Metastannic acid mixed with cemented silver...

[bhilton]

Hi all,

I attempted to do a gold inquartation with some sterling silver - unfortunately, I think the material was not all sterling and had some tin in it somewhere. It was a necklace a friend gave me.

After inquartation I boiled it in dilute nitric and it appears I had dissolved all or most of the base metals - I moved those metals to a separate aqua regia batch.

I first noticed the problem when I poured the (still semi-hot) dilute nitric containing what I thought would be silver and copper to a separate jar I have which contained silver and copper nitrates already.

As soon as my semi-hot solution entered the separate jar - which already had a piece of copper flat stock in it, a pile of fluffy white crystals jumped out and coated the bottom of the jar (maybe because mixing the solutions, the temperature dropped low enough to cause what I believe to be metastannic acid to rear its ugly head. At the same time the copper flat stock started cementing out silver.

Now I believe I have a jar with around 1/4" of white fluffy crystals on the bottom, plus some floating around in solution and 15-20g of cemented silver!

Any ideas how I can recover the silver?


Thank you all!

Bill


EDIT: I fixed the Title.

 

[Yggdrasil]

Hi all,

I attempted to do a gold inquartation with some sterling silver - unfortunately, I think the material was not all sterling and had some tin in it somewhere. It was a necklace a friend gave me.

After inquartation I boiled it in dilute nitric and it appears I had dissolved all or most of the base metals - I moved those metals to a separate aqua regia batch.

I first noticed the problem when I poured the (still semi-hot) dilute nitric containing what I thought would be silver and copper to a separate jar I have which contained silver and copper nitrates already.

As soon as my semi-hot solution entered the separate jar - which already had a piece of copper flat stock in it, a pile of fluffy white crystals jumped out and coated the bottom of the jar (maybe because mixing the solutions, the temperature dropped low enough to cause what I believe to be metastannic acid to rear its ugly head. At the same time the copper flat stock started cementing out silver.

Now I believe I have a jar with around 1/4" of white fluffy crystals on the bottom, plus some floating around in solution and 15-20g of cemented silver!

Any ideas how I can recover the silver?


Thank you all!

Bill


EDIT: I fixed the Title.

Metastannic would have formed in the first Nitric parting.

 

[bhilton]

Metastannic would have formed in the first Nitric parting.

ok, I wonder if it is copper that cemented itself out. I might try a small sample, rinse it well, incinerate it and run it through some heated hcl. That should dissolve the white salt looking stuff if it is copper right?

 

[Yggdrasil]

ok, I wonder if it is copper that cemented itself out. I might try a small sample, rinse it well, incinerate it and run it through some heated hcl. That should dissolve the white salt looking stuff if it is copper right?

Your white powder is probably Silver cementing on the Copper bar.

 

[kurtak]

The first test you should do is expose it (the white precipitate) to sun light to see if you somehow inadvertently created silver chloride

if it is silver chloride it will quickly turn purple/black when exposed to direct sun light

Kurt

 

[bhilton]

Your white powder is probably Silver cementing on the Copper bar.

It sure looks like metastannic based on pictures I see online. I let it settle last night and the grey silver cement settled at the bottom and the white metastannic stuff settled on the top, so much that I just poured almost all of it off!

The silver cement looks good, but who knows if the white stuff is hiding in there?

I'm doing another 4 or 5 rinses of the silver with a long settle in between, see if any white stuff floats to the top again.

 

[kurtak]

Your white powder is probably Silver cementing on the Copper bar.

silver cement should be gray (like cement) not white

he should post pics so we can see what he is seeing

Kurt

 

[Yggdrasil]

silver cement should be gray (like cement) not white

he should post pics so we can see what he is seeing

Kurt

I agree, but the color might be deceiving.
Silver Chloride and Metastannic will be "self evident" as the Metastannic will form during parting and the Chloride will darken.

 

[Martijn]

Put it outside in the sun and see if it turns purple and then black. If so, it's AgCl.

As said, metastannic acid would have formed before adding it to the nitrate pot.
But I think you have AgCl.
If so, a NaOh + sugar or a H2SO4 + Fe conversion will not harm the silver cement. You can treat them together.

 

[bhilton]

OK. Here is where I am now:

Last night I removed the copper flat stock, I went and did other things and came back an hour or two later and the silver cement had settled on top of the layer of white stuff at the bottom, plus some more white stuff was floating around in the solution still. I poured off most of the nitrate solution that had turned from blueish to greenish at this point, into a separate holding pot. I through some boiling water into the silver cement + white stuff, swirled it around, and went to bed.

This morning I checked it and the white stuff had formed a very distinct layer on top of the silver cement and I poured off this dilute solution into the same separate holding pot, the white stuff peeled away from the grey silver cement and it looks like 99% of it went out, I sacrificed a little silver cement, letting a wee bit of it pour over to get the white stuff all out.

I have since done 2 more boiling water rinses on the remaining silver cement.

Meanwhile the separate holding pot that has the white stuff, I'll try taking a sample and put it in the sun light as soon as I get a minute and share my results.

 

[bhilton]

Results:

 

[Yggdrasil]

Results:

Silver Chloride.
Which means you had Chloride in one of your batches.

 

[bhilton]

Ok, so I proactively started reading some of the forum topics on the H2SO4 and Fe conversion method, because I don't have any Lye.

My H2SO4 is 93% technical grade. My understanding is that putting some in a beaker and adding water to dilute it will cause a very hot reaction. Must I dilute it or can I use the 93% as is?

Could I filter this nitrate solution containing a little silver cement and mostly silver chloride and rinse thoroughly, then spray off the contents on the filter paper into a beaker to start?

 

[FrugalRefiner]

My H2SO4 is 93% technical grade. My understanding is that putting some in a beaker and adding water to dilute it will cause a very hot reaction. Must I dilute it or can I use the 93% as is?

Never add water to concentrated sulfuric acid. Always add the concentrated sulfuric acid to water. Either way, it is an exothermic reaction. But when you add water to the acid, there's not much volume of the acid into which the heat can dissipate. Adding the acid to the water, you'll have a much greater volume of water to absorb the heat. Even then, it's best practice to add the acid slowly with a lot of stirring to help spread the heat.

Yes, you should dilute to acid to about 10%.

Dave

 

[anarxi]

Ok, so I proactively started reading some of the forum topics on the H2SO4 and Fe conversion method, because I don't have any Lye.

My H2SO4 is 93% technical grade. My understanding is that putting some in a beaker and adding water to dilute it will cause a very hot reaction. Must I dilute it or can I use the 93% as is?

Could I filter this nitrate solution containing a little silver cement and mostly silver chloride and rinse thoroughly, then spray off the contents on the filter paper into a beaker to start?

You have already been answered, but I will say it again.
acid always pours into water.
especially with sulfuric acid.
take a tall glass
when pouring acid it will look like a shell exploding in water, with a fountain upwards..

and I wouldn't filter anything...
restore the chloride in a mixture with silver cement, rinse thoroughly with clean water and dissolve again in nitric acid.
for restoring the chloride I prefer aluminum and hydrochloric acid