decentdude21
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Many chemicals are used for precipitating gold from aquaregia like SMBS, Hydrazine hydrate, hydrogen peroxide and ferrous sulfate. Which is best for precipitating gold with 0 loss?
Best method of precipitating gold from aquaregia?
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Martijn
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Welcome to the forum.
I like smb. It gets everything out. But you will have tiny losses in processing anyway.
H2O2 is an oxidizer.
Copperas takes a lot to precipitate gold from what I've seen.
I like smb. It gets everything out. But you will have tiny losses in processing anyway.
H2O2 is an oxidizer.
Copperas takes a lot to precipitate gold from what I've seen.
SMB or any sulfite is a winner for me. Practically non-toxic, cheap and very effective. Also easy to tell when you added enough.
Ferrous sulfate has an disadvantage - it contain iron. So when dropping gold, you inevitably introduce a lot of iron to the solution. If we take it more analytically, iron (II) oxidation is one electron process. So for one auric ion, you need 3 ferrous sulfate molecules. This reaction has very low "atom economy", as it is named these days. Simply said, you produce (alongside the product) lots of unwanted sideproducts. Which could in the end contaminate your gold.
Be aware of hydrazine. I work my life hand in hand hydrazine, because I am in organic chemistry and use it a lot as building block. Very nasty, unforgiving, toxic and explosive stuff. Which will reduce not only gold, but also other junk from the solution.
To the 0 losses... It isn´t possible to have 0 losses. Most efficient way how to precipitate metal in quantitative way is make inslouble compound, which could be filtered (like AgCl). Or you can cement the metal with more reactive metal (gold with copper etc.). You will always lost some values, mainly in washing steps of the gold powder with acid. There is practically always some minor loss, but it could be recovered from washes.
Ferrous sulfate has an disadvantage - it contain iron. So when dropping gold, you inevitably introduce a lot of iron to the solution. If we take it more analytically, iron (II) oxidation is one electron process. So for one auric ion, you need 3 ferrous sulfate molecules. This reaction has very low "atom economy", as it is named these days. Simply said, you produce (alongside the product) lots of unwanted sideproducts. Which could in the end contaminate your gold.
Be aware of hydrazine. I work my life hand in hand hydrazine, because I am in organic chemistry and use it a lot as building block. Very nasty, unforgiving, toxic and explosive stuff. Which will reduce not only gold, but also other junk from the solution.
To the 0 losses... It isn´t possible to have 0 losses. Most efficient way how to precipitate metal in quantitative way is make inslouble compound, which could be filtered (like AgCl). Or you can cement the metal with more reactive metal (gold with copper etc.). You will always lost some values, mainly in washing steps of the gold powder with acid. There is practically always some minor loss, but it could be recovered from washes.
Yes I agree a lot of Ferrous Sulphate is required to drop the gold from AR.
I once used over 2.5Kg to completely drop 22 Ounces of Au powder, never again
shruli
Active member
I prefer using vitamin C. It's safe enough to eat 
& no horrible toxic smell like SMB. I read so many posts regarding gold not dropping, I always refine twice as in vids, dirty then clean solution, & up to now
have not had that problem.
& no horrible toxic smell like SMB. I read so many posts regarding gold not dropping, I always refine twice as in vids, dirty then clean solution, & up to nowhave not had that problem.
shruli
Active member
If all material is dissolved & potassium nitrate (or nitric acid) is still strong in solution, just add water to dilute. I have never neutralized solution.
There is no "Best Method" every percipient has its own set of advantages and disadvantages.
It is best to use more than one to refine gold as they each will eliminate different impuritys.
It is best to use more than one to refine gold as they each will eliminate different impuritys.
shruli
Active member
I guess that is what happens when you dilute with water then
Diluting with water will help dropping AgCl.
It will not remove excess Nitric.
Evaporate to syrup and add HCl until there are no more brown fumes.
It may take a few rounds.
Or add Sulfamic acid HOT.
Best approach, do not add more nitric than you need.
It will not remove excess Nitric.
Evaporate to syrup and add HCl until there are no more brown fumes.
It may take a few rounds.
Or add Sulfamic acid HOT.
Best approach, do not add more nitric than you need.
decentdude21
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Thanks for reply.
decentdude21
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Thank you
decentdude21
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Thanks, I will also try it.
