Hello, this is my first post as I have just been reading the forum for a long time.
I have been doing my own stone removal for some time and it works pretty well. I think the returns "romatic" is getting do not sound unrealistic taking the weight of the stones into consideration and that the carat can be more than 1/2 carat below actual carat. He is getting approx. 1/2 troy ounce less than calculated, not considering weight of stones etc.
Another important factor is how much or little gold he leaves around the stone and the size/weight of the stones.
I remove all the big stones manually and only the small stones are removed by digesting in AR. The process takes a lot of time especially because some of the material has a high silver content and does not dissolve so easily and some parts will take forever to dissolve.
The parts that did not completely dissolve (some almost do not dissolve) I always save for the next lot. But before I treat them with AR again I remove the silver chloride from the surface of these parts.
Some would probably use ammonia to dissolve the silver, which means they would have to use HCl to recover the silver as silver chloride. I have had great experience covering the parts with 10-15% Sulphuric acid and adding a few pieces of iron. I just leave the solution and just stir once in a while and within 2-3 hours all the silver chloride has been converted to metallic silver which has detached from the surface of the gold parts.
I wash the metallic silver with the gold parts, stones etc. a few times and then I can digest the metallic silver adding diluted nitric acid 1:1. Now only the undigested gold parts, stones, rhodium and some gold powder (maybe other PGMs) is left in the bottom.
I decant the silver nitrate solution, wash the residue and I can now easily remove the undigested gold parts for the next AR lot.
The stones with the gold powder, rhodium and other possible PGM's I digest in AR again. Then only the stones are left with some rhodium.
I recover the gold from the AR using SMB and the rest is sent to the stock pot for later treatment.
I would be glad if someone would give me any feedback on my stone removal process and maybe help with some improvements.
Thanks in advance