Zinc powder quality issues during high-temperature wet purification of electrozinc
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Let’s discuss what requirements are placed on the zinc powder used in the high-temperature purification process for electrowinning zinc. I use zinc powder with a particle size of 120 mesh and a zinc content of 97%, but once it is added to the reaction tank, all of it settles at the bottom of the tank. After stirring, only a small amount of zinc powder remains in the upper layer of the solution, resulting in poor impurity removal efficiency. (This phenomenon did not occur even when using 80-mesh mesh in the previous two years.)
It is caused by the generally large particle size of zinc powder, which affects the bulk density of zinc powder (its weight), the effective zinc content in zinc powder, and its particle size
It needs to be considered in light of how you joined
It’s possible that the zinc powder had already formed clumps before it was added, or it might be that the addition rate was too fast during handling, which reduced the mixing speed.
For the first stage of copper and cadmium removal, zinc powder with a particle size of 80-120 mesh is used, while for the second stage of cobalt removal, zinc powder with a particle size of 120-200 mesh is employed. It is possible to analyze the amount of effective zinc in the zinc powder; it should generally be above 92%. At the same time, it is necessary to check whether the mixing equipment and the method of addition meet the process requirements – the zinc can be added in several batches, or it is better to add it after the mixture has been homogenized.
First-stage purification: Zn≥98%, +80 mesh. Second-stage purification: Zn≥98%, -80 mesh. The situation you mentioned may be related to factors such as stirring intensity, flow rate, the physical properties of the Zn powder, slurry formation, and so on.
I think there might be a problem with this zinc powder of yours; although the total zinc content is ≥97%, the active zinc (i.e., metallic zinc) level may not be high.
It is related to the particle size of zinc powder, but it should not be the main reason. In my opinion, it is directly related to the quality of the solution (including the presence of impurities). Strengthen the approach starting from testing.
The speed at which zinc powder is added is too fast. Try using a filter when adding zinc powder, and control the speed. The stirring intensity should also play a role.
Adding zinc powder is a matter of responsibility; using a sieve can easily get clogged when there is a high amount of steam.
What style is this mixer of yours?