Products and main technical and economic indicators of nickel sulfide electrolysis (3)

2, a cell voltage) metallurgical composition of cell voltage, for the electrolytic reaction can be referred to as an applied voltage necessary for cell voltage, it may be measured with a voltmeter cell adjacent cathode, the voltage between the anode determined. The cell voltage is mainly used to overcome the following three voltage drops in the cell:
(1) a potential difference between the anode potential and the cathode potential (decomposition voltage);
(2) the voltage drop caused by the current flowing through the conductive strip, the conductive rod, the hook resistance and the resistance between them;
(3) The voltage drop caused by the current flowing through the electrolyte resistor.
Expressed as:
V- _groove = (¢ _a -¢ _c ) + IR _conductor + IR _electrolyte
Wherein V _groove - groove voltage, V;
¢ _a — electrode potential of the anode, V;
¢ _c — electrode potential of the cathode, V;
I—the current intensity in the circuit, A;
R _conductor - the resistance of the metal conductor, Ω;
R _electrolyte - the resistance of the electrolyte and diaphragm, Ω.
Here, ¢ _a — ¢ _c represents the lowest voltage at which the electrolytic solution is decomposed and the reaction between the anode and the anode is started after the electrolysis cell is energized, which is also called the actual decomposition voltage. The electrolysis process is irreversible due to the effects of anode overvoltage and cathode overvoltage caused by polarization after energization. As a result, the anode potential and the cathode potential move in the positive and negative directions, respectively, and deviate from the reversible potential.
As mentioned earlier, the main reactions that occur at the anode are:
Ni ₃ S ₂ -6e=3Ni ²⁺ +2S ¢=0.104+0.031lga _Ni ²⁺
That is, the calculated standard electrode potential (reversible potential) is about 0.1 V. However, in the case where the nickel sulfide anode is actually extremely impure, the reaction occurs only when the actually measured anode potential is about 1.2 V due to the influence of the polarization. Add the above reaction to the cathodic reaction 3(Ni ²⁺ +2e=Ni) ¢=-0.25+0.030lga _Ni ²⁺
The electrode potential measured according to the operating conditions of the Canadian International Nickel Company is shown in Figure 1, and the voltage drop across the electrolyte is 0.9V, so the cell voltage is:
V- _groove = (¢ _a -¢ _c ) + IR _fluid = 1.65 + 0.9 = 2.55V

In fact, the voltage must be increased to overcome the resistance of the conductive bar and its contact resistance, so the actual cell voltage of the new take-off anode is about 2.8V. When the nickel sulphide anode is dissolved, the anode slime forms a structure that is firmly adhered and loosely porous, which doubles the volume of the anode slime. The continuous thickening of the anode mud causes the resistance between the electrodes to rise and rise. When the 500 mm thick anode is dissolved to the later stage, the cell voltage rises to 4 to 5 V, or even more than 6 V. [next]
2) Reduction of the cell voltage The channel voltage of the nickel anodic anodic electrolysis is related to the composition of the solution, the composition of the anode plate, the temperature of the solution, etc., and also has a great relationship with the current density and anode cycle selection.
Under normal production conditions, the voltage drop of the electrolyte is the main component of the cell voltage, which accounts for about 65% of the cell voltage. Adjusting the composition of the electrolyte can change the internal resistance of the electrolyte, and increase the sodium and chloride ions in the solution. Increasing the acidity of the solution can lower the internal electricity of the solution, and increasing the temperature of the electrolyte is also beneficial to increase the conductivity of the solution and reduce the cell voltage.
In the process of soluble anodic electrolysis, especially the use of nickel sulfide anode, the quality of the anode is very good and the anode operation has an extremely important influence on the cell voltage. Generally, the anode quality is uniform (especially the anode plate with high sulfur content), the surface There is no scum, which is beneficial to the uniform dissolution of the anode. For the nickel sulfide anode, the excessive adhesion of the anode mud will cause the cell voltage to rise sharply, so the residual rate should be controlled to be no less than 15% to 25%, and in the intermediate stage of the anode cycle, that is, while the cathode is out of the groove. Remove the anode and scrape the anode mud to reduce the tank voltage.
3, electrical energy consumption Electrical energy consumption is one of the most important indicators to characterize the technical level of operation and economic benefits of nickel electrolysis process.
Electrical energy consumption refers to the electrical energy consumed by the cathode to precipitate a unit mass of metal during electrolysis. As mentioned above, the actual production of precipitated metal (G) = theoretical precipitation (qIt) × current efficiency (η), assuming W is the unit of electrical energy consumption, the calculation formula is:

Where W - electrical energy consumption, kWh.t ^-1 ;
V- _groove -slot voltage, V;
Η—current efficiency, %;
Q—electrochemical equivalent, 1.0954×10 ^-3 kg nickel. A ^-1 .h ^-1 .
In the previous example, the current efficiency of the nickel plant electrolysis workshop is 98%, and the average cell voltage is 3.6V. Then the electric energy consumption of It electrolytic nickel is:

The electrical energy consumption of nickel sinter anodic electrorefining is generally 3300-3500 kWh.t-1 nickel. If converted to alternating current, the power consumption is higher due to losses including silicon rectifier station, busbar and solution leakage, and it consumes 3,800 to 4,200 kWh per ton of nickel. This power consumption figure also includes the DC power consumption of the liquid-forming electrolysis and the power consumption of the acid pump, lighting, and crane.
Power consumption is proportional to the tank voltage and inversely proportional to current efficiency. Therefore, any factor that is beneficial to lowering the cell voltage and improving the current efficiency can reduce the power consumption.
4. Recovery rate of nickel The high-level recovery of nickel in the electrolysis workshop is a comprehensive evaluation index, which not only reflects the technical level and economic efficiency of the workshop, but also reflects the level of workshop management. The recovery rate of the nickel electrolysis workshop can be divided into two categories: nickel coffee high (η _total ) and nickel direct recovery (η _straight ).
The total yield of nickel refers to the ratio of the nickel content of electrowinning qualified nickel to the nickel content of the consumed material, which reflects the degree of nickel recovery during nickel electrolysis. Its calculation formula is as follows:

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Where G _Ni is the amount of nickel produced by the electric nickel;
G ₁ — the amount of nickel contained in the anode;
G ₂ — the difference between the amount of nickel contained in the anode, the anode and the electrolyte at the beginning and end of the period;
G ₃ - Nickel content of various recyclable materials.
The direct yield of nickel reflects the degree of recovery of the nickel content of the qualified nickel produced directly during the electrolysis process. Its calculation formula is:

In the well-managed electrolysis workshop, the total yield of nickel can generally reach more than 98%. Therefore, as long as the management is strengthened to prevent the non-recyclable loss of nickel formation (such as extravasation of nickel-containing solution, infiltration into the ground, etc.), the total yield is generally It can be guaranteed, but the direct yield is affected by the size of “variables of various recyclable materials”, generally only 60% to 75%. The term "variable recyclable materials" refers to the residual nickel produced in nickel electrolysis production (including purification processes), the nickel content in various slag anode muds, sponge copper and various nickel-containing waste materials. The increase in the nickel content will undoubtedly lead to a significant drop in the direct yield. Therefore, in order to reduce the gap between η total and η straight, the value of G ₃ should be reduced as much as possible in production.
It can be seen that reducing the residual rate, reducing the nickel content of copper, iron , cobalt slag, anode mud and sponge copper, and reducing the amount of various nickel-containing waste materials will contribute to the improvement of the direct yield.
The main technical and economic indicators for domestic nickel electrolysis production are shown in Table 3.

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