I prefer using vitamin C. It's safe enough to eat
decentdude21
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What is the average loss in gold refining? If we treat Aquaregia with SMBS, Vitamin C, Hydrazine Hydrate, and H2O2.
It is a bit more complicated. Remains of nitric acid are still present, but it does have much with redox potential of liquid vs. redox potential required to dissolve the gold back to the solution.I guess that is what happens when you dilute with water then
Nitric acid undergo decomposition in acidic chloride enviroment, producing mainly nitrosyl chloride and chlorine. Chlorine is very quick, reacting immediately with anything around, but also undergo slow decomposition to oxygen and hydrochloric acid (but this is minor and slow reaction). It also evaporates from reaction, mainly while still hot - removing "oxidizing force" of the juice. And alongside with NOCl, giving the AR fumes the unmistakeable "yellow" hue.
Nitrosyl chloride isn´t that powerful oxidant, and undergo quick degradation to nitrogen dioxide in AR solutions.
Also with strong solution of AR, dissolution of gold isn´t particulary quick reaction. When there are remains of "weak" AR, or better said some "oxidizing species", gold will be dissolved anyway, but VERY SLOWLY. So it buy you time to let it settle and filter the gold in usual fashion and only minor losses.
So, overall if you keep the AR hot for long periods of time, most of active oxidizers, capable of dissolving gold (mainly chlorine) will simply evaporate or dissociate into compounds, which are very mild oxidizers in terms of dissolving gold. It does not say that they cannot dissolve the precipitated gold, but it is a very slow reaction.
I personally experienced this to happen, when I just didn´t de-nox the AR solution afterwards. Gold drop appeared to be as normal as usual. Gold dropped, started to settle. Then I came back in the morning, and all gold was redissolved
so I decided to push it with more sodium sulfite. Again, gold dropped, I came next morning, and some precipitate was clearly on the bottom of the beaker, but stannous told gold presence in solution (after TWO subsequent drops). Third drop accomplished the thing, but it can illustrate how fine and long-settling are the reactions of residual nitric in AR.Similar thing happen when you denox with urea. Urea is incapable of reacting with nitric acid in a way it will be destroyed. It just form a salt. But nitric undergo decomposition in chloride enviroment as I discussed above. So the formed N(III) species like NOCl or nitrous acid finally react with urea, creating nitrogen and carbon dioxide. But also, this reaction is only driven by decomposition of nitric acid. Taking into account, that for nitric in presence of urea, it is needed to break free from the urea.HNO3 salt, settling the equilibrium takes even more time.
So it is fairly common to encounter the situation, when you take hot AR gold solution from heat, and directly treat it with urea. It will hiss with two or three spoonfuls, but then stop. That does not mean that you neutralized ALL nitric, but instead that you killed all N(III) species lurking around in the juice. There could be plenty of undecomposed nitric acid, which could be still present after "sucessfull" de-noxing with urea.
That is why we always advise to use sulfamic acid, because sulfamic acid is capable of destroying not only N(III) compounds into nitrogen, but also nitric acid to nitrous oxide. But it need to be hot to work on nitric itself.
So, dilution will help you to mitigate the re-dissolution of dropped gold, but it isn´t bulletproof and all reliable way how to do it. But if you master this way, good for you
I wouldn´t do it this way, but it could certainly work in your favor.Depends on how diligently you do your work. And also it depends on ammount of gold. Working in 100 g batch, and losing 100 mg in the process mean that your efficiency will be 99,9%. And it is all possible to accomplish this number with proper dissolution, nitric killing operation, proper settling and decantation and also with recovery of traces of gold from gold powder acid washes.
But when you work with only say 0,5 g gold, handling loss will be much greater than 0,1% - it is well known, that working with small ammounts make losses higher.
It you get out 99%+ from 1 kg of clean material running say 3g/kg (eg pins), you´ve done a good job, I would say. But with dirty stuff and lots of junk, possibilities for gold to adsorb on vast solid matrix (like leaching ashes from incinerated IC´s)... You could run as low as 80%, and you will happily throw away the ashes and remains, because stannous was negative. But if you will do the smelt and "assay-like" cupelation of the thoroughly leached ashes, you will found not-negligible ammount left behind.
It is maybe more complicated than you want to hear
but with deep knowledge of chemistry and what could possibly ruin your recovery, losses will shrink quite sharply Hope that it will help you in some way. Good luck with refining.
Stay safe.
