# Dissolving foils: AR vs Chlorox



## Bertho (Apr 25, 2014)

I have always been interested in refining and about 30 years ago I refined gold and silver using fire assaying method. I also refined mercury from mercury batteries that were common then. The it took a lot of effort to find good information. Today it is information overload. One very interesting book about old technology is called De Re Metallica by Agricola from 1556. Happily there is a translated to English version by Hoover with a lot of background notes explaining what the old terms meant. It covered all known technology at that time. From mining to refining to glass making to chemicals.

It is time to play again and I have collected a variety of scrap. The first part has been stripping plated material and I am now ready for the next step to dissolve the foils. There is lots of info and options but I have not been able to find pros and cons on the different options. No large amounts are involved, I only have a few grams of foils but I am curious and like to understand as much as practical.

Below are references and excerpts of the three processes:

#1: Hot HCl and dribble in nitric acid
http://www.goldnscrap.com/index.php...ers-how-to-recover-gold-from-electronic-scrap
From this point on, the process if fairly simple if you have done some recovery and/or refining before.
The foils with the ashes or the unburned filters are placed in an open mouth beaker and covered with a dilute HCl solution (50/50 32%HCl/water) and heated to medium heat (120-160F).
When the solution is quite hot, a small amount of nitric acid is added to the solution. No more than 3ml per each lb of fingers we started with.

The solution will gain distinctive yellow color as the gold and traces of copper goes into the solution. The dissolution process should be done under a fume-hood and the beaker must be covered with a watch glass. Also beware, the Gold solution must not be boiled.
The dissolution process will be over in less than 30 minutes, there’s really no need for more than that.

When done, the solution is allowed to cool back down to room temperature and then filtered into a clean beaker for precipitation.

#2: Hot HCl and Chlorx. What is the chemical reaction?
http://www.instructables.com/id/TRASH-TO-TREASURE/?ALLSTEPS
For this step I am going to use a 100 ml beaker a portion of recovered foils, about 3 grams.
I will be using Muriatic acid, and Clorox.
I will be adding only enough Muriatic acid to cover my 3 grams of foils, Using a Pipette I will slowly add Clorox until all of my foils have dissolved. you can use a glass rod to help felicitate the process.
After your foils have dissolved the resulting solution will be a deep golden yellow maybe a little orange in color.

Finally there are many references of just dissolving the foils in AR not dribbling in nitric acid.

What are the pros & cons fort eh three processes? The info is probably here but I have not been able to find it.
Thanks in advance,
Bertho


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## joubjonn (Apr 25, 2014)

The info is here. Search bar on the top right. Find plenty of chemical reactions for exactly this, many many threads on this topic for sure.. AR is faster and it will dissolve thicker pieces, and can be used on a variety of gold bearing items like karat gold, gold filled, cpu's and other kovar/iron/titanium containing material directly. HCl/Cl is slow will only work on fine gold powder or foils, it doesn't need nitric acid so you don't have to denox the solution, wait a few hours for Cl to gas off or add heat to speed that up then precipitate. I have done both. I prefer AR. HCl/Cl is difficult when you have a lot of solution, it needs to be stirred often, not recommended if you don't have a fume hood as it gasses chlorine. But works well for folks who don't want to buy or can't buy nitric and use the AP process to get rid of base metal.


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## joubjonn (Apr 25, 2014)

Not titanium I meant to say tungsten. Ti won't dissolve in Ar


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## Geo (Apr 26, 2014)

It is a waste of good chemicals to add Chlorine bleach to hot hcl. Other than making a huge cloud of noxious gas, you wont accomplish anything. Study on the reason gasses stay in cool liquids better than it does in hot liquids. Then study on why you want the gas to stay in the liquid in the first place. After that, you may be able to handle the rest.


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