Problems in platinum recovery

[Yggdrasil]

Chlorox is Hypochlorite

More specifically Sodium Hypochlorite.
Anything else you want to inform us about?

 

[4metals]

You started out by saying this,

I precipitate PGM's and base metals out of Aqua Regia with an Alloy of Aluminum and Magnesium, then I selectively leach different base metals out

and followed that up by saying this,

In my experience, I find Palladium chloride and Silver chloride co-precipitate when you add Salt to the Aqua Regia

The 2 processes you have mentioned will produce different, if not questionable results. I am afraid that anyone trying to follow this thread will be thrown off without clarification.

In your second quote you mention dropping the Palladium with salt. then later on you said;

Now filter the Silver Chloride out of the Aqua Regia Solution, and wash this with clean water until the water becomes clear. Now Filter the water away. Leach the water-free Silver Chloride with Hydrochloric acid/ Chlorox , you will find that the leach will turn orange, meaning that Palladium is extracted from the Silver Chloride.

While I do not understand the mechanism for just table salt dropping the Palladium I will concur that Silver Chloride is notorious for dragging down other metals with it and possibly, in your case, Palladium is dragged down.
The rinsing and addition of hypochlorite (or bleach, choose your terminology) can possibly reduce any Palladium the Silver Chloride may have dragged down.

How are you sure there is not additional Palladium in the mother solution, given the salt precipitation is not a well documented process and it may have only caused some of the Palladium to drop as a salt?

I realize you type slow, I too type with 2 fingers (with the thumb helping on the space bar) but I guess I can do it faster than you. I am not trying to pull out any guarded secrets from you but you did mention some process steps that can be questionable and I do not want to cause any members reading this to take it as doctrine without it being discussed fully.

There are too many missing parts to this for me. Nothing about what the starting material is or other PM's recovered and for now, until you clarify, it is just too big a pill for me to swallow.

 

[100tific]

in my experience, I find Paladium chloride and Silver chloride co-precipitate when you add Salt to the Aqua Regia

maybe you mean that they co-precipitate when you add salt to the solution of Pd and Ag in nitric acid (not in AR). I seem to remember that it also happened to me on one occasion.
thank you very much kurt and 4metals.
There were some things I didn't know like not using AR if PGMs are not the main metal, or that PGMs don't precipitate well in dilute solutions. Also the silver 10 times higher than the Pt so that it drags everything towards the silver part.
You are not aware of what a tremendous pleasure it is to read and learn from you.
I will reconsider everything you have told me and see again what path to take.
I come across platinum tunings more often than I would like and sometimes I don't understand why sometimes it turns out well and other times not so much.
So thanks again for providing your vision.
I take this opportunity to ask another question. I have noticed that sometimes the precipitate after adding ammonium chloride is yellow, other times orange, and even once I recovered it from a solution that had iridium it came out red. From what I have read, this depends on the temperature at which it is formed. But as I understand it, iridium precipitates black. The red I got was carmine red, it didn't look like a mixture of the orange powder and black. I leave a photo of the normal one, and that red that I tell you about. In case you can provide some valuable information through your experience.
Thanks guys

all images are ammonium hexachloroplatinate

 

[4metals]

When refining platinum I always start with a concentrate made by cementation. The gold from all of the solutions containing Platinum is dropped with ferrous sulfate and the accumulated Platinum is processed in bulk. This is possible by paying for the metals in customer bars by assay and only processing the PGM's when they are in larger quantities. The method I always used was to mix up a super saturated solution of ammonium chloride in a volume equal to the volume of Platinum solution I have to treat. The Platinum solution I am treating is heated in a vessel large enough to contain the extra volume of adding all of the ammonium chloride solution, which is also hot.

The Platinum comes down quickly and after about 30 minutes I filter it off and rinse it in a solution of distilled water with 15% ammonium chloride added (W/V). That keeps any of the ammonium chloroplatinate from dissolving in the rinse. (ammonium chloroplatinate has a slight solubility in water). The Platinum salt I recover is always the yellow color as @100tific shows in the bottom (third) photo.

I have no doubt @Lou can shed some light on possible causes for the varying shades of yellow/red you have pictured as Lou deals extensively with PGM's.

