# Pd Pt Rh mix industrial cat refining tips ?



## orvi (Apr 13, 2021)

Hi
for a longer time, we have a quite complex problem sitting in our refining shop. Solution containing approx.:
34% Pd
9% Pt
2% Rh
rest is base metals mainly Fe, Co, Ni, some trace Pb, no Ag nor Au.
Metals are in form of chlorides in used up AR soln. Some nitric is certainly present.
We aim to recover enriched rhodium fraction, more than 50% by mass would be fantastic, as we work with quite a lot of this material. Also Pt and Pd fractions need not to be super pure, also mixed fraction PtPd would be fine. 

I read whole bunch of papers, topics trough forum... And came with some DIY plan how to deal with the issue:

1. drop Pd with DMG - enriching soln with Rh, at pH ca 3 there shouldnt be much Ni coprecipitation, but if some, that is not big issue
2. drop impure Pt with NH4Cl along with some part of Rh as contaminant
3. rest of noble metals cement on something (Zn, Fe ?)
4. calcining impure ammonium hexachloroplatinate and melting remaining metal sponge in NaHSO4 - or leaching Rh with H2SO4 - which approach would be better ? or is there better approach than these ?
5. cemented noble metals leaching similar way as above.

I have no big experience in this field, but have great practical chemistry experience overall. Maybe im missing some point or its wrong in some way...
My question is: will it work ? 
Better question: what´s your suggestion ? how could this be done better/more efficently ? is it even possible ?

Thank you in advance for your opinion


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## nickvc (Apr 14, 2021)

Welcome to the forum.
I will say from the off I’m no expert at PGM refining as I have always avoided it when possible.
The one thing I do recall is that PGMs need concentrated solutions to be precipitated with any degree of success.
If you would be happy with cemented PGMs why not use copper buzz bars and agitation to cement the values from the solution which would give you a much richer concentrate to work with if your aim is to separate the metals or you could simply melt assay and sell.
Trying to work with wet chemistry on cats is a losing option in my opinion, we had a member who spent hundreds of thousands of dollars trying it and found it paid better to de can crush assay and sell as the residues left after filtering contained more values than the refiners charges, he was a very large cat buyer so I assume he got really good terms but it never hurts to ask.


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## JAREL (Apr 14, 2021)

If you have that in solution I believe it best to decompose any nitric acid in solution, add water of the liquid is very acid concentrated, then precipitate with aluminum or zinc putting a little at a time until solution is clear and you get no color from stannous chloride test. That precipitate can be then treated to separate the precious metals.


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## nickvc (Apr 14, 2021)

JAREL said:


> If you have that in solution I believe it best to decompose any nitric acid in solution, add water of the liquid is very acid concentrated, then precipitate with aluminum or zinc putting a little at a time until solution is clear and you get no color from stannous chloride test. That precipitate can be then treated to separate the precious metals.



Problem here is that all the metals will cement out not just the values so back to square one :shock:


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## orvi (Apr 14, 2021)

Thanks for invitation and suggestions  also im sorry for my english, im not native speaker 

I already have it in the HCl solution (ca 19% - by titration). Leaching was inefective, but prolonged heating get things dissolved (AR). XRF confirmed. already have it like this, so i must figure something out  at least i must try hard before giving up  
Cementing everything would be the next option, i wondered precipitating PGM black on zinc dust (excess), than stirring it til all base metals and excessive zinc dissolves in remaining acid (no metals insoluble in HCl are present except PGMs). Should be left with relatively nice enriched PGM mud (in theory).
Also i read in this forum that handling lots of DMG precipitate isnt very "friendly" approach to eliminate Pd.
So from the Pd/Pt/Rh drop on zinc i could proceed with hot nitric leaching (should be selective for Pd and remaining base m. junk and relatively fast due to surface area) to eliminate Pd.
The Pt/Rh residue heating in H2SO4 will be the final step.


