Redissolve cemented silver

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Bluebloomer

Bluebloomer

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Jul 7, 2014
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Netherlands
It appears that cemented silver does not redissolve in nitric acid, but it has to be melted first.

Could some one explain why that is ?

I incinerated some paper (coffee) filters with gold, and cemented silver. As you can guess, it made a mess, and now my cemented silver and gold foils, and gold powder is mixed into 1 slurry. Acids do not have any effect on the slurry, and my guess is that it is because of the greasy like apearence of the silver cement.

Should of kept the silver separate from the gold filters, and now I realize I had to melt the silver first, before doing anything else.

Now I have a mess on my hands, gold powder, gold foils, some base metals and cemented silver into 1 mixture and no idea how to seperate it.

Perhaps the only option would be to fuse all the metals in a melt, and turn it into shot, and then dissolve it in nitric acid ? There are still ashes from the burned filters in there, so would it hinder the melt ? Would I need a flux of any kind ? What other options would I have ?
 
I don't know why you are having problem dissolving cemented silver, I have never had any problems with that.

The only way silver can withstand nitric acid is if it is protected by something covering the surface, like silver chloride, oil or some other impregnable surface. Since you incinerated it there shouldn't be any oil left so most probably you made silver chloride someway.

I don't know what you were thinking by mixing cemented silver with gold foils. Usually we try to separate metals, not mixing them together, when refining.

Try to treat a sample with lye, if you have silver chloride it will turn into silver oxide and that will dissolve in nitric acid.

Göran
 
Göran

It never occured to me I had to separate the paper filters from the start. I just burned them all together, thinking it was easy enough to separate the metals. I was wrong.

I tried to dissolve cemented silver in the past, it dissolves just a little, then the rest of the powders settles to the bottom, and even though I boiled the solution for 2 hours, nothing more got dissolved.
I could be I did not rinse the paper filters good enough, so there might be more copper on the cement as there should be, perhaps that is why the nitric acid doesn't do anything with the cement, it's not even fuming out NOX gasses.

I should mention my HNO3 is just 60 percent as it is the highest I can buy. Could that be a problem too ?
I did dissolve 2,8 KG of Dutch Silver Coins in it, and I got a little bit over 2 KG of pure silver cement back from it. The cement in the filters is from that batch.

IF the gold and silver is mixed in together, what would the lye do to the gold powder that is in there ?

And if I was to treat the ash / powder mix with lye, and the silver chloride is converted, (and I think some is in there) would nitric acid to seperate copper / silver be the best way to go forward or melting and pouring shot from it, be the best way to go forward ?

My guess is there would be around an ounce of silver, and about 20 grams of gold, and perhaps about 10 grams of copper in there.
 
Am I getting this right? I'm just trying to get a grasp of your situation...

- You started with 2.8 kg of coins, dissolved it in nitric and then put it in a filter and washed it... or did you wash it in a beaker and filtered the water you poured off? The reason I ask is because you are talking about 2 kg of silver but only 30g incinerated.

- You have about 10g of gold in the form of foils mixed in this incinerated mass.

- Is this a lot of filters you are burning or just from two batches?

- How was the gold extracted? Copper chloride process?

So, you have $15 worth of silver together with $350 of gold... forget about the silver and go for the gold first.
If it was me and given my preference in chemicals and circumstances I would have treated the ash with lye, the NaOH converts the silver chloride into silver oxide, the gold is unaffected and any copper chloride is turned into hydroxide. Then wash out the excess lye and NaCl.
Then incinerate until there are no carbon left. The resulting ash would be leached with aqua regia to recover gold, the silver will turn into silver chloride and is trapped by filtering.
The leftover silver chloride can be turned back into silver oxide with lye and washed, then leached with nitric acid and filtered.

... but that is how I would do it with the material I think you have.

Göran
 
I can't understand why your silver cement will not dissolve in nitric, nitric even cold will slowly dissolve silver metal, did you rinse your silver cement in HCl ?
If in your incinerated filters you have silver chloride and an amount of gold simply use AR to dissolve the gold,allow it to go cold or add ice, filter and rinse it well and precipitate the gold, what's left in the filter will be silver chloride which you can then convert to silver with the method of your choice.
The gold powder will probably be dirty so I'd advise to redissolve it using a different mix of chemicals maybe HCl and bleach or peroxide, this should clean up your gold to an acceptable quality.
 
