Latest Platinum Drop

[4metals]

The ammoniumchloroplatinate can be reduced to pure platinum by heating it to 700+C. Heating to drive off oxides or in this case chlorides is often referred to as calcining. An electric assay furnace will work for small lots but if processing any quantity the chlorine you liberate is tough on heating elements.

The fused silica tray (99.9% SiO2) is temperature resistant pure and not likely to contaminate your metal which you've just worked very hard to bring to a high level of purity. Much better than the wifes muffin pan.

 

[golddie]

Hi 4metals
Thanks very much I appreciate your help

 

[HAuCl4]

Redissolving the salt, refiltering and dropping it again will improve purity but for the best purity you'll need to do a bromate hydrolysis.

Hi. Me again...

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?

 

[lazersteve]

I have redissolved it in water and also with HCl.

Steve

 

[9kuuby9]

What would be the ideal circumstances of precipitating ammonium chloro-platinate from Chloro-platinic acid, at it highest efficiency?

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.

 

[butcher]

Stock pot.

 

[Lou]

The "ideal" circumstances for platinum precipitation do not exist outside of a commercial facility. Platinates (IV) are potent allergens and persistent environmental contaminants in the work place. That said, handle them with utmost care! They are not only expensive, but they are dangerous to one's health on a long term-basis. I try to avoid producing them whenever possible and I work with platinum and its sister metals for a living!

The best conditions are situational--do you want purity, or do you want recovery? In many regards, this is like reducing gold with sulfur dioxide, the very best gold comes first, the fines afterwards are low purity. The same is largely true with Pt from dirty solutions. It's not all instant, there should be at least 3-4 hours wait by the operator and good stirring before the supernate is run off from the reactor.

If your solution is pure (say post, hydrolysis), skip the chloroplatinate precipitation--pointless. It can be reduced at that point after concentration and pH adjustments depending on reduction system.

I disagree with Hoke, the recovery is better than 95%, often exceeding 99.5%. Just operate with high concentration solutions and high concentration precipitant (probably best to use KCl if you plan on aqueous reduction). A good exercise for you would be to determine the concentration in excel using available solubility product data...

Lou

 

[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)

 

[FrugalRefiner]

Some people can talk (or write) all day, and not say anything.

Others can communicate volumes in just a few words.

Lou definitely falls in the latter category. Thank you for sharing so much with us. 8)

Dave

 

[nickvc]

Some people can talk (or write) all day, and not say anything.

Others can communicate volumes in just a few words.

Lou definitely falls in the latter category. Thank you for sharing so much with us. 8)

Dave

I can sure second that comment Dave, I accidentally made Adams catalyst some time back and had to ask Lou what the heck I had, still not sure how I did it but that's refining, especially PGMs.

Can I add that many PGM recovered and refined powders can be extremely unpleasant or downright dangerous and real care and a lot of knowledge is required before even attempting some processes.

 

[9kuuby9]

Can you relate to me how you accidentally made it? I'm very interested on hearing about that story!

You really must have gone beyond your borders in reaching that place, especially by accident. It's always fun to learn something new though. :lol:

 

[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