Brown sediment in A/P

After processing about 2kg of mixed (copper/brass) pins (from motherboards (PC/laptops), HDDs, graphic cards and PCI cards) using A/P - CuCl2 etching method (i had CUCl2 from the start - i didn't used hydrogen peroxide at all - neither air pump - it took couple of months to finish reaction) - i filtered solution several times using charmin plug with wet towels like on this picture:



I added fresh HCl when CuCl salt starts to form, and i was stirring solution occasionally.
I was sure that all gold particles was captured in those filters - just to be sure i filtered everything three times like described.

So i left solution (for future use ) and after about one month i noticed dark sediment on the bottom.
I decanted CuCl2 solution and this is a picture from the bottom of bucket.



I added little fresh HCl in the bucket and i gave it a good stir to detach those dark particles from bottom and i removed that material to small glass jar so i can inspect little closer that material.



I was surprised i see small gold particles there - i wonder how they went through really tight filters three times... I processed gold foils from pins long time ago and i thought that's it - little less than 2g / 2kg of mixed pins. But now - i am starting to think - maybe there is more - gold that could not be filtered - only collected by sedimentation / decanting.

Or, what possibly this material could be?

(I will see tommorow how it reacts with AR - i am hoping - the yellow way).

My guess is mostly tin that was dissolved at first but now have oxidized and falls out of solution, other metals that change oxidation state and so on. It can also be colloids that have clumped together enough to sediment over time.

Aqua regia combined with stannous testing will tell you if it contains anything of value. Please, let us know how it turns out.

Göran

g_axelsson said:

My guess is mostly tin that was dissolved at first but now have oxidized and falls out of solution, other metals that change oxidation state and so on. It can also be colloids that have clumped together enough to sediment over time.

Aqua regia combined with stannous testing will tell you if it contains anything of value. Please, let us know how it turns out.

Göran

Click to expand...

Thank you Göran!

I processed this material (sediment) with AR. Most of it dissolved.



After AR solution was neutralized and cooled down - this is picture of remaining sediment.



I filtered it without troubles and solution was clear. I added SMB and after about 15 minutes solution gets dark. And after that gold started to drop really slowly - this is a picture after 12 hours after adding SMB and solution still have dark color and gold is still dropping - but very, very slowly.



I will wait until all gold is dropped and solution becomes clear. I hope that it will eventually happen in case that is colloidal gold.

Alex

It just looks like there is much gold - but it is very thin layer of gold powder - if i point flashlight to opposite side of the bottom and look at gold powder - it is transparent. Result is 0.09g of gold from all of this.

Alex