I would just add that reaction of sulfamic acid with nitric acid starts around 75-80 °C, but it is wise to heat it past this temperature to speed up the process. Timed additions are necessary to see if the nitric/NOCl/nitrous acid are still present.
Easily said for Gold.refinery:
Generally, you add sulfamic acid similarly as urea - heat the solution to at least 80 °C, add sulfamic SLOWLY until it stop fizzing (not to foam over), then you wait at least 15 minutes - or better 30 minutes and add little ammount and observe if there is some fizzing. If it still reacts, add more and repeat the waiting step.
Be aware of the fact, that fizzing liquid in open beakers or reactors create aerosols, which carry your gold solution away. Best is to prevent this by using larger container, so liquid is well below the top of the vessel and popping bubbles cannot shoot the liquid out of the vessel
Both reagents (SO2 and SMB) smell like SO2, because SO2 is formed from SMB when reacting with acid in solution. SO2 gas coulld be very well regulated and bubbled from the cylinder - very very convenient. You can set up, open the valve and happily observe how the solution is losing the yellow colour while gold settle to the bottom And you will see with stannous how much gold you have in solution - so you adjust the next addition of gas.
Also, there is another advantage of using SO2 gas over metabisulfite. With sodium metabisulfite, you consume one equivalent of HCl to generate active SO2 gas - which actually reduce your gold.
SO2 is already an acidic gas - so it does not deplete your acid.
If the acid is depleated (concentration/strength goes down), impurities like silver chloride or copper (I) chloride become less soluble and drop together with gold.
That is why SO2 gas produce cleanest precipitate of gold. As established refinery, I would suggest to invest and purchase SO2 gas cylinder. It can be regulated very well, do not add contaminants, easily added to the solution via tube...
We need some photos or details about your scrubber - if it can scrubb the NOx gasses, I think it will scrubb also SO2 gas. Or there can be added simple NaOH bubbler at the end of your system - which catch like 90% of SO2 in first pass. And that would be enough to reduce the smell.
Easily said for Gold.refinery:
Generally, you add sulfamic acid similarly as urea - heat the solution to at least 80 °C, add sulfamic SLOWLY until it stop fizzing (not to foam over), then you wait at least 15 minutes - or better 30 minutes and add little ammount and observe if there is some fizzing. If it still reacts, add more and repeat the waiting step.
Be aware of the fact, that fizzing liquid in open beakers or reactors create aerosols, which carry your gold solution away. Best is to prevent this by using larger container, so liquid is well below the top of the vessel and popping bubbles cannot shoot the liquid out of the vessel
I know so2 creates the best gold Sediment.
Is the smell of sulfur created by so2 gas Sedimentation more or by SMB?
Now, We have food grade SMB available.
If we want to use SMB to deposit gold in the next operation, what points should we follow?
For example, what is the ratio of adding smb to gold? (Helps for less gas and less pollution of gold dust).
Do we have to dissolve it with water and add it or can it be added solid?
In terms of time, how long does smb deposition take (compared to hydrazine)?
Both reagents (SO2 and SMB) smell like SO2, because SO2 is formed from SMB when reacting with acid in solution. SO2 gas coulld be very well regulated and bubbled from the cylinder - very very convenient. You can set up, open the valve and happily observe how the solution is losing the yellow colour while gold settle to the bottom And you will see with stannous how much gold you have in solution - so you adjust the next addition of gas.
Also, there is another advantage of using SO2 gas over metabisulfite. With sodium metabisulfite, you consume one equivalent of HCl to generate active SO2 gas - which actually reduce your gold.
SO2 is already an acidic gas - so it does not deplete your acid.
If the acid is depleated (concentration/strength goes down), impurities like silver chloride or copper (I) chloride become less soluble and drop together with gold.
That is why SO2 gas produce cleanest precipitate of gold. As established refinery, I would suggest to invest and purchase SO2 gas cylinder. It can be regulated very well, do not add contaminants, easily added to the solution via tube...
We need some photos or details about your scrubber - if it can scrubb the NOx gasses, I think it will scrubb also SO2 gas. Or there can be added simple NaOH bubbler at the end of your system - which catch like 90% of SO2 in first pass. And that would be enough to reduce the smell.