# Why Platinum does not precipitate when I add NH4Cl



## Pierre2laps (May 26, 2020)

Hello everyone,

I have some problems concerning the precipitation of platinum using NH4Cl (ammonium chloride).

I have a spent leaching solution of gold (gold has been already removed). The solution has still 160 mg/L of Pt and 1600 mg/L of Pd. I would like first to remove platinum by precipitation using NH4Cl. I added a great quantity of NH4Cl satured solution to the solution, but nothing happened. The pH of the solution is around 0,5.

Can someone explain me why ? And what I should to succesfully precipitate platinum ?

Sorry for my english guys and thank you in advance for your help.


Pierre.


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## Lino1406 (May 26, 2020)

How was the gold removed?


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## Pierre2laps (May 26, 2020)

Gold has been removed using sodium metabisulfite.


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## FrugalRefiner (May 26, 2020)

I think you'll have trouble precipitating the Pt at that dilution. It needs to be precipitated from a concentrated solution. The ammonium chlor-platinate is slightly soluble, so at that level it's possible none will precipitate.

Dave


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## kurtak (May 26, 2020)

Dave is quite right - PGM "salts" (other then Pd precipitated with DMG) are quite water soluble

If you are simply trying to "recover" the PGMs you would be better served to cement the PGMs from the spent (gold already dropped) solution 

if you are wanting to actually "refine" the PGMs (part the Pt & Pd) I would still first cement them from the original solution (gold already dropped) & then go to work parting the cemented (& mixed) PGMs

Note; - working with PGM "salts" can be quite hazardous unless you are FULLY set up to work with them 

IMO (in my opinion) if you are not FULLY set up to deal with "refining" PGMs you are better served to cement them from solution & then pass them on to a refinery that deals with refining PGMs

Kurt


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## Palladium (May 26, 2020)

How much solution?


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## Pierre2laps (May 26, 2020)

Thank both of you for your answers. 

So, the problem could be the concentration which is not enough. It's strange because I read in this article (see attached picture, bottom of page 3) that 200 mg/L is a suitable concentration for precipitating Pt with NH4Cl.


What you guys do you think ?


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## kurtak (May 26, 2020)

Did not have time to read the document you attached (looked at it but did not have time to fully read)

its not a question of how much Pt &/or Pd is in the solution - its a question of how much water

Again - PGM "salts" are quite water soluble - so even if the amount of PGMs is relatively high - if the water content is also high it will prevent the PGMs from precipitating (as there salts)

Even if the water content is low - it "may" allow "some" PGM salt to precipitate - but not all of it

In other words it depend on how much water is in the solution whether - no PGM salt precipitates - some PGM salt precipitates but not all - or it all precipitates

You have two options - Evaporate most if not all the water from the solution --- or cement the PGMs from the solution as it is

That goes to the question palladium asked - how much solution do you have

Personally - I would cement them --- that said - cementing PGMs is "a bit" different then cementing gold or silver so be sure you understand it or it can be "somewhat" of a problem - its simple but needs to be done right

Kurt


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## Palladium (May 26, 2020)

kurtak said:


> That goes to the question palladium asked - how much solution do you have
> 
> Personally - I would cement them --- that said - cementing PGMs is "a bit" different then cementing gold or silver so be sure you understand it or it can be "somewhat" of a problem - its simple but needs to be done right
> 
> Kurt



Yeah i'm trying to figure out if we are dealing with a couple of grams or 100 grams in solution.
Since he knows what the concentrations of pd and pt are i'm wondering if he also knows what base metals are in there and the concentrations. If the solution is fairly clean you could drop the pt and pd with zinc, wash til clean and neutral, and then part with nitric to remove the pd. Then drop the pd with zinc again and wash until neutral, and then clean that up with hcl.That should get you a fairly clean product you can send for secondary refining or refine yourself. I don't like dealing with salts and all that work that comes with it.


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## Lino1406 (May 26, 2020)

Did you check the gold does not contain them both? (SMB is a very strong reducer and not selective)


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## Lou (May 26, 2020)

At those concentrations, it would be best to look into cementation.


