Oz said:
Well I am probably stepping into it here.
Harold_V said:
Dilute well with water (tap water is perfectly acceptable in this case). Siphon after the solids have settled.
Why would tap water be acceptable here if you are possibly removing silver with the nitric and perhaps creating silver chloride solids? Lead should also be considered.
In this instance, I am considering the recovery of gold, and nothing more. The process I recommended will solve all of the problems, and if traces of silver may be present (but likely are not), the silver would be recovered at some time in the future. My logic is that only a fool will spend premium time trying to recover a few cents worth of silver that may or may not be present. That which may have followed the rinse solution would be recovered with copper, so what we're talking about is nothing short of a miniscule trace.
Regards addressing the presence of lead, the rinses that follow the nitric digest should be with hot water, with decanting taking place prior to any lead nitrate self precipitating upon cooling of the solution. Hot water will generally facilitate rapid settlement, keeping any lead that may be present in solution.
Assuming there is a small amount of silver present, so what? No harm is done by creating a trace of silver chloride, nor is it lost so long as the solids (filter and contents) are not discarded. As Kenny Rogers said in his song, The Gambler, you have to know when to hold 'em, and know when to fold 'em.
Harold_V said:
An alternate to the second incineration. Rinse the solids with ammonium hydroxide, then rinse well with tap water. It is important that no nitric remain before introducing HCl for the second recommended wash
This ammonium hydroxide wash would solve the silver chloride problem if it indeed developed but if tap water was used in the first step it would have to be chloride free in order to skip this later step and have clean gold. [/quote]
It has nothing to do with silver chloride. It has to do with insuring that all of the nitric has been eliminated.
I refined for more than 20 years, using tap water for all of my operations aside from running my silver cell. In all that time, I never had a problem in dissolving gold because of the use of chlorinated tap water, and ours was heavily chlorinated. It was obvious by the smell, by the taste and by the traces of silver chloride that were precipitated from silver nitrate solutions. Again, so what? The silver chloride, to me, was a desirable byproduct. I processed all of my waste materials by furnace, relying on the presence of silver chloride to act as a collector for the greater values, The concept proved to be an excellent solution to harvesting greater values. I recommend it highly.
Always acidify hydroxide solutions that may contain silver.
Even if there was traces of silver present, in this particular application, the end result would not yield any problems having introduced ammonium hydroxide. I agree, otherwise, that the solution should be acidified if there is any chance there would be silver present. Remember, he was advised to rinse until the solution was free of color. At that point, so little of ANYTHING but the solids remains that the material could likely be then processed directly without incineration. The miniscule traces of silver chloride that may have resulted from the use of tap water would require that the entire ammonium hydroxide wash solution and rinse water be dried----which, in my opinion, is highly unlikely. I do agree that the hazards should be well understood, however.
The incineration, or the addition of the ammonium hydroxide (in place of the second incineration, as I advised) could in all likelihood be eliminated. It was suggested so the that those that read the comments gain knowledge that can, in the future, keep them out of trouble in the way of losing values.
Consider that my final advise would be to re-refine the yield if quality was an issue. I expect it would be, but his question was one of bailing out from a mess.
I stand 100% by the instructions I posted. They will guarantee success.
When it's all said and done, I rely on the picture that has been seen countless times. Proof positive that my method of refining yielded exception results.
Harold
edit: corrected spelling----no change in content otherwise
