Harold_V said:
When all of your material has been digested, you should then gather all of the resulting "mud" for lack of a better description. It will be placed in a filter, for the remaining solution to be filtered away. You want to get it dry, so it can be incinerated. If you prefer to eliminate this step, there's no need for me to continue, as I do NOT recommend you process this type of material unless you do the following operation.
Once filtered, the dry cake should be incinerated. Incinerate until all traces of carbon have been burned. Once cool, screen the material, to find any large piece of gold which may be present. Everything should go through the screen, or it should be checked to determine if it's precious metal, or not. If you find pieces of gold, it should be inquarted for further processing.
Back to the now screened solids. Run a magnet through the material, to remove any small bits of iron that may have survived the first dissolution. They should go to your stock pot, assuming you use scrap steel for recovery of values.
The now incinerated and screened solids should go back to a beaker, where they will be washed at a boil in HCl. This is a very important process, as it will remove traces of tin that will complicate filtration of the resulting gold chloride. Once well washed and rinsed (use tap water, rinse, allow to settle, siphon, then repeat, leaving behind ANYTHING that is not liquid). When your rinse water is clear, you can now dissolve the values, which will have had the rinse water remolved by siphoning (it need not be fully removed) with the solvent of your choice. My choice was always AR---but you may prefer a different method.
Harold
Hello, this step is so important and it is NOT included in lazersteve's DVD. If you don't incinerate then your final yield will suffer terribly. I once did a 500 gram batch of nice gold filled scrap and only got 7 grams of pure gold - I believe it was due to failure to incinerate and treat with hydrochloric acid as Harold points out above.
To incinerate, I place my filter with all the foils and "mud" in a pyroceram (Corning ware casserole dish). Then I use a regular propane torch with the flame set at about 2 inches long, very low, so as not to blow any of the incinerated material out of the Corning ware dish.
I then heat everything to redness, being careful not to concentrate the heat too long on any one spot of the dish (they are not indestructible and I have had one chatter on me once). You can actually do this with the filter and material still wet, the flame will dry it out as you go, but go slowly and try to heat evenly.
Once all the filter is burned to a white ash and all the solids have been heated to redness, the then allow the dish to cool to near room temp, then add the HCL right in the dish. This makes it easier to transfer the HCL/incinerated mixture to a tall beaker for settling and washing.
Once you've done the final rinse, the incinerated solids can be further processed in the same beaker from that point on.
Once I started doing this, my yields when processing filled scrap have been very high, at least 2.3 grams per 100 grams of scrap, but sometimes up to 4 grams per 100 grams of scrap ( with gold filled jewelry).
Watch covers are usually very high in gold content, if not worn too badly.
Hope this helps.
kadriver
