Little Problem

Hello guys,
I have a little problem with one AR batch of CPUs I did.
Most everything dissolved well (a few pieces weren't all dissolved) but now I'm at the precipitation stage and gold doesn't seem to want to come out... I added a lot of urea and about 10 g. of SMB (expecting 3 grams of gold). Unfortunately for me, I do not have a gold testing solution anymore...

My question is, can I use Dibutyl Diglyme to extract any gold or will it interact with SMB and Urea ??

Thanks

It won't react. Shouldn't at least.

Personally, I never add urea to deNOx. It doesn't actually destroy nitrate anion, it destroys nitrogen oxides. That's why I can add a heaping teaspoon of urea to red fuming 98% nitric acid and making it clear in color. It's still high strength nitric, it's just decolorized because all of the dissolved NO2 is gone. Just my $0.02. Oh wait, you're Canadian...so it's actually less for you

Thanks for your one cent Lou.
But still, when you add urea, you get rid of the nitric acid right ?

I'll add dibutyl tonight.

I personally don't think so; I mean I do not know for sure how it behaves when it's an aqua regia solution, but I know urea does not destroy nitric acid, it just ''deNOxes'' it. I think that might be the problem, because if you still have free NO3- you still can have nitrosyl chloride, NOCl, and that's what makes your aqua regia, well, aqua regia.

This gives an adduct, precipitate. Be carefull it's an explosive.
Therefore on adding water it returns to HNO3 - like Lou said.

i just want to bring that post up... this morning i have had a monstruous boil over( way over my catching pan) that cost me a lot of money and i think that is the cause... if urea dosent destroy nitric is theyr an other chemical that can do the trick?

watch the amount you use if you use nitric acid make sure its been diluted. the close calls I've had have always been with 70% nitric, reaction is on fast forward, but water has always helped.

Eric

Sometimes there is so much excess nitric in solution that the evaporation method or urea isn't feasible. The best thing to do is add small additions of base metal until its exhausted. If it’s a gold bearing solution use copper. I don't know exactly what urea does to nitric but it definitely doesn’t get rid of the nitric. I once heated a beaker with solution that was "neutralized" with urea and had gold precipitated on the bottom. I wanted to see if gold could be further cleaned by boiling the solution in the same HCl that it was precipitated in. After the solution heated a while the gold actually went back into solution and the familiar red fumes evolved. So I'm under the impression that urea can be boiled off. The nitric is still in solution alive and well.

Cement it with copper?. You are going to re-refine anyway. :idea:

I always thought urea was used because urea is soluble in water and urea nitrate is also soluble in water. are you sure it doesn't react with the nitric?
"Urea nitrate is produced in one step by reaction of urea with nitric acid", "(NH2)2CO (aq) + HNO3 (aq) → (NH2)2COHNO3 (s)" - http://en.wikipedia.org/wiki/Urea_nitrate
granted, wiki is not the world's most reliable source, but it is often a good one.

As for redissolving gold, what about pour man's nitric?
As I understand it, (sodium nitrate + HCl + heat) will dissolve gold
I would expect (potassium nitrate + HCl + heat) to also work
what about (urea nitrate + HCl + heat) ?

that also my opinion

urea nitrate is composed. it is fully dissociated in solution as carbamide protonized on oxygen and nitrate anion.

i also observed that when you heat up solution that was deNOxed with urea and then for example heated up or only put under UV, it can dissolve precious metals

there are bubbles( can be various gasses),when you cover the beaker brownish fumes, and high oxidizing power

i think that in highly acidic solution it can easily compose NOCl from a nitrate of urea

i use method of reheating solution when i drop not known lot of gold from dirty solutions deNOxed with urea with high SnCl4 content with SMB.some of SnCl4 is reduced to SnCl2 and colloidal gold appears.this reheating reoxidize all metals due to urea nitrate decomposition with nitrosyl chloride as a product.then i drop remaining gold ( not more than 1 g / litre) with minimal mass of SMB to prevent SnCl4 - SnCl2 reduction

this is only my opinion, i really dont know exact mechanism

What I understand at this point, is the urea destroys HNO2 nitrous acid, and NOx gases in the acid like NO2 nitrous acid from decomposition of nitric in solution, it does not destroy the nitric acid HNO3, but like other's here have stated it can also make the explosive compound Urea nitrate if too much is added into a solution of nitric acid, which can also decompose later in solution if conditions change, or if urea was used improperly could form some dangerous salts to be incinerating with metal powders.

