Electrowinning Zinc: Understanding the Process and Sulfuric Acid

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In summary, when zinc reacts with sulfuric acid, it produces zinc sulfate and hydrogen. However, during the electrowinning process, this reaction is reversed with zinc deposited on the cathode, oxygen evolved at the anode, and sulfuric acid also produced. This is possible because the applied voltage "holds off" the normal reaction between sulfuric acid and zinc, allowing for successful plating. Once the voltage is switched off, the normal reaction occurs and zinc will dissolve.
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SMD1990
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Zinc reacts with sulfuric acid to produce zinc sulfate and hydrogen. But then, when electrowinning zinc, this is reversed, with zinc deposited on the cathode, oxygen evolved at the anode, and sulfuric acid also produced.

So why does the sulfuric acid not immediately react with the zinc, negating the plating process? Does it have to do with the applied voltage somehow "holding off" the normal reaction?
 
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SMD1990 said:
So why does the sulfuric acid not immediately react with the zinc, negating the plating process? Does it have to do with the applied voltage somehow "holding off" the normal reaction?

Yes, once you switch off the voltage, zinc will dissolve.
 

1. What is electrowinning zinc?

Electrowinning is an electrochemical process used to extract metals from their ores or solutions. In the case of zinc, it involves passing an electric current through a solution containing zinc ions to deposit the metal onto a cathode.

2. How does the electrowinning process work?

The electrowinning process involves placing a zinc-containing solution into an electrolytic cell with a cathode (usually made of stainless steel) and an anode (usually made of lead). An electric current is then passed through the solution, causing the zinc ions to move towards the cathode and deposit onto it as solid zinc metal. The sulfuric acid in the solution acts as an electrolyte to facilitate the movement of ions.

3. What is the purpose of sulfuric acid in the electrowinning process?

Sulfuric acid is used as an electrolyte in the electrowinning process to facilitate the movement of ions. It helps to conduct electricity and allows the zinc ions to move towards the cathode where they are deposited as solid zinc metal. Sulfuric acid is also used to maintain a low pH in the solution, which is necessary for the electrowinning reaction to occur.

4. What factors can affect the efficiency of electrowinning zinc?

The efficiency of electrowinning zinc can be affected by several factors, including the concentration of zinc in the solution, the temperature of the solution, the current density (amount of current per unit area) applied, the composition of the solution (e.g. presence of impurities), and the design of the electrolytic cell.

5. What are the main uses of zinc extracted through electrowinning?

Zinc extracted through electrowinning is used for a variety of purposes, including galvanizing (coating iron or steel with a protective layer of zinc), producing brass and other alloys, and as a component in batteries, paints, and fertilizers. It is also used in the construction and automotive industries for corrosion protection.

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