# Refining PGMs



## nickvc (Dec 3, 2013)

I was reading an extrct of an article today on the Wiley website from the journal of chemical technology and biotechnology entitled the leaching of PGMs from spent automotive catalysts which contained limited but interesting information. According to the small amount I could access they tried to recover the values using hydrochloric acid and then used electrical generation of chlorine gas to dissolve the values which gave fairly poor recovery rates of around 60% but if the material was first treated in Formic acid the rates for recovery ran into the 90-97% of values recovered using the same process to dissolve the values, as I said it was fairly limited so no more details were freely available about exactly what the Formic treatment entailed.
I'm no expert on PGM refining,I'll happily leave that to Lou and Lazersteve,but I thought It may have some significance to our more learned members who could perhaps see some use for the information and if so could share it with the rest of us.
If this is already well known to you all please could one of the moderators delete this for me as I don't want to waste space on the forum with already posted information.


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## Lou (Dec 3, 2013)

The formate is to reduce the oxides of Pd (and Rh, but probably with a lot of heating) so that they are acid soluble.

I'm familiar with the paper and there is an associated patent you can find.


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## nickvc (Dec 3, 2013)

Thanks Lou, I wasn't sure if it had any relevance to the refining of PGMs generally but it seems it hasn't but it might be of use to our memebers who do refine their own small quantities of cats to get better results, I still believe that if you have volumes of catalysts your better off trading them to the big boys after decanning, blending and assaying of course.


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## butcher (Dec 3, 2013)

It did get me thinking.
When incinerating powders containing palladium we can oxidize them (making them insoluble to acid).
It sounds like this formate reduction, could be a method to reduce the palladium oxide, so that we could dissolve these powders.


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## nickvc (Dec 3, 2013)

Butcher that's what I hoped that someone could find a use for the information, I know I can't see it as I'm no expert but anyone else see a use for the data about Formic as a pretreatment? Just hoping it can help the members get better returns for their efforts.


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## Lou (Dec 3, 2013)

It's actually very important that the material be treated appropriately before sampling (or refining), even if you're just de-canning and milling. Certain Pd/Rh oxides will not digest well without a skilled analyst. A troy ounce of prevention is worth more than a troy pound of cure!

What I find to work the best for ceramic-based catalysts prior to analysis:

1. Sample the material after crushing and sizing.
2. Placed weighed sample in quartz tube, flush with CO2 during heat up.
3. At 300-400 C, switch to hydrogen and heat to 600oC and hold for 1 hour, switch to CO2 and slowly cool
4. Weigh material and proceed with wet chemical digestion and/or pressing WD-XRF puck

Doing this treatment ensures that metal is in a form that will dissolve and can be determined via gravimetry or spectroscopically. It also removes water and pyrolyzes or distills off any organic traces (which scum up the bubble trap on the back end). Now, one has the moisture content and the metals in a form that can be more easily analyzed.

Many energy dispersive bench top XRF units that are less than a new Ferrari in cost will not see the oxygen component of PM oxides and will erroneously report higher values than what are present. The larger floor model wavelength dispersive models will use a helium atmosphere to quantify lighter elements, but even then, lower Z "lighter" elements are more difficult to quantify this way. 

Hydrogen can be avoided if one heats the catalyst to over 1000 C and holds for some time to decompose all PM oxides.

I should also mention, if you calcine or otherwise incinerate a high surface area Pd or Rh rich material, be prepared to do a post incineration reduction if you intend on refining or otherwise upgrading the quality of the material. Failure to do so will result in incomplete dissolution.

I've attached a photo showing the setup.


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## nickvc (Dec 3, 2013)

Lou thank you yet again, those with a full interest in PGM refining I'm sure will know exactly what your talking about, to me it's just noise that sounds vaguely intelligible , I know my limits and I'm pleased we have a specialist like your good self to put things like this right for the members.


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## Lou (Dec 3, 2013)

Thanks. I'm sorry that I didn't explain it clearly enough.

The idea:

get acid-insoluble or poorly soluble precious metals values to be in a form that is more or completely soluble so that the assay or refining sequence goes smoothly.

take advantage of easy reduction of these troublesome oxides by decomposition to the elements (ex. 2 PdO <-->2 Pd + O2) or reduction with hydrogen (PdO + H2 --> Pd + H2O). In any case, a stream of gas helps push the equilibrium to the right, towards the metallic form.


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## nickvc (Dec 3, 2013)

Lou its not your problem but mine :roll: I'm sure many will follow your chemistry but not me far to dim  
Again thanks for clarifying for those that can understand :lol:


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## skippy (Dec 16, 2013)

Lou, when I was interested in catalytic converters I had experimented with doing a sulfuric acid roasting. It gave pretty good rhodium recovery, but I never had the palladium recovery quantified. Does hot concentrated sulfuric acid dissolve refractory palladium oxide?


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## Lou (Dec 16, 2013)

It will, but the best is using bromide to help it along (also helps with Rh recovery).

Much fumes though.


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