Copper Electrorefining Research Articles

The Role of Chelators in Electrodeposition of Cu-As Alloys from Copper Electrolyte

Copper electrorefining is a key part of copper metallurgical processes. The electrolyte is usually purified to prevent the accumulation of impurities and contamination of the cathode. Cyclone electrowinning is a widely applied purification method, but black copper mud that contains arsenic is produced after the process and endangers the environment. With the addition of effective chelators, controllable electroplating can be achieved. In order to investigate their role in electrodeposition, a variety of chelators were selected and applied in this study. LSV, XRD, and SEM were used to characterize Cu-As alloys produced from each test. The effects of chelators on the number and shifting of phase transition zones during the electrodeposition were analyzed.

Challenges for development of technology for prevention of anode passivation during electrorefining of low-grade copper

Challenges for development of technology for prevention of anode passivation during electrorefining of low-grade copper

Analysis of interelectrode short-circuit current in industrial copper electrorefining cells

Abstract In the process of copper electrorefining, detecting and treating the interelectrode short-circuit faults is one of the main tasks in the workshop. In this paper, the cathode current in industrial copper electrorefining cells was measured by an optical fiber current sensor, and the current curves caused by interelectrode short-circuit have been obtained. The relationship between the characteristics of cathode current and the mechanism of interelectrode short-circuit is discussed. A rapid diagnostic method of short-circuit faults by monitoring the change of cathode current slope and standard deviation is proposed. The applicable scope of the method is also given.

Metallurgical Process for Total Recovery of All Constituent Metals from Copper Anode Slimes: A Review of Established Technologies and Current Progress

Copper anode slimes, the by-product of the copper electrorefining process, have been the subject of extensive investigation for recovering precious metals viz., Au, Ag, Pt and Pd, in addition to being the main source of rare/energy-critical elements such as Se and Te. There have been various approaches aiming at the development of extraction processes involving thermal and aqueous approaches and their combination. In this paper, the literature relating to the treatments of copper anode slime is compiled to present the underlying concept for the total recovery of all valuable metals from anode slimes. The industrial and proposed scenarios gathered from various sources show that the basis of applying different streams essentially depends on the concentration of copper and selenium in the slimes. Copper anode slime processing has a history of being in a development period, though at times showing overlaps. The discussion of each metallurgical process is basically explained by thermodynamic analysis using suitable software as well as fundamentals of the chemistry. Recent progress is highlighted and compared to the established technologies with regard to environmental impact and economic consideration/feasibility. This discussion is followed by the construction of a conceptual flowsheet on the progress currently made. It is expected that further work regarding metal recovery from copper anode slimes would objectively shorten the number of stages for the pretreatment as well as metal separation from leach solutions.

Chlorine inclusion mechanism in high purity copper electrorefining from nitric acid system

Abstract A practical approach was introduced to study the inclusion mechanism of chlorine in high purity copper electrorefining from nitric acid system via cyclic voltammetry (CV) combined with electrodeposition experiments. The CV curves display an obvious reduction peak of CuCl intermediate, which can provide an insight into the electrochemical behavior of this inclusion. Experimental results show that the increase of HNO3 concentration is favorable to reducing the quantity of chlorine inclusion although there is a slight decline in cathodic current efficiency. The optimum conditions for copper electrorefining in nitric acid system are HNO3 concentration in solution of 1−2 mol/L, moderate temperature of ~35 °C with current density not exceeding 25 mA/cm2. Based on the theoretical studies, an optimized copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 μg/g and current efficiency higher than 90%.

銅の電解精製とアノード不動態化

銅の電解精製とアノード不動態化

The Mechanism of Nodular Growth in Copper Electrorefining

The Mechanism of Nodular Growth in Copper Electrorefining

Experimental analysis of the performance of innovative circulation configurations for cleaner copper electrolysis

