# Sodium formate reduction problem



## Inter Refiner (Jan 16, 2021)

Hello friends,

Every time I reduce my PGMs by sodium formate, I end up forming some kind of a white salt with by PGMs black, I suspect it is sodium chloride because of the reaction of sodium formate and hydrochloric acid, this salt forms in large quantity when there is iron in the solution, and it forms in less quantities when the concentration of metals in the solution is low, can anyone help out with this.

Note this salt is soluble in hot water, but it is not dissolving 100%.
How can I reduce my PGMs without forming this salt?

Thank you


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## Lino1406 (Jan 17, 2021)

Can be lead formate


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## Inter Refiner (Jan 17, 2021)

Lino1406 said:


> Can be lead formate


The lead is removed prior to that by sodium sulfate.
Note that this also happens when using ammonium formate but with much less salt to be formed


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## Inter Refiner (Jan 17, 2021)

Another question is: Does lead gets reduced with sodium or ammonium formate??


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## Lino1406 (Jan 17, 2021)

No. Formate reduction is slow, even to palladium


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## Inter Refiner (Jan 17, 2021)

Actually its happening rapidly at my lab, I might be wrong,
Can you please show the reactions happening in this process so I can guess what my water soluble salt is


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## Lino1406 (Jan 17, 2021)

HCOO- = 1/2H2 + CO2 + e- catalyzed by Pd, Pt, Ni


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## zacchy (Sep 20, 2021)

Should the sodium formate solution or the stock solution containing Pd be heated?


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## Lou (Sep 20, 2021)

60 degrees Celsius.


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## zacchy (Sep 23, 2021)

Thanks Lou, for answering,
I think that ammonium acetate can also be used, the PH of the solution is raised to a value of PH = 1, with sodium hydroxide and then it is boiled until the PH rises to approximately 3, and ammonium acetate is added, and the PH will rise to 4.2, at that point it is allowed to cool and filter, the palladium should be at the bottom, a new solution is needed to purify.


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## Lou (Sep 24, 2021)

Ammonium acetate will not reduce palladium.

What you are talking about is making Pd(NH3)2Cl2...the yellow diamine salt.

In my opinion, it is best to make this with ammonia and form the colorless tetrammine complex. This allows the opportunity of removing things that don't form amine complexes in that environment (like Cr) and removing rhodium and platinum from the palladium.


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## zacchy (Sep 24, 2021)

NH4OH pH buffer form palladium complex of [Pd(NH3)4Cl2] and [Pd(NH3)2C12] . Currently, the most widely
used palladium electrolyte for industrial and commercial Pd electrodeposition process is this ammoniacal system.

Using ammonia is a very good idea, but the smell is very penetrating, I don't know why the solution is blue, it must be because of the presence of copper, another problem is that a sediment is formed for filtration that is very difficult, and it covers the filter .

Well, I don't know if the salt produced by the ammonium acetate can be calcined, and thus reduce the Palladium.


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## Lou (Sep 26, 2021)

The sediment is base metal hydroxides. If there's a lot of sediment I have found it generally best to proceed like this:

From aqua regia digestion presuming not much in the way of Ir/Ru/Rh present, remove excess nitric with sulfuric

1. Dilute until 5 M in HCl or less, filter the AgCl and any lead sulfate off, rinse the AgCl filter cake with dilute HCl until filtrate is colorless
2.Boil solution for several hours until the ORP is 550-600 mV
3. Precipitate the bulk of the platinum with potassium chloride solution, as K2PtCl6, 50-100 ppm in the mother liquor of Pt remains. 
4. Re-oxidize the solution with chlorine gas and make strongly acidic, operating at room temp, adding more potassium chloride, K2PdCl6 comes down 50-100 ppm of Pd in the mother liquor remains, usually less than 50 ppm of Pd.
5. If desirable to purify the Pd, digest in ammonia, boiling it, filter, adjust pH to 2.8-3.2 and filter off the yellow diamine complex. The filtrate can go to zinc cementation with the mother liquor.


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## zacchy (Sep 26, 2021)

What a good method Lou, as always.
I believe that Palladium can also be reduced from the mother solution after precipitating platinum, using Formic acid and sodium hydroxide, this mixture is heated and added to the also hot mother solution.

I have also used potassium chloride to precipitate platinum, but the resulting yellow salt is not reduced by thermal decomposition. It is a yellow salt that becomes hard in the quartz crucible ... this salt is better reduced with Sodium Borohydride.

Another thing Lou, how is the handling with chlorine gas, this is very dangerous I think, and if I already have chlorine gas, it would not be best to inject this chlorine and obtain the precipitated red palladium salt? I would no longer have to use potassium chloride.


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## Lou (Sep 27, 2021)

It indeed can be done by reducing the mother liquor post Pt, that's probably the best thing to do depending on the solution analysis. 

All of the advices on a flow sheet are all dependent upon the ratio of the elements to one another. So without me knowing the analysis of the solution, or the feed material type, I cannot really make the best recommendations. A one size fits all shoe is going to leave a sore foot...because one size fits all doesn't exist. This is why hydrometallurgical separation science is difficult because there are many possible modulations to established flow sheets and some things need adjusted on the fly.

The K2PtCl6 must be reduced and well washed before calcining. It will thermally decompose to Pt(II) and eventually Pt but messily. It is not like ammonium hexachloroplatinate. 

As for the chlorine, it is very convenient to have, but also dangerous. Sodium chlorate is what's often used in strong HCl to generate Cl2. It's still not the same.


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## zacchy (Sep 27, 2021)

Alright lou
The solution contains, Pt, Pd, Rh, Ir, but the idea is to precipitate all the PGM, and leave the iron behind, There is no sodium chlorate for now, which makes me think about the precipitation with potassium chloride, as you say , but if Pt (ii) and eventually Pt metal is formed, it is not good to have a salt, and not a metal.

chlorine gas, will precipitate everything? or just the Pd?

the K2Pt Cl6 can be reduced with borohydride then, to get the metal from all the yellow sponge, and then I wash it with plenty of water, and it is calcined.

or better sodium formate, boiling both solutions. the mother liquor of the platinum, but it would only recover the palladium.

Everything has something in favor, but others against. as you say is better than flow chart is better.
The only certain thing with the PGM, is that no precipitation is complete, there is always precious metal in the mother liquor.


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## Lou (Sep 28, 2021)

Forget about getting the Ir with cementation.

If you want the iron gone, consider cementing on copper.


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## zacchy (Oct 4, 2021)

Hi Lou, yes, copper cements all precious metals, it is very good, but I think that rhodium would not be useful for use in electrolytic baths, also copper has problems in the treatment of mother liquor, it forms some compound with ammonium chloride and the waters are blue in the landfill.

I like the idea of using potassium chloride more, and being able to recover paltinum and palladium from the mother liquor.


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## Lou (Oct 4, 2021)

In USA, ammonia chloride-chelated waste water must have the chelated metals broken free.

So for me, it doesn’t matter. And no, making Rh plating bath…not easily done!


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## zacchy (Oct 10, 2021)

I think this method is good, they use KOH, to bring the appropriate PH and then add small amounts of formic acid, it can be good because you do not have to heat in another container, you just add everything in the same reactor and stir, but they do not explain what PH the initial precipitate forms and the fusion with a gas or acetylene torch seems strange, I think they carburize palladium, and use borax, it does not seem to be a good method to melt, but it can be to precipitate palladium black.

https://www.youtube.com/watch?v=0nCNHCwYTDY


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