I agree with butcher. No matter what I was dissolving, I would cover the material with HCl, heat it, and then add the 15% nitric in increments until the material is dissolved. I never pre-mix aqua regia.
65% Nitric acid
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Long dead thread, but just the answer I needed. I finally found some nitric, 42%. Paid $17.50/gallon, no idea if that's good or not, but glad to have some in my hands!
AndyWilliams,
That will be about the correct strength for silver or copper.
The 42 % HNO3 will be very close to using 70% HNO3 and diluting with water 50%-50%.
I would figure about 2.8ml of this to each gram of silver.
For 70% nitric use about 1.4ml nitric and 1.4ml water for each gram of silver.
The 42% HNO3 figure about 8.3ml per gram of copper.
For 70% HNO3 4.3 ml HNO3 and 4.3ml of water.
I will normally use a little more water or hydrogen peroxide with heating to keep fumes down, and keep the nitric in solution to react more with metals.
For Aqua regia to dissolve gold free of base metals 3.8 ml 32%HCl + 0.95ml 70% HNO3 per gram of gold, nitric acid is measured out in clean container and added in portions with a pipette, using heat after initial reaction, and heating to evaporate and drive off H2O, when I still have some gold undissolved gold left I will evaporate and concentrate the solution from a yellow solution to a red solution this will use up more nitric already in solution and dissolve more gold in the process, after solution is evaporated down to the burgundy red color, I will add a few drops of nitric at a time {adding splash of HCl just in case I am limited on HCL, and evaporating off the little water involved here with this added acid, as the HCl is about 68% H2O). Once concentrated the added drops of nitric finish dissolving the last bit of gold, this eliminates my need to spend long hours evaporating off free nitric acid, or from having to add pure gold to use up excess HNO3 in solution, I feel it is the best use of both GSP's trick of limiting HNO3, and Harold's trick of adding gold to eliminate free nitric acid, with this method I can then dilute solution (if I think I had a little nitric left in solution I will add a pinch of sulfamic acid, if done right this is not needed), and let it settle over night to precipitate any silver chloride before filtering into very clean vessel and precipitating the gold.
(Another option to insure not over using nitric is to leave a bit of undissolved gold to process with the next batch).
The formula I use above came from Hokes book and works very well, 4 floz 32% HCL and 1 floz 70% HNO3 for each troy ounce of gold.
Which is about 118ml HCL and 29.5ml HNO3 per troy ounce of gold.
Which is about 8 tablespoons HCl and 2 tablespoons HNO3 to dissolve a troy ounce of gold.
As you see here it takes very little acid to dissolve a lot of gold.
Your 42% HNO3 is more dilute with water, but you can use it just fine in the reaction described above to dissolve gold, you will have to about double the nitric volume measure, and you will also have to account for the excess water in the acid when concentrating the solution, or figure the excess water your adding (in the acid as you add more acid to the concentrated solution which will dilute it a little and the added water will need re-concentrated), but you will also have less nitric acid wasted as gas in the reaction if done right.
Edited to correct mistake in figures
That will be about the correct strength for silver or copper.
The 42 % HNO3 will be very close to using 70% HNO3 and diluting with water 50%-50%.
I would figure about 2.8ml of this to each gram of silver.
For 70% nitric use about 1.4ml nitric and 1.4ml water for each gram of silver.
The 42% HNO3 figure about 8.3ml per gram of copper.
For 70% HNO3 4.3 ml HNO3 and 4.3ml of water.
I will normally use a little more water or hydrogen peroxide with heating to keep fumes down, and keep the nitric in solution to react more with metals.
For Aqua regia to dissolve gold free of base metals 3.8 ml 32%HCl + 0.95ml 70% HNO3 per gram of gold, nitric acid is measured out in clean container and added in portions with a pipette, using heat after initial reaction, and heating to evaporate and drive off H2O, when I still have some gold undissolved gold left I will evaporate and concentrate the solution from a yellow solution to a red solution this will use up more nitric already in solution and dissolve more gold in the process, after solution is evaporated down to the burgundy red color, I will add a few drops of nitric at a time {adding splash of HCl just in case I am limited on HCL, and evaporating off the little water involved here with this added acid, as the HCl is about 68% H2O). Once concentrated the added drops of nitric finish dissolving the last bit of gold, this eliminates my need to spend long hours evaporating off free nitric acid, or from having to add pure gold to use up excess HNO3 in solution, I feel it is the best use of both GSP's trick of limiting HNO3, and Harold's trick of adding gold to eliminate free nitric acid, with this method I can then dilute solution (if I think I had a little nitric left in solution I will add a pinch of sulfamic acid, if done right this is not needed), and let it settle over night to precipitate any silver chloride before filtering into very clean vessel and precipitating the gold.
(Another option to insure not over using nitric is to leave a bit of undissolved gold to process with the next batch).
The formula I use above came from Hokes book and works very well, 4 floz 32% HCL and 1 floz 70% HNO3 for each troy ounce of gold.
Which is about 118ml HCL and 29.5ml HNO3 per troy ounce of gold.
Which is about 8 tablespoons HCl and 2 tablespoons HNO3 to dissolve a troy ounce of gold.
As you see here it takes very little acid to dissolve a lot of gold.
Your 42% HNO3 is more dilute with water, but you can use it just fine in the reaction described above to dissolve gold, you will have to about double the nitric volume measure, and you will also have to account for the excess water in the acid when concentrating the solution, or figure the excess water your adding (in the acid as you add more acid to the concentrated solution which will dilute it a little and the added water will need re-concentrated), but you will also have less nitric acid wasted as gas in the reaction if done right.
Edited to correct mistake in figures
mikeinkaty
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What pharmacy did you buy it from? The rest of us would like to know!Dude4ever said:Does 65% technical grade nitric acid, bought from pharmacy cut it in making AR?
This is really the highest (and only) concentration I can buy, if I don't want to buy 25L minimum of nitric though, and I really don't
jimdoc
Well-known member
mikeinkaty said:What pharmacy did you buy it from? The rest of us would like to know!Dude4ever said:Does 65% technical grade nitric acid, bought from pharmacy cut it in making AR?
This is really the highest (and only) concentration I can buy, if I don't want to buy 25L minimum of nitric though, and I really don't
Dude4ever is in Norway, and has not been on the forum since Wed Jun 13, 2012.
Jim
butcher said:
Thanks for the info butcher, it's much appreciated. I remember Hoke writing that most beginners use too much acid, now I can see why. It is easy to see that much money can be saved in these stages if I'm careful. My question though, wouldn't I need to use 5.6 ml of 42% nitric to dissolve a gram of silver and 16.6 ml per gram of copper?
Thanks again!
Andy
Andy
It looks like I goofed up those numbers I will edit them
Please see edited correction above in color
It looks like I goofed up those numbers I will edit them
Please see edited correction above in color
butcher said:
Wow! Even less acid! Thanks butcher!
Andy,
Depending how the reaction is driven, or run (dilution, refluxing, temperature, and other factors play a big role in how much acidis needed and how much is lost in gases evolved from the reaction), you may get by with even less than these figures, it really is amazing to me how little aqua regia it takes to dissolve gold, and how much gold can be in a concentrated gold chloride solution after de-noxing the solution and concentrating the solution (driving off most of the free acids).
Depending how the reaction is driven, or run (dilution, refluxing, temperature, and other factors play a big role in how much acidis needed and how much is lost in gases evolved from the reaction), you may get by with even less than these figures, it really is amazing to me how little aqua regia it takes to dissolve gold, and how much gold can be in a concentrated gold chloride solution after de-noxing the solution and concentrating the solution (driving off most of the free acids).
