Processing Fingers with CuCl2 etching solution

[g_axelsson]

Hi Alvi and welcome to the forum.

I can't find any major problems with your procedure, though I'm lacking a few steps that I usually include.
I can't comment on your result as I haven't made any yield measurements myself. Did you find any numbers on the forum? I know there are a couple of discussions about this.

- No testing, instead of believing you got all the gold when precipitating, test with stannous and then you know.
- No mentioning of a stock pot. I always put my barren solution after precipitating the gold into my stock pot. Smaller amounts of PGM will collect and any fine gold will have time to settle before I treat it as waste.
- Urea is usually not recommended, it has it's dangers and the excess nitric can be dealt with in a couple of other ways. (gold button, evaporation, minimizing usage, fighting it with a precipitant, sulfamic acid)
- Your washing procedure is lacking, read http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=325&p=2620#p2620
- Most people never filter off the gold powder, it is kept in the same vessel as it was precipitated in through the wash cycle and drying.
- SMB reacts with nitric or HCl by releasing SO₂. If the liquid is saturated by SO₂ gas it will just fizz and the SO₂ . DO NOT BREATH THE GAS!

Hey! This guy seems to have read up on the processes, can we keep him? Please! 8)

...ps, we want to see the resulting button in the gallery.

Göran

 

[shaftsinkerawc]

There's no mention of incineration between the Nitric use and the Hcl rinse!

 

[maynman1751]

Hi Alvi and welcome to the forum.

I can't find any major problems with your procedure, though I'm lacking a few steps that I usually include.
I can't comment on your result as I haven't made any yield measurements myself. Did you find any numbers on the forum? I know there are a couple of discussions about this.

- No testing, instead of believing you got all the gold when precipitating, test with stannous and then you know.
- No mentioning of a stock pot. I always put my barren solution after precipitating the gold into my stock pot. Smaller amounts of PGM will collect and any fine gold will have time to settle before I treat it as waste.
- Urea is usually not recommended, it has it's dangers and the excess nitric can be dealt with in a couple of other ways. (gold button, evaporation, minimizing usage, fighting it with a precipitant, sulfamic acid)
- Your washing procedure is lacking, read http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=325&p=2620#p2620
- Most people never filter off the gold powder, it is kept in the same vessel as it was precipitated in through the wash cycle and drying.
- SMB reacts with nitric or HCl by releasing SO₂. If the liquid is saturated by SO₂ gas it will just fizz and the SO₂ . DO NOT BREATH THE GAS!

Hey! This guy seems to have read up on the processes, can we keep him? Please! 8)

...ps, we want to see the resulting button in the gallery.

Göran

I have to agree with Goran except I would use the AP process to recover foils and save my nitric for dissolution, or better yet use HCl/Cl to dissolve foils. Just my thoughts on this subject.

 

[maynman1751]

There's no mention of incineration between the Nitric use and the Hcl rinse!

I didn't see that he used an HCl rinse after nitric, which maybe he should have, to make sure that most of the base metals had been removed prior to dissolution. But you are indeed correct in your statement if he was going to do an HCl wash. If he had used the AP method, that I suggested, he wouldn't need incineration before the HCl boil wash! He can simply decant the wash and go to dissolution with HCl/Cl or HCl/HN03.

 

[purgatory]

Hi
How are you all doing?

Well, thank you so much Goran and Maynman for welcoming me here at this very much informative and helpful forum, so nice of you.
Yes, you are right Goran, I did not test the solution after precipitation. I have noted down this mistake number 1.
I have saved the barren solution after precipitation of gold powder, I noticed that white colour precipitates are at the bottom but not dark colour powder present. What this white powder could be, probablly Urea Nitrate? I dont know.
I think 2nd mistake was using Urea to neutralize the nitric acid, as you have mentioned that Urea is not reccomended to neutralize the Nitric Acid, the white precipitated in the barren solution might be Urea Nitrate which I noticed today and this might be the reason behind not recommending Urea. I have figured my 2nd mistake.
3rd mistake was this that I surely did not wash the gold powder properly as per the topic you shared link about Harold's wash.
Yes you're righht Maynman, I did not rinse the foils with Hydochloric acid after stripping them off using Nitric acid. 4th mistake.
5th mistake was something like, While the last wash with de-ionized water, I poured all the gold powder onto the filter paper and melted this gold powder alongwith the filter paper.
I have noted down all of my mistakee and will have to be very much carefull in my upcoming attempt of recovering gold from the finger.
Thank you so much for your kind replies, I appreciate them all.
I need to learn more about this partcular aspect of recovering gold from e-scrap as the bulk quantity is available.

