Gold Leaching Research Articles

Improved thiourea leaching of gold from a gold ore using additives

Thiourea (TU) is a low-toxicity gold lixiviant that has the promise to replace the highly toxic cyanide for gold extraction. The significant issue of high thiourea consumption and the suspected carcinogenic nature, however, severely restricts its industrial application. In this paper, oxalate and citrate were used as additives to enhance the thiourea leaching of gold from a gold ore. The leaching results showed that the thiourea consumption was significantly reduced whilst the gold extraction improved to be comparable to that by cyanidation. The presence of additive was found to achieve a faster and higher gold adsorption by activated carbon due likely to the much-reduced side products from thiourea decomposition. In addition, citrate has a better performance than oxalate under the same additive dosage. Analytical results demonstrate the possible mechanisms for the additive-improved thiourea leaching of the ore. Oxalate and citrate can complex with the oxidant Fe3+ forming its complexes mainly of Fe(ox)+/Fe(ox)2− and Fe2(cit)2(OH)22−, which stabilizes Fe3+ and lowers the solution potential, thus decreasing thiourea consumption. The additive-improved thiourea leaching also significantly reduced the formation of the passivating product, i.e., calcium sulfate hydrate, and thus effectively weakened the impediment of gold leaching caused by calcium sulfate hydrate. The cyclic leaching results further suggested that high gold extraction with relatively low thiourea consumption was achieved in five cycles of the citrate-improved thiourea leaching. Thus, citrate-improved thiourea leaching technology appears promising for the extraction of gold from gold ores.

Study on the Galvanic Interaction of Gold and Main Associated Minerals Based on Density Functional Theory

The galvanic interaction of gold and associated sulfide minerals in thiocyanate systems has a significant impact on gold leaching. The density functional theory was used to further reveal the galvanic interaction between gold and associated minerals. The electron transfer between gold and its associated minerals at different galvanic interaction distances was simulated. The results show that with the increase of the contact distance between pyrite and gold, the charge of pyrite increases, indicating that it is losing electrons gradually; the charge of arsenopyrite and chalcocite decreases with the rise of the contact distance between gold and pyrite, suggesting that they are gaining electrons. In addition, gold has the greatest influence on the gain and loss of electrons in pyrite and arsenopyrite and has the least influence on chalcocite. Through the calculation of the density of states, it is found that different distances of galvanic interaction have a great influence on the density of states of surface atoms under the action of pyrite and arsenopyrite with gold but have little effect on the density of states of surface atoms under the action of chalcocite with gold.

Synergistical thiourea and thiosulfate leaching gold from a gold concentrate calcine with copper-ammonia catalysis

Thiosulfate leaching is a non-toxic and eco-friendly alternative method to cyanidation. However, thiosulfate leaching was used to leach gold from the gold concentrate calcine, and gold extraction effect was poor. To achieve effective leaching of gold, thiourea was added to facilitate gold extraction. This research not only investigated the leaching conditions and leaching kinetics but also discussed the potential reason and reaction mechanism of thiourea improving gold extraction. Gold extraction efficiency within 2 h was close to that of cyanidation (24 h) under the conditions: 0.2 mol/L thiosulfate, 0.12 mol/L thiourea, 5 mmol/L copper ion, 0.6 mol/L ammonia, 3 of liquid to solid ratio, and 308 K of leaching temperature. The gold in the leached solution was effectively recovered by the resin. According to the mechanism analysis, the gold in the leached solution existed in the form of gold(I) thiourea complex and gold(I) thiosulfate complex. The reason responsible for improving gold extraction efficiency lied in that inhibited the form of passivation layer and synergistically leached gold, and rapid leaching speed may be due to synergistical leaching. Thiourea is added in the thiosulfate leaching process, and offers a feasible, efficient, and fast leaching method for green development of the hydrometallurgy industry.

