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Thank you Martjin, there is very little gold in this wash water. I was editing, while you were editing, please see above for my description of what happened.
Gold back in solution when washing?
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Martijn
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With that little nitric, just go for SMB. It will use up the excess nitric, also by redissolving the precipitated gold.
I have seen this several times as well. Mine went back to my store brand distilled water. The amount going back into solution was very small but annoying. I would add a very small amount of smb to the wash and it would drop right back out. I then would continue the wash as usual, only changing the water, with no further problems.
I collect the "dirty" HCL from washings to separate bottle, and when I am about to process next batch in AR, I use this acid for the start. Then I have three separate beakers in the hood - one for gold "waste" (washings, last traces of powder from second settling etc...), second for silver waste (mainly AgCl from various tests of material etc., AgCl contamined with PdCl2, Sn oxides etc..) and third for Pd waste/dilute washings. Anytime the container fill up, I process it - usually by lye/sugar (Ag) or by cementation with copper dust (Pd, Au), dispose barren liquid and collect further
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Could the tap water have enough Fe2+ to precipitate the gold? My well water is packed with Fe2+ right out of the ground (it oxidizes to annoying rusty Fe3+ after sitting in air for a day), and iron pipes are common in city water systems.
If you had a very dilute gold solution, and added ferrous sulfate (the active ingredient being the Fe2+), you'd expect to have a clear solution that tests negative with stannous chloride, because the gold is no longer dissolved ions, but sub-micron dots of inert metal swirling around.
Dissolved ions are the big reason distilled water, or at least deionized or clean dehumidifer water, is preferred to tap or well water in refining. Depending on the process, chloride ions can drag down silver, ferrous ions could reduce and precipitate gold, calcium ions can precipitate sulfate giving a hard to filter and valueless precipitate, etc.
If you had a very dilute gold solution, and added ferrous sulfate (the active ingredient being the Fe2+), you'd expect to have a clear solution that tests negative with stannous chloride, because the gold is no longer dissolved ions, but sub-micron dots of inert metal swirling around.
Dissolved ions are the big reason distilled water, or at least deionized or clean dehumidifer water, is preferred to tap or well water in refining. Depending on the process, chloride ions can drag down silver, ferrous ions could reduce and precipitate gold, calcium ions can precipitate sulfate giving a hard to filter and valueless precipitate, etc.
608927101la
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That's interesting. Think all wells are the same in that regard?
AuCl3 , soluble in Et2O. Easy separation. Avoid flames.
Well, it would be [AuCl4]- but yes, there are better things than E2O for it, though I personally love the smell of ether in the morning.
In any event, the issue is the HCl. It will dissolve gold because air gets into it and makes small amounts of chlorine. Two ways around that are 1. small amount of SO2, 2. small amount of ethyl alcohol. This removes the Cl2 from the HCl.
Lou
In any event, the issue is the HCl. It will dissolve gold because air gets into it and makes small amounts of chlorine. Two ways around that are 1. small amount of SO2, 2. small amount of ethyl alcohol. This removes the Cl2 from the HCl.
Lou
I also love ether smell... And many more, which I certainly shouldn´t be smelling
but it happens from time to time... Accidentaly, not intentionally. Benzene and methyl chloride both has interesting sweet smell too, but in high concentration very annoying... Don´t ask how I know this Ethanol "trick" is good one
I think you mean that you first treat HCL with bit of EtOH and then use it for gold washing. Did I get it right ?yes, the plan being to kill off the oxidant.
I wouldn´t say it is oxygen scavenger, but it is a good reducing agent for many strong oxidizers, like chlorine, which the EtOH is supposed to react with. Either oxidizing alcohol to acetaldehyde/acetic acid, or by radical chlorination of carbon chain, if the mixture is somewhere on direct light. But radical chlorination is I think much slower, giving more room for it to proceed on oxidation to ethanal/acetaldehyde - which could then be again chlorinated to form chloroacetaldehyde etc...
I do not think oxygen reacts with alcohol under normal conditions at appreciable rate. In HCL, the equilibrium between ethanol and ethyl chloride is established, but since there is plenty of water in HCL, equilibrium is shifted towards reagents - EtOH and HCL.
But since EtCl has low boiling point, and bad solubility in water, it evaporates and slowly push the equilibrium forward.
Complex issue to be resolved by just thinking about it
One would need some GC-FID or better GC-MS to find out what is created by this reaction for sure But important conclusion is - chlorine gets used up. So there is none to react with gold
I know the feeling all to well……
If the precipitation was completed with metabisulfite without its hydrolysis (prelilminary dissolution in water), part of the gold could be redissolved in the sulfate complexes. (SO) gold complexes are very strong and mask the tin chloride test - it will be negative for such gold compounds. The only simple test option is complete evaporation and heating above 400C.
Or, long (more than 8 hours) electrolysis with graphite electrodes at low potential.
Or, long (more than 8 hours) electrolysis with graphite electrodes at low potential.
608927101la
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So can't just add more water later anyway and heat it?
If you're asking about SMB, no you can't add water later. SMB (Na2S2O5) should be hydrolyzed to NaHSO3 before adding it to the acidic solution. Because reducing agent for gold is SO2 in this reaction. If you're talking about evaporation, you don't need additional water anyway.
I have never used SMB other than as powder, and it has worked fine for me.😏
Hello,
I wrote "part of the gold could be redissolved in the sulfate complexes"
It depends on SMB quantity, solution pH, HCl-HNO3 proportions and concentrations, and availability of copper (Cu) or nickel(Ni) ions which significantly decreases Au oxidation potential.
I have often seen solutions of gold sulfate complexes thrown into waste after precipitation with non-hydrolyzed metabisulphite. Especially when someone trying to use a multi-stage process with different acids and get gold specifically from electronic components with large quantities of base metals (not from ore).
I wrote "part of the gold could be redissolved in the sulfate complexes"
It depends on SMB quantity, solution pH, HCl-HNO3 proportions and concentrations, and availability of copper (Cu) or nickel(Ni) ions which significantly decreases Au oxidation potential.
I have often seen solutions of gold sulfate complexes thrown into waste after precipitation with non-hydrolyzed metabisulphite. Especially when someone trying to use a multi-stage process with different acids and get gold specifically from electronic components with large quantities of base metals (not from ore).
I have had problems off and on for a long time. When I stopped doing much waste it got better. Then I got to doing a good bit of gold filled and started seeing it at random again. This is why I got to testing other precipitants over time. I never use smb anymore with out water, and very rarely with out heating both the AR and the smb.