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## orvi (Apr 16, 2021)

update:
i treated a small sample of soln. (100 ml - roughly 1g Pt/3g pd + 0,1-0,2g Rh) with NaOH to make roughly pH 2-3 for proper DMG drop of Pd. DMG was used just for removing Pd from the sample, in bulk run ill use nitric leaching for PGM mud which i drop with Zn.
After removing Pd, i treated the soln with powdered zinc to precipitate the Pt/Rh remains. After successful precipitation (XRF) of all valuables, i added some more HCl to eat up the excess zinc, filter the mud and dry it.

To this point, everything worked just fine  I than placed the Pt/Rh/trace Pd powder into 40-50 ml concentrated H2SO4 and cooked it with stirring at 200°C for 1h. But after dilution and filtration, filtrate doesnt have any Rh. No trace. 
I wonder if I should cook it for example for few days (?), or the reaction would finish after couple of hours... 
Hard to say, bit confused.
Any thoughts what ive done wrong ?


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## orvi (Apr 27, 2021)

update:

after numerous failed attempts, here is another one 
i decided that i "train" my approaches on pure, base metals free batch of Pt/Pd/Rh solution. so i managed to get solution with only PGMs dissolved in ratio roughly Pd50 Pt47 Rh3%. 
this was treated with powdered zinc until the solution was free of values. PGM black was filtered and washed well from chloride residues.
to this black ppt, 53% nitric acid was added very slowly in small increments. heating and magnetic stirrer were on and mixture was held at rolling boil for 2 days, with regular aditions of 53% nitric.
after this there comes the dissapointment... in the cake of undissolved metals there was still shitton of Pd (roughly 60-70% dissolved), but strangely enough about 30-40% Pt dissolved also. but afterall, Rh still managed to stay in ppt.
discouraged, i washed the remains of the cake and baked it in conc. sulfuric acid at 200° for 2 hours. after that, the content of Rh in the cake dropped from roughly 3,5% to 1%. also about 1/3 of Pd was gone to the soln. Pt seems to be inert to hot sulfuric acid, which is great news.

i still wonder what is the reason that im unable to dissolve that finely divided Pd in nitric acid. i used to refine Pd contacts, which were solid pieces of Pd and dissolved in nitric with no issue. perhaps as the metals are precipitated chaotically and quickly on the surface of zinc, they block access of nitric straightly to Pd, forming aggregates (???). i dont know what exactly is going on.

thing that comes to my mind was to alloy the PGMs with Al, and than eat Al in HCl, preparing ultrafine PGM dust. this should eliminate the aglomeration issue (if this is the issue). 
or "inquart" PGMs with silver, than proceed straightly to the nitric leach, leaving majority of Pt and Rh in powdered form.

anyone experienced similar behavior ?


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## nickvc (Apr 27, 2021)

As I have stated I’m no expert but I wouldn’t go with silver as that will allow all the Pd and some of the Pt and Rh to be dissolved as well, perhaps an expert could confirm that.
My suggestion would be to inquart with copper and then dissolve in nitric leaving a copper palladium nitrate solution to be treated and the Pt and Rh as a mixed powder again ready for further treatment.
The option I would follow would be to melt with copper and assay and sell the bar but that’s a personal choice.


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## orvi (Apr 30, 2021)

good point. copper seems to be legit choice.
i slowly start to disbelieve all statements in textbooks about Pt and Rh being so inert  mainly Pt.
i firstly blamed old XRF to show some bullsh... but another new (and certified one) clearly shown, that in hot sulfuric acid (200 °C, 24h leach) Pt is also dissolved (quite nicely). 

proceeded with clean PtPdRh chloride solution, i dropped everything on powdered zinc, filtered the PGM black, and cooked it in nitric for 1-2 days. about 60% Pd and 30-40 % Pt gone to the solution. no Rh could be detected in liquid.
the remaining powder (containing ca 3,5% Rh) was cooked in H2SO4 (200 °C) roughly 24 hours. Rh content in the solid residue dropped to less than 0,4 %. that was the good news. Bad news was that sulfuric leaching solution also contained shitton of Pt... :shock: 
Discouraged, i diluted the H2SO4 leaching solution with water to ca 25% concentration and dropped PGMs with zinc. 
The solid (after complete zinc dissolution in excess acid) contained 10 % Rh, ca 30% Pt and rest Pd.
Well done  

yes. youre right. if it was my decission, catalyst will go straightly to the crucible, melted with Pb plus right flux at minimum 1400°C, residue cupelled and sold 

it started to be too interesting  ill keep you informed if something worth sharing comes out from my experiments with it.


