Search Results (24)

The behavior of impurities in cast copper was investigated to simulate production with increased utilization of secondary sources within the framework of a circular economy. The incorporation of impurities, particularly Ni, Sn, and Sb, from recycled Cu may significantly impact the electrorefining process. In this study, commercial anodes were doped with Ni, Sn, and Sb concentrations of 2500–6500 g/t, 300–900 g/t, and 450–950 g/t, respectively. Anode concentrations of Pb and Bi were maintained at 1000 g/t and 350 g/t, respectively. As concentrations were examined at two levels, 860 or 1700 g/t, depending on the commercial anode used to create the doped samples. Electron microscopy with microprobe analysis revealed that the commercial anodes contained three predominant phases: Cu₂O, (Cu,Ag)₂(Se,Te), and a complex oxide phase of Cu, Pb, As, Sb, and/or Bi. Ni, the main impurity, primarily accumulated within the Cu grains, while Sn and Sb tended to form oxidized inclusions. The distribution of Ni in Cu grains was ca. 20% lower in the anodes doped at higher Ni concentrations due to the formation of nickel-bearing inclusions, such as Kupferglimmer and NiO. The doped anodes showed lower quantities of Cu₂O inclusions than the commercial anodes due to the preferential formation of oxides with other impurities, including SnO₂. These findings highlight potential challenges for Cu electrorefining in a circular economy, as Ni, Sb, and Sn may impact the deportment of these impurities to slimes or electrolyte and may cause copper depletion in the refining electrolyte. Full article

Copper anode slime (CAS) contains high concentrations of precious metals, particularly gold, which can reach up to 11 wt%. During copper anode electrorefining, 5–10 kg of CAS is generated per ton of copper cathode. Processing CAS is crucial for economic reasons, as gold significantly contributes to revenue for both miners and custom copper smelters. This paper provides a comprehensive review of industrial processes and technologies for CAS treatment, with a focus on gold recovery, covering studies from the early 1930s to the present. It documents traditional and recent trends and analyzes the advantages and disadvantages of existing methods. Key factors affecting revenue, such as gold production lead time, in-process inventory, and first-pass recovery rate, are discussed to mitigate losses in fluctuating gold markets. CAS processing routes are categorized into two main groups: traditional hybrid routes (involving hydrometallurgy, pyrometallurgy, and electrorefining/electrowinning) and rather recent purely hydrometallurgical routes. Traditional methods can take up to 45 days, with gold recovery occurring late in the process and losses arising in the anode, cathode, electrolyte, or slag. In contrast, purely hydrometallurgical routes have total processing times of 7–8 days, achieve early gold recovery, and can attain first-pass recovery rates as high as 99%. Additionally, the hydrometallurgical routes are more environmentally friendly, with lower pollution levels and reduced energy consumption compared to hybrid routes. These findings indicate that purely hydrometallurgical routes outperform traditional hybrid methods. This paper aims to serve as a guideline for industrial CAS processing, assisting custom copper smelters in navigating challenging market conditions marked by low treatment and refining charges, with an emphasis on enhancing gold recovery to promote sustainability. Full article

As the grade of the copper concentrate decreases and its composition becomes increasingly complex, the silver content in anode plates cast after fire refining increases, leading to a higher silver content in the copper cathode during electrorefining and a substantial loss of precious metals. This study investigates the impact of 5-amino-1H tetrazole (5-AT) on reducing silver in copper cathodes during electrorefining with high silver content anode plates. 5-AT forms an “adsorption layer” on the anode surface, reacting with Ag⁺ released by the anode to form a precipitate and prevent Ag⁺ from entering the electrolyte. This process agglomerates fine Ag-Se compounds and AgCl particles, creating larger anode slime particles that settle quickly, thus inhibiting fine silver-containing particles from adhering to the cathode. Furthermore, 5-AT adsorbs on the cathode, binding with Cu⁺ and promoting the Cu²⁺ electrodeposition process while inhibiting Ag⁺ electrodeposition. This facilitates uniform copper cathode grain growth and reduces inclusions in the copper cathode. The grain size of the copper cathode initially decreases and then increases as the concentration of 5-AT increases. At an optimal 5-AT concentration of 15 mg/L, the Ag content in the copper cathode decreased from 6.9 ppm to 4.7 ppm, indicating the potential efficacy of 5-AT in improving the quality of electrorefined copper. Full article

