TOO MUCH SMB

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ARMCO

ARMCO

Well-known member
Supporting Member
Joined
Jul 4, 2017
Messages
108
I have had a problem with adding to much sodium metabisulfite (SMB) and the AR going dark and then changing to light green or yellow. I can never seem to recover after that. What is happening?


1. It is usually when I have refined or leached something and I don't know how much gold is likely there. My understanding is that you can use the same amount of SMB in grams as the amount of gold you have in solution, but as I said, I don't know how much is there.

2. The gold concentration is too low and I should probably be evaporating and storing it to add to something else later.

3. There was more nitric acid than I thought and the solution chews up alot of SMB and then all of a sudden I've added too much. I've used urea to try to kill the nitric acid but I think I'm doing something wrong there because it doesn't work. I'll add carefully until the urea doesn't react anymore but the gold continues to redissolve when SMB is added, and then, poof!, too much and yellow/greenish fluid.

Questions:

1. Can anyone tell me what is happening chemically when too much SMB causes the gold that appears to be coming out of solution all of a sudden re-dissolves and I end up with this light yellow to green solution? That solution will test positive for gold with stannous chloride (if you add more drops than usual to the test solution) so the gold is still there but it hasn't precipitated and it's like it's hiding in the solution now.

2. Is there a way to recover if this happens? What should one do next if this happens? I've tried alot of things with no success.

3. If there is excess nitric acid, what are some ways to neutralize it and get the solution ready for dropping the gold? I know it would be best to only add juuuust enough nitric acid so there is not a lot of excess. But if it does happen, what are some ways that work well to kill the excess before adding the SMB?

I have successfully refined with AR; placer gold of at least an ounce or more; inquarting (about two ounces of pure gold yield), and others, but always there was a significant concentration, it was very clean to start with, and and storm precipitation was very suddenly evident, dramatic, and easy. No real risk of overdosing the SMB was present in those cases. But every time I've worked with a real dirty sample (leaching black sands for example) and the actual concentration/quantity of gold was questionable I end up overdoing the SMB and can never seem to recover from there.

Open to feedback and suggestions.

Thank you very much
 
Sounds like too much nitric.
Add in small increments and practice patience, Not adding more until the previous addition has reacted fully.

You can ALWAYS cement on copper. Basically stick in some clean copper bus bar, or tubing that is split open or hammered flat and let it replace the gold ions in solution with copper ions. The gold will be fine black powder.

Best way to get rid of excess nitric (besides not using it), is sulfamic acid. It removes nitric, unlike urea, and in doing so, it will convert lead chloride to insoluble lead sulfate, which can be filtered off with the AgCl before precipitation.
 
You're right about the needing to practice patience part. But part of the problem is trying to leach black sands. Don't know how much is just right so always end up with too much. I am trying a much weaker leach over a much longer amount of time (hey! I'm practicing patience! whaddyaknow? lol).

I've heard of sulfamic acid but never used it. Thanks for the response.

Can anyone tell me what is happening chemically when you add too much SMB?
 
You have divalent metals in solution along with the gold.

When dropping with any sulfite type you will initially drop the gold, the solution shows the familiar brown precipitate.

The divalent metals are still present at their higher valency and they will now re-oxidise the gold back into solution.

This effect is enhanced by the massive surface area per unit weight of the precipitated gold.

The solution colour will now be dominated by the colour of the lower valency metals in solution.

If you have several divalent metals in solution you will see a progression of colours as more sulfite is added and the divalent metals are, in series, reduced to their lowest valency.

If you continue to add sulfite in what seems to be massive amounts you will finally reduce all of the divalent metals to their lowest valencies and start to drop the gold in a solution which,cause it has no oxidisers of any type left, will finally allow the precipitated gold to act as you would initially expect.

As you approach this point you will see orangeish colors form around the solid sulfite as it is added to the solution, this is an indication that there is still gold in solution.

It is important that you add an excess of sulfite to prevent re-oxidation of the reduced divalent metals by oxygen from the air and thus get further redissolution of the gold.

The solution levels of this redissolved final stage gold are any where from a fraction of a ppm to several ppm in solution.

Take into account that 1 ppm gold in solution has 1 milligram of gold per litre and you see that the amounts of gold losses are small but still present.

This effect is caused purely by divalent metals acting as oxidisers and is a separate effect to having nitric present even though the result in terms of gold losses is similar.

Deano
 
Deano said:
You have divalent metals in solution along with the gold.

When dropping with any sulfite type you will initially drop the gold, the solution shows the familiar brown precipitate.

The divalent metals are still present at their higher valency and they will now re-oxidise the gold back into solution.

This effect is enhanced by the massive surface area per unit weight of the precipitated gold.

The solution colour will now be dominated by the colour of the lower valency metals in solution.

If you have several divalent metals in solution you will see a progression of colours as more sulfite is added and the divalent metals are, in series, reduced to their lowest valency.

