First off I wish to say that Harold is very correct in the advice he has given as it applies to most materials. And I'm not going to touch on the cyanide part, pun intended.
However, (here is the big but) the above process does not address chloride compounds made when digesting with AR as a beginning process. The AR, HCl/H2O2, or the HCl/Cl2 that Arthur said he tried would have formed chloride compounds with some elements, if the nitric soluble materials were not first removed. Arthur never stated the source that this material came from, but I have made some assumptions based on his prior postings here. He has good access to chemicals inexpensively that most do not have, and processes a lot of electronics. He also hits many things with a “club” chemically speaking, because he can cost effectively. This means that he may have silver, lead, or mercury chlorides that will not be eliminated by regular incinerations between HCl and HNO3 digestions once they have been formed without great hazard.
If I am right in my assumptions as to chlorides, taking silver, lead, or mercury chloride to a red heat will start volatilizing these salts. None of these are good to breath and the mercury could kill you rather quickly. Of the 3 silver would be the least harmful to breath (GSP knew a guy that died from it) but the idea is to keep your values.
I would think that at a minimum Arthur should first determine if silver or lead is present in this mass as a chloride (mercury is unlikely, and he should know if mercury is a possibility based on his feedstock) that he is having trouble getting his gold out of.
Those that have run much karat gold can attest to the fact that silver and lead chloride do a good job of encapsulating values, and this could easily be Arthur's difficulty. I would start with hot water for lead (then chilling), and then ammonia for silver (be sure to acidify, HCl preferably) on some small samples to see if they may be the culprits.
I must admit I am shooting in the dark here as the feedstock is not known. I just felt that although Harold's advice is perfect for most once refined materials, it lacks a bit when a chloride has already been formed. This is why we try to eliminate base metals and silver before other digestions in most cases.
I am not trying to discount tried and true processes, but this may be a case where they fail to deliver.
Input, suggestions, and criticism is always welcomed.
