why is my AR still positive to stannous-test after precipitafing gold?

[frank-20011]

hello,

yes, that's my question.

i dissolved sulfuric-acid-cell sludge in AR, get a yellow sollution which was strong positive to the stannous test.

after denoxing (evapotating the whole AR solution, dissolve the residue in aqua dest and double denox with sulfamic) make it a little bit acidic with a splash HCI and precipitating the gold with Potassiumpyrosulfite the solution is still possitive to the test, weak but clearly.

i waited 24hr but nothing changed, the gold precipitated down but the slution was still positive.

the solution smells strongly like SO2 but i try to add a little bit more HCI and P.-disulfite (-pyrosulfite, K2S2O5) and waited one day mor but anywas: the solution is still positive, color changed from a strong yellow to a weak green, gold sit on the bottom.

is there any other metal in the solllution which does not precipitate and cross-react with the stannous test?

best greetings, frank!

 

[kernels]

I believe remaining SO2 will give a reaction with Stannous Chloride, known as a 'false positive'

Depending on what your source material was, there could also be other precious metals still in solution ?

I tend to precipitate the Gold, settle, decant the solution, then finish it off with a Copper bar for a few days to make sure all precious metals from the solution are recovered.

 

[anachronism]

Frank

Can you post a picture of your stannous test please?

 

[frank-20011]

hello,

and thank you both!

i tried to make some pictures and this took some time.

During this time, I watched as the drop of stannous decolorized after it had fallen into the reaction solution.

The drop fell into the solution and was initially black-purple.

but soon after that the color changed from black-purple to black-blue, than to blue and after 30sec. more the few drops of test solution are green....

with a fresh drop of stannous in the used, now greenish test sollution the game start again: from black-purple to green within a minute.

I think that under these circumstances, any photos are absolutely superfluous.

i do not know what a kind of reacion is happening there but it is not gold what is proved!

thanks lot, sometimes it can be so easy!


best regards!

 

[FrugalRefiner]

It sounds like you may have excess oxidizer in your solution.

Dave