No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Abstract
This chapter explains how Cu²⁺ ions generated by leaching are reduced and electrowon as pure metallic copper in the form of cathodes.
The electrowinning process entails (a) immersing metal cathodes and inert (but conductive) anodes into a purified electrolyte containing CuSO4 and H2SO4; (b) applying an electrical current from an external source, such as a rectifier, which causes current to flow through the electrolyte between the cathodes and anodes; and (c) plating pure metallic copper from the electrolyte onto the cathodes using the energy provided by the electrical current to drive the reduction of the Cu²⁺ ions to copper metal.
Dynamic process models present an opportunity to investigate optimization and control strategies for the energy-intensive copper electrowinning process. In this paper, a dynamic semi-empirical model of the copper electrowinning process was developed to predict the copper yield, current efficiency, and specific energy consumption. The model uses input variables readily measured in industrial tankhouses and incorporates the ability to induce step or pulse disturbances in the electrolyte composition or flow rate. Dynamic bench-scale electrowinning data were used to show how the model may be calibrated and validated for use in predicting electrowinning performance. Overall, the performance of the developed dynamic model lends credence to the application thereof for operator training, process monitoring, and early fault detection. The model also represents a further step towards investigating advanced control strategies for the electrowinning process.
Ion exchange has traditionally been employed for water purification and the removal of metal contaminants from dilute waste streams. More recently, its use in removing trace metallic impurities from hydrometallurgical process streams (with typical background metal concentrations of 50–100 g/L) has increased substantially. It is also used as a primary recovery and concentration unit operation for certain commodities, where both technical and cost advantages become apparent for complex flow-sheets. This overview discusses selected modern applications of ion exchange in hydrometallurgical processes for uranium, precious metals, copper, cobalt, nickel, zinc, and the rare-earth elements, and identifies some opportunities for the future.
Lead-based alloys are used as the primary anodes for electrowinning from sulphate-based aqueous systems. Lead anode technology has evolved over the years, migrating from pure lead and lead-antimonial alloys to the present-day lead-calcium-tin alloys for copper electrowinning and lead-silver alloys for zinc electrowinning. Anode technology has also migrated from cast to rolled microstructures in search of improved mechanical properties and higher corrosion resistance. Although great strides have been made in the development of new alloys and production processes, the industry still has unresolved issues related to untimely corrosion, which limits anode life and may lead to higher contaminant levels in the metal being produced. Lead anodes corrode because of the difference in the chemical/electrochemical potential across the microstructural features of an anode. Given a very high purity material, we find that the grain boundary areas corrode significantly faster than the rest of the grain. A balance of alloying element selection and microstructural design allows the grain boundary area to be engineered, thus minimizing grain boundary corrosion. However, operational issues can lead to unexpected corrosion behaviours that we will discuss moving forward. The comments in this work, although directed toward copper electrowinning, can be extended to similar phenomena in other metals electrowon from sulphate media (i.e., zinc, nickel, cobalt, manganese). The life cycle of electrowinning anodes depends on tankhouse operating conditions and maintenance of the anodes, including cleaning and straightening. This paper will focus on the operational aspects of maximizing the utilization of lead anodes for base metals electrowinning.
Organic smoothing additives are used to produce dense, thick, high-quality cathodes in copper electrowinning. Glue had been used traditionally and is still used in operations that do not employ solvent extraction to produce the electrowinning electrolyte. With the advent of solvent extraction electrowinning, guar started to be used and remained in use for many years as it does not affect the phase disengagement in solvent extraction. Recently, however, guar has been replaced by less-expensive saccharide- and polyacrylamide-based additives. This paper is the first of a series of four papers that examine saccharides and polyacrylamides as new additives for copper electrowinning. A review of previous research related to copper electrowinning additives is presented here, along with a selected review of additives in other copper electrodeposition systems.
