Mercury coated gold

[Bonaro]

The area where I dredge has a LOT of mercury. Almost all the gold is coated and it's not uncommon to find puddles of HG in the sluice. To remove the HG from the gold I use a nitric acid bath to dissolve it. This works well but the gold left behind is always dull and low lustre.

Nitric alone should not etch the gold. I have a theory that the mercury, after being in contact with the gold for many many years, actually begins to soak into the surface of the gold. Then when its removed, the surface of the gold is left rough and dull.

Regardless of why it happens, the gold is dull and unattractive after removing the HG. Soaking in vinegar and salt doesn't seem to help and the only way I have found to brighten and shine to gold is to tumble it with mild abrasive....time consuming

What is going on and how do I fix it?

 

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[winners58]

with aqua regia the nitric acid oxides the surface to form gold ions that protect the gold from being dissolved more.
hydrochloric acid then reacts with the gold ions and with the oxide layer gone the nitric acid can
dissolve another layer of the gold and continues until all the gold is in solution. Aqua regia wiki
so my guess is there is a layer of Au3 ions, maybe test to see if muriatic acid would work (hydrochloric acid)

 

[KevinInColorado]

In the process of amalgamation, the gold very slowly dissolves into the mercury. When the Mercury is removed it leaves behind "gold sponge"...in your case a thin layer of it (maybe only a few atoms thick) on the surface of the individual pieces. As you've observed this isn't a smooth shiny surface. Take a look at it under high magnification, it's cool!

I'm interested to see what advice others have that may help you. My only experience getting sponge to look like shiny metal again is by putting it in a kiln

 

[russau]

Dan who cares what it looks like ! Gold looks good anytime! ESSPECIALLY when its in my poke!

 

[Hoser John]

A good tumble in a rock tumbler with some water and a few tablespoons of NON sudsing ammonia does the trick very well-John

 

[Ragnor]

I would purchase or build a retort. Now I am fully aware that this process requires fume mitigation and anyone doing it should familiarize themselves with that also. Mercury will short out your brain wires and clog your lungs. That being said, a good retort would clean up the gold and allow for salvaging the mercury for future projects.
Nitrated mercury carries it's own set of potentially unwanted and ....dynamic side effects.

 

[aa battery]

my wifes uncle used to bake it in a potato and said it worked. Me i never tried it.

 

[ratled]

vinegar and salt works for me. Use more salt than you would think but not so much you make it a slurry.

ratled

 

[Aufisher]

Mine looks like this

 

[OwenT]

You're not dredging in Washington yet are you?

 

[KevinInColorado]

Mine looks like thisView attachment 1298298

This looks more like what I'd expect sponge-y gold to look like. Nice photo, nice gold!

 

[chlsbrns]

Au + Hg Amalgamation

 

[KevinInColorado]

Au + Hg Amalgamation

Awesome pics in that link...very much illustrates what I was trying to describe, thanks Chlsbrns!

 

[chlsbrns]

Awesome pics in that link...very much illustrates what I was trying to describe, thanks Chlsbrns!

Your welcome Kevin! When you posted I thought that you would like the pics so I posted the link!

 

[IMAUDIGGER]

Burning the mercury off can kill you if precautions are not taken.....Retort is probably what most people do. Careful.

 

[Aufisher]

 

[paydirt1850]

After I burn the mercury off with nitric, I put the gold in a plastic jar with a little jewel luster coin cleaner. All you do is shake it for about a minute, rinse it off good with water. It comes out nice and bright.

 

[motohed]

I know this is a bit off topic , but I was wondering how much Mercury , do you guy retain when you sluicing or dredging , being for the East Coast , I have always wondered ?

 

[Bonaro]

I know this is a bit off topic , but I was wondering how much Mercury , do you guy retain when you sluicing or dredging , being for the East Coast , I have always wondered ?

A modern suction dredge is the most efficient, least complicated and lowest cost mercury recovery device ever invented. It is capable of retaining 97% of the mercury that enters it. In many places in the West, far more HG is recovered than gold.

 

[gold tramp]

This looks more like what I'd expect sponge-y gold to look like. Nice photo, nice gold!

Heres a piece of true sponge
GT...........
View attachment 1302280