As one of the main factors decreasing current efficiency and product quality, the growth of nodules deserves attention in the copper electrorefining process. Three-dimensional (3D) Finite Element Method models combining tertiary current distribution and fluid flow were established in this study to investigate the details of the growth of columnar nodules, including the electrolyte flow around the nodule and its effects. Compared with an inert nodule, a significant impact of the electrochemical reaction of an active nodule has been observed on the fluid flow, which may be one of the reasons for the formation of small nodule clusters on the cathode. Furthermore, the local current density is not even on the nodule surface under the comprehensive influence of local electrolyte flow, local overvoltage, and the angle with the anode surface. Thus, the head of an active nodule grows faster than the root, and the upper parts grow faster than the lower parts, leading to asymmetric growth of the nodules. Full article

In Northern Chile, large amounts of highly corrosive solutions are currently generated in the process of cathode washing after completing the electrowinning or electrorefining process of copper. This study investigates the electrochemical behavior of ASTM A36 carbon steel in pregnant-leach-solution (PLS) wash water. Measurements of electrochemical impedance spectroscopy and linear sweep voltammetry, complemented with weight loss measurements, were performed. Four ratios of PLS containing reverse osmosis (RO) water are evaluated, considering both quiescent and rotating conditions of the steel specimen. The results indicate that oxygen reduction, hydrogen evolution, and iron oxidation reactions are all involved during the corrosion of carbon steel in pure RO water, with the corrosion rate increasing up to 4 times under rotating conditions. In the case of corrosion in RO wash water containing PLS, a galvanic process occurs whereby copper is reduced at the expense of iron oxidation, superimposed on former partial reactions. The deposited copper induces notable corrosion inhibition of steel, observed as a significant drop in corrosion rate from high initial to constant residual values. Morphological and X-ray analyses support that corrosion is affected by oxide layer formation and galvanic copper deposition, confirming the results obtained from electrochemical analysis and weight loss measurements. Full article

This research aimed to evaluate the effectiveness of new organic substances, including a novel ionic liquid based on polyhexamethylenebiguanidine, polyhexamethyleneguanidine, and safranin in the copper electrorefining process. Experiments were conducted on a small laboratory scale using industrial copper anodes. Single doses of new additives did not improve process indicators (current efficiency, average cell voltage, specific energy consumption) or the quality of copper cathode deposits. However, a combination of a new ionic liquid based on polyhexamethylenebiguanidine and thiourea resulted in a satisfactory current efficiency of 97%, an average cell voltage of 0.110 V, a low specific energy consumption index of approximately 100 kWh/t_Cu, and smooth cathode surfaces. These results were superior to those obtained with industrial additives (bone glue and thiourea). The findings enhance our understanding of how these substances influence the electrorefining process and suggest the potential for more efficient and sustainable methods. Further research is recommended to validate these findings and explore their industrial applications. Full article

In this work, electrodialysis (ED) and electro-electrodialysis (EED) were investigated as technologies for the recovery of Sb from wastes and effluents generated during the pyrometallurgical processing of copper sulfide minerals and the hydrometallurgical treatment of low-copper-content mixed minerals. This work addresses the challenge of applying electrochemical methods for recovering these valuable materials and recycling highly concentrated acid solutions used in the latter separation stages of the electrorefining process. The electrochemical characterization of the solutions was conducted, and the electrodeposition of Sb and Bi was performed in electrochemical cells. Also, the implementation of membrane processes in the recovery of such materials was investigated. Full article

This study examined how pH hydrolysis affects the recovery process for antimony extracted from spent electrolytes. Various OH⁻ reagents were used to adjust the pH levels. The findings reveal that pH plays a crucial role in determining the optimal conditions for extracting antimony. The results show that NH₄OH and NaOH are more effective compared to water, with optimal conditions at pH 0.5 for water and pH 1 for NH₄OH and NaOH, resulting in average antimony extraction yields of 90.4%, 96.1%, and 96.7%, respectively. Furthermore, this approach helps to improve both crystallography and purity related to recovered antimony samples obtained through recycling processes. The solid precipitates obtained lack a crystalline structure, making it difficult to identify the compounds formed, but element concentrations suggest the presence of oxychloride or oxide compounds. Arsenic is incorporated into all solids, affecting the purity of the product, and water showing higher antimony content (68.38%) and lower arsenic values (8%) compared to NaOH and NH₄OH. Bismuth integration into solids is less than arsenic (less than 2%) and remains unaffected by pH levels except in tests with water, where a bismuth hydrolysis product is identified at pH 1, accounting for the observed reduction in antimony extraction yields. Full article