The idea of using urea from my understanding was you did not have much free nitric acid in left in solution as it decomposed to HNO2 and other nitrous oxides in solution, and the urea would remove the HNO2 in solution as well as other nitrous oxides, its use was not meant to destroy nitric acid (although this is what many authors of instruction on its use, claim it does).

With knowledge gained from this forum I really see no reason anyone would need urea, except for maybe a few prills used for testing for free nitric in solution.

theres a few equlibrii depending on various factors

solubilized NOx gases react with water to compose HNO2 and HNO3
HNO3 and HNO2 decomposition
urea reacts with HNO2 composing nitrogen, carbon dioxide and ammonia cation NH4+. HNO2 is composed by reaction of NOx with H2O
etc etc...

NOXX, i would suggest you to drop all values with zinc (dont like copper cementing because of very fine, almost colloidal particles) and reset the conditions with proper values
before this step i would suggest you to heat the solution enough to start reoxidation to highest ox. state of all metals, then pH adjust, zinc,redissolve with minimal volumes of acids and drop
this will reduce salinity of your solution and possible NOCl composition

Sucho, I was hoping you would go into more detail of the Etcetera.
guess I will just have to do the research on my own?
:lol:

well butcher :lol:

CO(NH2)2 + HNO2 + H+ ----> N2 + CO2 + NH4+ + H20

this is prooved by Pd dissolved in AR and deNOxxed with urea.after heating a sol to 80 degrees celzius for 20 minutes and let it cool down ( solution sit for few days before this procedure of reheating and no crystals) quite pretty (NH4)2PdCl6 crystals appeared ( beautiful shape, largest about 1 mm )

this procedure also prooved that Cl2/NOCl has to be produced.in a case of first reaction ( we have all HNO2 and NOx fumes away ), NO3- anion from urea nitrate (fully hydrolyzed) goes back into a reaction with hydrochloric acid and it reacts with a production of Cl2/NOCl.this can be also reached by UV(4 HNO3 → 2 H2O + 4 NO2 + O2)

from AR nature

HNO3+3HCl->NOCl + Cl2 +2H20
2NOCl -> 2NO +Cl2
3NOCl + 2H2O = HNO3 + 2NO + 3HCl
4 NO + 3 O2 + 2 H2O → 4 HNO3
2NO + O2 -> 2NO2
2 NO2 + H2O → HNO2 + HNO3
3 HNO2 → HNO3 + 2 NO + H2O


//chemists and wise people of this problematics, please add your piece of wisdom :roll:

Nice work, I like it,
No wisdom here from me, just some comments.

I think we have to take into account many of these gases leave the reaction vessel as they are forming, depending on temperature, concentration, acidity, metals involved, and which of these gases and reactions have formed salts of metals in solution or have depleted in solution, from the reactions involved, many of these reactions further pushing gases out of solution, or forming soluble metal salts in solution, in reality the equations would be much more complicated to write, or explain than in a simple equations.

In solution from your equation of urea and nitrous acid, what I find interesting is after we take away the gases produced we would form some ammonium chloride in our gold chloride solution, when urea was used.

Also the lower batch of equations ("aqua regia nature"), your equation seems to suggest nitric acid reforming in solution, this also would depend on which of these gases are leaving solution, temperature concentration how the metals in solution were reacting with acids and other factors, several of those reactions would occur out of the solution, example NO gas leaving solution into the air above the reaction forming NO2 gas, mixing with humidity in the air to form nitric acid.

Although we can write these equations for a few of the gases and how they react with each other (not considering other reactions in solution or metals), like how urea reacts with HNO2 alone, it is hard to use these equations to show all of what is actually happening in a more complicated solution of metals and several of these reactions happening simultaneously in solution, example we not only have HNO2 and urea in solution but also gold and HCL in solution and other reactions occurring, and several of these gases leaving solutions, and what is happening at different acidity levels or concentrations of solutions, the equations would be very hard to write.


Sucho, you have done a good job of showing how the reaction may occur, keep up the good work, I like it.

Very informative and interesting!