During copper electrowinning, a layer of PbO 2 forms on the surface of the lead-calcium-tin alloy anodes that are most commonly used in modern copper tankhouses. The PbO 2 layer is important for many reasons such as passivating the Pb metal to attack by acid and having a reasonable exchange current density for oxygen evolution. However, the electrochemical behavior of PbO 2 under upset or open-circuit conditions is one cause of anode degradation and can lead to high levels of lead contamination of the copper cathodes and to more frequent shutdowns in order to remove the accumulated anode mud from the bottom of cells. Upset conditions arise when power is lost to the cell, which occurs in electrical blackouts and when cells are taken off-line for cleaning. Some tank-houses deploy backup rectifiers of limited capacity which are used during such periods. This paper describes a study of the mechanisms for formation and breakdown of the PbO 2 layer and establishes the minimum current density required in order to maintain the integrity of the PbO 2 layer on the anode surface.
Hydrometallurgical processes for copper extraction have been applied successfully for over 100 years for the treatment of both oxide and secondary sulfide copper ores. Effective hydrometallurgical processes to treat primary sulfide ores and concentrates are now emerging and being commercialized. This paper investigates the total energy consumption for each of these processes and provides comparisons with the alternative processing routes, which include grinding, flotation, smelting and refining of primary and secondary copper sulfide ores. For each process, energy consumption was estimated based on the use of electricity, natural gas, diesel and wear steel energy equivalent. The results demonstrate that hydrometallurgical processes consume significantly less energy than the alternative grinding, flotation, smelting and refining routes in many applications. However, this analysis is strongly dependent on ore mineralogy, grade of copper and by-products, the metallurgical response of the ore to the process options and the presence of deleterious elements and other factors. The results are presented as ore grade versus specific energy consumption (kJ/lb copper) plots for typical ore types encountered in industrial applications.
The effect of cobalt ions in the electrolyte on the performance of lead alloy anodes used for oxygen evolution during electrolysis of copper/sulfuric acid solutions has been studied extensively over the past 90 years. A review of the literature has confirmed that cobalt both as constituent of the anode material and present as ions in the electrolyte reduces the rate of corrosion of the anodes, lowers the overpotential for the evolution of oxygen, and reduces lead contamination of the copper cathodes. Despite the fact that these effects have been developed into widespread applications in the electrowinning industry, a fundamental understanding of the mechanism of the action of cobalt ions remains a point of debate. A selection of the most relevant literature on this phenomenon has been reviewed and the data and proposed mechanisms critically evaluated.
It is known that lead anodes used in the industrial extraction of copper by electrolysis (electrowinning) suffer corrosion as a result of accidental or intended current interruptions. In order to improve understanding of the corrosion and protection of such anodes, the effects of the concentrations of copper, sulphuric acid, cobalt, iron, manganese, chloride and an organic additive (guar) on the corrosion of lead have been studied by means of weight loss tests and surface analysis techniques (X-ray photoelectron spectroscopy, X-ray diffraction, and wavelength dispersive spectroscopy). The rate of corrosion of lead during current interruptions increases with increasing concentration of sulphuric acid and copper, whereas it decreases markedly in the presence of cobalt and iron and, to a lesser extent, in the presence of chloride and the organic additive. Manganese is the only impurity whose presence does not reduce the rate of corrosion; it is also the only element which precipitates in significant amounts on the lead anode surface under the conditions studied. A method is proposed to establish the optimum anodic protection current density during current interruptions in electrowinning cells. Three current density ranges have been found, of which the ‘high’ protection range could be caused by the degree of compactness acquired by the PbO2 layer at applied anodic current densities in excess of 60 A m-2. The authors would like to thank the National Committee for Scientific and Technological Research (CONICYT, Chile) for funding this work via FONDECYT Projects No. 195 0532 and 101 0138.