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## Refining Rick (May 26, 2020)

If I remember correctly, don't you drop the PGMs with ammonium chloride first, then gold second (with copperas or SMB)? It's been awhile so I do not remember the why.


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## Lino1406 (May 26, 2020)

Here is why: redox potentials PdCl4= 0.62v, PtCl4= 0.72v, PtCl6= 0.7v while that of SMB -0.2v!! to precipitate gold (1v) selectively use copperas, 0.771v


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## Pierre2laps (May 27, 2020)

Initially the volume of the solution was 1,1 L. Yesterday, I reduced the volume by evaporation untill around 0,5 L. So the new concentration is about 300mg/L of Pt and 3g/L of Pd.

I have also lots of copper in solution, around 6g/L and traces of Zn, Fe, In, Ni.

I would like to avoid to cement the solution because I want a selective precipitation of Pt and Pd.


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## Pierre2laps (May 27, 2020)

This morning I found this solid particles onto the suface of the solution. As I said before, yesterday, I only evaporated the solution, I did not add any chemicals.

I'm wondering if it's precipitate or crystals. It's yellowish, but if it's Pt salts, it would be deep in the solution (because it's heavier than the solution) right ?


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## kurtak (May 27, 2020)

Not feeling so good this morning - woke up with a sore throat so not feeling up to posting much

That said - Lino is quite right - by using SMB to drop your gold - some - of the Pt/Pd may very well have dropped along with your gold

You would have been better served to drop your gold with copperas

I have a question - are you a student at a college/university ?

I ask because it sounds like you are able to have your solutions test with AA & that you are working on a school project ?

Please tell us more about you ?

Such as - is this a one time school project - or a hobby refiner - or refine on a regular bases - how well equipped are you to do refining - etc. etc. ????

Kurt


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## Pierre2laps (May 27, 2020)

I evaporated more and then add more NH4Cl, and after filtration I got a nice yellowish precipitate (really fine).

Now it will be the time for Pd (I will try with NaClO3), I keep you inform, you a really nice community, thank you very much for your help.

To answer you @Kurt : I'm a trainee and I'm working in a refinery company in France (I'm a material engineer student, not chemical engineer hahaha, it's the reason why !).I' m in charge of catalytic converter recycling developmment. And this is a try of my protocol to recover Pt,Pd and Rh from catalytic converter. I'm trying the protocol before on the spent leaching solution of gold before to try it on catalytic converter.


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## Palladium (May 27, 2020)

You need a much BIGGER test. Those recoveries are going to be so small that the results are not going to be accurate as far as yield, but with the equipment you have you already know the yields, but knowing the yields and recovering those yields can be a challenge as you are finding out.
I'm curious! If your doing cats where did all that copper come from?


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## Pierre2laps (May 28, 2020)

Palladium said:


> You need a much BIGGER test. Those recoveries are going to be so small that the results are not going to be accurate as far as yield, but with the equipment you have you already know the yields, but knowing the yields and recovering those yields can be a challenge as you are finding out.
> I'm curious! If your doing cats where did all that copper come from?




I have lot of copper because the solution is a spent leaching solution of gold (gold free). I used this solution for my test, because the quantities of Pt and Pd are quiet the same than what I can expect from the leaching of catalytic converter.


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## Palladium (May 28, 2020)

Yeah you can't really do that. It order for you to prove your theory about what process you will chose to use for recovering those metals, you are going to need to run it just like you would in production for what you are trying to accomplish. That's how you learn and work the kinks out. You can't use one type of process to prove another one. I thought maybe you had used copper as a collector in the melt to recover the pgm's.

Will you be recovering the metals from the cat yourself or will you only be dealing with the metals after they are collected? Being how this will be a business venture and your profit and lose will be based on it they are VERY important questions that need to be answered and your theories proven.


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## Lou (May 28, 2020)

You should still look at copper cementation for this product.


In production for autocatalyst solution chemistry, very high affinity resins are required and even then, the Rh is problematic because of speciation.


