In the huge electrolysis workshop, rows and rows of neat electrolysis tanks stand quietly, with anode
plates and cathode starters hanging densely in the tanks. Seemingly calm electrolyte depths, an invisible
force is quietly promoting the migration of copper ions and the crystallization of pure copper - the core
of this force, it is precisely controlled by the copper electrolysis refining voltage. It is like the “heartbeat”
of the entire refining process, and every tiny fluctuation affects the lifeblood of copper purity, energy
consumption and productivity. Understanding and mastering this key parameter is the core code to unlock
the production of high-purity electrolytic copper.
Voltage: the “driving force” of the electrolysis reaction
The essence of copper electrolytic refining is to utilize direct current to drive the directional transfer and
precipitation of copper at the cathode and anode:
Anodic dissolution: the anode (rough copper plate) loses electrons (oxidizes) in the presence of an electric current,
and the copper atoms are dissolved as copper ions (Cu²⁺) into the electrolyte: Cu (anode) → Cu²⁺ + 2e-.
Cathode precipitation: The cathode (stainless steel or titanium master plate) receives electrons (reduction) and Cu²⁺
in the electrolyte is deposited on its surface as high-purity copper: Cu²⁺ + 2e- → Cu (cathode).
For this reaction to proceed continuously, steadily and efficiently, a DC voltage must be applied between the cathode
and anode. This voltage is the total driving force that overcomes all the resistances in the entire electrolytic circuit and
drives ion migration and electrochemical reactions to proceed. It is not a simple set value, but rather a superposition
of several key components:
Components of Voltage: Anatomy of the Source of the “Drive”
The total voltage of a copper electrolyzer (V-tank) consists of the following components:
Theoretical Decomposition Voltage (E_decomp): This is the minimum theoretical voltage required to drive the precipitation
of copper ions at the cathode. It is determined by the equilibrium potential difference between the copper electrodes
themselves and is usually around 0.2 - 0.3 volts. This is the “threshold” at which the reaction takes place.
Anode overvoltage (η_anode): The actual anodic dissolution process is not ideal and there is a kinetic resistance. The additional
voltage required to overcome this resistance is called the anode overvoltage. It is significantly affected by anode composition
(impurity content), surface condition and current density. Impurities (especially As, Sb, Bi, etc.) substantially increase the anode
overvoltage.
Cathode overvoltage (η_cathode): Similarly, the deposition of copper cathodes requires overcoming certain energy barriers.
The cathodic overvoltage is relatively low, usually much smaller than the anodic overvoltage. It is affected by the state of the
cathode surface, the concentration of additives (e.g. gelatin, thiourea) and the current density.
Electrolyte Ohm's voltage drop (IR_soln): This is the voltage loss that occurs when current flows through an electrolyte with a
certain resistivity (copper sulfate-sulfuric acid solution). Its magnitude follows Ohm's law: V = I * R. This is the largest portion of
the total voltage, usually up to 60% or more. It depends on:
Current density: The higher the current passing per unit electrode area, the greater the IR_soln.
Electrolyte resistivity: It is affected by temperature, copper ion concentration (Cu²⁺), sulfuric acid concentration (H₂SO₄), and
impurity ion concentration. The higher the temperature, the moderate concentration of copper ions, the moderate concentration
of sulfuric acid, and the fewer the impurity ions, the lower the resistivity and the smaller the IR_soln.
The distance between the anode plate and the cathode plate. The larger the pole pitch, the longer the electrolyte path through
which the current flows, and the larger the IR_soln.
Conductor Ohmic Drop (IR_cond): The voltage loss that occurs when current flows through metal conductors such as bus bars,
electrode rods, and conductive tips. Although conductor resistance is low, at high currents (up to tens of thousands of amperes
in a single tank), this loss should not be ignored and should be minimized by optimizing the conductive design and maintaining
good contact.
Contact voltage drop: occurs in the electrode and conductive rod, conductive rod and busbar connection point, poor contact
will lead to this part of the voltage increases significantly, and produce local overheating.
Therefore, the total voltage of a single slot can be expressed as follows: V slot ≈ E_decomp + η_anode + η_cathode + IR_soln
+ IR_cond + contact voltage drop
Voltage control: a precision art that affects the whole body in one stroke
Maintaining a stable and appropriate tank voltage is one of the core objectives of efficient copper electrolytic refining operation.
Too high or too low a voltage, fluctuations are too large, will bring a series of problems:
The dangers of too much voltage:
Spike in energy consumption: Electrical energy consumption (W = V * I * t) is proportional to voltage. Voltage every 0.1 volts, tons of
copper power consumption may increase tens or even hundreds of kilowatt-hours, production costs increased dramatically.
Exacerbation of side reactions: High voltage may cause other ions in the electrolyte (e.g., H⁺) to precipitate hydrogen at the cathode
(2H⁺ + 2e- → H₂↑) or oxygen at the anode (2H₂O → O₂↑ + 4H⁺ + 4e-). -). This not only wastes electricity and reduces the current
efficiency (actual copper production/theoretical copper production), but also produces bubbles that damage the cathode copper
crystallization, resulting in long particles, surface roughness and even flaking. At the same time, impurities in the anode (e.g. As, Sb, Bi)
are more likely to enter the electrolyte in the form of harmful “floating anode sludge” and contaminate the copper cathode.
