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Author: Subject: Do PGMs react with hot NaOH solution ?
Sulaiman
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[*] posted on 21-4-2023 at 08:05
Do PGMs react with hot NaOH solution ?


I just watched a YTvideo of PGMs being dissolved from ore in a hot NaOH solution (refluxed for 24h)
https://www.youtube.com/watch?v=E4WjHgXqRcU

Is this true ?




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Rainwater
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[*] posted on 21-4-2023 at 11:17


Yes
Ore is a mix of metals, oxides, sulfates and .... well everything
I dought he got an effective extraction.

Lots of metal oxides are soluble in alkaline solutions.
I use a similar method to crush my ore, but not to perform a leaching.
The hot NaOH solution is great at bringing rock into solution, and glass to.
Filtering the boiled ore through
a filter fritz, will destroy the fritz.
1 to 1 by weight sounds right.

During the boiling, the oxides react and become soluble.

When he neturalized the solution with aqueous HCl, the white percipitate was likely AgCl, and the yellow tent could be Pd, but many other things produce similar colors in low consentration.

As for his safety practice. There is a lot lacking. He will get hurt@




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Sulaiman
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[*] posted on 21-4-2023 at 13:49


Thanks
Can I still assume that PGMs (especially platinum) in their metallic state would not be dissolved ?

I too was surprised by multiple unsafe (and at least three unwise) practices
but when he picked up the full/heavy beaker by the wall I almost shouted at the video !

Edit... It may be helpful to less experienced members if we have a
'spot the mistakes' discussion or 'contest' ?

@Andreas the Alchemist...are you an SM member?

[Edited on 22-4-2023 by Sulaiman]




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[*] posted on 21-4-2023 at 17:41


I want to say platinum metal would be unaffected, but in an unknown mixture, that would not be accurate.

That poor poor vacuum pump, shes not got much life left in her.
Sounds like its out of oil, or the oil has washed out.

Im looking foward to see how he processes the percipitate and filtrate.
It would be cool if he smelted the filtrate with a collector metal and processed it separately to determine how effective the leaching was.

Strange things happen with ore because it's never the same. Each batch is unique
Stannous chloride testing will tell whats in solution,




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Fleaker
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[*] posted on 25-4-2023 at 10:22


they're not appreciably attacked by 50% hot NaOH.

Molten NaOH will impact every PM but gold and silver. They really need an oxidant like KNO3 or KMnO4 to help though. Even then, it doesn't just dissolve, it just makes alkali metallates that are more or less soluble in aqua regia.

More silly people with rocks and chemicals is my take.




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metalresearcher
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[*] posted on 26-4-2023 at 09:11


Quote: Originally posted by Fleaker  
they're not appreciably attacked by 50% hot NaOH.

Molten NaOH will impact every PM but gold and silver. They really need an oxidant like KNO3 or KMnO4 to help though. Even then, it doesn't just dissolve, it just makes alkali metallates that are more or less soluble in aqua regia.


Does that mean that I can use a silver vessel and a silver anode to electrolyze NaOH ?
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[*] posted on 26-4-2023 at 09:41


I wouldnt consider silver as a pgm

To clean my silver castings, i boil them in 10% NaOH, and it gets the investment off

When crystallizing NaOH from solution by boiling off the water
Ive tried using a silver container and it contaminated my salt.
I dont know if is just a passiveation layer, or erosion, but the final product was gray.
Could be worth a try for molten salt electrolysis

Silver as an anode will passiviate quickly and not conduct current




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[*] posted on 26-4-2023 at 12:07


I just tried melting some NaOH prills on a piece of silver sheet (alloyed with Cu and Ge, so-called 'Argentium silver') and were after melting the lye wetted the sheet, it got very clean.
After cooling it got somewhat yellow but I put the sheet into water to dissolve the frozen NaOH and the photo shows the result.

So I'll try to electrolyze it another time.

Indeed, Ag is not a PGM, even Fe/Co/Ni are rather actually PGMs as they are in the same groups (8/9/10) of the periodic table. They share most properties with the other six metals, only being less noble.

[Edited on 2023-4-26 by metalresearcher]

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[*] posted on 26-4-2023 at 14:57


The six PGM have common properties but they actually differ significantly from Fe/Co/Ni despite being in the same groups. While Ag and Au are not considered PGMs they have more in common with their group member Cu.

For melting NaOH a simple steel container should do the job.

NaOH will etch PGMs with the aid of air oxygen as oxidizer.
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[*] posted on 26-4-2023 at 23:41


Cu, Ag and Au are, if you need a name for them, the coinage metals.
If you take a compound of Au or Ag and fuse it with NaOH, it will decompose and give silver metal.

Crucibles made from Ni and Pt/Au alloy are used in chemistry because they don't dissolve in molten alkali.

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