Dissolution of gold in the presence of copper ion and diethylenetriamine (DETA)

ABSTRACT Cyanidation is the most widely used technique for gold extraction worldwide. However, its efficiency in gold extraction has decreased due to gold association with base metals such as copper. Copper is known to form different complexes with cyanide depending on the pulp pH. These Cu-CN complexes deplete the pulp of free cyanide, thereby decreasing gold leaching. The study examined the application of diethylenetriamine (DETA) in cyanidation to minimise copper ions effect on gold cyanidation. Leaching tests performed in the presence of copper ions reduced gold recovery from 93% to 15% at a copper sulphate concentration of 1% and increased cyanide consumption by 10%. The introduction of DETA (between 0.2% and 1%) however restored gold recovery back to normal as the baseline without copper ions and also enabled gold extraction at a reduced cyanide strength. Based on the study, DETA could be used during gold–copper cyanide leaching to minimise the copper ion effect and enhance gold extraction.

Electrochemical analysis of copper-EDTA-ammonia-gold thiosulfate dissolution system

Abstract Ethylenediaminetetraacetic acid disodium (EDTA) can form stable complexes with many metals. To improve the leaching rate of gold and the consumption rate of thiosulfate, EDTA and ammonia were combined with copper ions to form a copper-EDTA-ammonia-thiosulfate system. Electrochemical methods were used to study the effect of thiosulfate, copper ion, EDTA, and polarization voltage. The results showed that increasing the concentrations of thiosulfate, copper ions, and EDTA promoted the dissolution of gold, which changed from electrochemical control to diffusion control after adding EDTA. The order of influence was thiosulfate > EDTA > copper ion. The pure gold leaching experiment showed that the dissolution rate of gold in the EDTA-ammonium-copper thiosulfate system was higher than that in the EDTA-copper-thiosulfuric acid system, thus achieving synergistic gold leaching.

Investigation of techniques to replace amalgamation in artisanal gold mining operations

Artisanal gold mining is the leading source of anthropogenic mercury emissions worldwide. This article explores cost-effective gold leaching methods for skilled miners to address mercury's environmental and health impacts in this sector. A sample from Colombia's La Maria deposit, containing 48.87 ppm gold, ground to 80% below 0.13 mm, served as the basis for comparison. The standard whole ore amalgamation approach, commonly used by miners, resulted in less than 19% gold extraction. However, employing cyanidation with 1g/L of free cyanide extracted 84% of the gold within 24 hours. Among the unconventional processes investigated, using effluent from a local cassava processing plant as a lixiviant demonstrated promise. Two cassava varieties produced liquids with 267 and 600 mg/L of free cyanide, leading to 50.9% and 82.4% gold extraction from the ore in 24 hours, respectively. Another alternative method involved employing Dimethyl sulfoxide, a water-free reagent, as a gold-leaching lixiviant, resulting in a remarkable 96.5% gold extraction in just 2 hours. The researchers also modified the Merrill-Crowe cyanidation process by eliminating filtration and vacuum, instead utilizing bags filled with zinc (or aluminum) in the pulp. With reduced agitation to prevent aeration, over 99% of the gold precipitated on the zinc shavings within 2 hours. Furthermore, testing a hydrochloric solution (50%) with an oxidant demonstrated 83.9% and 100% gold extraction in 8 hours at ambient temperature and 50°C, respectively. It is crucial to note that successful implementation of these alternative strategies necessitates knowledge, investment, and customization to suit specific site conditions.

From understanding the rate limitations of bioleaching mechanisms to improved bioleach process design

