How can I use iodine to recover gold from circuit boards?

[glondor]

I am working on a pilot project to recover gold from circuit boards. I have tried several methods and am interested in giving iodine a try. I know it will dissolve the gold but I cannot find an answer on how to get the iodine solution to drop the gold. Any ideas? Thanks.

 

[Nemus]

I am a bit sceptical that iodine actually dissolves gold but if you are correct I'd suggest that you use copper to precipitate the gold.

 

[Borek]

Bisulfite? I don't remember details and I don't plan to Google, but from what I have read similar project was described at tomshardware.com.

 

[glondor]

Thanks. Yes I believe copper will drop the gold, but it would render the iodine solution infective for further use. I would like to reuse the iodine solution. I am trying to cut down on chem use during the process.

 

[Borek]

This can be tricky. You want to reduce gold not reducing iodine, but most reducing agents will probably reduce both.

 

[Nemus]

Again, I am sceptical if the iodine dissolves gold properly. Are you sure? Where do you have it from? It goes against what I have learned. Either aqua regia or base + cyanide dissolves gold. However, is it possible that you are dissolving everything else and get some kind of gold suspension? Then you only need to centrifuge or filter off the gold to recover the iodine.

 

[glondor]

The information I have is partly based on this article>>>>http://webpages.charter.net/kwilliams00/bcftp/docs/halides.htm

 

[Borek]

https://www.physicsforums.com/showthread.php?t=240131

 

[glondor]

Thanks for the link Borek. Here is a quote>>>>

Originally Posted by Mapes
Good point. G01, what is the underlying sample made of?

Potassium iodide is another good selective etchant for gold.
Yes. In the mean time I have done some research and decided that a 1:2:10 mix of I2, KI, and H2O are best for my purposes. I here it's very selective and won't attack the material underneath.

Thanks for the advice!

RE: The 1/2/10 mix. I understand I2 as Iodine. 1 part. H20 of course is water.10 parts. Is K I some type of potassium? Thanks Mike.

 

[alxm]

Why dissolve the gold? Might just be easier to separate out everything not-gold.

 

[Borek]

Is K I some type of potassium?

Potassium iodide.

 

[glondor]

Why dissolve the gold? Might just be easier to separate out everything not-gold.

Many of the parts we work with are plated. Copper, nickel, Kovar base metals that must be removed or separated. Iodine is reported to be selective enough to just remove the gold. I am still looking for a way to "drop" the gold from the Iodine and still be able to reconstitute the Iodine solution for reuse.

 

[Nemus]

Iodine is volatile. Is there any economy in heating the solutions to dryness? The iodine will collect on any cold surface.

 

[Borek]

Iodine is volatile. Is there any economy in heating the solutions to dryness? The iodine will collect on any cold surface.

You are going to loose way too much.

 

[Nemus]

Why? Iodine is rather insoluble in pure water. I think I did something like this when I was a kid and made iodine from seaweeds. But it will cost a lot of energy, that's for sure.

 

[glondor]

I have used Aqua regia to disolve gold, but it is not as selective as I would like for some of the parts I do. I know that iodine will work, I just have not found the method to drop the gold and regenerate the solution for reuse. I know it was used commercially for a while before cyanide displaced it due to cost as cyanide was much cheaper. I will not use cyanide. I can still use Aqua Regia as well as HCL/bleach to recover the gold, however there are many steps that can be eliminated if I do not have to remove the base metals first. I can remove the base metals with HCL/peroxide solution but it takes time. I can also use dilute nitric acid, however nitric is very expensive for this task.

If anyone can shed more light on this I would be very grateful. I do have some friends working on this aspect of recovery as well, and they have developed it to a point but solid info would help to break some road blocks. It is all well and good to be able to dissolve the gold, but if we cannot drop it out of solution, it is a loosing proposition.

We will keep at it! Thanks for your help so far. I will refer people from another forum to this post.

Feel free to come visit at goldrefiningforum.com. It is a fascinating place and we have some great people there.

 

[Borek]

Why? Iodine is rather insoluble in pure water. I think I did something like this when I was a kid and made iodine from seaweeds. But it will cost a lot of energy, that's for sure.

Iodine is very volatile, so it will try to run as a gas. IMHO it is better to look for a way of recycling solution, than to recycle iodine getting it out from the solution first.

 

[glondor]

Can anyone add anything further to this?

 

[lightarrow]

Why? Iodine is rather insoluble in pure water.

But it's soluble in I^- water solution, for example in KI w. solution. It forms I₃^-.

 

[lightarrow]

Can anyone add anything further to this?

What about using Vitamin C?

http://www.freshpatents.com/Recover...tching-solution-dt20070920ptan20070217976.php

 

[glondor]

Vitamin c is relatively expensive for this process. I am looking for a way to cut the cost factor and reuse as much as possible.

That is a very good link to the patent. Thank you Lightarrow. Not being a chemist it will take me a while to decipher tho...

 

[lightarrow]

Vitamin c is relatively expensive for this process. I am looking for a way to cut the cost factor and reuse as much as possible.

The documents says to use "a weak acid, e.g. ascorbic acid" so you can use another weak acid, maybe citric acid, maybe oxalic, there are many (I would choose a non oxidant one, however).

 

[glondor]

Lightarrow. Thank you for your input. You seem to have a good knowlage of what we are trying to accomplish, would you consider looking over this thread here and see if you can shed some light? Thanks Mike

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=5690&start=80

 

[Borek]

This patent is so unclear it doesn't make any sense to me. Ascorbic acid is often used as a reducing agent, no idea whether is will be able to reduce gold (quite possible). However, I am more than sure it will reduce the iodine

titrations.info/iodometric-titration-Vitamin-C

which is a thing you want to avoid.