A series of copper electrorefining tests were performed to determine the effects of circulation configuration, as well as inlet flow rate and current density, on impurity particle behavior and cathode purity. SEM/EDS was utilized to acquire surface characteristics and impurity distributions on the harvested cathode copper and the collected anode slimes. The anode slime weight distributions under different operating conditions were analyzed to determine the effects of the three factors on anode slime behavior. ICP was used to obtain the concentrations of major impurities in the harvested cathode copper, and the results of selected impurities (As, Sb, Bi) were statistically analyzed to determine the relationship between the factors and impurities concentrations. The circulation configuration was identified as the most significant factor based on the statistical results, with the innovative configuration of two upper-inlets/one lower-outlet as the optimal configuration. Furthermore, a theoretical discussion of the effects of these factors on slime particle behavior is given, which demonstrates that these factors have significant impact on slime particle transport by influencing species distribution, electrolyte density gradient, and fluid flow field in the cell. In addition, SEM/EDS results of collected slimes show that the innovative circulation configurations have the advantage of converting more suspended slime particles to settled slimes.

Diffusion coefficient of cupric ion in a copper electrorefining electrolyte containing nickel and arsenic

Diffusion and convection are the main modes of mass transport that occur during copper electrorefining. Diffusion determines the rate of copper transfer across the diffusion layer, which in turn, affects the dissolution of the anode and deposition on the cathode. The diffusion coefficient of cupric ion (DCu(II)) is a typical property that can be defined from the limiting current density (jlim) values. In this work, the limiting current densities were measured for 24 different synthetic copper electrolytes over a temperature range of 50–70 °C using a rotating disc electrode (RDE). From this data, a model for jlim and the corresponding models for DCu(II) were constructed using Levich (Model L), Koutecký-Levich (Model K) and mixed-control Newman equations (Model M). The models for jlim and DCu(II) were designed, refined and analyzed using the modeling and design tool MODDE, with the temperature, copper, nickel, arsenic and sulfuric acid concentrations as variables. Results from this research show for the first time that an increase in arsenic concentration has a reciprocal effect on the DCu(II) under copper electrorefining conditions. Furthermore, the models were validated with 11 industrial electrorefining electrolytes with known compositions. Model L (DCu(II) based on Levich equation) was shown to provide the highest correlation with the industrial solutions when compared to the other models (Model K and M) considered and previously published diffusion coefficient models. Overall, this work provides an explanation for the previously observed data variances in the literature, investigates for the first time the combined effect of parameters on DCu(II) value in industrial copper electrolysis and clarifies the effect of arsenic on the DCu(II) of copper electrorefining electrolytes.

Effect of Jet Flow between Electrodes on the Cathode Quality in Copper Electrorefining with High Current Density

Increasing current density is one of the main methods for improving the productivity of copper electrorefining. However, in the conventional bottom-inlet/top-outlet mode, an increase in current density leads to a deterioration of the surface quality of the cathode copper. This paper describes an experimental study of the influence of the jet flow between electrodes on the cathode quality. The surface roughness and the standard deviation of the cathode copper were used to evaluate the cathode quality. The results showed that in the single-side jet inlet mode, the electrolyte circulation rate has great influence on the surface roughness of the cathode copper, which is inversely correlated. However, when the electrolyte circulation rate is small, the surface roughness of the cathode copper is not uniform. The farther the position at the surface of the cathode copper is to the jet region, the coarser the cathode copper surface, and vice versa.

Removal of Antimony and Bismuth from Copper Electrorefining Electrolyte: Part II—An Investigation of Two Proprietary Solvent Extraction Extractants

Antimony and bismuth recovery from copper electrorefining electrolyte could reduce the impacts of these problem elements and produce a new primary source for them. Two proprietary phosphonic acid ester extractants were examined (REX-1 and REX-2) for the removal of antimony and bismuth from copper electrorefining electrolytes. Experimentation included shakeout and break tests to determine the basic parameters for the extractants in terms of maximum loading, break times, and extraction and stripping efficiency. Five permutations of extractant mixtures (100 wt.% REX-1 and 25 wt.%, 50 wt.%, 75 wt.% and 100 wt.% REX-2) were studied. It was determined that REX-2 was able to extract Sb and Bi from the electrolyte, but required some mixture with REX-1 to better facilitate stripping with 400 g/L sulfuric acid. The laboratory electrorefining electrolyte containing glue had faster disengagement times than a synthetic solution without glue.