While bioleaching has become established technology for the leaching of refractory gold concentrates and in the heap leaching of copper sulfide minerals, many other applications, although demonstrated at the laboratory scale, have not found significant uptake in industrial biomining. The reasons for this are manifold, but generally relate back to engineering constraints in operating processes at large scale while remaining economically viable.The paper unpacks acidophile sulfide bioleaching mechanisms within bioreactors into various sub-processes and analyses them in terms of their rate limitations, such as gas-liquid mass transfer of oxygen and CO2, diffusion constraints between and within mineral particles, competing side reactions etc. It becomes clear that microbial metabolic reactions are generally not what limits the kinetics of bioleaching reactions overall but rather the reaction environment. Improved process design to enhance the economic performance of bioleaching therefore needs to target the slowest sub-process in the bioleaching mechanism, which is rarely the biological one.Conventional tank and heap bioleaching processes are discussed in this context and routes taken towards their improvement discussed. Further, various promising novel concepts in biomining, such as leaching with biogenic lixiviants, phytomining and tailings leaching are evaluated within this framework, in each case identifying the potentially limiting sub-processes. It becomes clear that the relative ‘slowness’ of these sub-processes prohibits exploitation through designed active industrial processes; they can, however, still be facilitated through suitably designed ‘passive’ processes in which the time taken for slow processes is less of an economic constraint. While this is an obvious approach in bioremediation, it can also be employed for the economic recovery of value from otherwise sub-economic mineral deposits and waste materials through heap bioleaching. This way it can also play a role in the drive towards a circular economy.

Radiation and Environmental Safety in the Exploration and Development of Metal Deposits in South Yakutia

Radiometric surveys of mining dumps on spent placers of gold, monazite and the exploited gold-uranium ore deposit in South Yakutia were carried out. It is established that the dumps of alluvial, overburden and waste rocks in terms of the effective specific activity of radionuclides when used in construction work are characterized by different degrees of tolerance. It is shown that stacked radioactive ore dumps at the “Lunnoye” deposit after heap leaching of gold become powerful uncontrolled sources of radioactive pollution of the environment. It is recommended to conduct periodic monitoring of their radioactivity levels by express methods of field radiometry for the safe use of mining dumps as building materials.

Novel approach for removing iron-cyanide complex ions and cesium ions from solutions using hydrogel-like beads

In the process of recycling cyanide leaching solutions, the presence of iron-cyanide complex ions in gold leaching solutions leads to increased cyanide consumption and competition with gold for adsorption onto activated carbon. Consequently, the removal of iron- cyanide complex ions from cyanide leaching solutions is crucial. This study presents a novel strategy for the treatment of metal ions in leaching solutions, achieving effective waste treatment using hydrogel-like beads. To remove iron-cyanide complex ions from cyanide leaching solutions, we synthesized carboxymethyl cellulose‑iron (CMCFe) hydrogel through a crosslinking method. The adsorbent, carboxymethyl cellulose-Prussian blue (CMC-PB) hydrogel, obtained after iron-cyanide complex ion adsorption, can directly remove Cs+ ions from solution without the need for desorption and regeneration. Notably, the CMC-Fe hydrogel exhibits exceptional adsorption performance and high selectivity toward iron-cyanide complex ions. The adsorption process of the CMC-Fe hydrogel follows a pseudo-second-order kinetic model, while the Freundlich isotherm model is more suitable for describing the adsorption equilibrium. Additionally, the CMC-PB hydrogel efficiently adsorbs 83.1% of Cs+ ions at a dosage of 86.5 μg, and desorption and regeneration studies reveal that its adsorption efficiency remains high even after three cycles. Furthermore, the proposed adsorption mechanism of CMC-PB for Cs+ ions involves a combination of chemisorption (K+/Na+ exchange) and physisorption (hole channels of hydrogels).

A Pretreatment of Refractory Gold Ores Containing Sulfide Minerals to Improve Gold Leaching by Ammonium Thiosulfate: A Model Experiment Using Gold Powder and Arsenic-Bearing Sulfide Minerals