Quick question about acid peroxide etching solution, is there any chance that the gold could be dissolved in this solution? Actually I could not find Hydrogen Peroxided which is 3%, the only Hydrogen Peroxide Available is 6%, I'm afraid using this 6% H2O2. Please help in this regard.

Thank you so much
Alvi

 

[shaftsinkerawc]

point I thought the nitic acid has been neutralized. Having this thought in my mind I proceeded to the addition of SMB.
I added a table spoon of Sodium Metabisulfite 98% pure (made in Germany) by Merck.
There was a violant reaction upon it's addition, I thought may be its the nitric acid reacting with SMB, I added 2 more spoons of SMB.
After the 1st addition of SMB the colour of the solution changed to brown and the gold powder started to precipitate instantly, I left the solution over night and the next morning the colour of the solution was almost colourless and the gold was precipitated at the bottom of the beaker, I filtered te solution using filter paper and washed the gold powder well with de-ionized water then with hcl

Does the Urea used and the dropping with DMG negate the need to incinerate before the Hcl wash?

 

[FrugalRefiner]

Quick question about acid peroxide etching solution, is there any chance that the gold could be dissolved in this solution? Actually I could not find Hydrogen Peroxided which is 3%, the only Hydrogen Peroxide Available is 6%, I'm afraid using this 6% H2O2. Please help in this regard.

Alvi,

Yes, hydrochloric acid and peroxide can definitely dissolve gold. Hydrochloric acid by itself cannot dissolve gold, but when you add hydrogen peroxide, the H₂O₂ provides oxygen which can oxidize the gold. The oxidized gold can then combine with the chlorine from the HCl to become auric chloride.

You only need a small amount of H₂O₂ to get the reaction started. I started my first batch of AP with just a capful of peroxide. The peroxide oxidizes a bit of copper, which combines with the chlorine to create CuCl₂. Once there's a bit of CuCl₂ in solution, it will dissolve more copper, which becomes more CuCl₂. Once you've started a batch, all you have to do is add air to keep the reaction going.

There's actually a little more to the process, but that's the basic idea. Lasersteve has an excellent document on his website with a lot more details about this process.

Dave

 

[maynman1751]

Does the Urea used and the dropping with DMG negate the need to incinerate before the Hcl wash?

Perhaps you meant dropping with SMB! Because he recovered the foils with nitric, he would need to incinerate before an HCl wash. Otherwise it would create a mild AR and dissolve some of the foils. However, after dropping the gold with SMB, the powders should be washed with HCl. That is just part of the correct washing procedure. You should always follow Harold's washing directions that you can find with a search here on the forum. Also, as was directed, DON"T use urea!!!!! Use sulfamic acid or just use the correct amount of nitric to do the job or you can use a gold bead to use up the excess nitric.

 

[shaftsinkerawc]

Thanks, my eyes and mind were going in different directions.

 

[purgatory]

Thank you Dave for the info, I appreciate it.

 

[Geo]

Quick question about acid peroxide etching solution, is there any chance that the gold could be dissolved in this solution? Actually I could not find Hydrogen Peroxided which is 3%, the only Hydrogen Peroxide Available is 6%, I'm afraid using this 6% H2O2. Please help in this regard.

Yes, the hydrogen peroxide and hcl will dissolve gold. There is another way to start your copper(II) chloride etching solution. You will need copper oxide which is the bright green corrosion that forms on bare copper. Copper oxide is easily made by exposing finely divided copper metal (like copper filings) to the atmosphere. Use a coarse file to cut as much copper dust from a heavy piece of clean, bare copper, like tubing. A few grams should do but you can make as much as you need for later. Place the copper dust in a dish and add just enough hcl to wet it. Leave exposed to the air for a couple of days. When you are ready to start you AP process, instead of adding H2O2, add the copper oxide that you have ready. Add until the solution turns green.

 

[g_axelsson]

Yes you're righht Maynman, I did not rinse the foils with Hydrochloric acid after stripping them off using Nitric acid. 4th mistake.

I don't think there is a need to do a HCl wash of the foils in most cases, you would risk dissolving some gold unless you do a thorough incineration.
The only time I would consider incineration and washing the foils in HCl before dissolving them is if I had a lot of metastannic acid that would trap gold chloride and make it hard to filter.

