SO2 gas reduction

[DIY5050]

No matter what I do I keep getting hit by SO2 gas when I drop the gold from AR. I have used so little nitric that I leave gold in the bottom and filter it out. I tried reducing it down and re-hydrate it with HCL. It doesn't matter if it was karat scrap, or gold filled. I have added SMB and I never see the foam but I stop adding and stannous test in between additions. Every time I pour off the waste, the SO2 just likes to knock my (enter foul words here) in the dirt.
Now my fume hood is a problem. I am trying to get the venturi to do the job, but even when using an in-line fan, same problem. I never smell the nitric, or the AR. I am shutting down my operation now that I have nothing in the hood to complete. Go back to the drawing board on the hood vent. I just don't understand how to stop producing so much SO2 at this point. Am I just sensitive and that's what it is, or am I messing up?

 

[Yggdrasil]

No matter what I do I keep getting hit by SO2 gas when I drop the gold from AR. I have used so little nitric that I leave gold in the bottom and filter it out. I tried reducing it down and re-hydrate it with HCL. It doesn't matter if it was karat scrap, or gold filled. I have added SMB and I never see the foam but I stop adding and stannous test in between additions. Every time I pour off the waste, the SO2 just likes to knock my (enter foul words here) in the dirt.
Now my fume hood is a problem. I am trying to get the venturi to do the job, but even when using an in-line fan, same problem. I never smell the nitric, or the AR. I am shutting down my operation now that I have nothing in the hood to complete. Go back to the drawing board on the hood vent. I just don't understand how to stop producing so much SO2 at this point. Am I just sensitive and that's what it is, or am I messing up?

I'm not entirely sure what you mean.
The SO₂ is what drops the Gold.
It is released when the SMB hits a sufficient acidic condition.
Nitric or no Nitric.
Of course over using it will create more of it.
If you make a saturated solution of SMB and water,
you can pour it into the pregnant solution and it will probably release less gas.

 

[4metals]

Try dropping your gold with ferrous sulfate. No stink. Then collect the precipitate and re-dissolve it in aqua regia (usually there is much less acid so easier to deal with). And drop the re-dissolve with SMB. Much less chemistry used so easier to divert the smell.

Of all the chemicals in refining, Sulfur Dioxide will definitely put you on your knees if you’re not careful!

 

[DIY5050]

I'm not entirely sure what you mean.
The SO₂ is what drops the Gold.
It is released when the SMB hits a sufficient acidic condition.
Nitric or no Nitric.
Of course over using it will create more of it.
If you make a saturated solution of SMB and water,
you can pour it into the pregnant solution and it will probably release less gas.

Ahhh that's why I have seen some do that. I will give that a try. Thanks

 

[eaglekeeper]

Now my fume hood is a problem.

When ever you have chosen your fume hood design, there is a way to visually test it to find any dead area's.
Get a small metal container and put in a piece of a smoldering oily rag. Let the hood fill with smoke, then turn on the fume hood. The smoke can show you where your hood needs attention. You can also use the smoke outside of the hood to see how/where your hood is drawing in fresh air.

Keep in mind that some fumes are heavier than air and will settle at the bottom of the hood. So if your hood draws air from the top it makes it hard to evacuate the fumes at the bottom.

 

[DIY5050]

I'm not entirely sure what you mean.
The SO₂ is what drops the Gold.
It is released when the SMB hits a sufficient acidic condition.
Nitric or no Nitric.
Of course over using it will create more of it.
If you make a saturated solution of SMB and water,
you can pour it into the pregnant solution and it will probably release less gas.

My friend, I cannot thank you enough. The thought of how much SMB I was wasting, no wonder. Making a solution also gives me a stopping point when I see the reaction of the pregnant AR turn brighter. I was dropping spoon full and waiting for a reaction.

 

[DIY5050]

Try dropping your gold with ferrous sulfate. No stink. Then collect the precipitate and re-dissolve it in aqua regia (usually there is much less acid so easier to deal with). And drop the re-dissolve with SMB. Much less chemistry used so easier to divert the smell.

Of all the chemicals in refining, Sulfur Dioxide will definitely put you on your knees if you’re not careful!

I don't know why I missed this. Isn't Ferrous Sulfate copperas? It doesn't create more waste water. I am guessing you mean first recovery use the ferrous, then the second round, where there is much less junk is in the material? I was worried about the waste water amount with this method, but it is something to try regardless.
I fixed the fume hood and seems to be performing much better. Just a few more tweeks needed.

 

[4metals]

Be selective when you acquire your ferrous sulfate. You want to find ferrous sulfate that is hydrated and the crystals should look like the photo below. Sometimes it is tan colored to light brown as it is old. That off color stuff just makes a mess. You want the green.

Some time back Butcher posted his method for making his own ferrous sulfate. I haven’t been successful today finding that post but I will keep looking.

 

[4metals]

Found it. This was originally posted by Butcher, moderator and contributor extraordinaire.

Copperas, ferrous sulfate, iron II sulfate, FeSO4, green vitriol, is easy to make from dilute 10% H2SO4 sulfuric acid (sulfuric acid can be found in automotive battery acid or some drain cleaners) and Iron metal (a good source of soft iron is from your old transformers, the iron laminates from the electronic scrap pile).

You can use crystals of copperas to test for gold in the solution, or you can use your homemade copperas to selectively precipitate gold from the solution.

copperas is a reducing agent. helpful in our processes, for example, besides reducing gold selectively from a gold chloride solution, copperas is also helpful as a reducing agent in solution where it is helpful in reducing the free nitric acid in solution to nitrogen monoxide gas and or the chlorine gas to chlorides, heat is helpful as always in removing gases from the solution...

6 FeSO4 + 3 H2SO4 + 2 HNO3 --> 3 Fe2(SO4)3 + 4 H2O + 2 NO

6 FeSO4 + 3 Cl2 → 2 Fe2(SO4)3 + 2 FeCl3