glorycloud said:
Most of the pros want you to incinerate between acids. In your case
they would want the solids brought to a read heat but not melted between
the nitric acid and the AR stage.
I'm not a pro, far from it, but I don't think you need to incinerate when going from nitric acid to AR. Two things you gain with incineration is to
1. eliminate one acid to not risk dissolving gold when switching acids, but in this case you are going to AR so you are going to dissolve gold. No need to eliminate the nitric acid.
2. Remove any organic residues (plastic, oil, carbon). But with ceramic CPU:s there shouldn't be any big problem.
Another thing I'm reacting on is why switch horses in the middle of the race? Going from AR to HCl/Cl isn't doing any good, it just complicates things. If you have nitric acid use that through all the processing and skip the clorox.
If I would come with a guess of what is happening here I would say that this is a likely scenario.
1. You start with a lot of scrap in a large batch. (Did you remove any lids on the CPU:s?)
2. You add nitric acid and start dissolving base metals.
3. After a while the exposed base metals were dissolved and the remaining was either quite resistant (Cu - tungsten lids of the PPro) or protected by gold plating so the process seemed to stop.
4. Now you took away the acid which had a lot of strength left which your finger batch proved.
5. You added AR (how much? Which concentration?) and it started to attack your gold and base metals. As you probably had a lot of base metals the gold cemented out on the base metal as a powder.
6. You stopped here and posted on the forum.
As you have brown powder and the reaction in AR have stopped, could it be that the nitric in the AR is exhausted?
I've never tested this myself but I think it should work as a nitric test. : Take a little bit of your solution and drop a bit of urea in it. If there is nitric left you should get a reaction.
If there is no or very little reaction then your nitric is exhausted and that is explaining why you see so little reaction.
I suggest that you decant off the majority of your solution, this removes the dissolved base metals.
Test your solutions, but also test your stannous chloride against a known gold solution so you know that it is working.
Now you have two ways to go, either continue to recover your gold with AR, dropping dirty gold from a dirty solution or incinerate and go back to straight nitric until all base metals are gone and then use AR and drop gold from a cleaner solution.
I suspect that some of your problems comes from the large heat sinks on the PPro:s. Maybe you should separate them out from the other CPU:s before going forward.
Good luck!
/Göran
