Poor Mans gold stripping solution

[Ayham Hafez]

I watched a video on YouTube done by Dusan of using sulfuric acid with hcl then add a bit nitric to dissolve only gold layer without effecting base metals, I wonder if this method is well tested by anyone here, I get tired from leaching circuit boards in hcl then AP then collect gold foils and if pins not made from copper I have to use another method than AP to strip gold foils.


And can I use same HCl-Sulfuric-Nitric solution before precipitating gold with new circuit boards to decrease the chemical cost?

Last thing, will sulfuric acid prevent tin from dissolving in the solution or I have to remove tin before?

 

[Martijn]

I watched a video on YouTube done by Dusan of using sulfuric acid with hcl then add a bit nitric to dissolve only gold layer without effecting base metals, I wonder if this method is well tested by anyone here, I get tired from leaching circuit boards in hcl then AP then collect gold foils and if pins not made from copper I have to use another method than AP to strip gold foils.


And can I use same HCl-Sulfuric-Nitric solution before precipitating gold with new circuit boards to decrease the chemical cost?

Last thing, will sulfuric acid prevent tin from dissolving in the solution or I have to remove tin before?

In theory it can work, copper and brass do not dissolve in very well H2SO4. The AR addition however, will.

If you have pm's in solution and basemetals, the gold will cement out on the basemetals.
It is never a good idea to dissolve gold in the presence of PCB'S qnd lots of base metals.
1: gold chloride will cement out on copper traces inside the often layered PCB'S.
2: gold chloride can get sucked in between the epoxy and glassfiber layers.

What does Dusan say about it? Or does he only make ( not very scientifically correct) video's to get subscribers?

New boards? Clean or full of components, heat sinks and solder?

 

[Martijn]

The sulfuric will not stop tin from forming tin paste i think.

 

[Ayham Hafez]

In theory it can work, copper and brass do not dissolve in very well H2SO4. The AR addition however, will.

If you have pm's in solution and basemetals, the gold will cement out on the basemetals.
It is never a good idea to dissolve gold in the presence of PCB'S qnd lots of base metals.
1: gold chloride will cement out on copper traces inside the often layered PCB'S.
2: gold chloride can get sucked in between the epoxy and glassfiber layers.

What does Dusan say about it? Or does he only make ( not very scientifically correct) video's to get subscribers?

New boards? Clean or full of components, heat sinks and solder?

New boards with full components

 

[Ayham Hafez]

The sulfuric will not stop tin from forming tin paste i think.

So if I leach first in HCl to get rid off tin, then use AR-Sulfuric that will dissolve only gold without loosing gold by cementing on base metals? Dusan mentioned that sulfuric acid make a layer on base metals so it will be isolated from dissolving

 

[Martijn]

So if I leach first in HCl to get rid off tin, then use AR-Sulfuric that will dissolve only gold without loosing gold by cementing on base metals?

It is never a good idea to dissolve gold in the presence of PCB'S qnd lots of base metals.
1: gold chloride will cement out on copper traces inside the often layered PCB'S.
2: gold chloride can get sucked in between the epoxy and glassfiber layers.

Dusan mentioned that sulfuric acid make a layer on base metals so it will be isolated from dissolving

Concentrated acids can passivate certain basemetals, some just do not react because they need water to go in solution.

 

[nickvc]

This reminds me of the reverse AR process but be aware if you have other metals that react to the AR they will dissolve first and the values last whether you have sulfuric there or not in my opinion unless the sulphuric passivities them which I’m not sure about.
Another point is that the sulphuric will be viscous and will chew up any filter papers so you may need to find something to handle the filtering.

 

[jphayesjr]

Try cotton or wads of fine glass wool (wear gloves). I think there's an Italian filter company who sell flat glass wool filtering discs. I ran across them once, it's a pre-filter for some Espresso machines.

 

[Ayham Hafez]

Try cotton or wads of fine glass wool (wear gloves). I think there's an Italian filter company who sell flat glass wool filtering discs. I ran across them once, it's a pre-filter for some Espresso machines.

Nice trick, I think it will work

 

[jphayesjr]

Hope it helps. Try a small test amount, if necessary, you should be able to dilute the solution to reduce the acid concentration if necessary.

 

[Ayham Hafez]

I would like to update thread with an experiment done with 50 Kg coax copper connectors plated with gold.

I divided the 50 kg connectors in 8 buckets then added 3 liter of HCL in one bucket and added 1 liter sulphuric acid, after mixing the HCl and Sulphuric acid I added the solution to the first plastic bucket contains the connectors, waited about 5 minutes to make sure all connectors is passivated, after that I added few nitric acid drops, waited about half an hour, then reaction start and gold foils start to be dissolved, each time reaction stopped I added few nitric drops till all gold is dissolved, then pour the solution to the next bucket and repeat the nitric dropping step till I finish all buckets, after that I diluted the solution with water and filter it then drop gold with ferrous sulfate.

Some copper sulphate appeared in the solution but it didn't make an issue.


I weighted the coax connectors after finished, noticed that only about 300 grams lost during the reaction, and almost I got all expected gold, and I used less than 100 ml of nitric acid.


I think using this method with such material is much better than using pyrometallurgy process, less time and less cost.

 

[tsfarley]

Ayham.
can I ask if the 300 gr was the resulting gold weight you pulled from all 50kg of connectors . I didn't quite understand the last sentence.
thank you
Tim

 

[Ayham Hafez]

Ayham.
can I ask if the 300 gr was the resulting gold weight you pulled from all 50kg of connectors . I didn't quite understand the last sentence.
thank you
Tim

300 grams lost from the whole weight of the connectors, mean only 300 grams of base metals dissolved, by the way I repeated this process many times and got good results, in average I got 0.25 gram of gold per 1 kg of coax connector plated with gold.