Physicochemical properties of copper electrolytes are a strong fundamental consideration in electrodeposition processes during electro-purification and recovery of copper. Their influence extends to mass transfer as well as energy consumption during the electrodeposition process. In this study, the influence of electrolyte composition on electrolyte physicochemical properties was investigated to review the existing literature data. This review of data is considered necessary as more and more electrowinning models are being developed for process prediction and optimisation and a need of such data is required for accurate prediction of physicochemical properties. The major components of importance to the formation of smooth high-quality and high-purity copper cathodes at optimum current efficiency are considered the species in solution. These include Cu ions, Fe ions (major impurity), H2SO4, and a smoothing agent additive. A 5-factor, 2- and 3-level experimental design was employed to determine the effect of copper (35 and 45 g/l), sulphuric acid (160 and 180 g/l), iron (1, 3, and 6 g/l), polyacrylamide additive (2, 5, and 10 mg/l), and temperature (45 and 55 °C) on electrolyte density, conductivity, and the diffusion coefficient in synthetic copper electrowinning electrolytes. The major species in a copper electrowinning electrolyte are found to be the most relevant for prediction of physicochemical properties. These results indicate that relatively simple empirical models are sufficient for modelling of the electrolyte domain in electrowinning, without the need for the generation of vast amounts of complex experimental data.
Copper electrowinning is an important recovery method in the copper industry, which accounts for a growing proportion of the world copper production. In copper electrowinning, not all the current is used for the deposition of Cu, in large part because of the existence of dissolved iron in the electrolyte. The reduction of ferric ions is often the main factor that causes the current efficiency to decrease. The current efficiency is influenced by parameters such as electrolyte temperature, current density, iron concentration, copper concentration, etc. To obtain optimal operating conditions, thus minimizing energy consumption, a copper electrowinning current efficiency model was established using empirical formulas and electrode kinetics. Electrochemistry, gas-liquid flow, transport phenomena and comparisons to experimental data are considered to enhance the accuracy of the model. The model can predict the current efficiency under a variety of conditions to provide valuable guidance for the optimization of process parameters.
The winning of high purity metal from aqueous solutions through electrodeposition is the final processing recovery step for many nonferrous metals. Direct electrical current/voltage provides the necessary driving force to promote the necessary reactions at an industrially relevant rate. Energy, especially electrical, is often the highest cost for electrowinning operations. Therefore, energy efficiency is a paramount concern for modern facilities. This chapter discusses electrical energy consumption in aqueous electrowinning with a specific focus on cell voltage and current efficiency. It also presents potential improvements.
Conventional lead alloys are widely used in the zinc industry, in spite of their high overpotential and Pb contamination of the deposit during zinc electrowinning. The Oxide Coated Catalytic Anodes (OCAs) are considered to improve cathodic zinc purity and decrease cell voltage during zinc electrowinning. Considering the Ti substrate and its coatings such as (70%) IrO2 + (30%) Ta2O5 coatings, the composites of OCAs have low overpotentials 400–500 mV less than Pb-Ag anode. It was found that the oxygen evolution potential of the Ti/(Ir-Co) is 370 mV lower than that of the lead alloy anode. Ta2O5 has more electric resistance than cobalt oxide and can lead to higher overpotentials. Also, RuO2 is an excellent electro-catalytic rutile structure. Considering generally a low cost coating of Ti substrate, Ni is more appreciable than that of zinc for the two systems of Co-Ni and Co-Zn coated over titanium. Addition of certain chemicals to the zinc electrolyte can decrease MnO2 deposition on the OCA anodes during zinc electrolysis. Moreover, the performance of OCA anodes increased with the nanoparticles addition of both IrO2 and the Sb-doped SnO2. To improve the service life of Ti substrate, procedures such as recrystallization, annealing treatment and surface anodic treatment could be employed. A conductive carbon-polymer has been developed to replace the titanium substrate, which is composed of graphite fibre, carbon black and polyolefin. Finally, aluminum has been studied for matrix because of its good electrical conductivity and mechanical strength.