An Intercell Busbar Topology to Surpass Anomalies of Copper Electrorefining Processes

In copper electrorefining, process anomalies impair current efficiency and productivity. Short circuits produce nodules or dendrites in copper cathodes, impaired contacts at busbars elevate current densities dispersion and, open contacts result in blank cathodes and overcurrents at nearby electrodes. This paper presents an intercell topology composed by a base board, main anode–cathode connectors, and a capping board with secondary connectors snapped on top. With this segmented intercell configuration the resilience to anomalies is improved by reducing short-circuit occurrence and their magnitude. Anomalies are pinpointed in 60 s with the addition of light mass secondary connectors placed on the capping board. Moreover, the new topology is capable of surpassing anomalies even without assistance to sustain production. Finite-element modeling predicts the performance of the proposed innovation for fast detection of short and open circuits using thermography scans. The paper includes experimental results to validate the effectiveness of the secondary connectors in the detection of process anomalies.

Removal of Antimony and Bismuth from Copper Electrorefining Electrolyte: Part I—A Review

Antimony and bismuth are two of the most problematic impurities in copper electrorefining. As a result, much research has been done investigating the ways to remove them. Processes that are currently being used industrially include anode additions, liberators, ion exchange (IX), and solvent extraction (SX). Of these, liberators and anode additions are the most common while SX is the least, mostly being used for arsenic removal. Other methods have been evaluated, but they are not in commercial use. These include the use of various electrolyte additives, as well as adsorbents such as bentonite clay and heavy metal sulfates.

Validation of electrolyte conductivity models in industrial copper electrorefining

Conductivity is a typical physico-chemical property that has a substantial effect on electrical energy consumption in the electrorefining process. The objective of this study was to examine the validity of regression models predicting the conductivity of industrial copper electrorefining electrolytes. The models were based on data measured with synthetic solutions on a laboratory scale. The variables included in the models were temperature and the concentrations of copper, nickel, arsenic and sulfuric acid. Both first-order and combined effects of the variables were investigated. The measured data were analyzed using MODDE 8.0 modeling and design software. The validity of the models was investigated by comparing the predicted values with tankhouse conductivity measurements taken at the Boliden Harjavalta Copper Refinery in Pori in Finland. During the tankhouse tests, the conductivity and temperature of the industrial electrolyte were measured, and the composition of the electrolyte was analyzed. The measured conductivity values were compared with the predicted conductivities calculated using the developed models. The conductivity model developed in this paper was shown to be more accurate than previous models and suitable for industrial use.

Temperature Monitoring and Flow Estimation in Electrolytic Cells Using Wireless Harsh Environment Sensors

Proper control of temperature and electrolyte circulation flow is mandatory in electrolytic cells to produce dense and high-purity cathodes. The electrochemical kinetics of cells is inherently dependent on these electrolyte variables. Continuous monitoring of electrolyte condition allows enhancing cathode quality, electrodeposition time, better utilization of electrolyte additives, early identification of temperature excursions, and electrolyte flow blockages. Abnormal cell conditions can produce excessive evaporation, higher energy consumption, anode passivation that impair cathode production in copper electrorefining, and safety issues because the production of flammable hydrogen in copper electrowinning. Therefore, the monitoring of changes in temperature and electrolyte flow can give critical indicators of process deviations. With real-time information about electrolyte variables, it is possible to provide early warnings to face the wide variability of cell performance and safety conditions caused by electrolyte condition mismanagement. This paper proposes a noninvasive wireless sensor for monitoring the electrolyte temperature inside cells and estimates the electrolyte circulation flow through each cell simultaneously. The sensor design is suitable to highly corrosive sulfuric acid environments. The condition-monitoring sensor proposed is small in size, lightweight, and meets battery-free operation and nonsparking safety requirements. It uses an inductive link-based system for powering and a radio frequency-link for communicating. The result is a sensor that surpasses the features of standard instrumentation not suitable for electrolytic process monitoring.