The effect of glue, thiourea, and chloride on the kinetics of copper reduction in CuSO₄–H₂SO₄ solutions of copper composition, and temperatures like those used in the copper electrorefining plants, were studied. The kinetic study was conducted by determining the kinetic parameters ${\mathrm{i}}_0$ and $\mathsf{\beta }$ under the activation control of the Tafel approximation, which is applied to polarization curves obtained via linear voltammetry. The results show that the incorporation of glue and thiourea decreases the exchange current density, while chloride does not significantly affect the kinetic parameters. The data on the fraction of the surface covered by glue and thiourea fitted to the Temkin adsorption isotherm indicate that the mechanism of action during the reduction of copper to low overpotentials is the adsorption of these additives on the electrode surface. The adsorption of additives reduces the cathodic area available for Cu²⁺ adsorption and lateral diffusion of Cu atoms to continue the reduction process and the growth of the crystalline deposit. The kinetic study was complemented with a comprehensive analysis of the effect of the additives on the morphological and textural characteristics of the deposits. The results of this work contribute to the understanding of the mechanisms of the main additives used during the copper electrorefining process. Full article

Arsenic content in copper concentrates is continuously increasing worldwide. It is desirable to remove arsenic from copper in the earlier stages of copper making due to the deposition of arsenic to cathode copper during the electrorefining process. Effects of temperature, flux, and oxygen on the distribution of arsenic during copper converting and fire refining processes were studied using FactSage 8.2. The results showed that arsenic can be effectively removed by proper selection of converting and refining slags. The decrease in Fe/SiO₂ or Fe/CaO ratio in the converting slag is favorable for arsenic distributed to slag. CaO is more effective than SiO₂ in decreasing the liquidus temperature of the slag and arsenic content in the blister copper during the converting process. Na₂O or CaO as a flux is effective to remove arsenic in the fire refining process. Full article

About 90% of selenium is obtained from treating copper anode slimes, which are a by-product of copper electrorefining. Selenium has been traditionally obtained by the pyrometallurgic treatment of anode slimes, which has been effective in recovery. However, in pyrometallurgical processes, there are increasingly strict environmental regulations. Hydrometallurgical treatments have been proposed to totally or partially replace conventional methods, some of which are in the developmental stage, while others are being used at the industrial scale. The selenium present in anode slimes is in the form of silver and copper selenides. This article proposes a hydrometallurgy alternative to recover selenium from decopperized anode slimes generated by a copper electrorefining plant in Chile by an alkaline-oxidizing leaching media (ClO⁻/OH⁻). The Taguchi experimental design was used to assess the effects of temperature, reagent concentration, and pH over time. The results indicated that the optimal selenium dissolution of 90% was achieved at pH 11.5, 45 °C, and 0.54 M of ClO⁻. According to the SEM/EDX characterization of the solid leaching residue, the undissolved percentage of selenium is due to the generation of a layer of AgCl around the selenium particles that hinders the effective diffusion of the reagent. Full article

A transient three-dimensional comprehensive numerical model was established to study ion transport caused by diffusion, convection, and electro-migration in the electro-refining process for scrap-metal recycling. The Poisson–Nernst–Planck equations were used to define ion transport within the electrolyte, while the Naiver–Stokes equations and the energy equation were employed to describe fluid flow and heat transfer. In addition, the Butler-Volmer formulation was used to represent the kinetics of the electrochemical reaction. The comparison between the measured and simulated data indicates the reliability of the model. Under the action of diffusion and electro-migration, the positive copper ion moves from the anode to the cathode, while the negative sulfate ion migrates in the opposite direction. The distribution of the ion concentration, however, greatly changes if the fluid flow is taken into account. The ion concentration around the anode and the rate of the electrochemical reaction that occurs at the anode surface are reduced by the fluid flow. The proposed computational framework offers a valuable basis for future research and development in the field of scrap-metal recycling technology. Full article