Acid mist abatement in base metal electrowinning cellhouses has advanced rapidly over the last 15 years as a result of both occupational health and economic pressures. Enablers include evolving designs and improved materials of construction. Cellhouse designs now typically include addition of surface tension modifying agents, cell hoods, and anode bags or anode skirts to reduce acid mist production. Automation is increasingly being considered to remove operators from the acid mist containing environment. In nickel electrowinning, chloride based anode bag technologies for chlorine recovery has been adapted to sulfate based systems. These improved technologies and design trends have resulted in cellhouse operating conditions giving greater operator comfort, while also achieving higher operational efficiency.
Acid mist abatement in base metal electrowinning cellhouses has advanced rapidly over the last 15 years as a result of both occupational health and economic pressures. Enablers include evolving designs and improved materials of construction. Cellhouse designs now typically include addition of surface tension modifying agents, cell hoods, and anode bags or anode skirts to reduce acid mist production. Automation is increasingly being considered to remove operators from the acid mist containing environment. In nickel electrowinning, chloride based anode bag technologies for chlorine recovery has been adapted to sulfate based systems. These improved technologies and design trends have resulted in cellhouse operating conditions giving greater operator comfort, while also achieving higher operational efficiency.
Current efficiency is one of the key matrices that all copper electrowinning operations monitor, track and attempt to improve. While it is well known that the main current inefficiencies in copper electrowinning stem from ferric reduction, short circuits and stray currents, operators generally lack the ability to quickly ascertain how much inefficiency should be attributed to each cause. Over the past several years, the University of Utah has developed an algebraic empirical model to evaluate the impact of ferric reduction and a measurement method to determine the impact of stray currents on current efficiency. By combining the model and method, an operator can obtain an understanding of what is causing current inefficiencies in a tankhouse. This paper will discuss how to use the model and method to improve copper electrowinning current efficiency.
Process technology and design trends for copper, zinc, and nickel electrowinning cellhouses include focusing on energy reduction, productivity, and acid mist abatement. Larger electrodes, longer cells, automation, and higher current densities are leading to more capital-effective designs. The latest cellhouse designs include installation of automated electrode-handling systems, thereby removing more operators from the cellhouse. These technology and design trends result in lower electrowinning operating costs and improved purity of electrowon cathode.
Copper electrowinning operations have dramatically improved their ability to produce high quality copper at low costs over the past several decades. Even so, some fundamental knowledge is still lacking that could allow operations to run even more efficiently. For example, a rule of thumb exists that estimates a current efficiency loss of 2-3% per gram per liter of iron in the electrolyte. While several laboratory studies have been performed that demonstrate this rule of thumb is likely true, no definitive relationship exists. In this paper, the first steps in developing a definitive relationship are presented. The effective diffusivity of ferric ions in synthetic copper electrowinning solutions was measured using chronoamperometry and the Cottrell equation. The effective diffusivity of ferric ion was determined as a function of electrolyte concentration and temperature. Synthetic electrolytes were then used in laboratory-scaled copper electrowinning experiments, where relationships between current efficiency and solution composition were found to exist under stagnant conditions.
An engineering house's perspective of required inputs in designing a copper electrowinning tank house and ancillary equipment calls for both understanding of the key fundamental controlling mechanisms and the practical requirements to optimize cost, schedule and product quality. For direct or post solvent extraction copper electrowinning design, key theoretical considerations include current density and efficiency, electrolyte ion concentrations, cell voltages and electrode overpotentials, physical cell dimensions, cell flow rates and electrode face velocities, and electrolyte temperature. Practical considerations for optimal project goals are location of plant, layout of tank house and ancillary equipment, elevations, type of cell furniture, required cathode quality, number and type of cells, material of construction of cells, structure and interconnecting equipment, production cycles, anode and cathode material of construction and dimensions, cathode stripping philosophy, plating aids, acid mist management, piping layouts, standard electrical equipment sizes, electrolyte filtration, impurity concentrations, bus bar and rectifier/transformer design, electrical isolation protection, crane management, sampling and quality control management, staffing skills and client expectations. All of the above are required to produce an engineered product that can be designed easily, constructed quickly and operated with flexibility. © The Southern African Institute of Mining and Metallurgy, 2009.
