pgm electrorefining

[Inter Refiner]

hello friends,
I am willing to start separating my pgm black that I recover regularly using electrorefining, my mix is
55% palladium,13% platinum,4% rhodium,23% lead,3% copper,2% iron, I know the basic principles of electrorefining, but I need to know the needed voltage for each metal and the needed current, in addition to the used solution in the cell, also I need to know the needed rectifier.
please note that this cell is for the refining of more than a kilogram.
any help would be highly appreciated, especially formulas and rules

thank you

 

[nickvc]

I don’t believe such a process exists or not one I know of.
For gold or silver electrorefining you start with a solution of the metal you want to refine and feed high grade 98%+ feed stock so you solution doesn’t foul too quickly you do the same in copper refining.
To refine the mix you have will need wet chemistry using acids and specific precipitants for each metal something I personally would avoid due to the high risk from the chlorides.
Lou may be able to shed some light on what you need to do if it’s not some of his trade secrets.
It may be possible to cupel the material to remove the lead and possibly some of the other base metals, try a small sample to find out, it’s certainly safer and almost certainly a cheaper method.

 

[Martijn]

Hi Inter refiner, I've read some of your posts, and you are doing some thorough research on the best applicable processes on how to refine PGM's. They are all about how to separate the values from PGM black from anode slimes.
But I get a feeling you are lost in what to do, am I right? I hope it is all limited to theoretical study only.
Spreading your questions over many threads will also not help. Keep it all together to get the bigger picture. it's all in the fine details. And we don't have to start over explaining every new post or read through your posts to understand why you've started yet another one.

Can you explain a bit about where the powders came from, and what the source material is? Did you produce the cell slimes or did you buy them from someone else? and if so, why did the seller sell it in the first place?

Reading Wikipedia to compare the characteristics of these PGM's you want separated, and having zero experience in refining PGM's, I've come to some conclusions (assumptions):

Palladium dissolves in Nitric.
Platina dissolves only in hot AR, very little or not at all in cold AR.
Rhodium only slightly dissolves in AR
Those facts would give you a fairly easy way to separate the palladium by first leaching out the lead and maybe parts of the iron with HCL, dissolving the palladium powders in nitric, filter and cement it out on copper. The copper and iron will also dissolve in nitric, and cementing on Copper will leave any Iron and of course Copper in solution.
That leaves you with cleaned powder only containing Pt and Rh, which I can not help you out with any further. This is advanced chemistry (to me).
The biggest value is in the 55% palladium anyway. Pt is half the value of gold now, and the bit of Rh can be sold in an alloy with the Pt? Do you have a furnace to melt these powders?
I'm probably underestimating it and thinking way to simple.

PGM's are no joke when in solution. Look up Platinosis and be very sure you can work without even getting a micro drop in the air you breathe, on your face or skin or clothes, that could leak trough, or get transferred to other surfaces your wife, children, pets, friends or neighbors may touch... :shock: I wouldn't want that on my conscience.
Consider an accidental glass beaker breaking at the worst possible time... do a risk assessment and setup a procedure and follow that to the tee. How are you going to catch spills and clean it without leaving an area contaminated. Safe disposal of chemical waste? lots to consider in advance

Just sell it at is and maybe live a bit longer?

Be very very very very extremely carefull and stay alive for your loved ones.

Martijn.
edited for correct spelling

 

[Inter Refiner]

I am recovering pgms from catalytic converters on large scale, about a ton a week, I have the right safety measures and chemicals safe disposal. The pgm powder is recovered from that origin, I am experienced in refining these metals chemically but on this large scale it is somehow painful and time consuming, so I am researching the electrorefining methods to separate these three metals through three stages, each stage refines one of the three metals, i know the basics of this electro refining but not the key details.
I would appreciate any help

 

[Martijn]

To add a quote from Wiki:
"Palladium is a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point of the platinum group metals. It is soft and ductile when annealed and is greatly increased in strength and hardness when cold-worked. Palladium dissolves slowly in concentrated nitric acid, in hot, concentrated sulfuric acid, and when finely ground, in hydrochloric acid.[4] It dissolves readily at room temperature in aqua regia.
Anode slime powders can be considered finely ground, I think.

 

[Martijn]

Looking at the different electro refining solutions:
for copper you use copper sulfate
for silver you use silver nitrate
for gold you use auric chloride
This leads me to assume you need relatively pure platinum in solution to ensure selective plating of platinum, palladium in solution for palladium plating, and so forth. Some metals will dissolve in the electrolyte, some will stay in the slimes, something to figure out with the different processes to determine the order of steps to execute.
To get these 'pure' electrolytes, you would have to first purify PGM's to make the electrolyte, which is kind of a chicken and egg question. First refine pure Pt from a PGM mix, to make a Pt electrolyte to recover Pt from a mix of PGM's.
Not trying to confuse you, but maybe stick to the tried and proven processes or leave the final refining step to a professional.
If there was an easy and safe way, PGM's wouldn't be that expensive.

Martijn.

 

[Inter Refiner]

I can buy some high purity pd, pt, rh to make my electrolyte, and to make the metals electrode to be plated

 

[nickvc]

You are missing my point in my original reply.
To successfully electrorefine you need very pure feed stock which you do not have at this point and to get them you will need to dissolve all your material and selectively precipitate out the various values and this will be very hard with the platinum which needs to be highly concentrated to precipitate successfully.
In your position I’d be looking for a buyer of the cats as they are, with volume you will get more money that way than by trying to refine them yourself, we had an ex member who spent many hundreds of thousands of dollars to learn this.
With what you leave in the filter the returns from a good refiner will put you well ahead.

 

[g_axelsson]

I'm far from an expert in electrochemistry, but I believe one of the major problem with electrorefining pgm is the hydrogen potential of the anode. In a water based electrolytic process the anode process is to breaking down H₂O into O₂ and H⁺. No pgm would go into solution.
Maybe with the exception of palladium, it behaves very close to silver and will go into solution in a silver cell, maybe palladium can be refined in a nitrate based cell, but I can't find any proof of that.
If there is a water based process, even a theoretical one without commercial value, it should be interesting to hear about.

There are a number of plating baths for plating palladium and the references of this patents contains a number of leads if someone feels for hunting them down.
https://patents.google.com/patent/US4411743A/en

A quick googling gives a hint of what it takes to electrorefine PGM, a water free process. For example a molten salt process.
https://patents.google.com/patent/CN103806044B/en

Theoretically, there are several other processes that should raise the amount or pgm in your material, both pyrometallurgical and wet chemistry. In the end the question is if it is worth the work and expense to just raise the grade of the final bar. It is easy for the pgm refinery to separate the base metals when they dissolve the pgm to refine the metal.

But an easy electrorefining method doesn't exist to my knowledge. If there is something like that then it is a well guarded industrial secret.

Göran