Reverse plating cell

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The Reverse plating cell, also called sulfuric acid cell, is an electrolytic reverse plating cell that only removes gold or silver plating. (reference?) It uses sulfuric acid at over 90% strength. (absolute limit? patents?)

Contents

Detailed description

Construction of the cell

Running the cell

When running the cell care must be taken so it doesn't overheat. The recommended maximum running temperature is about 38-43 C (100-110 F) to prevent attack on the base metals in the anode. As a rule of thumb, limit the current during operation to 5-6 ampere per gallon of cell volume.

Harvesting the powder

There are many ways of harvesting the gold powder from the cell. The main problem is that filtering with paper filters are not possible as concentrated sulfuric acid destroys the paper. Another problem is the high viscosity of the acid combined with the fine particle size of the gold, the particles tends to stay suspended in the acid for a long time and is easily disturbed.

Ways of harvesting the gold powder

  • Separatory funnel.
  • Glass fiber filter or plug in a funnel. Known as a charmin plug.
  • Dilution of the acid and normal filtering.
  • Settling and decanting the acid.

Storing the cell and acid

When not used the sulfuric acid should be stored in an air tight container. The acid will absorb moisture from the air and over time become too diluted to work properly.

After using the cell it is best to clean it out and store dry. The cell can be stored with acid in it if it is possible to close it off from air and keep it in a safe place. The acid might damage some metals, for example copper, over extended time.

Chemistry

Persulfuric acid is formed at the surface on the anode. This acid is strong enough to dissolve gold and other precious metals but is oxidizing so any base metals at the anode is protected by an oxide surface. This makes the removal of the precious metals a self regulating process, it shuts down by itself when the plating is gone.

Practical implementations

Patents

References

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