# Latest Platinum Drop



## Scrapper-aw- (Dec 16, 2009)

So in another thread I was talking about just learning about extracting Pt by itself. I keep attempting to drop with any batch that through assaying is known to have a decent enough percentage of Pt. If nothing else it's great practice and experience! 

I have over a dozen filters with the precip from that many different attempts over the last couple of weeks sitting in a tub waiting to be incinerated. Yesterday we were working as usual with a couple different batches at once and one of them was on the heater having just had the Au sponge filtered off. We raise the temperature to 170*F to 180*F and then add our ammonium chloride and, (in the past, but not with this particular batch), HCl. 

Now, normally we would also prepare an apx. 1 lb of ammonium chloride with 500ml of water for each 8 liters of Pt - Pd laden liquid. We mix it into a slurry and add it in that fashion.

With this batch we got it up to 189*F. When we added the ammonium chloride laden liquid from the top of the slurry we saw an INSTANT reaction. That was unusual. Immediately Pt started to drop out faster than I've ever seen it drop out. Since all the other Pt drops we've done have taken considerable time to complete we gave it about 90 minutes and filtered. This is what we captured on the filter!





For scale, this is a 22 cm filter paper. This should be about 1/4 to 1/2 oz. t. Pt. Our preliminary assay with our X-ray shows a purity of >93%! I will need to schedule some oven time in the near future. We've gotta have a cook off!!!

:lol:


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## Platdigger (Dec 18, 2009)

So, are you saying it is greater than 93 percent platinum chloride, which is about 45.7 percent platinum metal?


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## Scrapper-aw- (Dec 18, 2009)

Platdigger said:


> So, are you saying it is greater than 93 percent platinum chloride, which is about 45.7 percent platinum metal?



Well I can only say that when I have roasted and ignited other drops that measured in the 90% range with our x-ray in the chloride state, the metal button to come from the chloride was also in the same 90% when x-ray tested and assayed via ICP spectrometer.

I would put money on this batch being around 93% Pt in the final elemental stage.


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## 4metals (Dec 18, 2009)

Every 2.3 grams of ammonium chloroplatinate contains 1 gram of platinum. However if you rinse the salt with a solution containing ammonium chloride, which you should do because some of the salt will re-dissolve in distilled water, you are likely to have some ammonium chloride salt mixed in as well. Never an issue as it is driven off when calcining the salt anyway but my point is it could be less platinum than the 1 gram per 2.3 grams of salt which is the based on the formula weights.


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## Scrapper-aw- (Dec 18, 2009)

4metals said:


> Every 2.3 grams of ammonium chloroplatinate contains 1 gram of platinum.



The weight of Pt metal to come from this is yet to be determined. The % values I mentioned in my last post pertain only to the purity of the Pt, not the quantity. And I did indeed rinse with amonium chloride solution and surely do have some added salts there.

Also the x-ray instrument we use detects only metals.

Quantity is always nice, but I am most interested in knowing how complete of a separation we have achieved in our processes. My goals are to be able to produce 99.9% shot form of Au, Ag, Pd, and Pt. Au and Ag are easy enough. But Pd and Pt are quite challenging. I have on one occasion managed to produce a button of 99 % pure Pt that weighed in at a whopping 0.53 troy ounces. That was last spring; that level of purity has eluded us since then.

:mrgreen:


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## 4metals (Dec 18, 2009)

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.

Next you can drop your gold from the solution followed by dropping the Palladium via chlorination. 

Bromate hydrolysis is a tedious procedure usually performed on larger quantities but it does produce a high quality product. If you're interested in the bromate hydrolysis let me know and I'll post the procedure.


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## Scrapper-aw- (Dec 18, 2009)

4metals said:


> Bromate hydrolysis is a tedious procedure usually performed on larger quantities but it does produce a high quality product. If you're interested in the bromate hydrolysis let me know and I'll post the procedure.



Thanks, 4metals. I have been stockpiling all of our amonium chloroplatinate for further refinement. I also have many pounds of palladium amonium chloride that needs to be processed more to purity. We can save that for another time. But I am interested in learning how to purify our Pt. :mrgreen:


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## lazersteve (Dec 19, 2009)

You can further purify the incinerated platinum sponge buy repeating the AR process on the sponge before melting. 

Each successive cycle through the AR and ammonium chloride should increase the purity of the platinum. 

The incinerated sponge dissolves very easily in hot AR.

Proper denoxxing and ammonium chloride washing is very important to the purity. Of course you will reach a theoretical limit to your purity depending on the contaminating metals. 

Also Palladium ammonium chloride is soluble in excess ammonium hydroxide. The Palladium salt is then precipitated from the filtered hydroxide solution with HCl.


Steve


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## Scrapper-aw- (Dec 20, 2009)

Thanks Steve!

On the Pt, does that mean that the chloride neeeds to be incinerated after each subsequent drop?

And on the Pd, can you please explain what "excess ammonium hydroxide" is? I've looked it up, but I'm not getting the jist of the "excess" part of it.  

Scrap


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## 4metals (Dec 20, 2009)

Bromate Hydrolysis

Impure platinum sponge which has been reduced from de-noxed aqua regia solutions treated with ammonium chloride are collected and processed in 100 ounce lots by a process known as bromate hydrolysis. The objective of this technique is to separate the platinum from other platinum group metals and base metals by the formation of their hydroxides. Platinum, not forming a hydroxide remains in solution for further refining.