The use of thiosulfate to extract gold from refractory ores is promising because of its non-toxicity and high selectivity. Sulfide minerals (i.e., pyrite, arsenopyrite, chalcopyrite), major gold carriers in refractory gold ores, however, hinder gold extraction due to the high consumption of a lixiviant. In this study, a new method to improve gold extraction from sulfide bearing gold ores is proposed based on the model experiments using a mixture of gold powder and arsenopyrite-bearing sulfide (HAsBS) ore. The effects of HAsBS ore on gold leaching in ammonium thiosulfate solutions were investigated, and it was found that gold extraction in the presence of HAsBS ore was suppressed because of the unwanted decomposition of thiosulfate on the surface of sulfide minerals. To improve gold extraction in the presence of the sulfide minerals, this study investigated the effects of the pretreatment of HAsBS ore using ammonium solutions containing cupric ions and confirmed that HAsBS ore was oxidized in the pretreatment and its surface was covered by the oxidation products. As a result, thiosulfate consumption was minimized in the subsequent gold leaching step using ammonium thiosulfate, resulting in an improvement in gold extraction from 10% to 79%.

Susceptibility to cyanidation of pyrrhotite-associated gold in pyrite calcines from (non)oxidizing roasting environments

The susceptibility to leaching of pyrrhotite-associated gold in roasted pyrite calcines was studied, with emphasis on the effects of the roasting environment and galvanic contacts under cyanidation conditions. The first part scrutinized the thermal treatment of pyrite under different oxidizing and non-oxidizing atmospheres, and demonstrated that air roasting promoted the coexistence of multiple pyrrhotites, while He, CO2, and steam environments resulted in single hexagonal pyrrhotites with increasing iron deficiency and decreasing porosity. The second part employed a bilayer leach cell to control the electrochemical contacts between gold powder and raw/roasted pyrite during cyanidation, and found that the topology of pyrrhotite and iron oxides was influenced by the type of roasting treatment, which could impact the kinetics of gold dissolution, particularly in cases involving refractory gold or ore preg-robbing recalcitrance. Therefore, when it comes to extracting encapsulated gold associated with refractory pyrite that requires heat treatment, air roasting was the most effective for leaching gold from calcine, outperforming both inert and mild oxidative environments. In addition, the presence of CO2 (and/or moisture) in the roasting atmosphere to mimic the combustion of carbonaceous material could moderately enhance gold recovery regardless of whether or not there was galvanic contact with the roasted pyrite.

Role of foreign ions in the thiourea leaching of gold

Thiourea, as an environmentally friendly gold lixiviant, has the potential to replace highly toxic cyanide. The effect of foreign ions including Cu2+, Ag+, Pb2+, Zn2+, AsO33− and AsO43− on gold leaching in an acidic thiourea solution was investigated in this paper. Leaching results showed that the foreign ions had an adverse effect on thiourea leaching of gold. The gold dissolution (except low Pb2+ concentrations, i.e., < 20 mg/L) and thiourea stability both were in order of no foreign ions ≈ Zn2+ > Pb2+ > AsO33− > AsO43− > Ag+ > Cu2+. The thiourea dissolution of gold could be improved at low concentrations of Pb2+ (<20 mg/L), although the thiourea consumption was also increased. The thermodynamic analysis and the scanning electron microscope (SEM) and X-ray photon spectroscopy (XPS) analyses suggested that the foreign ions resulted in insignificant changes in the corrosion characteristics of leached gold surface and the quantity and chemical state of surface species. The possible mechanism for the effect of foreign ions on thiourea leaching of gold was proposed that the thiourea consumption in the presence of foreign ions was significantly increased, leading to the marked deterioration of thiourea dissolution of gold.

Research on gold leaching of carbonaceous pressure-oxidized gold ore via a highly effective, green and low toxic agent trichloroisocyanuric acid

In this work, trichloroisocynauric acid (TCCA) are used for gold leaching with the advantages of fast reaction rate, high leaching efficiency, low toxicity and environmentally friendly. In addition, an important feature is the continuous hydrolysis of TCCA in an aqueous solution to produce oxidants (HClO) while maintaining the effective chlorination concentration at a high level. The various factors affecting TCCA leaching carbonaceous pressure-oxidized gold ore were investigated and the leaching kinetics were established. According to the results of orthogonal experiments, the optimal conditions of TCCA concentration 0.25 mol L−1, NaCl concentration 50 g L−1, pH 5.5, leaching temperature 45 °C and solid-liquid ratio 1:6 could be obtained, and the gold leaching efficiency reached (88.64 ± 0.37) % within 3 h. After the three stages of TCCA leaching, a gold leaching efficiency was increased to 94.39%. Furthermore, TCCA leaching process could be divided into three steps, the findings of kinetic models revealed that in the early leaching step (0–2 h), TCCA leaching was controlled by solid products layer diffusion model, and yet shifted to be controlled by interfacial chemical reaction model in the final step. Importantly, TCCA leaching solution might be converted into a disinfectant with an effective chlorination concentration of 16.075% treated with resin adsorption and alum removal, enabling the secondary utilization of wastewater resources.

