Non-Chemical Avoiding loss gold

[Dr. Poe]

I can't count how many times I've visited another refiner and noticed the purple glasses on the center hole of their melting furnaces. All the hard work that they do to recover every last iota of gold, to see the evidence of their gold loss sort of breaks my heart. They all thought it was a symptom of sputtering and had no clue to the real reason for golden glass on the port.
I ask them;"Did you wash the precipitate and if so How? "Oh, we just added water to the filter, that's good enough." is the most common answer that I receive. I explain that it's not sufficient to just add water to the filter, that they need to wash in a beaker and several times (boiling if at all possible). "Oh, we don't lose that much."; they say. So I show them, I put a steel plate above the hole a few inches and heat it past 500C, then tell them to light the propane. Anywhere from 2 to four grams accumulates onto the hot metal from the remaining chlorides converting the gold to gold chloride and vaporizing even before the crucible is very hot. Two to four grams! That's $111 to $222 ! Doesn't seem to me to be a 'little amount'. Even If one does thoroughly rinse away chlorides from the gold drop, it doesn't hurt to utilize the hot steel, just to make sure. I'm Dr. Poe :|

 

[qst42know]

Would you recommend a final chemical wash?

I use the wash procedures as described by Harold which includes a hot ammonia wash to scavenge traces of silver chloride. Good enough do you think?

 

[Dr. Poe]

Would you recommend a final chemical wash?

I use the wash procedures as described by Harold which includes a hot ammonia wash to scavenge traces of silver chloride. Good enough do you think?

Did you mean a hot 'dilute' ammonium hydroxide wash followed by hot water washes? Ok, but whatever, don't wash in the filter. Use a beaker; emulate Butcher's methods or Glondor's methods of washing. Dr. Poe :mrgreen:

 

[qst42know]

Hot HCL, and then as many hot rinses to produce no color, hot household ammonia, and a couple hot water rinses. All boiled and in the vessel it was precipitated in.

I avoid putting it in a filter, I filter only the diluted solution with sulfuric added to remove silver and lead when present. It is even dried in the same vessel.

 

[butcher]

Dr. Poe make’s another good point.

From what I understand gold chloride (or even gold in table salt), when melted can volatize some gold, this I have seen happen condensing yellow liquid, or violet stains). And as we also know silver chloride will also go up in smoke as white fumes.


I believe when we precipitate our gold it is actually elemental gold metal powder of course in chloride solution, and can have a trace of other metal chloride salts involved (like silver chloride, or even lead chloride).

I feel the washing techniques Harold has taught us, washes most if not all of these salts from our powders, lead chloride in HCl and boiling hot water washes,(of course most chloride salts are water soluble except silver and lead and we should not have any Hg2)( and Harold’s wash procedure deals with these) the ammonium Hydroxide, will help to remove silver chloride, and help traces of chloride to convert ammonium chloride which are water soluble, it will also help to change the pH of solution and our gold powders.

I have never noticed any appreciable loss when melting gold with this washing procedure Harold taught us. Maybe slight tint of violet in borax, but this could be from slight base metal impurity in the gold mixing with impurity in flux.


I have not worried about gold loss in melting gold when using Harold’s wash.

I am especially careful to neutralize and wash out salt water from powdered chlorides I am incinerating.


Edited after getiing email about using wrong word above I had chloride.

Oz
Thank you for the email,
I may have not said what I meant very clear, and I will edit this for clarity, and I did use the word ammonium chloride twice when I only meant to use the word once.

When you use the ammonium hydroxide (NH4OH) solution on the powdered chloride salts like silver chloride (AgCl) in the wash procedure, the solution changes to ammonium chloride, the silver dissolves into this solution as silverdiammine or (diamminoargentate) [Ag(NH3)2]

AgCl (s) + 2NH4OH (aq) <--> [Ag(NH3)2] + NH4Cl + H2O
(Equation balance not checked).

Thank you for keeping me on my toes.