# NaOH leach of ashed powder, Advice please



## NoIdea (Aug 1, 2011)

Morning All – Just a quick Q. I have an ashed powder which contains all that is found within a computer circuit board, Au, Ag, Si, Pb, Sn, etc. I have done some preliminary test (qualitative/visual only) which included treating with sodium hydroxide, HCl, and Poor Mans AR, I don’t have sulphuric acid. 

Results: Poor Mans AR had very little effect in terms metal dissolution, light blue in colour. HCl also produced a light blue colouration. NaOH produced a very very light clear brown solution.

Extra test included reacting the NaOH leached powder with Poor Mans AR which produced on dilution AgCl precipitate and the colour of the resulting solution was bark green/blue.

I preformed electrolysis on the NaOH leach solution and got a black deposit on the cathode. That’s where I stopped.

My Question is: Lead, silica and tin oxide dissolve in hot concentrated NaOH, therefore allowing acid access to the residue. Is their a reason why no one else treats the trouble some tin oxide and lead oxide with NaOH and electro-depositing the lead and tin from the alkali leaching solution? . 

Regards

Deano


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## Lino1406 (Dec 16, 2011)

I think of 2 reasons:
1.Safety - the boiling point of concentrated caustic is
very high and handling it entirely unsympathetic
2.Melted Na2O2 can dissolve gold, so maybe boiling
NaOH in presence of air can too (to lower extent -
but that may be significant)


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