The mining industry has faced significant challenges to maintaining copper production technically, economically, and environmentally viable. Some of the major limitations that must be overcome in the coming years are the copper ore grade decline due to its intense exploitation, the increasing requirements for environmental protection, and the need to expand and construct new tailings dams. Furthermore, the risk of a supply crisis of critical metals, such as antimony and bismuth, has prompted efforts to increase their extraction from secondary resources in copper production. Therefore, improving conventional processes and developing new technologies is crucial to satisfying the world’s metal demands, while respecting the policies of environmental organizations. Hence, it is essential that the chemical composition of each copper production stage is known for conducting these studies, which may be challenging due to the huge variability of concentration data concerning the ore extraction region, the process type, and the operational conditions. This paper presents a review of chemical composition data of the main stages of copper production from sulfide minerals, such as (1) copper minerals, (2) flotation tailings, (3) flotation concentrates, (4) slags and (5) flue dust from the smelting/converting stage, (6) copper anodes, (7) anode slimes, (8) contaminated electrolytes from the electrorefining stage, (9) electrolytes cleaned by ion-exchange resins, and (10) elution solutions from the resins. In addition, the main contributions of recent works on copper production are summarized herein. This study is focused on production sites from Chile since it is responsible for almost one-third of the world’s copper production. Full article

Current density plays a major role in deciding the plant size, current efficiency, and energy consumption in electrorefining cells. In general, operating current density will be 40% of the limiting current density. Forced circulation of the electrolyte in the presence of promoters improves the mass transfer coefficient. In the present study, rectangular turbulence promoters are fitted at the bottom side of the cell to improve the mass transfer coefficient at the cathode support plate. The limiting current density technique is used to measure the mass transfer coefficient. The variables covered in the present study are the effects of flow rate, promoter height, and spacing among the promoters. The electrolyte consists of copper sulfate and sulphuric acid. At a regulated flow rate, the electrolyte is pumped from the recirculation tank to the cell through an intermediate overhead tank. The limiting current density increased with an increasing flow rate in the presence of promoters, and thus the overall mass transfer coefficient on the cathode support plate also improved. With an increase in the flow rate of the electrolyte from 6.67 × 10⁻⁶ to 153.33 m³/s, limiting current density increased from 356.8 to 488.8 A/m² for spacing of 0.30 m, with a promoter height of 0.01 m. However, it is noteworthy that when the promoter height is increased from 0.01 to 0.07 m, the overall mass transfer coefficient is found to increase up to 60%, but with the further increase in the promoter height to 0.30 m the mass transfer coefficient starts to decrease. Therefore, the optimized cell parameters are established in this work. The current sustainable concept of employing rectangular turbulence promoters will bring benefits to any precious metal refining or electrowinning tank house electrolytes. Full article

This work focused on purifying copper electrolytes from a bismuth impurity on a laboratory scale. The electrolyte came from Polish copper electrorefineries with the content of main components, g/dm³: 49.6 Cu, 160 H₂SO₄. The electrolyte was enriched in bismuth by Bi₂O₃ addition. Purification of bismuth contamination was carried out using selected agents with adsorbing effects, such as barium hydroxide octahydrate, strontium carbonate, barium carbonate, barium and lead sulfates. The trials were performed until achieving the Bi level—below 0.1 g/dm³. During the experiments, it was noticed that electrolyte purification degree depends on initial Bi concentration in electrolyte, time and temperature, as well as on the type and amount of the bismuth-lowering agent. The most satisfactory results of Bi impurity removal were with additions of barium hydroxide octahydrate, strontium carbonate and barium carbonate to electrolyte at 60 °C for 1 h. These parameters revealed the highest electrolyte purification degree. Bismuth is not removed effectively from electrolytes by barium sulfate or lead sulfate addition. The efficiency of the purification process is much higher when the agents are added to the solution in the form of carbonates or hydroxides. Extending the electrolyte purification process time may cause dissolution of bismuth from the resulting precipitate and increase of bismuth concentration in electrolytes. Full article