Latest Platinum Drop

[9kuuby9]

Thank you Butcher and Lou! I both extremely appreciate your sound and valid explanations.

I should have clarified what my intention is behind the question. I asked the question, because I wanted to recover as much as possible (at a satisfying efficiency) platinum (as ammonium chloro-platinate) from Chloro-platinic acid. In order to make Adam's Catalyst. I have some simple knowledge and experience regarding platinum refining, But I wanted to ask what the most efficient way in a simple lab to reduce ammonium chloro-platinate in the highest possible efficiency with the given possibilities.

A recovery rate exceeding 99.5% would be more satisfying that a 95% one, Time to take some valuable notes! :mrgreen:
As Butcher said, now the wastes should be viable for the Stock pot.

High concentration is key here for a high recovery rate. (noted)
Would a saturated participant (Ammonium chloride) be sufficient or would you advice another concentration? What concentration (60g/l-80g/l?) would you recommend for platinum? It their such a thing as a too high concentration when it comes to precipitating ammonium chloro-platinate? Should crashing-out be appropriate? As heating and saturating the precipitant and then adding it to a cold solution of Platinum chloride, essentially crashing out the precipitate. Or is their an alternative method?

I'm doing this on a small scale and so wanted to slowly increase my processing scale and efficiency wisely by acquiring sufficient knowledge from learned people as we have so many of them here on the forum (thankfully), to slowly broaden my competence with valuable knowledge and experience regarding the process.

 

[butcher]

My thoughts are you will leave traces behind in recovery and refining, but you can get those traces back later with zinc or the stock pot, I would be more concerned to get as much back as pure as possible, and gather those other traces later.

Lou would be much better help in this area.

 

[9kuuby9]

I keep a separate stock pot for this process, because my platinum feedstock is quite pure to begin with. Maybe some very minor contaminants, So it should be easy to recover given that I don't mix it with other solutions.

 

[Lou]

Alas I cannot allow myself to get into too much detail.



If you seek Adam's catalyst, be very careful. It's a nuisance in making it, especially in quantity. Your platinum should at least be spec'd to 3N5 purity, with special attention to the other PGMs, nickel, and copper (and sulfur).
If your material is already 3 N, you may want to hydrolyze base metals (taking special concern to do it at two pH regimes to cover amphoteric ions; that is our SOP when we refine it). Then you can slightly acidify and ppt with ammonium chloride (AFTER concentrating down). At some point you may consider adding a small bit of ethanol (or ascorbic acid/sulfite) to drop ORP slightly to avoid any Ir/Pd contamination, in the event you were over hasty in neutralization. This will move them from (IV) to (II) and (III) respectfully. You really need to be sure that platinum is freed from its sister metals as they can catalyze competing reactions and greatly annoy your customer when he goes to analyze his product made using your catalyst.


How concentrated can you go? 200-300 g/L is a good working range, but indeed you can go over 600 g/L. Too high and it forms a mud that needs additional precipitant to slurry and is a hassle to pump out of the reactor.

The sword cuts both ways here: more concentrated the solution, more concentrated the impurities, more likely to entrain them, higher Pt recovery.


If your platinum is quite pure, skip the stock pot and the zinc, and with good ventilation (and adjusting pH to 1.5-2.5) precipitate the Pt as its sulfide. Borohydride is far, far better yet. In either case, the sulfide and/or platinum cement can be re-dissolved and recovered.


The most efficient way to reduce ammonium hexachloroplatinate is to do it thermally @ 950-1000*C over night to make a dead burnt sponge. If you want a finer powder, lower temperatures and hydrogen are used.

 

[9kuuby9]

Thank you Lou!

You don't really have to go into much detail, as you already have given me a great deal of the stem of the tree, I'll have to grow its branches by builing upon the the blocks you provided.

And then enjoying the fruit of the tree that it bears after some hard work. :mrgreen:

To this day you probably already have grown a nice Forest. As many have done in this ecosystem (GRF). 8)

 

[freechemist]

One of these interesting threads, reaching back into the past, now almost four years. Please let me add a few comments.

December 18th, 2009 4metals wrote: "The most straight forward way to get your platinum is to drop it first before the gold. Unfortunately that requires the 3x boil down to get rid of the nitric and is time consuming. Drop the platinum with saturated ammonium chloride and you should get the best yield both in quantities dropped and purity. Redissolving the salt, refiltering and dropping it again will improve purity but for the best purity you'll need to do a bromate hydrolysis.

Working up big lots of Pd/Pt-rich dental alloy scrap led me to the conclusion, the most straight forward way, to recover Pd and Pt consists in precipitating them together, as a mixture of K₂PdCl₆ and K₂PtCl₆ salts, and only then going after the gold, remaining in solution. Applying this procedure routinely, made the tedious "denoxing" process unnecessary in my practice. The mixed, solid hexachloro-metallates(IV) can be partly redissolved by applying an appropriate reductant and thus separated into crystallized K₂PtCl₆ and into K₂PdCl₄, remaining dissolved in the mother-liquor.

