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Joined
Apr 8, 2022
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Location
Ohio
Whoever finds themselves reading this,

I am new to the gold refining world, but have spend a fair amount of time researching (famous last words). I have been reading through many of the posts on here trying to shed some light on what I am encountering right now. I have acquired roughly 800 various CPU's and a large array of laboratory equipment and chemicals. I finally got to the point last weekend that I was willing to try test a run of 30 CPU's to see if I could get any gold recovery. I gave them a several day Nitric acid bath, switching out the acid a couple times a day. Once all the visible gold was removed from the CPU's I washed them all with distilled H2O and vacuum filtered. I put the filtered medium back in a fresh beaker and started a 37% Hydrochloric acid bath with a few shots of 30% H2O2. Let this run over night on some heat and filtered in the morning. I was satisfied with the filtrate being pure enough gold foils to start the AR. All the foils dissolved no problem. I vacuum filters the solution and precipitates with sodium meta bisulfite. The gold precipitated fine, but it was such a small amount I decided to hold it as is to mix with my next attempt, hoping it would be a little better result.

Now for the second attempt. Using 26 CPU's, I started with a Nitric bath for a few days, switching the nitric out every 12 or so hours. Once all the gold was visibly off the CPU's I rinsed and vacuum filtered. All the filtrate was placed in a fresh beaker and I began a 98% sulfuric acid bath. I let this ride on high heat for 6 or 7 hours until it looked like most of the non-gold material was dissolved. I then vacuum filtered and took the first picture posted with this thread. It seemed to me like the gold foils were isolated enough to start the aqua regia. I put the filtrate in a new beaker and added 37% Hydrochloric acid then turned on the heat. Once boiling I started dosing 70% Nitric acid 1 mL at a time letting it react until it settled down some. I did this until the gold stopped dissolving into solution. Stannous test came back positive. I decided to vacuum filter this solution and start a fresh batch of AR to try and suspend the remaining gold, however I could not get the remaining gold to go. Is it possible it is not gold? The second picture shows what appears to be the remaining gold that I cannot get to dissolve. Meanwhile with the filtered solution of suspended gold, I precipitated with SMB and got a far greater yield than the first attempt.

Any expert input would be greatly appreciated. I wanted to make sure I am not just wasting time and money on this and flushing recoverable gold down the drain. Is it possible I passivated the remaining gold with the addition of the 70% Nitric into the aqua regia, and if so is there a way to un-passivate (not sure if that's a word)? I just got a 10L delivery of Nitric acid today so I want to make sure I have these kinks ironed out before doing a large run.

Thanks,
Dharr
 

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Welcome to the forum.
You may have dissolved some gold with the HCl H2O2 bath. Test it with stannous.
The gold that won't dissolve may not be gold but plastic? Its all floating.
 
I was wondering about that. I did stannous test and it appeared negative but that could be because it was so diluted I suppose.

I am going to filter the floaters out. Is there a test I could perform on the solid that may shed some light as to whether or not it’s gold?

Thanks
 
Do you denox the gold-ARsolution before trying to drop the gold? That's a critical step. If there's still free nitric in there, the recovery will fail to varying degrees.

You might want to try dissolving the gold with super-cheap HCl-bleach method. Just barely cover the material with HCl and add regular Chlorox bleach (or the generic equivalent) little by little (you will not need very much per gram of gold), swirling for a while before adding more, until the gold totally dissolves. The gold on CPUs is very thin, and this method dissolves it completely.

It doesn't need denoxing, only a slow boil OUTSIDE (in direct sunlight) to drive off the excess chlorine gas. No additional cost! I did a test on some uniform old pins all from the same equipment, so I could estimate the result fairly well. Ran the dissolve, did the de-chlorination. Then the SMB drop went SPECTACULARLY! I got basically 100% of what I'd expected, and negative stannous gold test on the waste solution! Not a surprising result with a small quantity, large volumes will have more measurable disparity, but it was more than enough proof-of-concept.
 
I did a stannous test after the HCL and H2O2 and it showed negative, although I don’t have much confidence in the premixed bottle of stannous chloride I bought from eBay. It has given me some strange colors during some tests.

I did not denox the AR solution. I have seen people say you need too and others say it wasn’t necessary if you were careful not to over do the Nitric. What’s best to denox with? I have seen many places suggest urea. The 2 successful precipitations I have had were not denox’d, but they were both relatively small runs and I was adding Nitric by the single mL and was careful not to go to heavy with it.
 
What type of CPU's. there are so many varieties.
Mostly intel and AMD 2005-2012 home/office style CPU’s. I have learned the newbie lesson that these don’t have enough PM’s to justify any nitric acid. I have successfully reclaimed some gold, a little silver, and what I think is a touch of platinum, but I’m significantly under water on them. On the bright side, I have gained volumes of knowledge and a little experience from working with them. My focus is changing to scrap jewelry, those results are far better.
 
I did a stannous test after the HCL and H2O2 and it showed negative, although I don’t have much confidence in the premixed bottle of stannous chloride I bought from eBay. It has given me some strange colors during some tests.

I did not denox the AR solution. I have seen people say you need too and others say it wasn’t necessary if you were careful not to over do the Nitric. What’s best to denox with? I have seen many places suggest urea. The 2 successful precipitations I have had were not denox’d, but they were both relatively small runs and I was adding Nitric by the single mL and was careful not to go to heavy with it.
That's why you need a weak reference solution of gold chloride. Just strong enough to show a bit of purple with good stannous.

When in doubt, check it out: Test the stannous test liquid.
 
That's why you need a weak reference solution of gold chloride. Just strong enough to show a bit of purple with good stannous.

When in doubt, check it out: Test the stannous test liquid.
I made mine out of a few flakes of gold foil, and several drops of AR. It was still so strongly positive I could dilute it 5-fold, and still get purple-black from the confirmed good stannous.
 
I'm having a little trouble with my beautiful yellow gold chloride solution in getting the gold to drop using smb in cold temperatures. Please help
 
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