Counting Chickens

[MysticColby]

I haven't worked with gold yet. At least I haven't completed a batch of gold yet.
Anyways, I had karat jewelry.
Some were labeled, I tested all of them.
I did the math, inquartered with silver.
Dissolved the base metals in nitric.
Noted that I didn't have as much gold as I thought I had, as the gold did not hold it's shape, but rather was left as a coarse black powder.
Rinsed well via decanting (the silver is currently cementing on copper in another beaker).
Added water, concentrated HCl, then slow additions of concentrated Nitric.
Liquid turned dark orangish with a white precipitant, which I assume is residual silver.
Decanted half the liquid through a filter into another beaker
Low heat to evaporate residual nitric, then added water (I should add a bit less nitric next time)
Let it cool, then added SMB while stirring. see-through liquid got very brown and murky.
Now here I am.
The liquid still has a bit of color to it; a stannous test would be next on the agenda for that. (I can't help but think of Mr. Baratheon every time I hear this)
I think everything's going alright, but I was just curious if there was an approximate volume-of-dropped-gold-powder to mass-of-gold ratio?
It looks like an approximate 30 ml of settled powder, which I will now drop the other half then rinse and melt, but I was just curious about how much gold I was looking at.

 

[Geo]

if you did not incinerate the powder before adding hcl, you have dissolved gold in the wash. i didnt see you mention it. you shouldnt go from one acid to another without expecting to make aqua regia.

 

[MysticColby]

I did expect to make aqua regia.
nitric to remove silver/copper/some others
then AR to dissolve gold
I haven't washed any powders since adding HCl
I believe the wash you're referring to is rinsing non-gold nitrates away, and this is before any HCl.

After nitric to remove silver and copper, what would be the benefit of adding HCl? remove tin? that could be what the white precipitate is... that would make more sense. It does settle very quickly so I didn't think it would be much problem.

edited out incorrect info.

 

[jeneje]

Tin in any process is a problem, best to deal with before going on to the next step.
Ken

 

[MysticColby]

agreed. I always forget about it; I should incinerate then HCl wash next time. Well, this gold will probably be less pure than I thought, but still not outside what I was expecting for my first time.

 

[MysticColby]

wait a sec...
nitric, then incinerate, then HCl = soluble tin chloride that you can wash away
nitric + HCl = insoluble tin nitrate?
why doesn't the HCl in AR produce tin chloride from any tin nitrate present, same way gold chloride and silver chloride are made? Chemistry is frustrating when similar-but-different things behave differently.
does the incineration decompose the tin nitrate?

 

[Geo]

tin in a nitrated solution makes metastannic acid (hydrated tin oxide). tin in AR will create this gooey mess and cause problems filtering. tin will follow gold all the way through the processes just like silver will.

ive asked before what was the mechanism that allows the tin oxide to go back to a metallic state when incinerated and have never really gotten a solid answer, all i know is it does. after you create metastannic acid, incineration is the best way to reduce it and hcl wash to remove it.

 

[g_axelsson]

Tin doesn't get back to a metal state when incinerating, it turns into a form that is soluble by acids.
The metastannic acid you get when dissolving tin in nitric acid has the formula H₂SnO₃. By incineration it is turned into tin dioxide SnO₂ that is soluble in acids.

Göran