Sulfamic acid

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bswartzwelder

Well-known member
Joined
Oct 24, 2011
Messages
660
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.
 
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).
 
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.

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).
Click to expand...
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
 
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 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
Click to expand...

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
 
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.
 
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.
 
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
 
Sunnyket said:
What if
We use proper equal amount of nitric to dissolve gold
And there is no excess nitric in that case we need to use sulphamic?
Click to expand...
It is somewhat tricky to use right ammount, and it takes too much time sometimes. Good technique is use less, then pour pregnant liquid and dissolve the rest. Little bit of nitric isn´t that catastrophic, SMB will kill it before dropping the gold, but the solution should be at least hot to the touch, otherwise reaction of nitric and SMB can have long induction period and liquors can eventually erupt gasses.

Convenient way is to make slurry of SMB (does not need to be dissolved truly), stir the pregnant hot liquid vigorously and pour the slurry in at rate that manage the controlled reaction.

Thing is, you does not need to de-NOx specifically with sulfamic acid, sulfite or SMB can do it too, but they are basic. This means, you are neutralizing your acid to begin with. Sulfamic acid is acidic. Of course, you can add more acid at beginning of gold drop :D there are many possibilities...

Cheapest de-NOxing agent and gold reducer is sodium sulfite. You grab still hot AR solution, make sulfite slurry and slowly pour it in with stirring. Be careful as reaction can be vigorous with eruption of gas - if you have excess nitric in. Do not use dry powder, as it is very wasteful technique. Particles of sulfite/SMB will start to hiss and are taken to the surface by the generated bubbles. This means, you will spend the acid in the place of contact, and simultaneously waste active reagent to the air - SO2. Slurry reacts under the level of liquid, so the SO2 generated is really adsorbed to the liquor. This works only when not overwhelming excess of nitric was used. Otherwise, it will take unhealthy ammount of SMB/sulfite to do this and that will severly deplete free acid in the juice. Causing silver or orther chloride resdues to come out of solution.

Of course, you will need to re-refine obtained gold. But it is much quicker than other techniques.
 
Sunnyket said:
What if
We use proper equal amount of nitric to dissolve gold
And there is no excess nitric in that case we need to use sulphamic?
Click to expand...
That was what I said.
If you use only the amount of Nitric needed or just a little more.
The SMB will take care if it, no need to use Sulfamic.

Orvi gave you some good advice, in the small scale it is practical to use the correct amount, if you are going bigger it gets more complicated as time becomes an driving factor.
 
Sunnyket said:
What if
We use proper equal amount of nitric to dissolve gold
And there is no excess nitric in that case we need to use sulphamic?
Click to expand...

Yggdrasil said:
That was what I said.
If you use only the amount of Nitric needed or just a little more.
The SMB will take care if it, no need to use Sulfamic.

Orvi gave you some good advice, in the small scale it is practical to use the correct amount, if you are going bigger it gets more complicated as time becomes an driving factor.
Click to expand...
It also depends in what form the gold is. If it is chunky, or shot to the water, than yes, you will need AR boiling to dissolve it. On the other hand, if it is gold precipitate from say SMB reduction, you does not need nitric at all. Acquire hydrogen peroxide and go with it. No de-NOxing needed afterwards. Just let the beaker with hot liquid open for few minutes and all chlorine and oxygen just escape out. And if not, SMB will very easily kill the chlorine in order of miliseconds :)
 

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