Oxidative pretreatment of refractory gold ore using persulfate under ultrasound for efficient leaching of gold by a novel eco-friendly lixiviant: Demonstration of the effect of particle size and economic benefits

A novel pretreatment method for refractory gold ore using ultrasound-activated persulfate was developed to overcome the low extraction efficiency of gold in the leaching process. The feasibility of the pretreatment method was verified primarily by EPR (Electron paramagnetic resonance) and pre-oxidation tests. The free radicals generated by ultrasound-activated persulfate effectively promoted the oxidation of sulfide in the gold ore. The pretreatment efficiency of this process was higher than that of traditional heat activation, and the oxidation efficiency was two times higher. Furthermore, the gold leaching efficiency was higher under ultrasound activation conditions when using a novel eco-friendly lixiviant (Jinchan-its main effective component is Na3CN3C3H3N6O3, i.e., carbonized sodium cyanurate). Morphology analysis indicated that the synergistic effect of persulfate and ultrasound effectively reduced the particle size of the refractory gold ore, improved the specific surface area, and facilitated the oxidation of the enclosures, which benefited the subsequent leaching process. The maximum leaching efficiency of gold reached 86.9% after ultrasonic activated persulfate pretreatment for 3 h. This study provides a promising refractory gold ore pretreatment to improve gold leaching through persulfate oxidation using ultrasound activation.

Facile synthesis of thiolated silica-encapsulated magnetic adsorbents: Effective adsorption and rapid separation of Au(Ⅰ) from thiosulfate solution

It is important to develop a facile and highly efficient synthetic strategy to fabricate an adsorbent exhibiting excellent adsorption performance and separation ability to recover Au from thiosulfate solutions. Herein, we report a magnetic silica composite (Fe3O4 @SiO2-SH) that was successfully fabricated using an economical, one-pot synthesis method for efficient Au(I) adsorption. The results revealed that the performance of the adsorbent was pH dependent, and the single saturated adsorption capacity was 15.11 mg/g. The adsorption process could be well-explained by the Elovich kinetic model and Langmuir isotherm model, indicating that chemical adsorption dominated the monolayer adsorption process. Furthermore, the adsorption process was exothermic. The chemical structures and properties of the adsorbents were analyzed using various characterization and analysis methods. The chelating interaction between -SH and Au(I) promoted the adsorption of Au on Fe3O4 @SiO2-SH. The gold-loaded, highly reusable adsorbent could be readily eluted using Na2S2O3 (3 mol/L), and > 90% of the gold could be recovered from the adsorbent in a thiosulfate gold leaching solution with Cu2+-NH3-S2O32- as the leaching system. Most of the adsorbent in the pulp could be collected using a magnet, and this reduced the separation cost. The adsorbent can recover more than 90% of gold in both simulated and actual thiosulfate-based gold leaching solutions, indicating that the results reported herein provide a cost-effective strategy for the fabrication of magnetic silica composites characterized by a satisfactory adsorption capacity.