I would not recommend melting the gold with silver chloride present, in best case you will create toxic silver chloride fumes and in worst case it will take some of the gold with it among the toxic silver chloride fumes.

Nickvc is also giving good advice.

Göran
 
g_axelsson said:
Am I getting this right? I'm just trying to get a grasp of your situation...

- You started with 2.8 kg of coins, dissolved it in nitric and then put it in a filter and washed it... or did you wash it in a beaker and filtered the water you poured off? The reason I ask is because you are talking about 2 kg of silver but only 30g incinerated.

- You have about 10g of gold in the form of foils mixed in this incinerated mass.

- Is this a lot of filters you are burning or just from two batches?

- How was the gold extracted? Copper chloride process?

So, you have $15 worth of silver together with $350 of gold... forget about the silver and go for the gold first.
If it was me and given my preference in chemicals and circumstances I would have treated the ash with lye, the NaOH converts the silver chloride into silver oxide, the gold is unaffected and any copper chloride is turned into hydroxide. Then wash out the excess lye and NaCl.
Then incinerate until there are no carbon left. The resulting ash would be leached with aqua regia to recover gold, the silver will turn into silver chloride and is trapped by filtering.
The leftover silver chloride can be turned back into silver oxide with lye and washed, then leached with nitric acid and filtered.

... but that is how I would do it with the material I think you have.

Göran
Click to expand...

Sorry for being incomplete. The 2,8 kg coins yielded 2 kg of silver cement, that sits in a jar ready to be melted. The last bits of cement are in the coffee filters, but it had some copper in it. The coins were 78% silver so the 2 kg of cement was spot on.

10 grams of gold may be a bit low, it also has the content of an older stockpot, and a lot of filters with just half a gram or so. But there also a lot of gold foils in the mix. Most of the gold was precipitated with smb, but I just added it to the waste filters so I could get all the gold and silver out at once. The small batches where learning curves, experiments, and small scale setups over the last 2 years.

Thank you for the advice, Göran

@Nickvc

No I never rinsed the silver cement in HCL, and as I said before, it has a velvet feel to it, you can smeer it between your fingers as wet paint, but it is a powder. I thought this was normal.
Never thought about washing it in HCL, only used hot water.

If the dirty gold gets precipitated, I could always do a second refing after a good washing.

Thank you nickvc
 
If you had a lot of different filters with odd content then I would suspect that the silver reacted with chlorides during the incineration or when trying to dissolve it with nitric.
I would also count on a lot of different garbage in the other filters, like tin oxide, lead sulfate, silver chloride and other undissolvable compounds. A lot of this won't dissolve in pure nitric, or even aqua regia.

Göran
 
I guess it must be that, because I treated the ashes with NaOh. Washed and rinsed untill most of the black was gone.

Vacuum filtered, and then dried the cake in a stainless steel bowl on a heatplate.

Then I roasted the ashes as best I could, many glowing flakes, no more green or blue flames, just glowing hot pieces.

After cooling I heated it for about 30 minutes in HCL, then started additions of nitric acid in incerements.

Now it's fuming, and dissolving.

But now what's the next step ? Cooling and filtering. Then force the AgCl with ice, or should I just use salt, then filter again and get the gold ?
 
Either allow the pregnant solution to go completely cold or add ice and allow any silver chloride in the solution to precipitate out before filtering, once filtered rinse the filter fully and precipitate your solution if it is crystal clear, if not put it back through the same filter, as the sediment builds up it filters more of the fine particles out so you may need to filter it several times to get a clear solution.
 
Guys, thank you for all the help but due to a sudden medical issue I have decided to add it all to two different stockpots, and hold all projects for now, untill my health is oke again.
I'm taking too much morfine for now to be messing with this away, and with a possible 2 surgeries coming up I just can't risk making mistakes or doing stupid things.

Pregant solution containing silver and gold are seperated over 2 buckets with a bubbler. The silver has some agcl and cemented silver, and the gold is from a previous stockpot and some new refinings, but for now I just can't think straight anymore.

Hope you guys can help me out, cleaning up the stockpots after my health gets back up.
Thanks again
 

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