3) Current density Current density is the intensity of the current passing through the unit (cathode) electrode area. The production capacity of the electrolytic cell increases almost proportionally with the increase of the current density. Therefore, when the current density is increased, the depreciation expense, maintenance cost and infrastructure investment of fixed assets per unit area of ​​cathode deposition of nickel will be reduced accordingly. However, too high a current density can cause hydrogen to precipitate, resulting in the formation of sulfur-like deposits. The cathode current density of the nickel sulfide anodic electrolysis process is generally 200 A/m 2 . With proper control of operating conditions, the current density can be increased to above 220 A/m 2 .
In the sulphate-chloride mixed system, when the pH is low (pH<2.5) and the current density is D1=110A/m 2 , the electro-nickel product crystallizes coarsely, and the coarse-grain structure can be seen by the naked eye, but the surface smooth, non-metal particles junction; when D k = 170A / m 2, the fine crystals, surface gloss / m. 110A 2 better than when. However, when D k = 200 A/m 2 , the crystals are markedly deteriorated, and have a ruthenium-like structure with metal agglomerates on the surface. However, when the pH is increased to 4.5 or more, although D k is increased to 220 to 280 A/m 2 , an electroless nickel having fine crystals and good metallic luster can be obtained. Therefore, after increasing the current density, the pH of the solution should be correspondingly increased, and the temperature of the current solution should be appropriately increased. The temperature of the electrolyte is preferably maintained between 60 and 70 °C.
Of course, as the current density increases, the tank voltage will increase accordingly, so the power consumption will also increase. For the problem of increasing the current density to increase the production capacity of the electrolytic cell, economic analysis must be carried out, and it cannot be generalized.
4) Electrolyte temperature Correctly controlling the temperature of the nickel electrolyte is an important factor to improve the technical and economic indicators of the electrolysis process and ensure the quality of the product. Increasing the electrolyte temperature can reduce the viscosity of the electrolyte and reduce power consumption. Accelerate the ion diffusion rate, reduce the concentration polarization of the electrolysis process and the ion depletion near the cathode, and reduce the precipitation of hydrogen and impurity ions on the cathode to affect the product quality.
If the temperature is too high, the evaporation amount of the solution will be increased, which not only deteriorates the working conditions of the solution, but also concentrates the solution, and the cathode deposit becomes thick. Excessive temperatures also increase energy consumption and increase costs.
When the current density is 150-200 A/m 2 , the electrolyte temperature is 55-60 ° C; when the current density is increased to 220-280 A/m 2 , the electrolyte temperature is increased accordingly, and the temperature is controlled at 65-70 ° C.
5) Yin and anode liquid level difference The yin and anocein surface difference refers to the difference between the cathode liquid level and the diaphragm pocket in the diaphragm bag and the anode liquid level height (see Figure 2). The static pressure generated by the liquid level difference causes the solution to penetrate from the cathode chamber to the anode chamber to prevent reverse osmosis of the anolyte, and the contaminated milk liquid generally has a control difference of H=30-50 mm. [next]
6) Same-pole center distance The same-pole center distance (L) refers to the distance between the centers of two adjacent anodes (or cathodes) in the electrolytic cell (see Figure 2).
The distance between the poles has an impact on the technical and economic indicators and product quality of the electrolysis process. Reducing the distance between the electrodes may reduce the resistance of the electrolyte and lower the cell voltage, thereby reducing power consumption. In addition, the number of poles in the tank can be increased to increase the production capacity of the equipment and increase the output. However, too small a pole pitch causes troubles in operation, and the possibility of short-circuiting between the electrode pocket and the pole contact is increased.
The nickel anodic anodic electrolysis process is used for diaphragm electrolysis. The cathode and anode of the tank are separated by a diaphragm frame. Therefore, the same pole center distance is much larger than the membraneless electrolysis. Generally, the same pole center distance is maintained at 180 to 200 mm.
7) Yin and Anode Cycles The nickel electrolysis anode cycle depends on the thickness of the anode plate, current density, and residual voltage. Generally, the anode period is 8 to 10 days. In addition to the current density and the surface quality of the cathode product, the cathode cycle is also related to labor organizations and is generally one-half of the anode cycle.
8) Slotting cycle After the nickel sulphide anode is electrolyzed for a certain period of time, an anode mud layer is formed on the surface. The anode mud rate is between 6% and 25% depending on the amount of sulfur in the anode. The rate of nickel sulfide anode mud is much higher than that of the crude nickel anode.
In order to prevent the electrolyte circulation in the lower part of the cathode diaphragm from deteriorating due to the accumulation of the anode mud at the bottom of the electrolytic cell, and the occurrence of the cathode and the anode short circuit, the gutter cleaning is generally performed within 3 to 6 months depending on the magnitude of the current intensity.
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