Search Results (29)

This study addresses the dual challenges of low copper recovery and persistent arsenic pollution in the bioleaching of low-grade, high-arsenic copper ores containing enargite (Cu₃AsS₄). Through integrated electrochemical, chemical, and biological investigations, a selective and environmentally sustainable two-stage hybrid leaching process was developed. Electrochemical analysis identified a critical oxidation threshold of ~750 mV governing enargite dissolution. Chemical leaching and X-ray Photoelectron Spectroscopy (XPS) analysis revealed a temperature-dependent sulfur transformation pathway, enabling a staged thermal strategy: flotation below 40 °C to maximize hydrophobic elemental sulfur (S⁰) formation, and bioleaching at 40–55 °C to promote complete sulfur oxidation to sulfate. Optimization produced a two-stage process comprising 10-day chemical pre-leaching with FeSO₄ (10.0 g/L Fe²⁺) followed by bioleaching, achieving 78.3% copper extraction while suppressing arsenic dissolution to approximately 10%. The use of FeSO₄ instead of Fe₂(SO₄)₃ reduces reagent costs by ~70%, saving an estimated CNY 47,250 daily at 1000 t/d scale. Leaching toxicity tests confirm residue As < 0.10 mg/L, meeting non-hazardous waste standards (GB5085.3-2007). This work provides the first integrated demonstration of electrochemical threshold control combined with temperature-dependent sulfur speciation for selective copper extraction from arsenic-bearing enargite ores, offering a scalable, reagent-economical, and environmentally sustainable metallurgical route. Full article

Tennantite (Cu₁₂As₄S₁₃) and enargite (Cu₃AsS₄) are two important minerals that simultaneously contain copper and arsenic. Detailed studies of their structure and properties are crucial for understanding their oxidation, flotation, and leaching. This study investigates the crystal structures, electronic properties, and reactivity of these two copper-arsenic minerals from the perspectives of atomic bonding, charge, density of states, and d-orbital splitting. The results indicate that tennantite is a crystal with mixed Cu valence states of +2 and +1 (predominantly +1), while the Cu in enargite is in the +1 state. The valence state of As in tennantite (+3) is lower than that in enargite (+5). Orbital energy level calculations show that the energy gaps between the copper d-orbitals are small in both minerals, indicating strong electron delocalization and, consequently, strong covalent character in the crystals, which is also confirmed by Mulliken bond population calculations. The presence of arsenic is the reason for the enhanced covalency. It is noteworthy that tennantite exhibits stronger covalency. The Cu 3d and As 4p electrons in tennantite are more electronically active than those in enargite. In tennantite, the strong d-electron delocalization caused by d-p hybridization between Cu and S leads to similar 3d electronic properties between 3-coordinated and 4-coordinated Cu. The energies of the five d-orbitals of the 4-coordinated Cu in enargite are lower than those of the 4-coordinated Cu in tennantite, which may affect the ability of Cu 3d electrons to enter the empty orbitals of S atoms in sulfur-containing collectors to form π back-bonding, thereby reducing the collecting ability of enargite. On the other hand, the splitting energy of the 4-coordinated Cu 3d orbitals in enargite is significantly smaller than that in tennantite, making the structure less stable and, thus, potentially more prone to dissolution. Full article

