 g/L, and the use of Puerto Berrío ore resulting in the highest gold recovery, reaching 18.38 ppm. The mass balance confirmed that gold adsorption on PAcC was the most efficient, leaving less than 0.13% gold in the leachate. These results demonstrate the superiority of PAcC and stainless steel reactors in mitigating the preg-robbing effect, offering an effective solution for scaling up gold recovery processes.

Developing an extremely efficient and highly selective process for gold recovery is urgently desired for maintaining a sustainable ecological environment. Herein, we report a highly efficient gold-recovery protocol on the basis of the instantaneous assembly between cucurbit[6]uril (CB[6]) and [AuX4]- (X = Cl/Br) anions. Upon mixing CB[6] with the four gold-bearing salts MAuX4 (M = H/K, X = Cl/Br) in aqueous solutions, yellow or brown coprecipitates form immediately, as a result of multiple weak [Au-X···H-C] (X = Cl/Br) hydrogen-bonding and [Au-X···C=O] (X = Cl/Br) ion-dipole interactions. The gold-recovery efficiency, based on CB[6]·HAuCl4 coprecipitation, reaches 99.2% under optimized conditions. In the X-ray crystal superstructures, [AuCl4]- anions and CB[6] molecules adopt an alternating arrangement to form doubly connected supramolecular polymers, while [AuBr4]- anions are accommodated in the lattice between two-dimensional layered nanostructures composed of CB[6] molecules. DFT calculations have revealed that the binding energy (34.8 kcal mol-1) between CB[6] molecules and [AuCl4]- anions is higher than that (11.3-31.3 kcal mol-1) between CB[6] molecules and [AuBr4]- anions, leading to improved crystallinity and higher yields of CB[6]·MAuCl4 (M = H/K) coprecipitates. Additionally, a laboratory-scale gold-recovery protocol, aligned with an attractive strategy for the practical recovery of gold, was established based on the highly efficient coprecipitation of CB[6]·HAuCl4. The use of CB[6] as a gold extractant provides us with a new opportunity to develop more efficient processes for gold recovery.

Considering the increasing environmental concerns and the potential for small gold deposits to be exploited in the future, the uses of environmentally friendly processes are essential. Recent developments point to the potential for greatly increased plant performance through a separation process that combines the cyanide and flotation processes. In addition, this kind of alternative treatment processes to the traditional gold recovery processes may reduce the environmental risks of present small‐scale gold mining. Gold recovery processes that applied to different types of gold bearing ore deposits show that the type of deposits plays an important role for the selection of mineral processing technologies in the production of gold and other precious metals. In the last 25 years, different alternative processes have been investigated on gold deposits located in areas where environmental issues are a great concern. In 1988, gold particles were first recovered by successful pilot trial of coal‐gold agglomeration (CGA) process in Australia. The current paper reviews the importance of CGA in the production of gold ore and identifies areas for further development work.

A process for gold recovery from a complex Chilean ore from Burladora (IV Region) which integrates concentration by flotation, bacterial leaching and cyanidation was studied at a laboratory scale. The chemical composition of the ore is 8.2% Fe, 0.78% Cu, 0.88% As and 3.5 g/t Au, with pyrite, hematite, covelite, arsenopyrite and chalcopyrite as the main metal-bearing minerals. The initial gold recovery by conventional cyanidation on a crushed ore sample was only 54%. The ore was ground and concentrated by flotation with a gold recovery of only 56%. The gold content of the concentrate is 17 g/I Au. Concentrate samples were leached in 1.5 l stirred reactors at 10% pulp density in 1000 ml of acid medium (pH 1.8). Some experiments were inoculated with harvested bacteria previously isolated from mining solutions. Dissolved metals, pH and bacteria concentration in the leaching solutions were periodically determined. In the presence of bacteria, oxidation of the ferrous ion produced by acid dissolution of the concentrate was observed, and after 4 days of leaching 100% of the dissolved iron was present as ferric ion. Gold recovery by cyanidation increased from 13% for the initial concentrate to 34% after 10 days of chemical acid leaching and 97% after 10 days of bacterial leaching. To increase the total gold recovery, the flotation tailings were submitted to cyanidation. A complete flowsheet of the process and a first economical evalualion are proposed. As a possible alternative process, heap bacterial leaching and further cyanidation of the ore are suggested.

Flotation as a separation technique in the coal gold agglomeration process

Reducing preg-robbing in carbonaceous gold ores using passivative or blanking agents

Thiosulfate leaching combined with ion-exchange resins is an innovative alternative for gold recovery. According to the properties of activated carbon, it could replace resins in the gold recovery process, improve efficiency, and reduce operating cost. In this research, the adsorption process of gold thiosulfate complex on thiol-modified activated carbon was studied. Thioglycolic acid (ATG) was impregnated in activated carbon, and its adsorption ability was tested with synthetic solutions of gold and sodium thiosulfate (Au 10 mg·L−1, Na2S2O3 0.1 mol·L−1, pH = 10.0). Carbon was characterized by infrared spectroscopy, SEM-EDS, PZC titration, hardness number measures, and proximal analysis. Synthetic solutions were also characterized by UV-vis spectroscopy and cyclic voltammetry. The percentage of volatile material increased from 10.0 to 13.9% due to the impregnation process of ATG. Infrared spectra show characteristic bands of C-H, S-H, and C-S bonds. In the adsorption tests, the ATG-impregnated carbon achieved 91% of gold recovery, while the same amount of ATG in the liquid phase stirred with unmodified activated carbon reached 90% of gold recovery. The 44.9% of gold recovered with activated carbon impregnated with ATG was eluted with sodium cyanide ([NaCN] = 0.2 mol·L−1; [NaOH] = 0.25 mol·L−1; [CH3CH2OH] = 30% V/V; pH = 12.0; t = 24 h). These results suggest the gold transferred from the thiosulfate complex to a new gold thiolate complex.