Risk of equipment overheating: Energy losses are ultimately converted into heat, which can lead to high electrolyte temperatures
(requiring additional cooling), overheating of conductive parts and even damage.
Risk of low or unstable voltage:
Poor cathode precipitation: Insufficient voltage may result in slow copper deposition on the cathode, loose crystallization, darkened
surfaces or even “burnt plates” (no localized copper deposition).
Anode passivation: Low voltage may cause the anode to dissolve insufficiently, forming a dense passivation film on the surface,
hindering dissolution and leading to an abnormal increase in tank voltage.
Increased risk of impurity co-precipitation: Under too low a voltage, certain impurity ions close to the copper potential (such as arsenic,
antimony, bismuth) may precipitate at the cathode, contaminating the copper cathode and reducing the purity.
Unstable production: Voltage fluctuation reflects the unstable production status (e.g. uneven concentration of additives, change of
pole distance, poor contact), which directly affects the quality uniformity of copper cathode.
Optimization strategy: to make every volt cost-effective
In order to stabilize the tank voltage in the ideal range of 0.25 - 0.35 volts (the exact value depends on the process conditions)
and to minimize energy consumption, the industry has adopted a series of fine management and technology optimization measures:
Precise regulation of electrolyte composition:
Copper ion concentration: Maintain stability (typically in the 40-50 g/L range). Too low to increase resistance, too high easy to crystallize.
Sulfuric acid concentration: Maintain stable (usually in the range of 160-200 g/L). Moderate concentration reduces resistance, too high increases solution viscosity.
Impurity control: Strictly control the concentration of impurity ions such as As, Sb, Bi, Ni, Fe, etc., to prevent excessive accumulation of impurity
ions, leading to increased resistivity and anode overvoltage. Regular electrolyte purification (e.g. arsenic and antimony removal).
Additives management: precisely control the concentration and proportion of additives such as gelatin, thiourea and hydrochloric acid. They can
effectively reduce the cathode over-voltage, improve crystallization, inhibit impurity precipitation, but too much will significantly increase the tank voltage.
Stabilizing the electrolyte temperature: Adopting high efficient heat exchange system to stabilize the electrolyte temperature at 55 - 65°C. Higher
temperature can significantly reduce the viscosity and resistivity of the electrolyte, which is one of the most effective means to reduce IR_soln
(usually, resistivity decreases by about 2% for every 1°C increase in temperature).
Optimize the design and management of pole spacing: Under the premise of ensuring insulation safety and preventing cathode and anode short
circuits, reduce the pole spacing as much as possible (modern large tanks are generally in the range of 90-110mm). Shortening the ion migration
path is the key to reducing IR_soln. High-precision electrode positioning and strict short-circuit detection are required.
Enhance the efficiency of the conductive system:
Optimize busbar design: Use large cross-section, low resistivity electrolytic copper busbars to reduce path voltage drop.
Ensure good contact: Regularly clean and polish the contact surfaces of the conductive head and conductive rod to ensure low-resistance contact.
Use of reliable crimping or soldering methods.
Shorten the current path: Optimize the arrangement of electrolytic tanks and the design of busbars.
Strict control of anode quality: Ensure that the physical specifications (thickness, straightness) and chemical composition (low impurity content)
of the anode plates meet the standards. Anodes with high impurities not only increase overvoltage, but also pollute the electrolyte.
Intelligent voltage monitoring and regulation:
Online monitoring: Install voltage sensor in each tank to monitor voltage changes in real time.
Data analysis: Collect voltage data by DCS/SCADA system, analyze the fluctuation pattern, and identify abnormalities (e.g. short circuit, poor contact,
insufficient additives).
Trend warning: Setting up voltage alarms with upper and lower limits to detect potential problems in time.
Guiding operation: Voltage data is an important basis for guiding the adjustment of additive addition, electrolyte circulation, temperature setting,
short circuit treatment and other operations. The advanced intelligent tank control system can automatically optimize the adjustment to a certain
extent according to the voltage and other parameters.
Conclusion: the string of voltage, playing the music of high efficiency and purity
Copper electrolysis refining voltage, behind this seemingly simple figure, cohesion of the precise laws of physical chemistry and industrial control
of extraordinary wisdom. It is the driving force for copper atoms to move from roughness to purity, and it is also the core yardstick for measuring
production economy and technology level. From the careful proportioning of each electrolyte, to the precise setting of each millimeter of pole
distance, to the careful maintenance of each contact point, all are aimed at taming this “beast of volts”, so that it can serve the sacred mission of
producing high purity copper in a stable and efficient manner.
In the pursuit of green manufacturing and dual-carbon goals, in-depth understanding and continuous optimization of copper electrolytic refining
voltage is more important than ever. Every successful voltage control means a real reduction of energy consumption per ton of copper, a reliable
improvement of cathode quality and a continuous optimization of production cost. This silent “heartbeat” is powerfully pushing the “golden
blood” of modern industry to flow more purely and efficiently. When you hold the mirror-like high-purity copper cathode plate in your hand,
please remember that it is this precisely controlled “power of Volt” that achieves the ultimate purity of this metal.