The surface of chalcopyrite was studied by XPS characterization for an unleached chalcopyrite, and, after being leached in an alkaline oxidant medium at room temperature, pH 12.5, and [ClO⁻] 0.34 M, the reaction of enargite presented high selectivity with respect to chalcopyrite, allowing the removal of arsenic from copper concentrates with high arsenic content prior to smelting. Based on the XPS analysis, the original chalcopyrite is composed of a combination of its constituents in different oxidation states, and chalcopyrite has the following stoichiometric formula: Cu(I)_0.85Cu(II)_0.15Fe(II)_0.65Fe(III)_0.35S²⁻_1.5S₂²⁻_0.17S_n0.08²⁻. The unleached chalcopyrite on its surface presents an iron deficiency, which raises the ratio Cu/Fe up to 2, reaching the chalcopyrite Cu/Fe rate in the fifth cycle. The Cu/S ratio of chalcopyrite, 0.5, remains constant at the surface as after the peeling. Surface sulfur shows a decrease in monosulfides, increasing the S_n²⁻/S²⁻ y S₂²⁻/S²⁻ ratio. Chalcopyrite leached with ClO⁻/OH⁻ media generates surface layers with the following intermediate products: Chalcopyrite → CuFe_1-xS₂/CuS_n/Fe³⁺ -OH → Fe³⁺-OH/CuO/SO₄²⁻. Neither sulfur intermediates nor oxidized final products are passivating, allowing the chalcopyrite transformation to progress in depth with increasing reaction time. Full article

High alkalinity facilitates copper–sulfur flotation separation but also leads to issues such as high reagent consumption, pipeline scaling, and gold loss in tailings. The ore from a copper mine in Serbia contains 2.86% copper, 1.64 g/t gold, and 20.39% sulfur, with copper occurring mainly in covellite and enargite. To achieve efficient separation and recovery of copper–sulfur, a systematic study was conducted using micro-flotation, Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle analysis to investigate the inhibition and activation patterns of pyrite under low and high alkalinity conditions. The results indicate that the combined use of hydrogen peroxide and lime as inhibitor enables efficient separation of pyrite and covellite under low-alkalinity conditions. This effect is attributed to its ability to enhance oxidation of the pyrite surface, which generates more hydrophilic substances. Under low-alkalinity conditions (slurry pH = 10) regulated with hydrogen peroxide and lime in a covellite flotation cycle, and under acidic conditions (slurry pH = 6) in the pyrite flotation cycle, satisfactory results are obtained in both flotation cycles in comparison with industrial data. The copper flotation index was similar, but pyrite and gold recovery increased by 2.3% and ~4%, respectively, over those using lime alone. This process reduced the activator dosage required for pyrite activation substantially, while improving gold recovery. Results demonstrate an efficient method for copper–sulfur separation and recovery, providing theoretical guidance or industrial production processes. Full article

The presence of arsenic-bearing minerals in ores, notably enargite (${Cu}_{3}As{S}_4$), remains an unresolved issue for copper beneficiation processes, including those for porphyry copper deposits. In particular, several operational challenges remain for the selective flotation of enargite from copper–sulphide ores, as well as the selective leaching of arsenic from enargite in copper concentrates. This study addresses these challenges from the standpoint of mediator science, where structures with specific elemental compositions observed by several authors at the surface of enargite and chalcopyrite, under different conditions and analytical techniques, are compiled and analysed. Most probable surface species, observed using technologies measuring the outmost surface layer and occurring onto the mentioned minerals, are identified and compared to species predicted by classic thermodynamic calculations. The results indicate that for chalcopyrite the major species formed in acidic conditions is elemental sulphur, while copper oxide and iron oxides and oxy-hydroxides species predominate with increasing pH. For the case of enargite, a similar situation is observed at low pH values, although slightly acidic conditions appear as a less examined condition for this mineral. Some of the observed species were found to be consistent with thermodynamic predictions, while others are notably absent. Particularly, for the case of enargite researchers have reported the formation of arsenic (III) oxide at pH values as high as 13, and observation not predicted by Pourbaix diagrams. Thus As₂O₃ could be considered a metastable species at highly alkaline conditions, which opens an option to beneficiation from froth flotation. Interestingly, at the same pH condition, iron oxide and oxyhydroxides species predominate at the surface of chalcopyrite. Therefore, applying the mediator concept, the initial alkaline flotation of sulphide ores turns into an oxide flotation case. Full article

