Okay i'm no expert so correct me if im wrong. The recipe for aqua regia is 1 part nitric acid to 3 parts hydrochloric acid. Searching online i can find no where that sells either of those in pure form. So what percentage of purity do you use?
A question on AR
- Thread starter danny987
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The most concentrated you'll find HCl is 38.5%, that's about it's maximum concentration in water.
You also won't find 100% nitric acid, or even red fuming nitric acid (90%) as those have a limited shelf life and are orders of magnitude more dangerous than normal ~65% nitric.
There's an exact formula for aqua regia, but generally speaking 1 part concentrated nitric to 3 or 4 parts concentrated HCl is fine.
If you really want to get fancy, then we'll have to go into molarity and molar equivalents per unit of solution. If you want to go there, let me know. Otherwise, just stick with dissolving stuff with HCl and adding nitric as needed. It's what Chris does, and it does work and yes, he is a real professional. If you do it right, you can even save a step or reduce the time a step would normally take.
You also won't find 100% nitric acid, or even red fuming nitric acid (90%) as those have a limited shelf life and are orders of magnitude more dangerous than normal ~65% nitric.
There's an exact formula for aqua regia, but generally speaking 1 part concentrated nitric to 3 or 4 parts concentrated HCl is fine.
If you really want to get fancy, then we'll have to go into molarity and molar equivalents per unit of solution. If you want to go there, let me know. Otherwise, just stick with dissolving stuff with HCl and adding nitric as needed. It's what Chris does, and it does work and yes, he is a real professional. If you do it right, you can even save a step or reduce the time a step would normally take.
Thanks, Lou. I've pushed this method since day one. You're the first person, besides Harold, to understand its value and I really appreciate it. Considering your background, I truly value your acknowledgment.
Yes, treating the 2 acids as separate acids, instead of premixing them, really does work better. This becomes very important when refining karat gold, dental gold, or gold powder derived from any another type of gold bearing scrap.
I usually calculate how much of each acid I need. Then, I cover the gold with the HCl calculated, plus an excess - maybe 20-30% extra. To make this work, you should have an excess of HCl. Unlike nitric, an excess of this quantity of HCl produces zero problems. Then I heat to near boiling and add a small portion of the required amount of nitric. When the reactions subsides, I stir it and then add another portion of nitric. I repeat until an addition of nitric produces no reaction. You need to do it a few times to get the hang of it.
I learned this in about 1980. Since then, I have never had to add urea. Of the many 100's of batches I have run since then, I have only needed to boil the aqua regia down about 5 times - these occurred because I added larger amounts of nitric due to my impatience. Greater amounts of nitric will make the dissolving go faster, but you always end up paying the piper. The 2 acid method saves a lot of time, saves a lot of nitric, and is much easier. Although the concept is simple, is is not commonly known. I would consider that it was a true trade secret, until I placed it on this forum.
Yes, treating the 2 acids as separate acids, instead of premixing them, really does work better. This becomes very important when refining karat gold, dental gold, or gold powder derived from any another type of gold bearing scrap.
I usually calculate how much of each acid I need. Then, I cover the gold with the HCl calculated, plus an excess - maybe 20-30% extra. To make this work, you should have an excess of HCl. Unlike nitric, an excess of this quantity of HCl produces zero problems. Then I heat to near boiling and add a small portion of the required amount of nitric. When the reactions subsides, I stir it and then add another portion of nitric. I repeat until an addition of nitric produces no reaction. You need to do it a few times to get the hang of it.
I learned this in about 1980. Since then, I have never had to add urea. Of the many 100's of batches I have run since then, I have only needed to boil the aqua regia down about 5 times - these occurred because I added larger amounts of nitric due to my impatience. Greater amounts of nitric will make the dissolving go faster, but you always end up paying the piper. The 2 acid method saves a lot of time, saves a lot of nitric, and is much easier. Although the concept is simple, is is not commonly known. I would consider that it was a true trade secret, until I placed it on this forum.
lazersteve
Well-known member
Chris,
For the record, when I use AR, I always follow your suggestions since you first posted them. I start off with straight HCl on the scrap and bring it up to medium heat. I've gotten in the habit of putting my nitric in a small 60mL plastic squeeze bottle and dispense it as required until the gold is dissolved. It sure saves on wasted nitric and cuts way back on the fumes.
Steve
For the record, when I use AR, I always follow your suggestions since you first posted them. I start off with straight HCl on the scrap and bring it up to medium heat. I've gotten in the habit of putting my nitric in a small 60mL plastic squeeze bottle and dispense it as required until the gold is dissolved. It sure saves on wasted nitric and cuts way back on the fumes.
Steve
Sorry, Steve,
I didn't know you were doing it that way.
I didn't know you were doing it that way.
