Access nitric acid

[Pumice]

I just started out a few weeks ago and have done a few batches of card fingers and ceramic cpu's in AR. It seems like I was able to avoid having access nitric acid in my solution as everything went well and I recovered a decent amount of gold without problems.

I hear of people that realize they have access nitric when they do precipitations-the brown fumes and bubbles start.

I am just wondering why not just add some copper to your solution after your reaction is complete? This would give indications that you would have unused nitric, and also use up any of that nitric. I am aware of Hokes method of boiling to syrup and so on. Is using copper to kill access nitric something that would work? Just something I have been wondering about...

 

[butcher]

Well normally my goal is to use aqua regia only on relatively pure gold, having removed all base metals as much as possibly, using aqua regia as a refining method, not as a recovery method, this way the gold is purified more and precipitating goes more smoothly.

Very seldom will I use it as a recovery method, as other metals or materials in solution just make it harder to get back all of the gold and without troubles, given other materials or even if solution is just loaded with copper the gold not only is harder to recover all of it, if solution is loaded with copper the as gold and copper is reduced in solution the gold can combine with gold (gold plating out onto copper) and copper holding gold in solution, if solution is dirty with organics or other materials this just seems worse where gold can actually be held in solution for very long periods of time, add just a little tin and you have a real mess.

For dirty solutions or recovery from dirty solution cementing onto copper is one of the best choices (as long as tin is not a problem and colloids the gold.

Very seldom would you choose to use aqua regia as a recovery method, I do not recommend it because people may begin to think it is a good way to go, when actually I consider it as a last resort, when other methods would not work well.

If you were to use it as a recovery method why would you want to add more copper or other base metal if you do not have to? When you have base metals like copper already in the material you are trying to recover the gold from, by just using less acid you would be using those metals you are recovering gold from to cement out the gold, without adding more copper.

To remove excess nitric acid from solution gold would be a better metal of choice, unless the solution was so contaminated that normal precipitation would be a problem where the choice would then be to cement out gold on copper and start over.

 

[rustyle]

Very seldom will I use it as a recovery method, as other metals or materials in solution just make it harder to get back all of the gold and without troubles, given other materials or even if solution is just loaded with copper the gold not only is harder to recover all of it, if solution is loaded with copper the as gold and copper is reduced in solution the gold can combine with gold (gold plating out onto copper) and copper holding gold in solution, if solution is dirty with organics or other materials this just seems worse where gold can actually be held in solution for very long periods of time, add just a little tin and you have a real mess.



How to handle if tin is in dirty AR solution?

 

[necromancer]

Very seldom will I use it as a recovery method, as other metals or materials in solution just make it harder to get back all of the gold and without troubles, given other materials or even if solution is just loaded with copper the gold not only is harder to recover all of it, if solution is loaded with copper the as gold and copper is reduced in solution the gold can combine with gold (gold plating out onto copper) and copper holding gold in solution, if solution is dirty with organics or other materials this just seems worse where gold can actually be held in solution for very long periods of time, add just a little tin and you have a real mess.



How to handle if tin is in dirty AR solution?

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=17049&hilit=ugly#p172586

here is a start for your tin problem

 

[iamtheman240]

One question I have about evaporating off access nitric acid in AR is what prevents the gold which is actually liquid at this point from being evaporated along with the water and acid?

 

[FrugalRefiner]

One question I have about evaporating off access nitric acid in AR is what prevents the gold which is actually liquid at this point from being evaporated along with the water and acid?

Well, your gold isn't really a liquid. It's in solution.

Without getting overly technical, think about this. If you dissolve sugar, a solid compound, into water, it appears to be a liquid. But the sugar is really just in solution, like your gold. If you let the water naturally evaporate from your sugar water, you'll be left with sugar crystals - rock candy. You don't lose your sugar, or your gold, as long as you evaporate carefully.

Now if you put your sugar water on the stove and crank up the heat till it's a rolling boil, it goes a lot faster, but after you're done, you'll find lots of little sugar crystals all over your stove where the bursting of bubbles in the boiling liquid propelled tiny droplets of sugar water (or gold) out of your solution.

Dave

 

[iamtheman240]

Thanks FrugalRefiner, that explanes it clearly.

 

[butcher]

FrugalRefiner,
That was a very good explanation.

 

[FrugalRefiner]

Thank you.

Dave

 

[glondor]

When there is tin, and your dirty solution goes colloidal, I remove the solution from whatever gold powder has settled, Then add sulfuric acid to the colloidal solution and evaporate with heat until the colloids break up and the gold gathers and falls.

 

[iamtheman240]

Hi Glondor, when you say "colloidal" do you mean the crystals or snowflake like formation, I have a bit of those, or are you talking about something else, please give us a word picture.

 

[butcher]

When you look at the violet color in the reaction of stannous chloride when you are testing for gold, you are actually looking at colloidal gold, the elemental metal particulars are so small you cannot see them with your eyes, the solution can actually look clear but colored, the color comes from the reflection of light off of the gold floating around in solution.