Enargite (Cu₃AsS₄), a copper–arsenic sulfosalt, represents a critical challenge in copper mineral processing due to its high arsenic content, which poses significant environmental, metallurgical, and economic issues. Its flotation behavior closely resembles that of other copper sulfides such as chalcopyrite and chalcocite, complicating selective separation at early beneficiation stages. This review presents a comprehensive examination of enargite’s surface chemistry and electrochemical behavior, focusing on the influence of oxidation, pH, and pulp potential on surface reactivity, charge distribution (zeta potential), and hydrophobicity. Detailed insights into the formation of surface oxidation layers, passivation mechanisms, and contact angle variations are provided to elucidate collector-mineral interactions. Advances in selective flotation techniques are also discussed, including the use of depressant reagents, controlled redox environments, and reagent conditioning strategies. Special attention is given to flotation in seawater, where ionic strength and multivalent ions significantly influence mineral-reagent interactions and flotation outcomes. Galvanic interactions between enargite and other sulfide minerals are identified as critical factors affecting floatability and selectivity. The review consolidates findings from recent experimental and electrochemical studies, highlighting promising approaches to enhance enargite rejection and copper concentrate purity. It concludes with perspectives on future research aimed at optimizing flotation processes and developing sustainable solutions for processing arsenic-bearing copper ores. Full article

In Chile, copper concentrate production through mineral flotation is increasing while production through hydrometallurgical processes is decreasing due to the depletion of oxidized ores. Using the idle capacity of hydrometallurgy plants for acid pretreatment of sulfate ores before the leaching stage is an attractive alternative; however, a deeper understanding of the process and the products of such treatment is required. In this study, the mineral species formed during acid pretreatment are characterized to identify new mineralogical species. Pretreatment was conducted at 50 °C with 210 kg/t H₂SO₄ over 15 days on a copper concentrate mainly composed of enargite (35.93%). The characterization techniques used were X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and X-ray Photoelectron Spectroscopy (XPS). XRD identified copper sulfate (CuSO₄) formation and the disappearance of chalcocite/digenite (Cu₂S) and bornite (Cu₅FeS₄), indicating their transformation into sulfates. FESEM showed that enargite particles were oxidized, suggesting they did not form copper sulfates. The XPS results confirmed the presence of copper in species such as sulfides and sulfates. The results indicate that chalcocite and bornite transformed into copper sulfates, while chalcopyrite and enargite were only superficially oxidized. The combination of techniques allowed for a detailed identification of mineral transformations during pretreatment. Full article

As a result of changes in copper mineralogy, various treatment options for copper sulfides have been explored, including pretreatment processes aimed at enhancing material permeability and improving the dissolution of valuable minerals. Despite its significance, this topic has only recently gained attention. In this research, a copper concentrate with a high arsenic content was studied, with enargite (Cu₃AsS₄) as the main mineral phase. The objective was to evaluate the effect of pretreatment on copper extraction efficiency prior to leaching. Three key variables were investigated: curing time (0, 5, 10, and 15 days), H₂SO₄ dosage (0, 70, 140, and 210 kg/t), and FeCl₃ concentration (0, 0.5, 1, and 1.5 M). The sample was characterized both before and after pretreatment, revealing the formation of new species such as CuSO₄·5H₂O and Cu₂Cl(OH)₃ under optimal conditions of 15 days curing time, 70 kg/t of H₂SO₄, and 1 M FeCl₃. Copper extraction solely through curing reached 20.79%. The analysis suggests that curing time is the most influential factor in the process, accounting for 46% of the overall contribution. In comparison, sulfuric acid and ferric chloride contribute less, with 20% and 10% contributions, respectively. Full article