 

[Lou]

I should point out that you really should not be drying the ammonium hexachloroplatinate like that. It is best to always handle it damp, with full PPE and preferably in a filter box. Then take a shower after!

That admonition aside, the color of the ammonium hexachloroplatinate you have shown and talked about indicates contamination. It's highly suggested to either dissolve the salt in aqua regia (or otherwise remove the ammonium cation) and complete a hydrolytic refining from oxidizing conditions, as described in 4metals other thread titled Bromate Hydrolysis. You do not need to use bromate, chlorine and caustic soda are use industrially. Bromate just happens to give a better result.

the iridate salt, which comes down substantially completely with the platinum from highly oxidized solutions, will darken your platinum precipitate orange to red. Palladium can also do this, and is far more likely.

 

[4metals]

When treating the solution with ammonium chloride it should be noted that platinum will come down first and then iridium will fall a short time later without you doing anything else to the reaction. This is why I mentioned 30 minutes. I typically siphoned off the majority of the liquid as soon as it settles and filter the rest. I have had success waiting as long as 30 minutes but if you let it go overnight any Iridium will be mixed in as well.

Please pay particular attention to Lou's advice about handling the powders, Platinosis is a serious illness which you can find information about HERE

 

[slsmp40]

Why does this forum update every so often and wipe out what you have painstakingly typed? Not so much on a computer but when you use a phone.

 

[slsmp40]

The classic assay books tell you in order to get all of the PGM's away from the Gold you should inquart with Silver at 10 times the Platinum content to allow it all to follow the Silver. That also implies making the Gold 25% or less. But the texts do specify this will cause all of the Platinum to migrate over. But if your parting has less than 10 times the Silver as Platinum there will be Platinum on both sides of the equation, meaning some Platinum remaining with the Gold and some Platinum following the silver. From a practical refining method, chasing PGM's two different ways is not efficient.

The inquartation with Silver to allow all of the Platinum to follow the Silver is only a reasonable option if @100tific has a Silver cell operating to recover the Platinum after cementing the Silver and any PGM's with copper and running it in a cell.

The aqua regia option would be my choice after lowering the Silver content below 9-10% with copper. The gold should be dropped first and with that much copper added it will not come down clean. It will need a second aqua regia refine.

Wether or not the copper causes issues with dropping PGM's completely if the copper completely dissolved it should not as cementation works on metallic copper. If it were me, I would cement the PGM's on copper, and a clean copper slab would work for this as well. Then, once the original solution is barren of values, the insolubles should be filtered and digested in aqua regia and the Platinum recovered either by ammonium chloride or cementing with sparing additions of copper powder.

As far as the Jahn-Teller effect is concerned it is commonly seen in transition metal complexes so copper does apply. The exact effect the Jahn-Teller effect will have on this particular reaction is subject for debate, there are so many variables that present themselves in acid refining that determining that would be a difficult process. Seeing as you have an alloy and apparently a customer or boss that wants to see the refined metal to sell it, I think the Jahn-Teller effect is a wormhole that may absorb your efforts for a very long time. On the bright side, your research may re-define refining as we know it and your efforts may result in a Nobel prize. Considering Nobel prizes in chemistry are awarded overwhelmingly to men, I would be happy to see it!

Is better to chase the platinum from two solutions than the gold. If you inquart the gold too much below 25% then it too will follow the silver into solution. Inquarting with copper is gods way of punishing the cheap for being lazy. I tell my people all the time that procedure is written in order for a reason. Until and unless you understand why it is in the order as written it is best to not adjust unless you want to have a mess on your hands. This green solution is a mess and it is going to fight you for the value it contains. I know I will catch hell for this but if you are inquarting with copper then you are wrong. If you have to do it so be it, but its more expensive and will waste more material in the end. If your pgms will follow silver into solution, then why would they not follow copper?

 

[slsmp40]

In what form does the Pd precipitate?

Sodium chloride in AR should not participate silver chloride under any circumstances. It would be created from the chloride in the hcl alone.

 

[slsmp40]

The most economical way to handle this if you absolutely had to work with the copper diluted alloy would be to completely dissolve it in AR and then drop the gold. If smb was used to drop the gold you would need to let the solution rest in the open atmosphere for a few days to make sure the sulfur containing gases were gone from the solution.
Then cement the values so you can get a clean solution to work with when you add Ar again.

