Copper electrowinning

The basic principle of electrowinning uses an insoluble (inert) anode. During the electrowinning process, all of the copper deposited on the cathode is derived from the copper solution, and the copper concentration of the solution is continuously decreased. The cathodic reaction of the electrolysis and electrowinning processes is the same and can be expressed by the following equation:

Cu ²⁺ +2e —→ Cu

However, in the electrowinning process of copper sulfate solution, the anode reaction is to generate oxygen:

1
2OH ^- —→ ——O ₂ + H ₂ O + 2e
2

The total cell voltage of the electrowinning is between 1.9 and 2.3V. The tank voltage multiplied by the amount of electricity required to restore each ton of copper is the DC power consumed. Considering the efficiency of rectification, the electric energy consumption of the electrowinning It copper is about 2000~2700kW·ho.
Copper electrowinning originally used thin copper primary poles as cathodes. Since the 1980s, the Australian copper electroplating plant of Monte Asha Mining Company has directly used stainless steel mother plates as cathodes, and many copper electrowinning plants have also been used for more than a decade. They are all used in production. Are now using degenerate Pb-Sn-Ca alloy, each slightly different composition containing Pb 93% ~ 98%, 1% to 2% tin, Ca <0.1%. Adding 100~200mg/L of cobalt ion to the electrolyte can form an activation center together with lead oxide, which is beneficial to reduce the overpotential of oxygen evolution. It also helps to form strong oxides and reduce lead-containing particles.
Effect of electrolyte components power consumption factor has a direct impact on the electrolyte composition conductivity, typically copper stripping solution 40 ~ 50g / L, sulfuric acid 140 ~ 170g / L, the resistance rate of 0.6 Ω / cm, than the soluble anode electrolysis The liquid is much higher at 0.2 Ω / cm.
Some of the ions in the electrolyte participate in the electrode reaction and can cause additional power consumption. The most important one is iron . Fe ²⁺ is oxidized to Fe ³⁺ , and Fe ³⁺ diffuses to the cathode and is reduced to Fe ²⁺ . This repeated oxidation-reduction process causes current loss. For example, the electrolyte of a certain plant contains Fe ³⁺ 3g/L, Fe ²⁺ 4g/L, and the current efficiency is 77%; while the electrolyte of another plant contains Fe ³⁺ 0.3g/L, Fe ²⁺ 0.9g/L, and the current efficiency is greater than 90%.
If the feed liquid contains manganese , it is entrained into the electrolyte and can be oxidized to high oxidation state manganese or even permanganic acid on the anode. When in contact with the organic phase, the extractant can be oxidized to form a surface active material, delaying the phase separation time, resulting in emulsification and exacerbation of the formation of interphase. If there is ferrous ion in the electrolyte, it is possible to reduce high-priced manganese and avoid damage to the organic phase. Therefore, many plants maintain a total iron content of about 1 in the electrolyte ^[1] .
The entry of chloride ions into the electrolyte can also cause problems such as corrosion of the anode plate and even precipitation of chlorine gas, which deteriorates the workshop environment and corrodes the equipment. Therefore, it is necessary to strictly control the extraction section and take measures to reduce the amount of water phase entrainment in the organic phase, and even increase the washing section. The chloride ion in the electrolyte should not exceed 30 mg/L.
The current flowing outside the copper electrolysis in the stray current electrolysis workshop is collectively referred to as stray current. Although many measures have been taken in the design of the electrolysis workshop to strengthen the insulation between the electrolyzer, the bus, the pump and other conductors, if the insulator is contaminated by the electrolyte, it may still cause leakage and generate stray current.
The method of reducing stray current is to use two loops in the circuit arrangement and ground in the middle to reduce the total potential difference. In addition, when the liquid supply pipe and the return pipe of the electrolytic cell are arranged, the potential difference between the two is minimized according to the potential map of the groove column.
Behavioral factors affect the quality of copper impurities in the electrolytic solution after solvent extraction of the electrolyte composition higher than the soluble anode in an electrolytic solution purity, in particular free of arsenic, antimony, and other impurities secret. Moreover, even if some other metal ions, such as Fe ³⁺ and Fe ²⁺ , are contained, the electrode potential is far above the copper, and the copper does not precipitate to affect the quality of the copper.
The suspended particles in the electrolyte can cause great damage to the quality of the electrowinned copper. The source of the suspended particles is filtered when the electrolyte is filtered, or it may be copper or copper oxide particles generated during electrowinning, or floating dust from the air. However, the main source is often the anode. Insoluble anodes are almost all lead alloys. When electrowinning, the surface is oxidized to lead sulfate or lead oxide, sometimes falling off and suspended in the solution. When it migrates and adsorbs on the surface of the cathode, it forms a crystal center, which leads to growth on the copper plate. Copper particles of different sizes.
Analysis shows that the impurity content of such particles is often tens to hundreds of times of the base copper plate. Moreover, in severe cases, the particles develop into dendrites, which can cause short circuits between the plates. [next]
Organic phase
The electrolyte which is in contact with the organic phase inevitably contains a trace amount of an organic phase. When the content reaches a certain amount, the copper which causes the cathode deposition is discolored, especially the upper portion of the cathode plate. This dark chocolate deposit is called "organic burnt spots." The deposits in the organic burned area are fragile and powdery, and most of the impurity solids entrainment occurs in the burnt area.
Studies have shown that organic burn spots are caused by extractants, and the diluent has little effect. Some plants reduce the organic phase concentration in the electrolyte to less than 5 mg/L. However, if it can be controlled below l0 mg/L, there is generally no organic burn-in phenomenon.
The main operating parameters of the electrolysis operation parameters are as follows: the same pole pitch is 9.5~10.2cm, the cathode surface electrolyte flow rate is 0.12m ³ /(h·m ² ), and the bath temperature is 40~46`C. Although the current density of many plants is still 190~240A/m ² , the high has reached 320~340A/m ² . Most of the solvent extracts - electrowinning plants have a cathode copper purity of 99.99% or even 99.999%, which is higher than that of the soluble anode method. The operating parameters of the two large electric power plants are listed in the table below.

The copper products listed in the table are of good quality, impurity content (10~4%): Margma's St. Manuel plant, Pb<1, S is 2~3, Fe is 2, Ni <1, other ≤1; Zambian Enchangjia United Copper Company (ZCCM), Pb ≤ 10, S is 15, Ca is 2, Fe is 10, Si is 30, Ag is 5, and other ≤ 3.
It should also be mentioned that many new electrowinning technologies are being researched and developed, notable, such as fluidized electrolyzers, etc. However, the current trial scale is still relatively small. However, a tubular electrolytic cell called EMEW has recently been trial-produced in Australia, and the operation and effects have not been reported in detail.

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