The choice of dissolving gold foils in AR, HCl+Cl or HCl + peroxide is personal. I use all three methods depending on different factors but usually if you have HNO₃ available it is the easiest and fastest method as long as you don't use too much. HCl+Cl is more forgiving for overdosing and for the newbie it avoids the problem with too much nitric acid.

Drawbacks with HCl + Cl is that it adds NaCl to the solution and that can't be evaporated. Both HNO₃ and H₂O₂ excess can easily be evaporated, giving a cleaner auric chloride solution.

Göran

 

[purgatory]

Hi
How are you all doing?

Goran, I have noted down all the important factors which must be followed doing recovery process.
I have cut off the fingers from different boards which are heavily gold plated, I was kinda carefull in cutting them off properly, this time I will take pictures on every step I will perform and post them here. I shoukd rather post my plan before attempting as I do not want to make anymore mistakes this time, hopefully I will perform better while paying close attentions on all the respected members advises and the info which I gathered from this forum.

The only thing which is still bothering me to make copper chloride etching solution, I enquired about copper salts with which this can be made easily are damn expensive and I do not want to have them as the overall cost of refining will exceed the amount of recovery, And the process which Steve mentioned in his website is kinda time consuming, I simply do not want to take a risk of getting the gold foils stripped from the fingers using hcl and peroxide as there is a chance of dissolving the gold as my working temperature these days is almost 40 degree centigrade and the 2nd problem I'm facing is that I can not find H2O2 3%. The only one available is 6%. I'm afraid to get gold dissolved.
Would that be fine if I use Nitric Acid to strip them off with a ratio of 1:2 acid:water?
Any negative impact on the yield using this method?
Do you guys think de-ionized water could be a problem in my previous attempt to strip gold off from 10 kilos Ram Sticks in which i only recovered 2 grams of gold? I never checked its conductivity though, I found out that the best de-ionized water is of zero conductivity, is that right? I do not know the water I use is of zero conductivity.
Or I just simply use tap water as distilled water is not available here. The only distilled water which is available is of the same cost as (Nitric Acid 60%) cost which is $7/litre, strange is'nt it?
I'm kind of undeceisive this time.
Please help.

Alvi

 

[Geo]

In smaller batches, ferric chloride works several times faster than copper chloride with out the need for added oxygen.

 

[maynman1751]

I don't think there is a need to do a HCl wash of the foils in most cases, you would risk dissolving some gold unless you do a thorough incineration.

Goran, I was suggesting the HCl hot wash after AP to help remove any left over copper and such. It has always been directed here on the forum to do a HCl boil of the foils. I neglected to express that point explicitly and that is my fault. I wouldn't do it after nitric. I believe that nitric would probably do a better job of removing most base metals versus AP. I myself, wouldn't use nitric on foils. To each his own!

 

[maynman1751]

Hi
How are you all doing?

Goran, I have noted down all the important factors which must be followed doing recovery process.
I have cut off the fingers from different boards which are heavily gold plated, I was kinda carefull in cutting them off properly, this time I will take pictures on every step I will perform and post them here. I shoukd rather post my plan before attempting as I do not want to make anymore mistakes this time, hopefully I will perform better while paying close attentions on all the respected members advises and the info which I gathered from this forum.

The only thing which is still bothering me to make copper chloride etching solution, I enquired about copper salts with which this can be made easily are damn expensive and I do not want to have them as the overall cost of refining will exceed the amount of recovery, And the process which Steve mentioned in his website is kinda time consuming, I simply do not want to take a risk of getting the gold foils stripped from the fingers using hcl and peroxide as there is a chance of dissolving the gold as my working temperature these days is almost 40 degree centigrade and the 2nd problem I'm facing is that I can not find H2O2 3%. The only one available is 6%. I'm afraid to get gold dissolved.
Would that be fine if I use Nitric Acid to strip them off with a ratio of 1:2 acid:water?
Any negative impact on the yield using this method?
Do you guys think de-ionized water could be a problem in my previous attempt to strip gold off from 10 kilos Ram Sticks in which i only recovered 2 grams of gold? I never checked its conductivity though, I found out that the best de-ionized water is of zero conductivity, is that right? I do not know the water I use is of zero conductivity.
Or I just simply use tap water as distilled water is not available here. The only distilled water which is available is of the same cost as (Nitric Acid 60%) cost which is $7/litre, strange is'nt it?
I'm kind of undeceisive this time.
Please help.