If you continue to add sulfite in what seems to be massive amounts you will finally reduce all of the divalent metals to their lowest valencies and start to drop the gold in a solution which,cause it has no oxidisers of any type left, will finally allow the precipitated gold to act as you would initially expect.

As you approach this point you will see orangeish colors form around the solid sulfite as it is added to the solution, this is an indication that there is still gold in solution.

It is important that you add an excess of sulfite to prevent re-oxidation of the reduced divalent metals by oxygen from the air and thus get further redissolution of the gold.

The solution levels of this redissolved final stage gold are any where from a fraction of a ppm to several ppm in solution.

Take into account that 1 ppm gold in solution has 1 milligram of gold per litre and you see that the amounts of gold losses are small but still present.

This effect is caused purely by divalent metals acting as oxidisers and is a separate effect to having nitric present even though the result in terms of gold losses is similar.

Deano
Click to expand...

I appreciate you taking the time to give that thorough and interesting explanation. I have had to spend some time reading and refreshing my chemistry. And I will be doing some experiments as well.

Again,

You took the time to respond. Time is the one commodity that is more precious than our precious metals. And I thank you for your time.

Sincerely,
Scott
 
One extra point is that when you have reached the end point of the sulfite addition as measured by the disappearance of the orange colour around the solid sulfite addition, you will be presented with the phenomenon of the entire solution bubbling SO2 gas.

This will happen for several hours even though you are not adding further sulfite.

It is caused by the sulfite in solution reacting with both residual divalent metals still in the higher valency and divalent metals which are being oxidised up to the higher valency by the oxygen dissolved in the solution.

In the end the dissolved oxygen will have been consumed and the cycle will stop, presuming that the residual metals have been reduced.

While the gold is slowly precipitating overnight there will be some small level of adsorption of oxygen from the air and there will form a equilibrium state between the oxygen from the air oxidising the metals to higher valencies and so oxidising some of the gold back into solution and the sulfite in solution reducing this newly oxidised gold back to metallic form.

This equilibrium will maintain low gold levels in solution but these levels are not significant in litre sized batches.

Deano
 
Deano said:
This equilibrium will maintain low gold levels in solution but these levels are not significant in litre sized batches.
Click to expand...
And this is why we love you, Deano. Excellent explanation!

And also an excellent reason to put your "barren" liquors in a stockpot! :wink:
 
ARMCO said:
You're right about the needing to practice patience part. But part of the problem is trying to leach black sands. Don't know how much is just right so always end up with too much. I am trying a much weaker leach over a much longer amount of time (hey! I'm practicing patience! whaddyaknow? lol).

I've heard of sulfamic acid but never used it. Thanks for the response.

Can anyone tell me what is happening chemically when you add too much SMB?
Click to expand...
Leaching black sands is a HUGELY difficult prospect because you have no idea what other metals are present, how much sulfide there is, and what other minerals are there which could also react and produce unexpected complexes.

Smelting is best with black sand concentrates. Otherwise, for SMALL amounts of black sand, you CAN use HCl to remove a fair amount of junk... but it takes quite a long time and uses a lot of HCl.
 
Yggdrasil said:
What is this question aimed at?
There has been no discussion regarding Sulfamic here??
Ask questions in related threads please.
Click to expand...
Hi there, I was going through this conversations. Somewhere on top there is a thread suggest to use sulfamic acid its better solution to denox nitric than urea. If you don't mind could you guide me on this appreciate your kind assistance.

Firstly I might have to much nitric in my solution therefore I try to denox with urea. I had to use few spoons to denox but It result to never ending bubble. So I decided to start precipitate some gold with smb unfortunately fail. However I have already test the solution with stannous chloride it has a good volume of gold. Therefore I don't understand what went wrong my solution is filled with smb now.
 
Jesudass said:
Hi there, I was going through this conversations. Somewhere on top there is a thread suggest to use sulfamic acid its better solution to denox nitric than urea. If you don't mind could you guide me on this appreciate your kind assistance.

Firstly I might have to much nitric in my solution therefore I try to denox with urea. I had to use few spoons to denox but It result to never ending bubble. So I decided to start precipitate some gold with smb unfortunately fail. However I have already test the solution with stannous chloride it has a good volume of gold. Therefore I don't understand what went wrong my solution is filled with smb now.
Click to expand...
It is getting harder to find information here.
There are at least three reasons for that.
One is the shear number of threads.
Two is our policy of not deleting threads/posts
Three is the highjacking posting in unrelated threads.

Well back to you😏
It is always much easier to give a good answer to people who quote the origin/cause of their question of the same reasons I mentioned.

Answer:
I have not used Sulfamic acid at all, it is my understanding though that most people buy Sulfamic acid as a solid and use straight or dissolves to a saturated mix before use.
It has to be used hot, around 80 Centigrade to work.
Search the forum and you will find it.
 

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