Mineralogical Characteristics and Refractory Properties of Arsenic-bearing Gold Concentrate

The arsenic-bearing gold ore in Anhui, China is an extremely refractory gold ore, and the cyanide leaching rate of gold concentrate is only 30%. The mineralogical factors of the low leaching rate were discussed by process mineralogical analysis. The results demonstrate that the gold concentrate contains 20.30 g/t gold, 3.39% arsenic, 29.80% sulfur, and 4.10% iron. Gold exists in the occurrence states of metallic mineral-wrapped gold, gangue mineral-wrapped gold, and fissure gold, which account for 64.90%, 8.31%, and 26.79% respectively. Pyrite, arsenopyrite, realgar, sphalerite, and pyrrhotite are the main metallic minerals in the gold concentrate. Among them, pyrite accounts for 51.20%, and arsenopyrite accounts for 24.30%. Gangue minerals include feldspar, sericite, quartz, calcite, and chlorite. Among them, feldspar, sericite, and quartz account for 30.30%, 22.70%, and 22.10% respectively. In addition, the grain size distribution and distribution characteristics of various minerals are obtained, and the texture and structure of the gold ore are analyzed. Pyrite and arsenic phase are the main factors causing the low gold leaching rate. The presence of carbonate minerals and clay minerals also has an effect on the rate of gold leaching. The oxidation pretreatment can increase the gold leaching rate to about 94%. The findings provide a theoretical foundation for the selection of manufacturing techniques in businesses and play an important guiding role in the development of similar ores.

Selective alkaline leaching of antimony from Low-grade refractory gold ores and process optimization

To eliminate the adverse effect of antimony on extracting of gold in matte smelting process from Sb-bearing refractory gold ores, the sodium sulfide leaching method was proposed to selectively remove antimony in advance. On the basis of the analysis and characterization of raw materials (XRD, SEM-EDS, mineralogical phase analysis, etc.), it can be detected that the antimony in refractory gold ores is mainly in form of stibnite with small quantities of oxides, and the gold is mainly wrapped up in sulfides and silicates. The effects of sodium sulfide and sodium hydroxide concentration, temperature, leaching time and liquid–solid ratio on the extraction rate of antimony and gold were discussed. Furthermore, the response surface method was applied to distinguish the interaction influence of process parameters on the antimony and gold extraction rate. It is detected that the polysulfides and thiosulfates are the main cause of associated leaching of gold. Furthermore, the regression equation model is established adopting the antimony extraction rate as response value, and it can be deduced that the relevance degree is Na2S concentration > temperature > NaOH concentration. Accordingly, the optimized process results are determined as follows: the extraction rates of antimony and gold reach 94.15% and 3.37%, respectively, under Na2S concentration of 85.66 g/L, NaOH concentration of 45.5 g/L, liquid–solid ratio of 1.5, leaching at 90 °C for 5 min, which are very consistent with the predicted values of the regression equation, proving the feasibility of the proposed optimization model.

Inhibition of carbonaceous matters adsorbing gold using a green and efficient chlorinating agent TCCA: Inhibition behavior, kinetics and isotherms, inhibition mechanism

Refractory carbonaceous gold ore contains carbonaceous matters that seriously interfere with gold leaching. Therefore, this paper presented an in-depth experimental investigation on the inhibition gold-adsorbing behavior using Trichloroisocyanuric acid (TCCA). Various factors affecting the inhibition were analyzed. Moreover, the kinetics and isotherms associated with the adsorption were established to describe the gold adsorption of carbonaceous matters after TCCA treatment. A variety of analytical techniques were used to clarify the inhibition mechanism. The results showed the average gold adsorption percentage of elemental carbon decreased from 89.79 % to 9.33 % at pH 3.0, TCCA volume 15.17 mL, TCCA concentration 0.104 mol·L−1, 35 ℃ and 3 h. The average adsorption percentage of humic acid decreased from 56.19 % to 3.13 % at pH 5.0, TCCA volume 5.10 mL, TCCA concentration 0.012 mol·L−1, 35 ℃ and 4.5 h. The gold-adsorption behavior of the treated elemental carbon conformed to the pseudo-second-order and Langmuir model, accompanied by an activation energy of 9.42 kJ·mol−1. And the adsorption process of the treated humic acid could be explained by the pseudo-first-order and Langmuir model with an activation energy of 40.11 kJ·mol−1. TCCA molecules and their hydrolysis products covered the elemental carbon surface, resulting in a reduction in the size of the porous structure, which further affected the number and activity of surface-active sites. Treated with TCCA, the surface area of humic acid reduced from 42.84 m2·g−1 to 9.96 m2·g−1. Furthermore, spectroscopic analysis showed that the chemical groups of humic acid were destroyed, suggesting a sharp decrease in chemisorption capability.

