Gold stuck on copper while cementing

[Ayham Hafez]

I have an issue related to cement gold on copper bar, I used water splash but most of plated gold still on the bar, tried to use piece of cotton but it also failed, I just cemented for couple hours, have I splash water each while to avoid gold stuck on copper?

Is it a good idea to put the copper bar in dilute nitric acid so gold foil will dropped after nitric start dissolving copper?

 

[FrugalRefiner]

Agitation is important to keep the cementing material from forming an adherent coating. See When In Doubt, Cement It Out.

Putting it in nitric could help.

Dave

 

[Ayham Hafez]

Agitation is important to keep the cementing material from forming an adherent coating. See When In Doubt, Cement It Out.

Putting it in nitric could help.

Dave

Really useful article, many thanks for share

I think my mistake is I didn't dilute the solution before start cementing, I got most of the cemented gold by water spray, then I use sulfuric acid with aquaregia to strip rest cemented gold, I only dissolved a little copper in this process with the cemented gold.

 

[orvi]

Really useful article, many thanks for share

I think my mistake is I didn't dilute the solution before start cementing, I got most of the cemented gold by water spray, then I use sulfuric acid with aquaregia to strip rest cemented gold, I only dissolved a little copper in this process with the cemented gold.

I never had this issue. With gold cementation on copper, I usually cemented pregnant AR solutions from e-scrap dissolutions (1-2g/L Au), and gold very nicely cemented, with visible "gold bleeding" from the copper surface. I was always heating the solution, and maybe this helped the outer layer of copper to be etched (solutions always contained loads of dissolved Cu as CuCl2) and all gold fell down. Spray bottle conveniently washed all of it from the surface.

I experienced some clinging issues with re-precipitation of gold on the processed material when using I2/KI stripping method. But in this case, ultrasonic cleaner conveniently drossed off vast majority of it.

Nitric dip will do. Or some spent properly de-NOx-ed AR solution with good ammount of CuCl2 in it - it will etch outer layer of copper, forming CuCl in the process.

 

[Ayham Hafez]

I never had this issue. With gold cementation on copper, I usually cemented pregnant AR solutions from e-scrap dissolutions (1-2g/L Au), and gold very nicely cemented, with visible "gold bleeding" from the copper surface. I was always heating the solution, and maybe this helped the outer layer of copper to be etched (solutions always contained loads of dissolved Cu as CuCl2) and all gold fell down. Spray bottle conveniently washed all of it from the surface.

I experienced some clinging issues with re-precipitation of gold on the processed material when using I2/KI stripping method. But in this case, ultrasonic cleaner conveniently drossed off vast majority of it.

Nitric dip will do. Or some spent properly de-NOx-ed AR solution with good ammount of CuCl2 in it - it will etch outer layer of copper, forming CuCl in the process.

Using CuCl2 is a nice trick. BTW can I reuse saturated CuCl2 again by just adding fresh HCl? I have 30 galone of saturated CuCl2 which immediately came white when add water to it, I wonder if I can still use it again.

 

[Yggdrasil]

Using CuCl2 is a nice trick. BTW can I reuse saturated CuCl2 again by just adding fresh HCl? I have 30 galone of saturated CuCl2 which immediately came white when add water to it, I wonder if I can still use it again.

Bubble air through it and add a bit of HCl.

 

[BAGross85]

Bubble air through it and add a bit of HCl.

This was the difference between finely divided particles floating in solution/stuck to my copper, and all of it dropping to the bottom for easy decantation.

Thank you!