Rhodium plating solutions contain dilute sulfuric and/or phosphoric acids. When the rhodium plating solutions are exhausted, the solution can be treated by the following simple process that neutralizes the acid and removes any remaining metals.

Equipment needed
  • 2 plastic containers of adequate size to hold the solution
  • 1 plastic colander large enough to hold a coffee filter and fit the top of the plastic container.
  • 1 package of coffee filters. Large filters are available from restaurant supply companies.
  • 1 long-handled wooden or plastic spoon.
  • 1 pair of rubber gloves (household type).
  • 1 pair of plastic safety glasses.
  • 1 large box of baking soda (sodium bicarbonate)
  • Most of the items can be purchased at your local supermarket

Process in Steps

Step 1. Put the rubber gloves and safety glasses on.

Step 2. Carefully pour the spent rhodium plating solution into one of the plastic containers until it is half full. Leave space in the top of the container for the bubbling action in this process.

Step 3. Put the long-handled spoon into the solution. Open the box of baking soda and very slowly add a small amount at a time to the spent rhodium solution. The addition of baking soda will cause a bubbling action and slow additions need to be used.

Step 4. Stir the solution with the long-handled spoon regularly during this process. The gas given off by the bubbling is carbon dioxide, which is relatively harmless.

Step 5. Eventually, the baking soda additions will no longer cause bubbling. This means that the solution has a neutral pH balance.

Step 6. Add some more baking soda (approx. 1/2 to 1 cup depending on the amount of solution) to make the solution alkaline and stir the solution very well.

Step 7. Allow the solution to settle for an hour or so.

Step 8. Place the plastic colander in the top of the second bucket lined with three layers of coffee filters. It is helpful to wet the filters with water first.

Step 9. Carefully pour the contents of the first container through the filter-lined colander into the second container. Any residue left in the first container should be rinsed out with water and run through the filter as well. The solution coming through the filter should be clear.

Step 10. When completed, the liquid in the second container can be washed down the drain and the solids in the filter can be put in with the sweeps. The filter can be allowed to air dry before putting in with the sweeps material. This process neutralizes the acids and recovers any metals in the solution as carbonate sludge in the filter.

Note: The materials used in this process can be stored in a box in the plating area for future use.