Effects of lead nitrate and pre-aeration on the deportment of base/precious metals in cyanide leaching of a pyritic refractory gold concentrate

This study was undertaken to improve gold and silver extraction from a pyritic gold flotation concentrate, which assayed 11 g/t Au, 42 g/t Ag, 0.21% Cu, 3.57% Zn, and 31% Fe. Direct cyanide leaching of the concentrate at 1.5 g/L NaCN yielded a low gold extraction (37%), confirming its refractory nature. Effects of lead nitrate (200-500 g/t Pb(NO3)2) and pre-aeration (24 h) before cyanide leaching at 1.5-3.5 g/L NaCN were investigated. Earlier studies have focused on the impact of these parameters on gold leaching. Besides gold, this study demonstrated the behaviour of silver and base metals (copper and zinc) from the pyritic gold concentrate. Adding lead nitrate had a negligible effect on gold extraction whilst improving silver extraction. Dissolution of copper was substantially suppressed by adding lead nitrate, i.e., from 23% (no Pb(NO3)2) to 4% (500 g/t Pb(NO3)2) over 24 h. Zinc dissolution was negligible (≤0.01%). Pre-aeration of the concentrate improved the gold and silver extractions by 4-14% and 23-44% at the subsequent cyanide leaching (1.5-3.5 g/L NaCN). However, it did not affect the leaching of copper. Only negligible leaching of zinc (≤0.6%) occurred during cyanide leaching. Pre-aeration also reduced cyanide consumption in subsequent cyanide leaching (1.5 g/L NaCN), i.e., from 2.83 kg/t to 2.03 kg/t NaCN per solids. These results suggested that lead nitrate can improve silver extraction while suppressing copper dissolution, which would be advantageous in the leaching-adsorption circuit (CIP), mitigating the dissolved copper-associated problems. Pre-aeration can also be suitable for improved gold/silver extractions and reduced reagent consumption.

Plant biomass driven synthesis of gAu/RGO nanocomposite towards photocatalytic degradation of phenolic compounds in wastewater

A plant biomass mediated ecofriendly synthesis approach was adopted for designing gold nanoparticles (gAuNPs) on reduced graphene oxide (RGO) using Averrhoa carambola leaf extract at room temperature. Introduction of folded RGO sheets and polar biomolecules of leaf extract collectively enhances growth inhibition effect and magnificently reduces the size of gAuNPs in the nanocomposite. The structure, morphology, optoelectronic properties, and thermogravimetric analysis of the synthesized compound was studied by XRD, TEM, STEM-HAADF, Raman, FT-IR, and UV-Vis DRS spectra. The size of gAuNPs were 8 ± 3 nm on 2D-RGO sheet as per TEM and STEM-HAADF analysis. 2 wt% loaded gAuNPs exhibited photocatalytic degradation of 98.92 %, 97.64 %, 92.67 %, and 89.16 % of bisphenol-A, 2-nitrophenol, 2-cholorophenol, and phenol, respectively under visible light irradiation. The degradation dynamics was found to follow pseudo first order kinetic model having highest rate constant of 0.034 min−1 for bisphenol A. The superior photocatalytic efficiency 2gAu/RGO can be attributed to synergistic effect of ultra nano Au and π-conjugated carbon network of RGO sheet. A mechanism was proposed for the degradation of phenol based on the free radical scavenger experiment, fluorescence, and transient photocurrent analysis. The green synthesized gAu/RGO nanocomposite can be reused up to 6th cycle effectively without any leaching of gold for elimination of the priority pollutant phenol and its derivatives.