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aqua regia


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#1 ronmoper76

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Posted 18 April 2021 - 08:22 PM

Anyone have first hand experience with metal refining? I have been saving computers,car amplifiers,power supplies,etc,i have a shit load at this point and i wanna take a crack at pulling all the silver and gold from everything....I just have the basics from google,i figured out how to dilute my nitric acid to get it down to 68%,and muriatic acid is readily available about anywhere...  Do i just break up the circuit boards so they fit in my container and let it set and work on its own or is there a more recommended way that isn't so crude? How much of the regia should i start with to be able to consume a decent amount of material? Just looking for ideas before i set off on this adventure.


Edited by ronmoper76, 18 April 2021 - 08:24 PM.


#2 sefrez

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Posted 18 April 2021 - 10:36 PM

No actual experience but would do it if I had much of anything to refine and a safe setup. I have watched several videos by "sreetips" on youtube where he seems to be going by the "book" and no posing as someone who thinks they know what they are doing. I don't know if he has done circuit boards specifically, but I imagine knowing the fundamentals, this would hardly be an obstacle.

 

I may be wrong, but I think dilution of nitric acid isn't really relevant. 68% may be safer to handle by itself, but your usually adding it into the reaction vessel as metal is dissolved - to save nitric acid as aqua regia isn't stable.

 

One thing I do know for sure with metal refining involving nitric acid - nitrogen dioxide, and then some. 



#3 Arthur

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Posted 19 April 2021 - 12:28 AM

Youtube is awash with "recycling computers and chips for precious metals" videos, watch and understand at least 100 vids from at least 10 different people. Remember that a good YT vid is edited down from 12 hours work to 12 minutes of interesting stuff. Remember also that the computer manufacturers have reduced the gold content to about a tenth of what it once was.

 

Note also that you may possibly recover 1 gram of gold from a computer then you have 10 kilos of waste to dispose of, which may cost you money. 

Everything done with nitric acid risks evolving brown fumes of NOx that are probably dangerous enough to be a war gas, prepare to cope with it.

 

Remember that the best practice is to dissolve the copper then to float off the remaining foils of gold and clean them up, BUT dissolving copper costs acid and creates a solution containing copper -which is toxic and cannot be put down the drain.

 

https://www.lmine.com/assaying-processing-c-223_307/refining-precious-metal-wastes-p-7361.html  

May be a useful text, available in the USA It's an old book but gold is old and the book is still valid though some processes are less than safe by modern standards (don't taste anything or dump waste down the drain, in particular).


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#4 sefrez

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Posted 19 April 2021 - 09:24 AM

Youtube is awash with "recycling computers and chips for precious metals" videos, watch and understand at least 100 vids from at least 10 different people. Remember that a good YT vid is edited down from 12 hours work to 12 minutes of interesting stuff. Remember also that the computer manufacturers have reduced the gold content to about a tenth of what it once was.

 

Note also that you may possibly recover 1 gram of gold from a computer then you have 10 kilos of waste to dispose of, which may cost you money. 

Everything done with nitric acid risks evolving brown fumes of NOx that are probably dangerous enough to be a war gas, prepare to cope with it.

 

Remember that the best practice is to dissolve the copper then to float off the remaining foils of gold and clean them up, BUT dissolving copper costs acid and creates a solution containing copper -which is toxic and cannot be put down the drain.

 

https://www.lmine.com/assaying-processing-c-223_307/refining-precious-metal-wastes-p-7361.html  

May be a useful text, available in the USA It's an old book but gold is old and the book is still valid though some processes are less than safe by modern standards (don't taste anything or dump waste down the drain, in particular).

 

How about using iron to displace copper leaving an iron salt? It seems some iron salts undergo hydrolysis leaving iron oxides/hydroxides which should be a non issue.


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#5 MadMat

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Posted 19 April 2021 - 10:16 AM

Every gold reclamation process I have seen, from motherboards ect. used fuming nitric acid to dissolve the baseboard of the circuit boards along with other metals. This leaves the metallic gold behind. Using Aqua regia is going to contaminate the precious metal with any other metal on the circuit board and then you have to reclaim metallic gold from solution and that can be a bit involved (and expensive) once it is dissolved in aqua regia. It either has to be electro-plated out or you need to use very strong reducing agents such as sodium borohydride. As Arthur stated, there are going to be poisonous fumes involved. Those NOx gases can be quite insidious, causing damage to your lungs that isn't even noticeable at first. Believe it or not, if you are dead set on dissolving the gold off the board, a cyanide solution is probably safer. It would take some time but as long as no acid comes into contact with the solution (and of course you don't drink it or get skin contact) it can be relatively benign. Cyanide was used a LOT in the electro-plating industry years ago. It was used for both plating solutions and solutions to strip plating off of parts. Gold dissolved in cyanide produces a beautiful purple solution. OR you could use mercury to amalgamate the gold and then distill the mercury/gold and recover the gold. This was used by old time  "49ers" to recover their gold from the silt they panned from rivers. But here again you have to contend with poisonous fumes. Just a few ideas of how to reclaim the gold from circuit boards. No matter what process you use it is complicated and involves dangerous chemicals. This is probably the reason why very few people have attempted it. With all the chemical knowledge I have from working in laboratories in the electro-plating industry, I have never done more than give it a passing thought and I have a huge old computer "junk yard" taking up space in my basement lol


Edited by MadMat, 19 April 2021 - 10:29 AM.

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#6 Arthur

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Posted 19 April 2021 - 01:21 PM

Stage one of gold recovery from PCBs is to cut and keep only the gold plated bits, stage two is to etch in PCB etchant to undercut all the gold by dissolving the copper, then you should be left with micron fine flakes of gold of reasonable purity, then you wash and purify the gold and melt it into small ingots.

 

search youtube for "How To Recover Gold From Computer Scrap with Household Chemicals" and other videos by Sreetips.

 

Early pentium 1 chips had gold lead wires from the pins to the chip inside, later ones had so little gold inside it may not be worth recovering. -Ball mill the chips and separate the gold from the plastic dust with flowing water then purify the gold. You need P1 chips by the thousand to be financially viable.


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#7 ronmoper76

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Posted 27 April 2021 - 06:29 AM

Thank you guys for all the input.Im still in the process of working on this. I will post my results




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