# Sulfamic acid



## bswartzwelder (Jun 28, 2013)

Hi All,

I finally got my order of Sulfamic acid and have a question. Firstly, I know that gold has an affinity for sulfur. It just likes the stuff. The first time I read it, I was blown away that Oxalic acid can be used to precipitate gold from solution with a very high degree of purity.

Now, onto the Sulfamic acid. When I tried to dissolve some gold (small nuggets and flakes), I made a typical newbie mistake by using way too much NaNO3. I knew I made a mistake, so I set the beaker aside until I made a decision as to which way would be the best way to get out of this mess. Hey, if it evaporates down to a syrup (three times according to Ms Hoke), that's one way to fix it. It has been several weeks now and it's really not evaporating, but I really didn't think it would at ambient temperatures. I also know that Sulfamic acid added to the solution in small increments (while stirring) will get rid of excess Nitric. I have searched the forum but have not seen this discussed anywhere. Sulfamic acid (H3NSO3) contains sulfur. Will Sulfamic acid precipitate gold? I would have thought the sulfur might precipitate gold. I do know Sulfamic acid will combine with excess Nitric acid and form a weak Sulfuric acid which helps scavenge unwanted tin and lead from the solution. At this point, I don't want to precipitate the gold, but I do want to be ready to do that soon.


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## butcher (Jun 28, 2013)

bswartzwelder.

Hello.
These are just my thoughts, sulfur dioxide gas can be made from sulfur, but it is no longer sulfur, and it will precipitate gold, H2SO4 sulfuric acid can also be made from sulfur, but it is no longer sulfur, and will not precipitate gold, just because it was made from sulfur or sulfur compounds does not mean it is sulfur, or will precipitate gold, sulfamic acid used as it is normally to de-Nox a solution of excess nitric acid will not precipitate gold, it does convert to sulfuric acid in solution.

Here are my thoughts on overuse of NaNO3 or other nitrate salts, these are not nitric acid, although if there is enough acid in solution they will take the hydrogen (H3O hydronium ions) and become nitric acid in solution.

Metals in solution are also depleting free acids in solution making ionic salts of metals in solution.

If we have a situation with more NaNO3 than we have available acid in solution the excess nitrate salts will not convert to acid, this excess nitrate salts can remain as salts in solution either dissolved or precipitated depending on solution mechanics, if we had this situation evaporation will not remove the sodium nitrate salts, as the solution concentrates some may go into solution as acid if there is free acid (or hydronium), but remember also metals if undissolved will also compete, we could cook this solution dry and still have nitrates in the powders.

I think sulfamic acid would also have a hard time removing the excess nitrates, they can somewhat, and the sulfuric formed from the reaction would convert some of the nitrate salts to nitric acid, so that more sulfamic could de-nox the free nitric, but the amount of sulfamic needed this would not work well in my opinion.

OK so if I believe evaporation would not work with an overly excess use of nitrates, and I do not think sulfamic would work that well.
How would I try to handle this situation?

I would add more acid, convert the nitrate salts to acid in solution, and then add more metals to use up this acid, with heat.

So if I had a solution and used too much NaNO3 nitrates to make the poor mans aqua regia to dissolve the gold, I would add more acid and more gold, converting nitrates salts into nitric acid (or poor mans aqua regia) and adding more gold to dissolve in the solution to consume the acids, heating to put as much metal into solution as possible, now after this I can us the normal de-noxing methods, such as evaporation, (gold addition), and sulfamic acid, to insure I have removed all of the free nitric acid (and nitrate salts from my solution).


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## g_axelsson (Jun 28, 2013)

butcher said:


> If we have a situation with more NaNO3 than we have available acid in solution the excess nitrate salts will not convert to acid, this excess nitrate salts can remain as salts in solution either dissolved or precipitated depending on solution mechanics, if we had this situation evaporation will not remove the sodium nitrate salts, as the solution concentrates some may go into solution as acid if there is free acid (or hydronium), but remember also metals if undissolved will also compete, we could cook this solution dry and still have nitrates in the powders.
> 
> I think sulfamic acid would also have a hard time removing the excess nitrates, they can somewhat, and the sulfuric formed from the reaction would convert some of the nitrate salts to nitric acid, so that more sulfamic could de-nox the free nitric, but the amount of sulfamic needed this would not work well in my opinion.
> 
> ...


I agree that with too much nitrate salts in a solution we could evaporate it until it is dry without removing the nitric ions. In the same way the sulfamic acid only reacts with free nitric acid.

You almost nailed the way to solve that problem. You shouldn't add any metal after adding hydrocloric acid, if you use up the acid you would be in the same situation again with nitric salts.
With the addition of acid we now have free nitric acid so from this point we could either do the normal evaporation - add acid cycles until we don't get any reaction. Or we could use sulfamic acid to denox the solution.
Just add a bit of HCl at the end, no reaction means there is no more nitric ions locked in a salt.

If you think of it this is what happens even when we use nitric acid. In the reaction we create nitric salts, for example copper nitrate. When we evaporate it down the nitric ions is locked in as a salt and stays in the solution (or as a solid). When we add HCl to this we add Cl ions that can take the place of the nitric ion and now we can evaporate HNO3 as a gas. We also lose HCl when evaporating so we do this several times until there is no reaction when we add HCl at the end.

I don't know exactly how sulfamic acid works as I have never used it myself but I'm pretty sure that it will work in a similar way and as long as we add enough hydrocloric acid it can denox a nitrate salt solution.

Göran


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## Wyndham (Jun 30, 2013)

I googled sulfamic acid and found places like home depot has it in 1 lb containers for about $5
Is this a good source or is it mixed with different stuff that would keep it from working.
Wyndham


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## modtheworld44 (Jun 30, 2013)

Wyndham said:


> I googled sulfamic acid and found places like home depot has it in 1 lb containers for about $5
> Is this a good source or is it mixed with different stuff that would keep it from working.
> Wyndham



Wyndham

Yes the Home Depot kind is what I use, you'll need a pry tool to open it with, since the seal is made like a five gallon plastic paint bucket.You can use it dry but if you do, you'll definitely have to filter the AR afterwards because it leaves granules behind.



modtheworld44


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## Wyndham (Jun 30, 2013)

Great, nice to find an easy supply of something.
Wyndham


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## 4metals (Jun 30, 2013)

The sulfamic acid will get rid of excess nitric acid and release nitrogen gas or nitrous oxide (AKA laughing gas)

With HNO2, sulfamic acid reacts to give N2, while with HNO3, it gives N2O.

HNO2 + H3NSO3 → H2SO4 + N2 + H2O
HNO3 + H3NSO3 → H2SO4 + N2O + H2O

But the old rule still applies, at all costs avoid excess nitric acid to begin with.


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## goldsilverpro (Jul 1, 2013)

To eliminate 1 liter of nitric acid, it would take about 3.4 pounds of sulfamic acid - a little over 1.5g/ml. That's a lot. Another reason for not using too much nitric.


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## lazersteve (Jul 1, 2013)

A secondary benefit of sulfamic acid is that there is no need to add any sulfuric acid to scavenge any dissolved lead from the pregnant solution. As 4Metals equations show, the sulfuric acid is produced in situ when using sulfamic acid to remove excess nitric acid.

It's great stuff.

Steve


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