Against the backdrop of the increasing copper demand in a low-carbon economy, this work statistically forecasted the distribution of China’s copper tailings for the first time, and then characterized them as finely crushed and low-grade mining solid wastes containing copper mainly in the form of chalcopyrite, bornite, covelline, enargite and chalcocite based on available research data. China is the globally leading refined copper producer and consumer, where the typical commercial-scale bioleaching of copper tailings is conducted in the Dexing, Zijinshan and Jinchuan mining regions. And these leaching processes were compared in this study. Widely used chemolithoautotrophic and mesophilic bacteria are Acidithiobacillus, Leptospirillum, Acidiphilium, Alicyclobacillus and Thiobacillus with varied metal resistance. They can be used to treat copper sulfide tailings such as pyrite, chalcopyrite, enargite, chalcocite, bornite and covellite under sufficient dissolved oxygen from 1.5 to 4.1 mg/L and pH values ranging from 0.5 to 7.2. Moderate thermophiles (Acidithiobacillus caldus, Acidimicrobium, Acidiplasma, Ferroplasma and Sulfobacillus) and extreme thermophilic archaea (Acidianus, Metallosphaera, Sulfurococcus and Sulfolobus) are dominant in leaching systems with operating temperatures higher than 40 °C. However, these species are vulnerable to high pulp density and heavy metals. Heterotrophic Acidiphilium multivorum, Ferrimicrobium, Thermoplasma and fungi use organic carbon as energy to treat copper oxides (malachite, chrysocolla and azurite) and weathered sulfides (bornite, chalcocite, digenite and covellite) under a wide pH range and high pulp density. We also compared autotrophs in a planktonic state or biofilm to treat different metal sulfides using various sulfur-cycling enzymes involved in the polysulfide or thiosulfate pathways against fungi that produce various organic acids to chelate copper from oxides. Finally, we recommended a bioinformatic analysis of functional genes involved in Fe/S oxidization and C/N metabolism, as well as advanced representation that can create new possibilities for the development of high-efficiency leaching microorganisms and insight into the mechanisms of bioleaching desired metals from complex and low-grade copper tailings. Full article

Water recycling in mining is essential to decrease water usage, which results in the accumulation of high concentrations of inorganic and organic substances in the process water. Consequently, adverse impacts on the flotation process of copper sulfides may arise. High-molecular-weight polymers based on anionic polyacrylamides (PAMs) are used as tailing flocculants in mineral processing plants. The recirculation of water recovered from the tailing thickeners to the flotation process introduces residual PAMs, which can impact the flotation of important copper sulfides like chalcopyrite, bornite, and enargite. This issue has been rarely studied. In this work, results on the effect of an anionic polyacrylamide (PAM) of medium–low anionicity on the flotation of chalcopyrite, enargite, and bornite are reported and analyzed. The results show that PAM molecules depress the flotation of chalcopyrite, enargite, and bornite under a wide range of pH values. The experimental data indicate that the depressing effect of PAMs on copper sulfides increases with pH. The zeta potential results reveal that this parameter becomes less negative with the addition of PAMs, indicating interactions between PAM molecules and the surfaces of the copper sulfides. PAM adsorption on copper sulfides increases with pH, which correlates with the flotation and zeta potential data. It is proposed that the interactions between PAM molecules and copper sulfides are explained by the presence of surface iron and copper hydroxides that create chemically active adsorption sites. Full article

Chilean mining faces challenges associated with the depletion of oxidized copper ore and the environmental complexity of treating concentrates with high arsenic content. Given this, hydrometallurgy emerges as an alternative for the treatment of these concentrates. This research analyzes the interaction of sulfuric acid (0, 70, 140, and 210 kg/t), sodium chloride (0, 25, 50, and 100 kg/t), curing time (1, 5, 10, and 15 days), and temperature (25, 35, 50, and 75 °C) in the pretreatment of a copper concentrate with 35.57% total copper and 5.91% arsenic (enargite, 35.93%). In the pretreatment, a maximum copper extraction of 26.71% is achieved using 210 kg/t sulfuric acid at 50 °C over 15 days of curing. The experimental results are analyzed through an empirical model, where the interaction between sulfuric acid and curing time is identified as beneficial when the sulfuric acid addition is above 70 kg/t, leading to higher moisture content in the sample. In the absence of sulfuric acid, sodium chloride significantly influences the achievement of higher copper extractions. During curing at higher temperatures, the importance of maintaining a moisture level is emphasized to prevent solution evaporation and hinder diffusion through the particles, thereby ensuring reactivity in the sample. Full article