 

[Yggdrasil]

Sodium chloride in AR should not participate silver chloride under any circumstances. It would be created from the chloride in the hcl alone.

Absolutely true.
I was so focused on the claim of precipitating the Pd that I completely overlooked the AgCl claim.

 

[orvi]

I should point out that you really should not be drying the ammonium hexachloroplatinate like that. It is best to always handle it damp, with full PPE and preferably in a filter box. Then take a shower after!

That admonition aside, the color of the ammonium hexachloroplatinate you have shown and talked about indicates contamination. It's highly suggested to either dissolve the salt in aqua regia (or otherwise remove the ammonium cation) and complete a hydrolytic refining from oxidizing conditions, as described in 4metals other thread titled Bromate Hydrolysis. You do not need to use bromate, chlorine and caustic soda are use industrially. Bromate just happens to give a better result.

the iridate salt, which comes down substantially completely with the platinum from highly oxidized solutions, will darken your platinum precipitate orange to red. Palladium can also do this, and is far more likely.

Palladium co-precipitation was also my first bet.

 

[orvi]

maybe you mean that they co-precipitate when you add salt to the solution of Pd and Ag in nitric acid (not in AR). I seem to remember that it also happened to me on one occasion.
thank you very much kurt and 4metals.
There were some things I didn't know like not using AR if PGMs are not the main metal, or that PGMs don't precipitate well in dilute solutions. Also the silver 10 times higher than the Pt so that it drags everything towards the silver part.
You are not aware of what a tremendous pleasure it is to read and learn from you.
I will reconsider everything you have told me and see again what path to take.
I come across platinum tunings more often than I would like and sometimes I don't understand why sometimes it turns out well and other times not so much.
So thanks again for providing your vision.
I take this opportunity to ask another question. I have noticed that sometimes the precipitate after adding ammonium chloride is yellow, other times orange, and even once I recovered it from a solution that had iridium it came out red. From what I have read, this depends on the temperature at which it is formed. But as I understand it, iridium precipitates black. The red I got was carmine red, it didn't look like a mixture of the orange powder and black. I leave a photo of the normal one, and that red that I tell you about. In case you can provide some valuable information through your experience.
Thanks guys

all images are ammonium hexachloroplatinate

With amounts of platinum and palladium in material, I would suggest (as other experienced members suggested) to go for the gold and accumulate PGM residue for later processing. Working with PGMs is much more complex and tedious task, and it is best to combine the leftovers from multiple runs to save time and your sanity

In PGM refining, ammonium hexachloroplatinate is something like silver chloride for refiners If you really do not need to produce it, you avoid it and refine with other methods. If you do not happen to have nice tube furnance equipped with hydrogen cylinder for complete and convenient reduction to platinum sponge of course

With this feed you have, I will probably go with dissolution in AR as you did, AgCl bulk filtration, then gold precipitation.
Leftover liquid containing PGMs would be then cemented (either with appropriate amount of iron or with copper) to concentrate values (this will allow you to skip evaporation) as metallic powders.

And from there, you can either process them (nicely concentrated feed = easy to do) either cumulatively or individually (each batch separately).

If you need to somehow clean the PtPd and resolve it to Pt and Pd part, good and easy method to use is to de-NOx the solution to get rid of any leftover oxidizing species and precipitate palladium with ascorbic acid. Silver and also some copper will follow, but co-precipitation of platinum is minimal. It needs pH adjustment (which also usually lead to one necessary filtration of eventual hydroxides precipitate) to around 1 to work OK. There are threads discussing the ascorbic reduction of Pd on the forum. Relatively Pt free palladium powder will be obtained, and liquid will contain reduced Pt(II) species alongside with majority of base metals.

------------
Maybe I missed it, but is there a reason why you isolate platinum and palladium from feeds ? From my experience, if you don´t produce high purity added value products from PGMs (like catalysts, pure PGM salts, pure PGM metal wires/sheets etc.), I see no benefit in refining these quantities of metals yourself. Melt the enriched PGM leftover from cementation (this should have very decent PGM content) and sell it to larger PGM processors. In small quantities, your time as employee can be sometimes more valuable than money you can make selling 99% pure PGMs.