It has been 10 years since RSR Technologies introduced a new rolled anode for Zinc Electrowinning. The anode contains calcium and significantly less silver than the traditional cast or rolled lead silver anodes. The anodes are rolled to produce uniform dispersion of calcium and silver. These anodes have much higher mechanical properties than lead-silver which makes them more resistant to deformation. The calcium allows the anode to condition in several days. The anodes have been extensively tested in Japan, North America, South America, Europe, and South Africa. Anodes have been service for up to 5 years without significant thinning or corrosion. The anodes remain straight and MnO2 removal is easier than with cast or rolled lead silver anodes. The anodes yield a 1% improvement in current efficiency when compared to conventional anodes. This paper describes the experiences with rolled lead-calcium-silver anodes, the resistance or inertia to their use, the manufacturing process, and improvements to surface treatment and handling which will enhance the use of the anodes in cellhouse operations. The paper also compares the significant economic benefits in utilizing RSR rolled lead-calcium-silver anodes in today's environment.
The effect of various parameters on the current efficiency and energy consumption during copper electrowinning were studied under relevant conditions to the industrial operations using statistical analysis with the aim of developing statistical models that describe the variation of current efficiency and energy consumption during copper electrowinning. The current efficiency was found to be affected by the ferric concentration, the copper concentration, the current density and the interaction between these parameters. The energy consumption was proved to be a function of the ferric concentration, the copper concentration and the interaction existing between them. These models were proved to predict laboratory test results as well as the output of industrial operations with high accuracy.
Manganese has both direct and consequential effects on the operation of copper solvent extraction (SX) and electrowinning circuits, as well as some other unit processes. These, in turn, generate further symptoms which can form positive feedback loops and can very quickly lead to catastrophic reductions in plant performance. Many of the manganese incidents have been the result of polymerizable silica in the pregnant leach solution (PLS). This has caused the uncontrolled transfer of PLS into the electrolyte, with subsequent manganese effects in the SX plant becoming apparent. Improved silica management in plant design has allowed new solvent-extraction plants to operate stably with silica and manganese in the PLS. Mechanisms for the treatment of symptoms and reduction of primary effects have been identified, along with rehabilitation strategies for the main process operations. Changes have been made in the plant design and control methods for newer projects with a greater emphasis on identification of potential problem chemistries for both silica and manganese. This is coupled with more flexible plant designs to include prevention and remediation hardware.
In 2006, the Freeport-McMoRan Copper & Gold Inc. (FCX) Technology Center in Safford, Arizona undertook research to develop an alternative anode for copper electrowinning. The objectives of the development included a 15% voltage reduction versus conventional Pb-Ca-Sn anodes and the removal of lead and associated lead contamination from the copper electrowinning circuit. An anode development lab was established that included bench-scale electrowinning cells as well as accelerated life testing cells. This paper describes the development of the FCX alternative anode including its structure and associated anode coating. In 2008, the Chino electrowinning plant was fully converted to the new FCX anode becoming the first electrowinning plant in the world to exclusively utilize non-lead anodes. A 15% electrowinning voltage reduction was achieved. Cleaning of electrowinning cells for lead sludge and addition of cobalt to the circuit for stabilizing lead anodes were discontinued. Lead content of copper cathodes measured less than 0.3 ppm.
Sulfuric acid mist, which is generated in electrowinning tankhouses, poses corrosion problems to the tankhouse structure and adverse health effects to employees. The literature pertaining to the generation of acid mist from bursting bubbles as film and jet droplets is reviewed. In addition, various methods of suppressing acid mist, such as the use of surfactants, balls, and hoods, are presented and discussed. The occupational exposure limits in various countries are presented and the commonly accepted methods of sampling acid mist are reviewed. Data on acid mist from a survey of 25 zinc and copper tankhouses are summarized.
