Polishing waste

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Polishing wastes are the dust and particles created when polishing jewellery and other precious metal objects. It is made up of polishing grit, wax, fibers from the polishing wheel and small metal particles.


Processing by furnace

A great way to process polishing wastes is to process them in a furnace. If done with litharge as a collector and fluorspar to get the flux liquid a very high extraction rate can be achieved.

Short description

  1. Incinerate to remove carbon and reduce volume.
  2. Melt in a furnace with litharge as a collector and a thinning agent for the flux.
  3. Cupellation to recover the precious metals from the lead.
  4. Refine the gold and other metals in the waste.

The process is very hard on the crucible and the liner of the furnace so this method should probably only be used by experienced individuals with the proper equipment. The resulting slag should be checked for any residual precious metals to see if the process works as planned.

Process by acid leaching

For the small refiner without a furnace the wet chemical method offers a good path.

Short description (Harold's version)

  1. Incinerate to remove carbon and reduce volume.
  2. Screen to remove larger gold particles that needs inquarting.
  3. Use a magnet to remove iron particles, these are put into the stock pot for recovery of small pieces of precious metals stuck to the iron.
  4. Place the screened material in a beaker and cover with hydrochloric acid and heat to a slow boil while stirring to prevent any heat shock.
  5. Add tap water, stir and let settle.
  6. Decant and test the wash water for dissolved values.
  7. Repeat wash cycle until wash water is almost clear.
  8. Add circa 5 ml of aqua regia for each gram of expected metal. Heat to a slow boil while stirring.
  9. When the reactions stops, add bit of water, stir and let settle. Decant and filter the solution.
  10. Repeat above step until the bulk of the values are extracted.
  11. Put the solids in a filter and wash until the filtrate runs clear.
  12. Combine the solutions with values and evaporate to denox the solution. Add a bit of sulfuric acid to precipitate any lead.
  13. After denoxing is done, dilute with some water and filter off silver chloride and lead sulfate.
  14. Precipitate the gold, wash and dry.
  15. If enough PGM is present, precipitate the PGM. Else test for any values and send to the stock pot if there is any.

The remaining solids can be dried and saved for extraction of any silver left if there is enough to warrant the work.

See also


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