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## nickvc (May 29, 2020)

If you are looking to wet refine cats I believe you will fail to compete with the big boys who use massive plasma furnaces and melt the metals out and then refine the resultant bars.
We have had several members try to compete using wet chemistry but the problem they all encountered was the amount of pregnant solution left in the sludges after filtration which amounted to more than the charges from the refiner, I’m sure Lou will chime in here if I’m wrong , the other problem you will encounter is that the resultant sludges are highly toxic and will still hold values as pointed out above and you will struggle to recover them economically.


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## kurtak (May 29, 2020)

Ok - so you want to leach PGMs from CATS - & that is fine - at least on the face of "the idea' of doing so

However - the problem is NOT in getting the PGMs back from the leach solution

The problem is going to be leaching the CATs in order to get the PGMs into a solution from which you can recover the PGMs in the CATS

Leaching the PGMs from CATs is nothing like most &/or any other leaching process

In other words - its not as simple as put the CAT (material) in reaction vessel with some AR (&/or other leach) 

Wet leaching CATs is a "stand alone" specialized process that only a few companies/people in the world know

Lou is "one" of those that knows/understands the requirements for processing CATs - so he is the one person here that can at least give you a "heads up" on what is going to be "required" to even get started down this road

That said - could you please tell us some more about how/what you are planning to do to proceed with leaching CATs

Kurt


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## Yggdrasil (May 29, 2020)

Hi Kurt.
I think you have missed this section:


> To answer you @Kurt : I'm a trainee and I'm working in a refinery company in France (I'm a material engineer student, not chemical engineer hahaha, it's the reason why !).I' m in charge of catalytic converter recycling developmment. And this is a try of my protocol to recover Pt,Pd and Rh from catalytic converter. I'm trying the protocol before on the spent leaching solution of gold before to try it on catalytic converter.



But still I'd love more information on the topic.
Like: how are they doing it now and how his protocol for leaching is designed (if he is allowed to disclose it, that is) getting it out of solution is the easy part, at least in my eyes.


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## Lou (May 29, 2020)

I'd say leaching commercial autocatalyst is pretty much all but a fool's errand. Much better to smelt and go after it from there.

It can be done, and done well, but the attrition rates on equipment, the amount of "tricks" required to do the job (such as in situ resin-in-pulp after reducing ORP and adjusting content) and the resultant acid laden waste...what Kurt said. 

Now industrial catalysts, like foil corrugates, soluble alumina substrates, anything that can be easily value concentrated/densified.

Typically, at least at my place, when things go into the refining circuit, they're already many thousands of dollars per gallon of solution. The final solutions are then (depending on what it is) 200-400 g/L in the finished precious metal. In the case of Rh, you can imagine that it is very expensive!


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## kurtak (May 30, 2020)

Yggdrasil said:


> Hi Kurt.
> I think you have missed this section:
> 
> 
> ...



Hi Yggdrasil

No I did not miss that at all - Pierre2laps said he is in charge of CAT recycling "development" --- in other words he is "working on" the "potential" idea of adding CAT leaching to the company (he is working for) refining possibility/potential - & that is fine

The problem (at least as I am seeing it) is that he is "not" working with a leach solution that came from leaching CAT(s) --- instead the solution is from a "gold leach" which also contained PGMs - once the gold was dropped he is now going after recovering the PGMs from that solution

In other words (as best I can tell) he is trying to figure out how to recover PGMs from a solution - so that once he moves ahead with leaching a CAT he will then know how to recover PGMs from a solution that has PGMs in it --- which is fine because if he is going to work with solutions that contain PGMs he is going need to know how the get the PGMs back from those solutions

BUT - if he is going to work on "developing" a CAT leaching process then - in my opinion - he needs to START by leaching some CATs --- not a solution with PGMs in solution from a process other then leaching CATs

Why ? 