In the copper solvent extraction–electrowinning (SX–EW) process, Mn2+ entrained in the organic solution may be transferred to the loaded electrolyte. It will then be oxidised during copper EW. The high-oxidation state manganese formed may in turn return to the SX circuit. The presence of high-oxidation state manganese has been associated with deterioration in the phase separation characteristics of the organic and aqueous mixture, resulting in increased phase disengagement times and the formation of stable mixed phases and emulsions. In the current work, recycle of manganese from copper EW to SX was simulated on a laboratory scale in continuous trials to investigate the mechanism of organic degradation via recycle of manganese from EW.
Densities, electrical conductivities and viscosities of CuSO4-H2SO4-H2O solutions are reported for electrorefining electrolytes over the ranges: Temperature 50 to 70°C Copper concentration 40 to 55 g · dm-3 H2SO4 concentration 160 to 220 g · dm-3 and for electrowinning electrolytes over the ranges: Temperature 20 to 70°C Copper concentration 10 to 60 g · dm-3 H2SO4 concentration 10 to 170 g · dm-3 Empirical and semiempirical equations describing the measured properties are presented. © 1980 American society for metals and the metallurgical society of AIME.
This work describes the use of Mistop®, a novel surfactant of natural origin that contains primarily triterpenoid saponins (active ingredient), to control acid mist in copper electrowinning (EW). Previous laboratory tests indicated that Mistop® has no negative effects on cathode quality, current efficiency, and overall solvent extraction (SX) process conditions (e.g. phase disengagement time, extraction/stripping kinetics, maximum charge/discharge, etc.).In this work Mistop® was tested at pilot plant, semi-industrial and industrial scale. The work was performed in the facilities of Radomiro Tomic (RT), which produces approximately 900 tons copper/day. Pilot plant tests were performed during 6 months with product dosages in the electrolyte entering the EW cells within 0 and 32 ppm. The tests indicated that total acid aerosols could be significantly decreased at Mistop® dosages within 6 and 8 ppm in the electrolyte entering the EW cells. At these dosages no operational problems in the SX/EW process were encountered. The semi-industrial tests indicated that with 6 ppm of Mistop® in the electrolyte entering the EW system, acid mist aerosols decreased significantly with no negative impact on EW operational parameters (e.g. cathode quality, current efficiency). Industrial scale implementation showed that the addition of 8–9 ppm of Mistop® to the total electrolyte inventory (24,000 m3) every 24 h, decreased total acid mist aerosols in the tankhouse below present Chilean environmental regulatory requirements (e.g. 0.58 mg/m3). Under the operational conditions tested (e.g. electrolyte average temperature 45 °C, average current density 280 A/m2) the specific product consumption was approximately 0.21 kg Mistop®/ton copper cathodes, resulting in Mistop® usage costs significantly lower than that of alternative chemical surfactants.
The simulation of current distribution in cells during the electrowinning of copper
- Blackett
Effective grain modification in copper electrowinning with DXG-F7
- Cifuentes
Improvement in copper EW and ER processes by using a multi-frequency AC + DC current
- Hecker
Advancements in commercialization of De Nora’s “self protected anode – SPA” for metal electrowinning
- Iacopetti
Operation of alternative anodes at Chino SXEW
- Sandoval
Copper electrowinning: 2018 global survey of tankhouse operating practice and performance
- Sole
Acid mist capture and recycling for copper electrowinning tankhouses
- Vainio
Chiquicamata: Quality challenges throughout 100 years of copper electrorefining and electrowinning
- Salas
Cathode current monitoring technology enables current efficiency improvements
- Fraser
Investigation of Permascand coated titanium anodes in copper electrowinning at Glencore Nikkelverk
- Holmin
Cathode condition based maintenance and improved quality control
- Larinkari
Total acid mist quantification within a full-scale copper electrowinning cell
- Mohanarangam
Ion exchange in hydrometallurgy
- Shaw
Electrowinning – some recent developments
- Hopkins
Evolution of the behaviour of anodes for copper electrowinning
- Pagliero
Copper electrowinning developments at Glencore Nikkelverk
- Åkre
Developments in cathode stripping machines. An integrated approach for improved efficiency
- Aslin