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Author: Subject: Zinc from Zinc Sulfate
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[*] posted on 22-5-2004 at 14:40
Zinc from Zinc Sulfate


I wish to produce around 10g of powdered zinc. I have some ZnSO4. What would be the best way to reduce this, so that I end up with metalic zinc in powder form?

My first thought is electrolysis of a water solution of the zinc sulfate. However, as electrolysis proceeds and zinc is deposited, the solution will become more and more acidic from the sulfate left behind. I think eventually this will start dissolving my zinc as quickly as its produced. Unless I change the solution frequently and thus waste a lot of ZnSO4.

A thought I had was to separate the cathode and anode with a porous membrane. However, I have had bad luck with mixing when using membranes before.

Another thought, which seems to be my best idea so far, is to convert the zinc sulfate to zinc chloride (using NaOH, washing, and adding HCl). Electrolyzing zinc chloride should produce chlorine gas as opposed to the sulfuric acid produced electrolyzing zinc sulfate. Therefore, the zinc produced should not be attacked.

Any thoughts?
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[*] posted on 22-5-2004 at 16:41


It is zinv-sulfate which is used in industry for the electrolytic production of zinc - it is superior for this purpose and avoids the nasty chlorine.
The electrodes are made from aluminium (where the zinc is deposited) and lead (carbon should work too). The sulfate is dissolved in 30% sulfuric acid and electrolysed until the cincentration of the acid has reached about 40%.
This makes me guess that the acid will have no negative influebce as long as the concentration is not too high and - IMPORTANT - as long the there is current supplied to the electrodes. Of course neither Al nor Zn will survive very long in H2SO4 if not the electrolytic deposition of fresh Zn protects them.
The Al is used as the Zn can be scraped away lateron very easily and does not bind to it.

A "U" shaped cell is favorable or at least a divider - no direct way from anode to cathode should exist. Otherwise Zn deposited will bridge the circuit soon. This happens much faster in a cell which uses Zinc-chloride as the zinc deposites in another way there - building up fractal "trees".
The electrodes must be inserted only with the current switched on, and have to be removed before the current is shut down and it will work fine. Of course you can start without any H2SO4 - it will take a little longer then and more electricity is wasted - not important to us but for industry it is.




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[*] posted on 23-5-2004 at 00:45


What about displacing zinc from zinc sulphate? Use lets say, finely divided aluminium powder and throw it into the solution of zinc sulfate.



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[*] posted on 23-5-2004 at 02:50


I wouldn't use aluminium in displacing zinc since the aluminium sulphate in solution would hydrolyse resulting in some quantity of H2SO4 produced and this would react with the formed Zn. Why not use Magnesium instead.



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[*] posted on 23-5-2004 at 13:03


Al for replacing the zinc will work but it is a mess and far from producing a clean product. I tried it with zinc-chloride and cannot recommend it.

The electrolysis of the sulfate works fine, lead is the material of choice for the anode - dont use carbon, it will detoriate. I looked it up. Al for the cathode is right, dont overdo voltage and current, if gas evolves at the cathode then you know its to much (voltage). A U-shaped cell and at the bottom of the U some glasswool as celldivider, the cathode chamber filled with a zinc-sulfate/H2SO4 mixture and the anode chamber with 30% H2SO4, thats perfect. It will work in a undivided cell too though, no problem.




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[*] posted on 27-5-2004 at 05:12


Also, zinc may be electrolytically obtained by electrolysing zinc ammonium hydroxide - the zinc ion is complexed by ammonia, and this prevents precipitation as Zn(OH)2. No acid or alkali (if you decide to use zincate salts) made, the zinc deposited isn't in danger of chemical attack. And no chlorine fumes either.
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[*] posted on 4-12-2020 at 12:19


Why nurdrage talked about making sulfuric acid from copper sulfate? Zinc sulfate should be cheaper I guess and how fast does zinc reacts with sulfuric acid?
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