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
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