Aqua Regia is about the only method, for the small refiner, to purify gold to 999.9 Fine - no matter what anyone says. Not only does this method work on most karat golds, it is also the final re-fining step that is used to purify the gold collected from all types of scrap. Once you learn the steps for karat gold, which is the most difficult, you can easily adapt to gold from most other sources.
It's not easy to get 999.9 fine gold. In that purity, there is only one part of impurities to every 9,999 parts of gold. Not much. Everybody learns to do it a little differently. Many small refiners never learn to do it. Since reaching this goal is foremost in my mind, I have begged, borrowed, stolen, and invented tricks, in order to achieve this purity. It's sort of a pride thing, with me, to be able to to produce beautiful 999.9 bars. Also, I get more money for the very pure gold. It's not that hard to do. The most important things are: (1) Keep excess nitric out of the aqua regia. I have a good way to do this. (2) Rinse the final gold very well. Have a plan.
To do aqua regia, you almost have to have a fume hood. You can do things outside but, you then must deal with the weather and other problems. When it comes to automobiles, metal buildings, lungs, etc., aqua regia fumes are one of the most corrosive things around. Also, aqua regia fumes are heavy and tend to cling to the ground in inverse weather conditions. It's best to not have any neighbors nearby. When you are very small, you can probably get away with exhausting the fumes into the air. When you get big, you'll have to get a fume scrubber. Besides the corrosive nature of the fumes, one other problem is the high visibility of the red/brown nitric oxide fumes that are produced.
Commercial fume hoods are expensive. I usually build my own. I briefly discussed fume hoods on this thread:
http://goldrefiningforum.com/phpBB3/viewtopic.php?t=10
The last fume hood I built, a 10 footer, was made as follows. I first built a bench 10 feet long with a 2" X 4" framework, 4" X 4" legs, and a 3/4", 3 feet wide plywood top. The top was about 36" high, a height that is good for siphoning the solutions out of buckets. The room I installed it in was in a metal building with 10' ceilings. I then built a frontless plywood box to enclose the bench with full sides, a full back, and a full top. I built it about a foot, or so, short of the ceiling, in order to mount the blower motor on top of the box and keep it away from the fumes. I ran a piece of plywood across the top front of the hood. I made the bottom edge of this strip of plywood about 6' off the floor, to keep from bumping my head on it. I then got 2 blowers, mounted in tandem, out of the junk yard. I think they were of 10" size. I mounted them at the top, back, center, inside of the hood and ran them to the motor above with a belt. I exhausted the fumes from the blowers through large fiberglass ducting to the outside of the building.
I didn't have a complete front on the hood or, sliding doors. You can add a series of 3 or 4 sliding, overlapping, plywood doors, on wooden tracks, that you can close when the blowers are shut down at night. They get in the way and I worked around the shutting down problem in other ways. I kept all acids under the hood in containers with lids, such as buckets, that I sealed before leaving at night. I never left open containers when the blowers were off. If I had a dissolving reaction going on that would work overnight, I left the blowers on. Also, I had the hood in a fairly small room, in which the walls and ceiling had been covered with low grade 1/2" plywood. I also had a couple of light bulbs, in PVC receptacles, covered with fume proof globes, mounted inside of the hood.
This is hard to explain. If anything is unclear, please ask questions. Constructing the hood only took a day, or two. It's really pretty simple. For a smaller hood, you can use the same basics.
Next: Dissolving the Gold
It's not easy to get 999.9 fine gold. In that purity, there is only one part of impurities to every 9,999 parts of gold. Not much. Everybody learns to do it a little differently. Many small refiners never learn to do it. Since reaching this goal is foremost in my mind, I have begged, borrowed, stolen, and invented tricks, in order to achieve this purity. It's sort of a pride thing, with me, to be able to to produce beautiful 999.9 bars. Also, I get more money for the very pure gold. It's not that hard to do. The most important things are: (1) Keep excess nitric out of the aqua regia. I have a good way to do this. (2) Rinse the final gold very well. Have a plan.
To do aqua regia, you almost have to have a fume hood. You can do things outside but, you then must deal with the weather and other problems. When it comes to automobiles, metal buildings, lungs, etc., aqua regia fumes are one of the most corrosive things around. Also, aqua regia fumes are heavy and tend to cling to the ground in inverse weather conditions. It's best to not have any neighbors nearby. When you are very small, you can probably get away with exhausting the fumes into the air. When you get big, you'll have to get a fume scrubber. Besides the corrosive nature of the fumes, one other problem is the high visibility of the red/brown nitric oxide fumes that are produced.
Commercial fume hoods are expensive. I usually build my own. I briefly discussed fume hoods on this thread:
http://goldrefiningforum.com/phpBB3/viewtopic.php?t=10
The last fume hood I built, a 10 footer, was made as follows. I first built a bench 10 feet long with a 2" X 4" framework, 4" X 4" legs, and a 3/4", 3 feet wide plywood top. The top was about 36" high, a height that is good for siphoning the solutions out of buckets. The room I installed it in was in a metal building with 10' ceilings. I then built a frontless plywood box to enclose the bench with full sides, a full back, and a full top. I built it about a foot, or so, short of the ceiling, in order to mount the blower motor on top of the box and keep it away from the fumes. I ran a piece of plywood across the top front of the hood. I made the bottom edge of this strip of plywood about 6' off the floor, to keep from bumping my head on it. I then got 2 blowers, mounted in tandem, out of the junk yard. I think they were of 10" size. I mounted them at the top, back, center, inside of the hood and ran them to the motor above with a belt. I exhausted the fumes from the blowers through large fiberglass ducting to the outside of the building.
I didn't have a complete front on the hood or, sliding doors. You can add a series of 3 or 4 sliding, overlapping, plywood doors, on wooden tracks, that you can close when the blowers are shut down at night. They get in the way and I worked around the shutting down problem in other ways. I kept all acids under the hood in containers with lids, such as buckets, that I sealed before leaving at night. I never left open containers when the blowers were off. If I had a dissolving reaction going on that would work overnight, I left the blowers on. Also, I had the hood in a fairly small room, in which the walls and ceiling had been covered with low grade 1/2" plywood. I also had a couple of light bulbs, in PVC receptacles, covered with fume proof globes, mounted inside of the hood.
This is hard to explain. If anything is unclear, please ask questions. Constructing the hood only took a day, or two. It's really pretty simple. For a smaller hood, you can use the same basics.
Next: Dissolving the Gold
