I just read that article that you linked to. There are a couple other things in it that should be addressed, so other new people that see this thread can know as well.
Step 1
Cut the parts of the circuit boards that contain gold and put them in the bucket & throw away the other parts of the board. If you also have CPU chips hot them with a hammer as the gold parts are usually inside the chip. Place these in the bucket too.
Dont throw it away. Recycle it!
Step 2
Take a clean 5 gallon bucket and either use aqua regia (nitric acid and hydrochloric acid) In the ratio 1:3. Remember to use gloves these are very hazardous materials.
Either AR or..? 1 part nitric to 3 HCl is too much still, even in an open reaction. Its best to use a reflux and add your calculated HCl, then small small additions of nitric until your gold is Fully dissolved, that will prevent you from having to spend a bunch of extra time denoxxing the solution, which is a requirement to precipitate the gold.
Step 3
Place your CPU chips and cut up boards in a plastic wire mesh basket and then place this in the solution. The metal should start to fizz and give off a brown fume. (these fumes are toxic so make sure you are doing this process with an adequate mask or in an open area!) This chemical reaction is the gold dissolving into the acid solution, this process can take up to 2 hours so leave the boards in the solution for a while. Come back in 2 hours and check the boards to see that all the gold has been dissolved.
Gold yes, but also base metals, which are competing with the gold to be in solution, and if there isnt enough acid to accomodate them all, the base metals will win, and bully the gold out of solution.. Making the gold bruised from the scuffle, leaving it black and brown.-2 hours may not be long enough. Especially if the reaction isnt heated, or if there is a vast amount of metal to dissolve
Step 4
The gold is now dissolved into the acid solution. This acid is reusable until there is no longer a chemical reaction of fizzing and fuming. Once the acid liquid is no longer reacting and dissolving the boards then remove the basket and check the liquid to see if any lumps of other material still remain in the liquid. If there are then filter this liquid or simply decant it into another container leaving the solid lumps behind.
I dont know what kind of plastic basket he is using, but nitric is pretty hard on most plastic. Although there are some members that do their reactions in a 5 gallon bucket. AR shouldnt be one of them. Glass vessels are a must. Even if its just a coffee pot sitting in a corningware dish. If it breaks its fixable. With an AR reaction in a bucket, it could easily become perforated from a ceramic chip wearing on one spot over n over and when the levee breaks?...oh man, i know id be sad...very very sad.
Step 5
Your acid liquid should be a dark green clear liquid, if it looks cloudy or there are bits floating in it then you need to decant it or filter it until it is clear. Once its done then add some urea to the acid liquid little by little. It should react by fizzing - keep on adding the urea until the liquid does not fizz anymore.
It really shouldnt be a dark green color. Not if you are refining your gold....if you are recovering, thats a different story. Stay away from urea in refining. As Dave mentioned, sulfamic acid is a much much better way to denox. As it removes NOx AND make some sulfuric in the solution, which in turn will precipitate lead as lead sulfate, which will be filtered off before ppt of the gold (win-win!)
Step 6
Once it has stopped fizzing you need to add precipitant to the acid liquid to extract the pure gold. You need roughly 1.5 spoonfuls of precipitant (Sodium Bisulfite (Na2HSO3) for every ounce of metal dissolved so remember to roughly weigh what you dissolved in the first place. Add the precipitant to a clean bucket and then add the acid solution. The precipitant and the acid will react forming a muddy solution that should sink to the bottom. This mud is your pure gold! To know whether you have extracted all the gold from the acid liquid - test some of the acid for gold content - using a gold detection liquid - if there is any gold in the acid still the gold detection liquid will turn purple brown. If there is still gold in the acid then add more precipitant.
I would personally just dissolve the ppt in water, then put it in my ar solution, stirring well. Or just add the powder directly to the AR solution. But, the solution must have some free acid to liberate SO2, which is really what is reducing the gold.
The brown stain on his stannous test, is too much precipitant. Purple to black is gold.
Step 7
The acid should now be a clear green or amber color with mud sunk to the bottom. Pour off the acid into another container leaving only the mud. When the acid has been poured off add 2 or 3 gallons of water to the mud then pour off the water making sure you dont pour off any of the mud. The rinsing ensures the high purity of the gold. Test the mud with aqua ammonia for the purity of the gold. If it turns blue then you need to keep rinsing. Give a final rinse with distilled water.
Test the solution. If its amber, id think pgms or iron maybe.
3 gallons of water?...man.. Thats alot. I think id rather just barely cover it. Stir... Decant... Barely cover it again...stir..decant... By the 3rd time, its usually good to go.
Be careful with ammonia in the lab, it can form unwanted (explosive) compounds with silver... Be sure to reacidify with HCl after so it isnt an issue.
I think i covered it all. Best of luck to ya!
