Features of the electrowinning system

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Characteristics of electrowinning systems: In an era focused on cost control, energy savings, and environmental protection, optimization and innovation of electrowinning systems are of utmost importance in the hydrometallurgy industry, particularly in the nickel-cobalt-copper sector, where the effects are also most significant. In terms of energy consumption, the electrowinning system accounts for over 80% of the total energy used in the system; in terms of investment, it constitutes more than 60% of the total investment required for the system. As for environmental protection requirements, the collection and treatment of waste generated by the electrowinning system account for no less than 70% of the overall efforts related to environmental protection in this system. Therefore, all relevant manufacturers are working to optimize and innovate the electrowinning system. Since the principle of electrodeposition cannot be changed, the general process flow also cannot be altered. Therefore, everyone can only focus on aspects such as equipment efficiency, materials, and environmental protection. The specific new equipment and related items will be shared with everyone in the future; for now, let’s take a look at some of the characteristics of electrowinning itself, so that it can be used for comparison and optimization. In the development of metal electroreduction systems, they have been divided into two categories based on the properties of the anode: soluble anodes and insoluble anodes. Strictly speaking, a soluble anode system is what is known as an electrolysis system, also referred to as electrolytic refining, whereas an insoluble anode system is called an electrowinning system. In electrolytic systems, since the anode itself is impure and needs to be replaced periodically, a diaphragm (cathode membrane) must be used to separate the anode solution from the cathode solution in order to ensure the purity of the liquid in the cathode area (such as in the electrolytic refining of nickel). On the other hand, due to its inherent properties, copper does not require any separation of liquids, whether through electrolysis or electrowinning. In the electrowinning system, the use of an inert, insoluble anode results in the substances that are oxidized at the anode being different from those that are reduced at the cathode, giving it its own characteristics in many aspects compared to electrolytic systems. Specifically, it is roughly as follows: 1. The slot voltage is high. In an electrolysis system, since the main component of the anode is the same as that of the cathode, only with a relatively lower purity, oxidation-reduction reactions of the same metal occur at the anode and cathode during the electrolysis process. Therefore, in theory, a voltage that is merely higher than its standard electrochemical potential difference is sufficient to initiate the electrolysis reaction. In reality, to speed up the reaction, a voltage more than double that is applied. The electrowinning system is different in this regard. Since the anode does not dissolve and merely serves a conductive role, it is another substance – water – that actually undergoes oxidation. Because the decomposition voltage of water is relatively high, and moreover different reaction surfaces have varying catalytic effects on the decomposition of water, the material of the anode varies, which in turn causes the electrowinning voltage to change. Regardless of the anode chosen, the voltage required for electrowinning of the same metal is more than 1.5 times higher than the electrolysis voltage; this means that the energy consumption in the electrowinning process is at least as high. (The effect of the anode on the electrodeposition voltage is manifested in two main aspects. 1. The electrical conductivity of the anode material itself; the better the conductivity, the lower the resistance, and consequently the total voltage will be lower as well. 2. The catalytic efficiency of the anode material in the oxidative decomposition of water: the better the catalytic effect, the lower the overvoltage required for oxygen generation, and consequently the total voltage will also be lower. For example, compared to a surface coated with platinum, the surface of lead has a higher overvoltage; therefore, many manufacturers now choose titanium anodes or surfaces coated with precious metals, as these materials offer good electrical conductivity, low overvoltage, and strong corrosion resistance. II. Low efficiency. In an electrolysis system, since redox reactions occur between the same type of metals, there is little change in the acidity of the anode and cathode solutions, and hydrogen evolution hardly occurs at the cathode. In the electrowinning system, since water is oxidized at the anode to produce oxygen, an equivalent amount of hydrogen ions remain in the anodic solution. Although a membrane separates the liquids at the anode and cathode, under the influence of a strong electric current, a considerable number of hydrogen ions still diffuse into the cathodic region, where they compete with the main metal ions for reduction through discharge – a process commonly known as hydrogen evolution. This results in not all of the current being available for the reduction of metal ions, thereby reducing the efficiency of the current. Through the upgrading of technology and equipment, the current efficiency of electrodeposition has increased from 80% in the past to 93–95% (for anode membrane electrodeposition). III. Severe environmental pollution. Due to the hydrogen evolution reaction at the cathode during the electrowinning process, a large amount of oxygen is released at the anode. These gases carry with them a significant amount of acidic electrolyte liquid as they are released, and coupled with the high temperature of the electrolyte itself which leads to vaporization, this results in acid mist filling the entire electrowinning area. The operating environment becomes extremely harsh, and the environmental protection challenges are very serious; the costs associated with environmental treatment are high. No matter how many environmental protection devices are used, it is not possible to completely eliminate the acid mist. However, the use of new types of electrowinning systems as well as cathode-anode diaphragm electrowinning systems has **solved this problem. IV. The purity is relatively low. By \"relatively lower\" here, it is meant that when the same catholyte is used, the purity of the metal obtained through electrolysis is higher than that obtained through electrowinning (for each process individually, metals of equal purity can be produced; the only difference lies in the cost). The reason is that the voltage required for electrowinning is about 1.5 times higher than that needed for electrolysis; this allows more types of metal ions in the same liquid to receive electrons and be reduced, resulting in a slight decrease in the concentration of the main metal that gets reduced at the cathode. (According to available information, the high-purity nickel (99999) used in China’s first successfully detonated nuclear device was produced by the Chengdu Electro-Metallurgical Plant using electrolytic methods back then.) The above are my personal insights regarding the electrowinning system (the nickel electrowinning system); they also represent the basic directions for optimizing this system. I am now sharing them with everyone for mutual reference and discussion!