Layer forms after gold drop w/SMB

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JimEarns

Member
Joined
Mar 30, 2021
Messages
5
I’ve seen this happen maybe twice before in the 10+ years I’ve been doing karat scrap refining. Any ideas as to what is happening here?

My best guess is either platinum metal groups OR leftover base metals separating from the gold after settling? I have a healthy amount is gold settled out on the bottom after the solution has been left alone for about 8 hours. The layer in question is about 1/2” thick and right at the top. This is the second refine of this particular batch using SMB.

In the past, I’ve simply poured this off into my gold waste solutions and proceeded as normal with my gold washing. Thanks in advance.
 

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I would like to share a hypothesis regarding gold refining and would appreciate your insights and feedback. Please note that I don't possess extensive experience in this field, so your expertise would be invaluable.

Hypothesis: I propose that tiny gold particles could be adhered to gas bubbles, specifically sulfur dioxide from the SMB (Sulphuric Acid + Sodium Metabisulfite) process, resulting in their ability to float.

Reasoning:

  1. Optical appearance: Upon visual examination, the layer in question appears to contain precipitated gold. This suggests the potential presence of gold particles.
  2. Density: As we know, gold is denser than the solution in which it is present. Therefore, if gold particles were to float, it would imply their incorporation with a substance less dense than the liquid. In this case, gas bubbles, such as sulfur dioxide, could potentially provide buoyancy to the gold particles.
It could be, that the Gold has an unusual oxidation state. One of those that are quite unstable but do sometimes occur and the sulfur dioxide is attracted by this special Gold type, tries to reduce it. It will adhere to the Gold until the Gold is reduced to its typical oxidation state.
So if you wait a little, that floating Gold may also sink down to the bottom as well. That could confirm this theory.
 
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I would like to share a hypothesis regarding gold refining and would appreciate your insights and feedback. Please note that I don't possess extensive experience in this field, so your expertise would be invaluable.

Hypothesis: I propose that tiny gold particles could be adhered to gas bubbles, specifically sulfur dioxide from the SMB (Sulphuric Acid + Sodium Metabisulfite) process, resulting in their ability to float.

Reasoning:

  1. Optical appearance: Upon visual examination, the layer in question appears to contain precipitated gold. This suggests the potential presence of gold particles.
  2. Density: As we know, gold is denser than the solution in which it is present. Therefore, if gold particles were to float, it would imply their incorporation with a substance less dense than the liquid. In this case, gas bubbles, such as sulfur dioxide, could potentially provide buoyancy to the gold particles.
It could be, that the Gold has an unusual oxidation state. One of those that are quite unstable but do sometimes occur and the sulfur dioxide is attracted by this special Gold type, tries to reduce it. It will adhere to the Gold until the Gold is reduced to its typical oxidation state.
So if you wait a little, that floating Gold may also sink down to the bottom as well. That could confirm this theory.
With very thin foils and special forms, that may host gas the loss of weight by buoyancy can cause floating meaning being lighter then water. Also surface tension of water floats gold which is hydrophobic
 
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I’ve seen this happen maybe twice before in the 10+ years I’ve been doing karat scrap refining. Any ideas as to what is happening here?

My best guess is either platinum metal groups OR leftover base metals separating from the gold after settling? I have a healthy amount is gold settled out on the bottom after the solution has been left alone for about 8 hours. The layer in question is about 1/2” thick and right at the top. This is the second refine of this particular batch using SMB.

In the past, I’ve simply poured this off into my gold waste solutions and proceeded as normal with my gold washing. Thanks in advance.
Sreetips make a point in many of his videos that you should torch your scrap to prevent random organic contamination of your AR solution.

With a layer like that I would take a sample and see if it is able to be precipitated with the help of some detergent or volatile solvent.

There should be very little gas after rinsing.

Intriguing.
 
I see this when one of 2 situations exists.
1) my SMB has begun to clump.
2) excess Sulfamic acid crystals are in the solution.

In either case I simply pour the solution back and forth between 2 beakers and allow all of the suspended particles to settle.

I believe that is just Au trapped in gas bubbles that are slowly being released by the excess/clumped chemical that is mixed in with the Au powder that settles quickly.

Crushing up smb clumps prior to use and adding extra water + heat to dissolve the excess Sulfamic crystals prior to adding smb are other possible work around to avoid this.

Overall it's not unusual or a serious problem.

Steve
 
Interesting discussion with several different causes described, as well as how they can be fixed and prevented. Then I also learned a lot from your wise explanations, today again :). This is a wonderful forum with so many incredibly knowledgeable people. In summary, in my eyes @goldenchild hit the bullseye with his response:
Suspended gold.
Which was then elaborated further in detail by the rest of you.
Thanks for your knowledge everyone.
/Dennis
 
This just occurred with me also. I had a perfect gold drop using SMB - I then decanted the excess solution and then slowly added boiling hot water to the gold mud. Then, surprisingly, most of the gold precipitant floated on the surface of the hot water. I followed lazersteve's advice and poured the solution back and forth between 2 beakers and allowed all of the suspended particles to settle. Worked like a champ! Thank you.
 
If your stannous test didn't indicate a platinum group metal there's probably none.
I have this happen with gold and silver every once in a while, silver floats often while I am washing out nitric and very often when washing my powders after sugar/lye conversion so I just mist it with water and it will sink.
Have you tried spraying to with water to see if it will settle?
 
A couple of things:
1) A stannous test was negative for any PGMs after the SMB gold drop
2) There may have been a trace of baking soda in my hot water beaker
3) The floating problem was solved by pouring the solution back and forth between 2 beakers

Thank you.
 
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