Because getting the PGMs back out of solution once you put them in solution is not the problem --- putting the PGMs into solution --- based on the material containing the PGMs --- is where the problem can/will be

Refining gold scrap (such as white gold &/or dental scrap) that contains PGMs is not a problem - the scrap goes into AR - the gold & PGMs go into solution - you drop the gold from the solution - then go after the remaining PGMs by ether cementing then as a mixed PGM (sponge) - or selectively precipitate them as there individual salts (or other methods that work) 

In other words - with this kind of material - parting the PGMs & the gold is not a real problem - its a "basic" gold refining process

On the other hand - leaching CATs is a VERY different process then refining gold/PGM scrap because of the nature of the material

In other words - due to the nature of CAT material (how they are made) leaching them is a "stand alone" process - meaning it "needs" its very own set up for processing - it needs its own leaching/refining circuit - completely separate from a standard gold/PGM scrap refining circuit --- you can not simply run CATs through the same circuit that you run gold/PGM scrap through

Not only are the leach circuits different - but the leach solutions are completely different - AR leaching will not even come close to getting all the PGMs out of CATs - AR leaching will get a fair amount of the Pd - some Pt & little or no Rh --- HCl/Cl is "a bit" more effective then AR in that it gets more of the Pd/Pt & "some" of the Rh --- that said - nether of these leaches will come close to covering cost let along make a profit

Out side of those two leaches I have no idea what would work for a leach that would actually pay (bromine maybe)

In other words - when it comes to leaching CATs - its not so much a question of getting the PGMs out of solution once they are in solution - the BIG question is getting them into solution in the first place 

Knowing how to get then out of solution does you no good - if you don't know how to put them in solution first

Therefore - what Pierre2laps needs to work on - if he is go to work on "developing" a CAT leaching process - then he needs to work on the leaching process before he even thinks/worries about getting the PGMs from solution

Kurt


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## kurtak (May 30, 2020)

Pierre2laps

Please read this thread - it will tell you "some" (& only some) of the problems you will run into in trying to leach CATs

:arrow: Large Volume vs. Small Volume CAT Processing

Kurt


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## kurtak (May 30, 2020)

Pierre2laps

Please also read this thread - in this thread - take note of the discussion between Lou & myself

In that discussion note that Lou "touches" on (limited/basic) of "some" things that are required for a CAT leaching circuit --- as well as the volume of CATs needed before such a venture even becomes profitable --- as well as the kind of cost your company will be looking at in order to work on a volume to pay for & profit on the investment to set up such a leaching process

:arrow: Verifying Catalytic Converter Recycling Process

Kurt


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## Yggdrasil (May 30, 2020)

Thanks Kurt.
It was not intended as any kind of critics of You or Pierre or any comment on the process. :wink: 
He is an trainee and I have no idea on how their regime regarding trainees are.
And as I wrote, but in other words: getting things out of solution is a minor thing comparing to getting it in.
Happy weekend folks


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## Pierre2laps (Jun 1, 2020)

Thank you every one for your advices which are really precious regarding your experience in the field.

I'm aware that the real challenge here is "How to get PGMs into the solution ?"

I started to deal with the second phase which is "How to get PGMs out of the solution" because at the moment we didn't receive the cat samples, so I couldn't start to work on the leaching process.

But now, we received the samples. Unfortunately (or not) most of them are metallic cats. On Friday, I tried two different leaching solution on two samples (50 gramms of metallic cats) for each solution.

1) HCl + HNO3 (added HNO3 untill no reaction)
2) HCl + HNO3 + H2SO4 (added HNO3 untill no reaction)

Under vigourous stirring for both at 120°C during 6h.

I'm aware that is definitively not the correct and optimal process. It's just a beginning to give me an idea of how many pgms I can leach with that.

I believe that H2SO4 in presence of HNO3 forms the NO2+ elecrolyte which can be kind of shield for the iron sheets. By this way, the leaching solution doesn't not leach that much the iron sheets, and so the amount of Fe in solution is not that much, which can help later to getting out more easily the PGMs.

This week, I will check the PGMs concentration in the leaching solution by ICP-AES. I keep you infom. Again thank's every one.


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## Pierre2laps (Jun 5, 2020)

Here is the precipitation I got for Pd when I added NaClO3. Really nice I think. The solution was definitevly much richer in Pd than Pt.


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## Liquidau (Jun 14, 2020)

I'm seeing the same thing. My XRF analysis showed surprisingly low to ZERO Platinum. So there might not be any Pt there to drop! But the palladium is definitely there-----the telltale red colour. I'm dropping the Pd now with zinc strips; should know the yield in a couple of days.
Cheers.


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