In mineral processing, arsenic-bearing minerals are particularly difficult to separate from their non-arsenic counterparts because they possess similar surface properties. Peptides are well known for their target specificity and can offer a ‘green’ alternative to traditional flotation reagents. However, the use of peptide technologies in mineral processing for developing novel flotation reagents has not been explored. Hence, this work aims to develop a screening method to identify mineral-binding peptides as potential reagent candidates. It is hypothesised that peptides can selectively adsorb onto mineral surfaces, and this method can efficiently identify mineral-binding peptides with high specificity toward the target minerals. The methodology presented involves a selection of peptide candidates from existing literature that show affinity toward arsenic species. These peptides were tested for their adsorption performance onto selected mineral surfaces to evaluate their mineral selectivity under flotation conditions. The study demonstrates that the screening method developed is effective in identifying peptides that have an affinity for target minerals, in this case, arsenic minerals. The screening method can be applied to other minerals, thus, unlocking the potential for developing new reagent chemistries for use in mineral processing. Full article

In this work, the roasting of an enargite mix was carried out in oxidative conditions. The temperature range of the study was 773–973 K. The mixture had a 4:6:6 molar ratio of enargite, magnetite and coal, respectively. The roasting was made in an open atmosphere. The time was 1 h for each isothermal test. The effect of temperature and weight loss were studied. The results indicate that the temperature affects the products. At 773–873 K, the copper phases were sulfates. When the temperature was increased to 973 K, all the present phases were oxidized, and no arsenic phase was encountered in the XRDs. Therefore, this process is an excellent alternative for roasting copper concentrates with enargite, removing arsenic in the gas phase and generating a calcine that could then go to lixiviation to finally recover the copper through electrowinning. Full article

The selective leaching of arsenic using sodium hypochlorite was evaluated in order to reduce its concentration in a copper concentrate. The best conditions achieved in the synthetic concentrate were applied to the industrial concentrate. First, the individual behaviors of pure samples of enargite and chalcopyrite were evaluated under a hypochlorite medium. The enargite reaction is significantly faster than chalcopyrite, allowing for greater selectivity to ClO⁻ (0.1–0.3 M), pH 12–12.5; 20 to 40 °C, reaction time <60 min. Under these conditions, the reagent consumption for pure compounds approaches the stoichiometric consumption and presents a selectivity factor of 5/1. Furthermore, concentrate leaching in a sodium hypochlorite medium, containing enargite, releases arsenic ions into the solution, while copper and iron remain in the solid phase, as CuO and Fe(OH)₃, respectively. A novel copper concentrate cleaning process by selective leaching is proposed, which transforms unacceptable copper concentrate for smelters (>0.5%As) into clean concentrates (<0.2%As) or low penalty concentrates (0.2 < %As < 0.5). The estimated consumption for the cleaning process is in the order of 0.4–0.6 kg Cl₂ equivalent per kg of concentrate. Full article

The effect of microwave pre-treatment on the magnetic properties of tennantite and enargite was investigated. Magnetic susceptibility, XRD, and XPS characterization of tennantite and enargite before and after treatment were conducted to explore the changes in their magnetic properties. Moreover, magnetic separation of chalcopyrite binary mixtures with enargite and tennantite was performed. The results showed insignificant effects on the magnetic susceptibility of the two minerals after microwave pre-treatment. Magnetic separation results showed arsenic rejection by 84.2%, and 76.3% in the case of enargite and tennantite binary mixtures with chalcopyrite; respectively. Full article