# can someone explain me how stannous chloride work



## ericrm (Feb 4, 2012)

i know it is a reducing agent
what happen with aucl when you add sncl?
why it doesnt also reduce copper or any other metal?
could it be used to get gold back from solution?


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## butcher (Feb 4, 2012)

ericrm,

I do not know if I can answer this, but here is how I see it.

The tin chloride (stannous chloride) does reduce the gold (gold from solution gains an electron), and goes back to being a metallic gold, the gold does not precipitate (at least not for a very long time), as this tin kind of makes a gel in solution holding the very small fine flakes of gold in suspension floating around reflecting the violet color we see (in a way the gold is in an almost colloidal form.

I am sure stannous chloride does also reduce copper in solution, but copper does not give us the color change gold does.

It (tin) would only give us troubles if we tried using stannous chloride to get gold from our solutions, the reasons it works so well for testing is also the reasons it would not make a good reducing agent to try and get our gold from solutions. (We try to avoid colloids keeping our gold in solution, and not being able to test for it presence in solution, also tin would also replace other metals from solution’s and on and on).


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## ericrm (Feb 4, 2012)

alright
thank you butcher, that realy answer my question,i was hoping to recycle ap in free precipitant..
i have read that there is a possibility that smb dont drop all the gold in solution,do you know if it is true?


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## butcher (Feb 4, 2012)

ericrm,
What we get is determined by what we do and how we do it.

Acid peroxide (copper II Chloride) solution can be regenerated and reused, especially if solder is kept out of mix, also some base metals other than copper can degrade it also.

The stannous chloride is a very (very), sensitive test for gold, it can detect gold in solution almost to nothing.

All of the gold can be precipitated from solutions.

Now does this mean we will do this every time? (No).
Does this mean that we will not drag down some other metals? (No).
Does this mean we may need to re-refine a second time? (Yes).
Does this mean that my solution will precipitate all of my gold?
how are you working, dirty solutions loaded with base metals and tin, oils and dirt, not eliminating oxidizers properly, or using too much acids, sloppy work gives sloppy results.

If the solution is clean from base metals, clean from oils and carbonous trash, nothing in solution like tin, dirt, and oils that can form gold colloids in solution (that by the way we cannot test for with stannous chloride), nothing re-oxidizing the precipitated gold back into solution, basically nothing but clean gold in solution, we can basically precipitate every last drop of it, and a second refining will even make it easier to precipitate every drop of gold much cleaner and easier.

But if we have much base metals, dirty solution, colloids, oxidizers, we could basically throw out most all of our gold into our waste bucket without even knowing that is what is happening.

Sodium metabisulfite can also precipitate some copper in solution, but if we eliminated most of the copper, and refined our gold twice from clean solutions our gold will be of very high quality.

What we get is determined by what we do and how we do it.

I have answered best I can.


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## Geo (Feb 5, 2012)

stannous does give a test result for copper, its just that gold is so much more dramatic it overides the color of the copper. copper in a stannous chloride test will be brown and is refered to as a "false positive".


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## samuel-a (Feb 5, 2012)

ericrm

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=84&t=10491#p125338


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## ericrm (Feb 5, 2012)

geo normaly i think a false positive is not from copper but from sulfite(?) precipitating tin out of tin chloride,plz correct me if im wrong
anyway thank for all the response
im waiting to start making my nitric acid again, so i think i will avoid a lot of probleme that way...


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## Geo (Feb 5, 2012)

actually, a solution with high copper content will give a false positive. there are several factors involved in a false positive stannous test. to think its just one will get you in trouble.


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## Geo (Feb 5, 2012)

here you go ericrm,

http://www.goldnscrap.com/index.php?option=com_content&view=article&id=63:stannous-chloride-test-for-gold-platinum-and-palladium-presence&catid=25:scrap-gold-9k-24k&Itemid=20


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## ericrm (Feb 5, 2012)

once again i have to recognise my mistake  ah well ,im the farrest from perfect of them all :roll: 
thank you geo


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## lazersteve (Feb 5, 2012)

The false positive is a result of in situ formation of sodium/hydrogen sulfide which is an excellent reducing agent for just about any metal in solution as most sulfides are insoluble, hence the brown color of the resulting sulfides and the rotten egg smell of the highly toxic H2S gas.

The correct chemistry of the false positive reaction is: 

Sulfurous acid + base metal higher in activity than hydrogen + acidic pH = Sulfide formation = false positive (brown preciptate) + rotten egg smell.

Here's the thread where the process was originally detailed on the forum:

Sulfurous Acid and False Positives

and 

Early False Positives Thread

and

Sulfurous Acid Document Information

The reaction with copper and sulfur dioxide give a off-white to gray colored copper I chloride which can also be considered a false positive, it's the tin that actually reacts to form the sulfurous in this case as it is higher than hydrogen in the series, copper is not. Any color change due to copper without sulfur dioxide present is due to valence change of the metal and not a preciptaion due to sulfide formation, a false positive in the truer sense.

Steve


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## ericrm (Feb 5, 2012)

thank you lazersteve
i have to place my chemical on the shelf(ranger mes produit chimique dans mes armoire) and i dont know what to DONT put beside what...
is it already on a post ,if yes can somebody tell me.
if not can we make one now?

sulfuric acid
XX chloride from spent ap(all kind from lead to iron)
HCl
sodium hypochlorite
smb
urea
trisodium phosphate
H2O
lye
borax
sodium bicarbonate
sodium carbonate
sodium nitrate
potassium nitrate
table salt
ferrous sulfate 
nitric acid
of course the usual gaz,oil,diesel,paint,wd40,gigaloo,etc
thank you


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## ericrm (Feb 5, 2012)

just found my answer.. if someone else need it
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=56&t=9342&p=98633&hilit=chemical+compatibility#p98633


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