Washing foils

[pcecycle]

I have some foils recovered from a batch of CPUs in AP. I washed and rinsed the foils several times with HCL and water. They were then incinerated. The foils looked to be pale yellow afterward and I thought there might be some silver mixed in. I made up a batch of Nitric acid using Steve's recipe and added some to the foils. Immediately, I got a white flocculation. Could the foils have had some copper and silver contamination that the nitric would dissolve and then the silver be pushed out by the copper? Suggestions welcome.

Mike

 

[samuel-a]

this is only an educated guess, but i belive that you have there some Pb

 

[pcecycle]

Thanks! Good point, did not think of lead! I guess I will soak them in nitric a couple of times then wash and incinerate again before going to HCL/CL. I am trying to get them as pure as possible before dissolving and precipitating.

 

[Barren Realms 007]

Boil it in hot water to get the lead out.

 

[samuel-a]

yup.

if you had lead (and you probably did from the solder), the nitric will turn in to lead(II) nitrate which is soluble in water but not really soluble in stong nitric (70%).
therefore you have to make sure, that if you do have silver in the mixed powders, you first dissolve it with nitric (along side the other base metals), stir well with heat. and only then treat the powder with water (boiling) to remove as much lead and lead(II) nitrate as possible from the left over gold powder.

after boling with water, make sure you filter while the solution is hot, otherwise the Lead(II) nitrate will re-precipitate as white crystals on your gold.
most of the lead will be out of the mixture by now, but some will be left, dont worrey, when you will treat the gold powder with HCL+Cl or AR, it will stay out of solution if form of crystals and you could filter it of.

be very cerful with the fumes, and wear gloves, lead nitrate is considerd as " probably carcinogenic to humans "

which type of CPU's did you process and what amount of them?

good luck