 

[iamtheman240]

Thanks for the explanation Butcher because that will be my next step. Here's my situation...I bought a (1/4 lb bar of high grade gold plated computer pins) on eBay, anyway that's what it was listed as, and may I add I won't be doing that again because of the huge amounts of nitric acid and time it took to dissolve the thing.
Once I had washed the mud (from the disolved bar) at least 4 times and let settle I added AR to it and watched in amazement as almost all of the mud turned to a rich yellow liquid. So I filtered it, added 4 times its volume of distilled water (all in all about 2 ltrs liquid) and added urea bit by bit till it wouldn't dissolve any more (no violent fizzing like I've seen on some tutorials) just a very thin stream of micro bubbles rising, that done I added 1 tsp smb...nothing, 2nd tsp...nothing, 3rd tsp...maybe something, 4th tsp...poof, liquid turns cloudy brown (I did swirl it betwean teaspoons) so I let it sit over night and the next day a thin layer of dark brown sediment sits at the bottom... But the liquid is still yellow, much lighter, but still yellow.SO...I added "more" smb a bit at a time until the water reeked... Nothing.
So I pored off the liquid from the sediment, and placed the jar of yellow liquid on a skillet with sand to evaporate (henc the earlier evaporating question)
Low and behold, when the yellow liquid was 2/3rds evaporated it started turning from yellow, to brown, so I let left it on till almost all the water was gone and just a rich brown mud remained.
That done I filled the jar with boiling water again, and in 15 mins the water was clear again with all the brown sediment on the bottom.
NOW.....QUESTION' is that brown mud...dare I ask...GOLD??????

 

[butcher]

Yes most likely it is the gold, as gold is a brown powder.

Iron can color or solution to look green (like copper), or it can color a solution yellow to look like gold.

Stannous chloride solution is your eyes, without it you are just working blind, just guessing, that is a good way to waste your gold.

You should calculate how much acid you need based on how much gold you have, and measure HCl and add it to the gold, but the calculated amount of nitric add only in very small proportions, use up all of the nitric dissolving gold with heat before adding more, the goal is to have excess HCl, but every last drop of nitric used up.

I say you did not eliminate the nitric acid in solution, urea as far as I am concerned is just too dangerous and really does not work as most people think or say it does, as far as I am concerned urea is useless to me in refining, I would give that fertilizer to my wife to put on her flowers, sulfamic acid can be used instead, if you do not control how much nitric you use, the best method to use only the amount needed, is add nitric only in very small amounts (drops toward the end, using heat at the same time to insure you are using up all of the nitric in the reaction, this way, it is simpler to deal with, evaporation can also be used, actually I begin it as I am dissolving the gold, and close to when I have the gold dissolved I have very little left to complete the first evaporation, leaving a little gold or adding a button of gold to use up the free nitric is another method, I use a combination of all of these, there are several posts that describe better, and give more detail of what I am talking about here.

 

[iamtheman240]

You got it Butcher, the grass gets the urea.
Getting back to the Sulfamic acid, is that the same stuff Home depot sells for grout cleaning?
That stuff only comes in crystal form here in Winnipeg, can you please give me an idea how strong I should mix some up to be affective, I have maybe 2 to 2.5 grams of gold powder to work with. Thanks

 

[butcher]

Trouble I see with figuring how much is you would have to know how much unused nitric you had left in solution, (not much of a way to calculate unless you already figured before you started), but if you went to the trouble to calculate you would probably have calculated how much nitric you needed in the first place and would not have overused the nitric then anyway, if you did know how much nitric was left (unreacted in solution), you could use the formula below, which shows one mole of sulfamic acid reacted with one mole of HNO3 yields one mole of sulfuric acid diluted in water and some NOx gas.

I could spend all day calculating this formula out, but I do not see much reason to do it, it is far better to calculate nitric acid needed, and use bare minimum, I also use heat to dissolve the gold, heating as I add small portions of nitric, by the time I have almost all of the gold dissolved I have concentrated the solution, basically drove water out through evaporation, and HNO3, has been reacting through the process so at this point I have very little UN-dissolved gold left in a gold chloride solution and some free HCl and no free HNO3, now I will finish concentrating the solution, which started off yellow and now is orange, at this point I can add drops of HNO3 to finish dissolving any gold I wish to, or I can leave the last bit of gold for the next batch.
Now I have very little if any free nitric acid.

If I by mistake added too much it is no problem at this point to add a few ml of HCl, and do another evaporation, doing this a couple of time to remove the free HNO3.
When working this way I can use very little sulfamic as just insurance, to be sure I have the nitric out (just sprinkling a little in from a plastic spoon) I do not normally use much at all, and I usually add it just before diluting the gold chloride with water.
I use the grout cleaner at Home depot comes in a small tub where they sell floor tiles, but if you buy grout cleaner check the label and MSDS.
Also I normally do a stannous test before I precipitate gold, this can also help to be an indicator if I still have free HNO3 in solution.


Sulfamic acid mixed with nitrous acid, gives dilute sulfuric acid and nitrogen gas
H3NSO3 + HNO2 --> H2SO4 + N2 + H2O
Sulfamic acid with nitric acid gives, nitrous oxide (laughing gas) and dilute sulfuric acid.
H3NSO3 + HNO3 --> H2SO4 + N2O + H2O