Metastannic acid discovery?

[Yggdrasil]

I got some of that gray goo, i tried to dissolve some barely magnetic connectors, fairly light in weight and with gold plating, the solution barely reacted with oxy water grade peroxide, so, just in case i decided to, eventho still transparent to keep dissolving that batch of magnets in a different container, I done very well because i got A LOT of that gray goo there after, it still sitting there in a separate container this might come in handy.

Anyhow, my point is that it could be something else than tin.
It will dissolve in fresh acid/hp but will re-cement on something after a while.

Not much dissolves in low grade Peroxide alone so you must have had some Acid too, true?
If something cements out either you have inadvertently dissolved some Gold that cements on the base metals.
Or the Tin itself may be cementing on some of the base metals or the Tin hydrolyses somehow.

 

[andu]

There should be only iron, REEs nickel and copper, and ofcourse whatever those connectors had, but no tin.
Yes HCL, with variation between 17 and 24% strenght. I never seen gold as grey material. The connector is really low iron stainless with a bath of gold, i guess the stainless done it.
I still have the funnel with the gold foils from the 2 boards i done like almost a year ago.
https://goldrefiningforum.com/threads/average-pm-and-metal-content-in-rrus.33130/post-358076 those connectors more specifically, I was told yard pays 90e a kilo for them.

 

[KKris]

What state are boards in before shredding?
Are they "clean" or do they still have components on them?

They do have some components but the heat sinks, fan, main processor and large steel pins would be removed. But solders are still there.
Sometimes we directly get shredded boards so don’t even know what all has been clearly removed

 

[KKris]

If you have the option to dilute the acid you use to leach out copper, you may avoid creating meta stannic acid. I don't know the exact number for "sulphuric + nitric", but for nitric just keep it under 4M concentration (about 1+3 of 65~70% HNO3 + water).

source: https://eprints.ncl.ac.uk/65770

We use 25% sulfuric (98%) 25% nitric (67%) and 50% water.

 

[KKris]

Don't go too dilute. Under 2.73M of nitric only (about 1+5) it will cease leaching out copper.
With your billet contains 75% copper, all remaining tin and iron that happen to be located under copper can not react as well.

Should you by any cause unable to dilute the acid, and prefer to use coagulant to extract the meta stannic acid, make sure to desulphur before you continue with another wet process on the extract. It tend to form Sn-S cover that protect the meta stannic.

Is there a coagulant we can use??

 

[Joseph Pramudito]

Is there a coagulant we can use??

If this one is near you, Brenntag (brenntag.com) you can use their product Brenntamer A3322. You may contact similar company near you.

You can then reduce the meta stannic to tin II with Mg, Zn or Al with wet process at 90°C, in acid after desulfuring.
You may as well use Pyro route dehydrate it to tin oxide or reducing to tin metal with carbon.

 

[Wonka]

I’ve found that 50/50 sulfuric acid will dissolve stannous acid easily, leaving behind gold and copper aswell. Also can be used to rapidly remove solder.

 

[Yggdrasil]

I’ve found that 50/50 sulfuric acid will dissolve stannous acid easily, leaving behind gold and copper aswell. Also can be used to rapidly remove solder.

Keep your names straight please.
Stannous are already dissolved in water and HCl, Metastannic acid on the other hand do not dissolve.
And I did not find any references regarding Metastannic acid dissolving in Sulfuric.
So please share a link.

 

[Yggdrasil]

On a whim I did a search in Hokes book again.
According to C.M. Hoke, Metastannic acid dissolves in both concentrated and dilute Sulfuric acid.

If you still have some tin paste, left over from an earlier experiment, try
the effect of sulphuric acid upon it. . . It dissolves it, whether dilute
or concentrated.

From page 71 in Hokes book.

Can anyone confirm this?

 

[Wonka]

I figured it out by experimenting. Took a small amount mixed it in 50/50 sulfuric acid and it dissolved and left a small amount of gold and copper at the bottom of the beaker after a couple hours. If the concentration of metastatic acid gets to high the solution will turn orange.

Looking at this site and the different combinations gave me the idea.