Cage-like amine-rich polymeric capsule with internal 3D center-radial channels for efficient and selective gold recovery

Gold recovery process is well known. The following paper presents the problematic related to the influence of Copper and Arsenic on the recovery of gold in the Yalea deposit. Multielement tests (Au, Cu, As) carried out on 37 blocks made it possible to understand that there is a correlation between these elements. This correlation has been observed since the analysis of block models (the block model for Copper, block model for Arsenic and the block model for gold. These models have shown that the Yalea deposit areas with a high gold content correspond to areas of high copper content and arsenic. Those who made it clear that copper and Arsenic are tracing elements of Gold in the Yalea deposit. In this paper, the mineralurgical tests carried out on 28 blocks revealed that the copper and the arsenic content in the ore penalize the recovery of Gold (146 ppm for copper and 4710 ppm for Arsenic). The Yalea deposit was emplaced by several hydrothermal phases that reactivated the structures. These phases are responsible for the establishment of large quantities of copper sulphides. Copper and Arsenic are elements that have a considerable influence on the gold recovery in the Yalea deposit.

Electrochemical oscillation behaviors of gold during its recovery from waste printed circuit boards through slurry electrolysis

The residual waste of synthesis and use of radioactive elements of gold 198Au as a radiopharmaceutical and tracer after decaying can be reused as an irradiated target material. The gold recovery process was carried out on Au-198 radioactive nano gold waste with the redox replacement method using Zn-foil as metal reducing agent. Radioactive Au-gold waste was stored until it decayed to its background, so it is not dangerous and does not interfere with the optical characterization process. The sample was dissolved with aquaregia and evaporated so that the chelating or dendrimer material can be released and oxidized. The evaporation was done to reduce acidity and obtain the salt. Furthermore, the salt solution of HAuCl4 is reduced with Zn-foil so that the pure gold deposits can be obtained through a redox process. The results of the XRF analysis showed that the gold deposits formed have fairly good purity with little Zn and Zr impurities derived from the erosion of the melting container. The yield calculation results based on ICP-OES data obtained a recovery percentage of 68.73%. The method of taking gold deposits must be increased to reduce the gold particles attached to the bar stirrer and to the melting pottery container.

The main purpose of this paper was to obtain a material with efficient adsorbing properties and selectivity, to recover the gold (III) from residual diluted solutions resulted from the electroplating process. In this regard, a material was obtained by physico-chemical functionalization of a chemically inert support with functional groups of nitrogen and carboxyl. As a source of functional groups glutamic acid was used, and Amberlite XAD7 type acrylic resin was used as solid support. In order to establish the mechanism of the adsorption process, kinetic, thermodynamic and equilibrium studies were performed. The maximum adsorption capacity of the material has been established, and a gold (III) recovery process has been proposed using thermal decomposition of the exhausted adsorbed material. Main objective of this study was to evaluate an environmental friendly adsorbent material to recover gold from secondary industrial sources.

Jewelry fabrication process that includes technique like filing, piercing, grinding and drilling are amongst the popular application that have been widely used for such a long time. It is a known fact these processes usually would produce various type of metal scrap at the end of the process cycle. Thus, the gold scrap that is generated from the jewelry fabrication process need to be collected and refined back to pure gold. Interestingly, the nitrogen dioxide formed during the traditional (small scale) gold recovery process has been observed as hazardous i.e. air pollution and profile some risk on safety. The research intent is to measure reliability and effectiveness of local traditional gold recovery method for jewellery scrap and to determine weather the traditional (small scale) process is able to produce a higher percentage of gold purity from the jewellery scrap as compared to the modern techniques. To verify this, a full cycle of physical and chemical testing via traditional methods have been conducted to derive and validate the research findings and conclusions. The analysis of the gold chemical compositions, hardness and metallography are tabulated to strengthen the research findings.

An increasing number of low‐grade gold ore deposits are characterized by the presence of gold as solid solution into the mineral matrix of sulphide minerals which is not directly amenable to gold cyanidation. In order to liberate this submicroscopic gold the ore has to be oxidized before being subjected to gold cyanidation and exctraction. This is mainly done by autoclave pressure oxidation (AC POX) or roasting, two major technologies used by the mining industry. Very often, these ores contain an active carbonaceous compound which has the ability to adsorb, or preg‐rob gold from the cyanide solution. Gold recovery can be adversely affected by preg‐robbing on inherent carbonaceous material during autoclave pressure oxidation of sulphide ores. The time of flight (TOF) SIMS (TOF‐SIMS) technique has been applied for direct determination of gold species on individual carbonaceous particulates from AC POX stream samples. The speciation of the gold preg‐robbed on carbonaceous matter from CIL tail sample showed presence of both metallic gold and Au(CN) 2 compound. Direct quantification of the metallic and compound gold provided an estimate for the fraction of gold losses due to preg‐robbing in carbonaceous matter. Copyright © 2010 John Wiley & Sons, Ltd.