Cleaning Contaminated Gold

[chickenminer 42]

Have a friend that was working old tailings this summer. He ended up with a lot of gold that is covered

with mercury. He plans to retort the fines and send to refinery.

 

 He is trying to clean up the coarser stuff, +14 mesh, so he can sell direct to customers.

 He is using Nitric acid, fresh 70% solution.

 Problem he is having is the nitric doesn't seem to be dissolving the mercury coating very well.

He has had it in solution for 3 days now.

 Question is ... I know acids work better when heated, but does the reaction slow down that much

when an acid is cool ?  He has this outside in 20 to 30 degree temps.

[Eric N 22]

Better to have the acid at room temperature or warmer.

Haven't used acid since the mid 70's in Oregon.

Can't remember which, acid or retort, that left the gold brown in color.

Melting it brought the natural color back.

 

What I can remember is my youngest daughter (2YO) got into the nitric acid, got it on her hands and got a burn.

The odd part was it was locked up in a foot locker.

The stranger part is her older sister (4YO) got her hands washed off and then disposed of the acid.

She wouldn't tell anyone where and it was never found.

Be safe.

 

eric

[chickenminer 42]

Eric,

 Thanks for the feedback. Yeah, this nitric is nasty stuff but it does the job.

 

 I was surprised how slow this nitric is reacting in cooler weather! Bringing it in

the house to be warmer isn't an option. So we'll just see how long it takes to clean

the mercury up.

 

 The discoloration must depend on the impurities present. The first batch we did when it was warmer

did not discolor the gold at all. Came out a nice bright "golden".

 

 In the past when I retorted the gold never came out a nice color but it didn't matter as it was going

to the refinery anyway.

[chickenminer 42]

A sample of the contaminated gold..

 

 

 

 

 

[Harry Lipke 13]

If you leave it too long, won't it sort of etch the gold?. Eating the impurities on the surface.

[chickenminer 42]

Harry,

 I don't know. Depends on the impurities I would think.

At this time I am not seeing that, but again with the slow reaction time of

cool acid it seems to be cleaning well with minimal impact to the physical

characteristics of the gold.

  I'll post some after pics when I get the next batch cleaned and neutralized.

 

 Here is first batch all cleaned.

[Reno Chris 101]

Hi Dick - any possibility of putting in on a backing of black plastic around it to get a bit of solar heating? I know you guys don't get a lot of sun this time of year but it might help warm it up at least a bit during the day. Nitric freezes solid at -43 F.
Nitric is the best acid to use for your purpose.

[chickenminer 42]

Chris..

  That's a good idea. I could set it in a type of solar cooker. Not too much power in the sun anymore but

I bet it would raise it 20 degrees or better.

  Dang, I didn't realize nitric froze at -43 !  I wonder if it'll freeze hard enough at -60 to break the glass bottle?

Hmmm... might have to bury the bottle for the winter.

[Rick N 3]

cardboard box lined with aluminum foil and some glass over the top, solar oven.

[JR BOI 11]

We've been recovering a lot of mercury gold here in Idaho while dredging this summer.  I invested in a small mercury retort I bought off eBay and it does a decent job for the small batches that we run.  Last weekend we recovered 9.6 grams of tainted gold and after the retort process it yielded 6.3 grams of dingy, dirty looking gold that was clumped together.  Most of the mercury is gone but there is still some trace elements of it left.  I'd like to try Nitric acid to see if it will restore the luster to the gold.  Also after the retort, the gold has stuck together, I assume I can simply break it apart before I try the Nitric acid bath or will the Nitric acid bath take care of that for me?

 

Dick, with your 70% Nitric bath you mentioned above, I assume you diluted it with water or used it straight?  

[chickenminer 42]

JR,

  The nitric was a 70% solution. The first batch we did I diluted it 2:1. Seems to work fine when it's warm.

With this colder wx I used it straight and it is taking a long time to react. Eventually it cleans

it up.

 I know what you mean on the retorted gold. My experience is the same. End result was always a dirty

looking clump of gold. I never tried nitric on a batch after retorting because it was going to the refinery anyway.

 

 So far very good results using the nitric and ending up with nice bright colored gold.

 

 Second batch of cleaned gold +14 mesh

 

 Be extremely careful when working with an acid !!  Wear those rubber gloves, do it outside and stay upwind of

the fumes produced.  Anytime I work with this stuff or the retort  I burn one of those mosquito coils so I can constantly

watch the wind direction.

 

 

[JR BOI 11]

I like the idea of a mosquito coil for sure.......On another note, what do you do with the leftover acid that was used to clean the gold?  I would not think it is still usable?

[chickenminer 42]

JR,

  Sure it's still useable, so save it. There are ways to "drop" the mercury out of the nitric solution.

I won't go into it here but you can do a little research and find out how.

 Be sure to store it safely and out of reach.

[carter 3]

Dick, I know nothing about this process but the first picture of the gold I wondered where in all that sand the gold was hiding till you posted the cleaned picture,WOW, thanx for the colorful illustrations

[carter 3]

Also it is a wonderful example of what the modern miner can be doing to help clean up the past!! Seen pictures of modern dredgers in the lower 48 with piles of lead(fishing sinkers, ect.) that got removed from streams too.

[JR BOI 11]

Carter,

I put the end of that cast/copper retort (pic above) in a glass jar with about 1/2" of water and during the process the mercury vaporizes and retorts in the copper tube and then is deposited in its liquid form in the water.  I keep a lid on the jar to collect all the mercury.  It is not naturally occurring so to your point, we are absolutely cleaning up the rivers/creeks.    

[Harry Lipke 13]

I think mercury does occur naturally.....?

[JR BOI 11]

Harry, you are right, I meant to imply that this mercury I'm dredging up is in the center of a very active mining district and a direct result of the of timers using it to extract gold.

[Reno Chris 101]

Metallic mercury and even mercury contaminated gold do occur naturally (though natural mercury contaminated gold is pretty rare).
I recently detected some heavily iron stained gold - gold coated with rust. This is more common in places where you are detecting the gold before it has rolled around in any river or stream. In these cases, I use Whink, a commercial cleaning product made to remove rust stains. It also contains small amounts of hydrofluoric acid. Its sold at places like Walmart. It does a great job of removing rust stains.

[JR BOI 11]

Chris,

Do you think "Whink" might work to clean up my retorted gold?  As it turns out nitric acid isn't the easiest thing to find and it is also fairly expensive as there is a MSDS uplift if you mail order it.  

 

JR  

[Goldgeo 1]

JR,

  Sure it's still useable, so save it. There are ways to "drop" the mercury out of the nitric solution.

I won't go into it here but you can do a little research and find out how.

 Be sure to store it safely and out of reach.

I just stick a flat piece of copper in to recover the mercury, it will come out of the solution almost instantly.

[Reno Chris 101]

I use iron to recover the mercury as it will stick to the copper (and need to be separated from it), whereas it will not stick to iron and can just be run through a shammy and stored for future use. 

[Goldgeo 1]

Cheers Chris, will give that a try next time.