Alvi

Alvi, simply follow the video at the beginning of this thread and you can't go wrong. Sam knows his stuff. If you are afraid of dissolving some gold, make your copper chloride with just copper, Hcl and some peroxide. Then add it to your reaction as shown on the video. Your de-ionized water is fine......no problems there. Also go to Sam's web site and watch his other videos at Gold n Scrap.

 

[g_axelsson]

I don't think there is a need to do a HCl wash of the foils in most cases, you would risk dissolving some gold unless you do a thorough incineration.

Goran, I was suggesting the HCl hot wash after AP to help remove any left over copper and such. It has always been directed here on the forum to do a HCl boil of the foils. I neglected to express that point explicitly and that is my fault. I wouldn't do it after nitric. I believe that nitric would probably do a better job of removing most base metals versus AP. I myself, wouldn't use nitric on foils. To each his own!

But earlier you wrote

There's no mention of incineration between the Nitric use and the Hcl rinse!

I didn't see that he used an HCl rinse after nitric, which maybe he should have, to make sure that most of the base metals had been removed prior to dissolution. But you are indeed correct in your statement if he was going to do an HCl wash. If he had used the AP method, that I suggested, he wouldn't need incineration before the HCl boil wash! He can simply decant the wash and go to dissolution with HCl/Cl or HCl/HN03.

Anyhow, I feel it isn't necessarily to wash the foils in HCl prior to dissolving them. With SMB you can precipitate gold from quite dirty solutions and the following wash of the gold powder takes care of most of the drag down. A HCl boil can't affect any metals alloyed in the foils (1 % chromium for hard gold plating). As copper doesn't dissolve in HCl any copper left will survive that step and any metals more reactive than copper is easily dissolved in copper chloride solution.
In my experience, if you let the copper chloride do it's work it's enough to wash the foils in water. If you get a milky solution when adding water then there is some CuCl (insoluble in pure water) left and you could add some HCl until it clears up. The visual clues are quite clear so it is easy to "only use enought". This step should be done with minimal amount of water so you don't need to add too much HCl to dissolve the CuCl.
If the process has been driven to it's point and the copper chloride solution is emerald green then the copper chloride consists of mostly water soluble CuCl₂ (750 g/liter @ 20 C) and it will be easily removed with water washes.

I usually don't care if there are some copper chloride left with the foils and when I'm done with the gold drop I'm left with a slightly bluish tinted barren solution. That's copper II chloride, the copper I chloride from the previous step but oxidized by the AR.

A minor part of copper chloride among the foils will not harm the result. For example red gold carat jewellery is suggested for direct dissolving in AR and is perfectly fine to precipitate gold from.

As you all can see, there are more than one way to run the common processes. Small variations depending on your situation. As long as you have a good grasp of what's happening and can interpret the clues correct and plan ahead you will be fine.

Maynman, what is the color of your HCl boil? It should give some hints of what metals you remove in that step.

Alvi, if your peroxide is too strong, just mix it with water to get the concentration you want. You can actually start without any peroxide at all, but it will take a week or two until the process is up and running. There will always be some minute copper oxide in the beginning and that will build up the copper concentration. The more copper in solution the faster the etch will work and add more copper to the solution until the oxygen is the limiting factor.

Göran

 

[maynman1751]

Goran, I submit to your experience and knowledge. I respect what you say. I was simply giving the advice that has been given to me. Thank you for your appraisal.

 

[g_axelsson]

maynman, we all learn from each other by discussing these topics. For example I had to think a lot of why it would benefit to boil the foils in HCl. The only reason I could find was first to remove aluminum or some steel that would resist nitric acid.
Then when we drifted in on the copper chloride process I had to think hard until it hit me that any leftover CuCl wouldn't dissolve in a water wash only. Depending on how far you push the process you end up with various amounts of CuCl, so for someone maybe the HCl wash is necessary, and boiling it will speed up the dissolving process.

By thinking about the details I have learned some more and gained a deeper understanding of the process. I thank you for that and hope we both and others too have learned something in this thread.

8)

... this is the scientific process, do question all the steps and rules and if it stands up to scrutiny it is good. If not, we learn something new and that's also good.

If you see something I say without motivation and you don't know why, put me to the test. If I'm wrong then I want to be corrected.

Sometimes the forum has a way of propagating ideas that is unnecessary or wrong, by questioning them we develop more nuanced methods over time.

Göran

 

[Geo]

Actually, the hcl rinse, hot or not, is to remove any left over copper oxide from the foils before the dissolution.