December 21st, 2009 Lou wrote: "Also, the sulfite drops any Ir as its dioxide if I remember correctly. EDIT: Also forgot, sometimes it is necessary (especially after the sulfite, well known for reducing Pt (IV) to Pt (II) to sparge with chlorine gas or add extra HCl and sodium chlorate/bromate (either work, but chlorate is cheaper). This ensures that all platinum is "H₂PtCl₆"."

In strongly acidic solution, there is no precipitation of IrO₂, if sulfite is added. Instead Ir(IV) is reduced to Ir(III), and thus K₂IrCl₆, eventually crystallized already, redissolved slowly.
The easy reduction of Pt(IV) to Pt(II), mentioned by Lou, is a fact, well explaining the sometimes only small yields of solid hexachloroplatinate, obtained after precipitation of gold by the known, usual procedure.

September 4th, 2010 HAuCl₄ wrote: "Can the platinum salt be redissolved without reducing to metal, re-digesting, etc.?"
"I know the palladium salt can be redissolved with ammonia, etc."
"Is there a suitable solvent to dissolve/re-crystallize the ammonium chloroplatinate?"

- Yes, the platinum salt can be redissolved, there exist a few practicable procedures, but these belong to the realms of the more or less secret arts of PGM-refining.
- As far as I know, there are only water and/or dilute aqueous HCl appropriate solvents, in a possible procedure, where (NH₄)₂PtCl₆ is carefully reduced with a slightly less than stoichiometric amount of hydrazinium sulfate (the process is described in "Inorganic Syntheses") and recrystallized from the filtered solution of (NH₄)₂PtCl₄ by reoxidation.

December 31st, 2013 9kuuby9 wrote: "Given that Hoke states that only about 95% of the platinum is recovered as ammonium chloro-platinate from a platinum chloride solution by the addition of saturated ammonium chloride.
It is a pain to hunt down that 5%, especially when dealing with batches of 1kg, At 80g/l (12,5l of solution or more) that would be quite a lot to acidify and reduce with Zn."

In the case of your sample I would recommend, to use an anion exchanger, quaternary ammonium-type, chloride form. Give 500 grams resin beads into the reactor, containing the remaining 5% Pt and stir the suspension constantly, until no more dissolved Pt is detectable. The platinum should then be absorbed quantitatively by the resin, and the mother liquor contain not much more, than 1 to a few milligrams Pt per liter.

Here two links to two quite recent posts concerning ion-exchange:

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=86&t=19554#p198434
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=86&t=19554#p198631

 

[9kuuby9]

Thank you freechemist! I get wiser in refining every time you reply on the subject! :mrgreen:

I will try both Borohydride and ion-exchange resins and see which one fits my needs.

Ion-exchange resins would be better suited than Borohydride in dirty solutions, but it would be a good feat to have both of them and apply them in the necessary moments.

 

[Lou]

You will find borohydride better than IX.

You can skip the incineration of the resin if you pick the proper eluent; perhaps freechemist has some suggestions. I'm sure thiourea/HCl would work (works on practically everything) but it has waste treatment consequences.

 

[freechemist]

Sodium borohydride is indeed a valuable tool in recovering Pt, even from very dilute solutions. If it is better than ion-exchange, depends on situation, solution to be treated and finally, on individual working-preferences and personal judgement.

I am sorry, to have no idea, what would be a proper eluent, to recover Pt from the loaden resin, thus skipping incineration and reusing the Pt-depleted resin a second (multiple) time. However, compared to the value of platinum, the resins I used, are cheap. The working procedure is really simple, just add resin, stir some hours and separate the loaden resin by filtration.

 

[kadriver]

Bromate Hydrolysis


Solution should be added below the solution level in the reactor by delivering through a glass tube which extends below the solution level in the reactor.

4metals,

Should the tube extend to the bottom, into the middle, or just under the surface?

Thanks

kadriver

 

[Lou]

Kevin, it should go to the bottom. I don't like glass, it can break off. I like to use 3/8" FEP tubing and a dosing pump.

You have to remember that the bromate accomplishes several things: 1. it makes sure that all of the metals are in their highest oxidation state (especially important for the PGM impurities), 2. removes Ru (hence the boiling), 3. slowly raises pH to allow for a more "ripened" particle size which allows faster settling.

In commercial practice, what is done is a fast neutralization to pH 0.5, then slow, slow neutralization to 7 or so; this is all done by sparging Cl2 through the mixture (much cheaper than bromate).

 

[4metals]

The moderators would like to thank all of the members that contributed to the original thread upon which this thread was based, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Latest Platinum Drop

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.