Digest the impure sponge and destroy the nitrates by classic evaporation to syrup to drive off the excess nitric. Dilute the syrup with HCl to a concentration of 1.75 troy ounces of Platinum per liter of solution for hydrolysis. This is usually done in a glass lined reactor capable of stirring and either boiling via steam jacketing or heating mantle. Vessel should be sized to allow it to operate at ½ capacity. (for 100 ounces that is approx. 50 liters of solution)

Heat solution to boiling and add 5% of the precious metal weight in zinc chloride. This acts as a coagulating agent. Stir for a few minutes and begin adding a saturated solution of sodium bromate. Solution should be added slowly as it will boil up. 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. Add a total of ½ ounce of sodium bromate (in a saturated solution) for each ounce of precious metal in the reactor. Go slowly as it will foam up, take your time and add water to maintain the original level of the boiling solution. 

Siphon a saturated solution of sodium bi-carbonate into the vessel to neutralize the solution. Adjust the pH to exactly 7.5. Shut off the heat and adjust the volume with water to the original starting level. 

Add 1 liter of a coagulant (magna floc) and allow solution to cool to 40 C. 

Allow the solution to settle for at least 2 hours then decant the clear the liquid followed by siphoning the settled hydroxides which are collected on a filter and washed. Washes are added to the decanted solution.

The decanted solution is now acidified with 2 liters of HCl for every 100 ounces of metal and boiled for 1 hour. Add 5 ounces of oxalic acid for every 100 ounces of metal to precipitate any gold in the solution. If iridium is present, add 1 oz of sodium sulfite for every 100 ounces of metal. The solution is now filtered and transferred to precipitation tanks for conversion to ammonium chloroplatinate.

Heat the solution to 70 C and drop the ammonium chloroplatinate with ammonium chloride. Decant the solution and wash the collected salts in a room temperature solution of 1/3 saturated ammonium chloride solution, 1/3 HCl, and 1/3 H2O.

Either transfer the salts to a glass reactor and reduce with hydrazine or calcine in a silica tray at 800 C for 20 minutes. 

If you started with relatively pure salts (99%) this will produce high purity sponge.

This procedure is completely scalable depending on your reaction equipment. The first time you do it will be the hardest, once you get the required addition volumes down, routine reproduction of results is predictable.


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## Scrapper-aw- (Dec 21, 2009)

Wow, thank you 4metals!

That sounds like a very interesting process. I'm game! 

Time to make my shopping list...... :lol:


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## Lou (Dec 21, 2009)

Some of the things you say fourmetals, some would be displeased to hear. It's all in the literature though.

Some additional points to mention:
- use only sodium bromate, not potassium bromate (supposedly you can lose platinum to a potassium platinum double salt, plus it is less reactive than NaBrO3).
- use sodium carbonate, not bicarbonate--more acid neutralized per amount of mass
- if adding bulk Na2CO3, use overhead stirring to break the foam.


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".


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## 4metals (Dec 21, 2009)

Lou said:


> Some of the things you say fourmetals, some would be displeased to hear.



But by posting it here some are quite pleased to hear. I worked out the specifics of this method from the literature and trial and error. No-one was lining up to give me a procedure. I've used this process since the late 70's and for years produced multiple hundred ounce lots per month producing fine metal for resale. 

The important part of what I said and the reason I posted it on scrappers request is that he also has a use for fine platinum that he produces. If you have no market to resell the platinum, either as jewelers alloy as I did or other reasons, it is not cost effective to do it. It's better to refine it to impure sponge and sell it as a refining lot. Unless you can get premiums for the pure metal it's better to bite the bullet and ship it than to put the time and expense into refining it only to have the buyers discount it anyway.


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## lazersteve (Dec 21, 2009)

scrap said:


> On the Pt, does that mean that the chloride neeeds to be incinerated after each subsequent drop?


The platinum is reduced to the sponge form before each digestion.



scrap said:


> And on the Pd, can you please explain what "excess ammonium hydroxide" is? I've looked it up, but I'm not getting the jist of the "excess" part of it.


 Excess means to add the ammonium hydroxide until all of the palladium salt is dissolved. The process is complete when subsequent additions of ammonium hydroxide with stirring do not dissolve any more of the solids. The initial addition will typically form a burnt orange colored ('flesh colored') precipitate, upon further addition of ammonium hydroxide the flesh colored precipitate will redissolve in the 'excess' ammonium hydroxide solution.

Filter out the solids, rinsing with ammonium hydroxide, and add HCl to the filtered solution. The purified yellow palladium salt will precipitate. Hoke covers this process.

Steve


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## 4metals (Jan 2, 2010)

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.


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## HAuCl4 (Sep 4, 2010)

4metals said:


> 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?


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## lazersteve (Sep 4, 2010)

I have redissolved it in water and also with HCl.

Steve


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## 9kuuby9 (Dec 31, 2013)

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.


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## butcher (Dec 31, 2013)

Stock pot.


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## Lou (Jan 1, 2014)

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


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## 9kuuby9 (Jan 1, 2014)

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.


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## butcher (Jan 1, 2014)

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.


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## 9kuuby9 (Jan 1, 2014)

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.


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## Lou (Jan 2, 2014)

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.


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## 9kuuby9 (Jan 2, 2014)

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)


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## freechemist (Jan 6, 2014)

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


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## 9kuuby9 (Jan 10, 2014)

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.


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## Lou (Jan 10, 2014)

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.


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## freechemist (Jan 17, 2014)

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.


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## kadriver (Mar 4, 2014)

4metals said:


> 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


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## Lou (Mar 4, 2014)

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).


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## 4metals (May 26, 2015)

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.


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