Evaluation of flow behavior in copper electro-refining cell with different inlet arrangements

Abstract The arrangement of electrolyte inlet in the copper electro-refining (ER) cell has a great influence on the local flow field, which affects the distribution of electrical current density in consequence. In order to understand the complicated phenomena of electrolyte flow behavior in vertical counter electrodes in full-scale copper ER cell, the three-dimensional computational fluid dynamics (CFD) models with four different arrangements of electrolyte inlets, i.e., single inlet (SI), central bottom inlets (CBI), top side interlaced inlets (TII), and bottom side interlaced inlets (BII), were established to simulate the flow behavior. Simulation results have revealed that the parallel injection devices help to improve the electrolyte velocity between electrodes, and while the relative range of electrolyte velocity in CBI exceeds that of TII and BII, which is more than 4 times, indicating its severer unequal flow distribution. Meanwhile, the average velocity of electrolyte in BII is 4 times larger than that of SI due to its higher turbulence intensity. Generally, one of the efficient ways to supply fresh copper solution rapidly and uniformly into the inter-electrode space is to adapt the arrangement of BII. By utilizing such an arrangement, the electro-refining under high electrical current density is possible, and the productivity can be increased in sequence.

Effect of typical impurities for the formation of floating slimes in copper electrorefining

In electrorefining, Group 15 impurities arsenic, antimony and bismuth, may precipitate within the bulk electrolyte as floating slimes and contaminate the copper cathodes. In order to determine the impurity specific thresholds related to the formation of suspended solids, synthetic copper electrorefining electrolytes with different concentrations of arsenic, antimony and bismuth were investigated by a continuous filtration method. The amount and composition of the floating slimes obtained were evaluated in terms of the initial impurity concentrations present in the synthetic electrolyte. As a result, the specific influence of arsenic, antimony and bismuth on the floating slime formation was ascertained. The results suggest that there is an upper limit in electrorefining electrolytes for antimony (Sb) of 800mg/L for floating slime formation, although the limit for Bi was less clear. Furthermore, the structure of the synthetic floating precipitates produced were analyzed using both SEM-EDS and XRD and showed typical amorphous structure of floating slimes with particle size of approximately 25μm and predicted composition of BiAsO4, SbAsO4, Sb2O3 and Bi2O3.

Natural convection effects in electrochemical systems

Natural (free) convection influences electrochemical processes that occur in areas as disparate as electroanalytical sensing and copper electrorefining. The modeling of natural convection requires solving a set of coupled partial differential equations reflecting the interplay between the transport of mass, heat and momentum that lies at the core of this phenomenon. This article reviews recent developments in the study of the subject, and covers various cases, e.g. free convection driven by concentration and/or temperature gradients, bubble-induced convection, and natural convection coupled with an external force. Literature on free convective flows in practical contexts such as fuel and thermogalvanic cells and electrochemical sensors is also discussed. Recent articles that describe experimental approaches for minimizing the effect of natural convection are covered. Studies which take advantage of the analogy between mass and heat transfer in order to probe the latter are discussed in brief. Particular attention is devoted to a critical assessment of the concept of ‘spontaneous convection’, which has been invoked in a number of recent papers.

Models for viscosity and density of copper electrorefining electrolytes

Models for viscosity and density of copper electrorefining electrolytes

Extracting silver from anode slime after lead and gold separations

Anode slime, a byproduct from the process of copper electrorefining into the copper cathode, contains several valuable elements that can be extracted after Cu and Pb separations. Another alternative route for extracting the precious metals is still needed in terms of gaining more economical route. This research aims to seek the new route to extract the precious metals, especially silver from anode slime. In these experiments, the anode slime was obtained from PT Smelting Gresik. The lead was separated to produce the residue which was then chlorinated to extract the gold. Later the residue was used for extracting the silver by dissolving it in ammonium hydroxide solution with varying time dissolutions and concentrations and later dissolving in hydrochloric acid to form silver chloride which was reduced to metallic silver. These experiments had two trials. The first one related to directly using residual chlorination after gold separation and the second one employed the same residual chlorination but processed through de-chlorination by adding sodium carbonate. The result showed that the highest silver recovery of 53.56% related to 5 M ammonium hydroxide concentration, the temperature of 30°C, dissolution time of 60 minutes. Recovery of 53.78% was achieved at 7 M ammonium hydroxide, the temperature of 30°C, dissolution time of 60 minutes. The feed of those experiments came from direct residual chlorination, while chlorination residue that underwent de-chlorination produced silver recovery of 94.95% with leaching conditions of 5 M ammonium hydroxide, the heating temperature of 30°C and leaching time of 60 minutes. The latest recovery was relatively high resulted in the process could be scaled up to a continuous system.