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## Geo (Dec 10, 2021)

To your solution, add a concentrated solution of ammonium chloride. Amounts and volumes are relative. Add the concentrated solution to the pregnant solution in amounts that are relative to the starting amount of pregnant solution. The ammonium chloride does two important things. First it drops Pt as a yellow salt. This is what you are looking for. Add until no more yellow salt is produced. Second, the ammonium binds with the palladium chloride. This allows the Pd salt to be converted to a solid by adding chlorine gas. The Pd salt will precipitate as a red to dull-red salt. None of this effects the rhodium to any great degree, which remains in the solution. I recover the Rh and can clean it somewhat but have never tried to refine Rh. Be aware that finely divided Rh powder will dissolve in concentrated HCl without an oxidizer. Palladium is difficult to cement from acidic solutions. It tends to dissolve in dilute HCl. To successfully cement all Pd from an acidic solution, the PH must be adjusted up. From my own observations, the less reactive a metal is, the harder it is to drop as an oxide. You can dilute gold solution until the solution has no color but still test positive for gold. All of the less reactive metals exhibit the same behavior. In an electrowinning cell, the solution entering the cell has very little dissolved metal initially.


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## Geo (Dec 10, 2021)

Geo said:


> To your solution, add a concentrated solution of ammonium chloride. Amounts and volumes are relative. Add the concentrated solution to the pregnant solution in amounts that are relative to the starting amount of pregnant solution. The ammonium chloride does two important things. First it drops Pt as a yellow salt. This is what you are looking for. Add until no more yellow salt is produced. Second, the ammonium binds with the palladium chloride. This allows the Pd salt to be converted to a solid by adding chlorine gas. The Pd salt will precipitate as a red to dull-red salt. None of this effects the rhodium to any great degree, which remains in the solution. I recover the Rh and can clean it somewhat but have never tried to refine Rh. Be aware that finely divided Rh powder will dissolve in concentrated HCl without an oxidizer. Palladium is difficult to cement from acidic solutions. It tends to dissolve in dilute HCl. To successfully cement all Pd from an acidic solution, the PH must be adjusted up. From my own observations, the less reactive a metal is, the harder it is to drop as an oxide. You can dilute gold solution until the solution has no color but still test positive for gold. All of the less reactive metals exhibit the same behavior. In an electrowinning cell, the solution entering the cell has very little dissolved metal initially.


Also, I use tri-chloro pool chlorine powder to generate the chlorine gas. Make sure the solution is acidic and add the pool chlorinator in really small doses while stirring. A very small amount creates a lot of chlorine gas. This is a recovery process and not refining. The resulting Pd salt is not pure.


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## orvi (Dec 11, 2021)

Geo said:


> To your solution, add a concentrated solution of ammonium chloride. Amounts and volumes are relative. Add the concentrated solution to the pregnant solution in amounts that are relative to the starting amount of pregnant solution. The ammonium chloride does two important things. First it drops Pt as a yellow salt. This is what you are looking for. Add until no more yellow salt is produced. Second, the ammonium binds with the palladium chloride. This allows the Pd salt to be converted to a solid by adding chlorine gas. The Pd salt will precipitate as a red to dull-red salt. None of this effects the rhodium to any great degree, which remains in the solution. I recover the Rh and can clean it somewhat but have never tried to refine Rh. Be aware that finely divided Rh powder will dissolve in concentrated HCl without an oxidizer. Palladium is difficult to cement from acidic solutions. It tends to dissolve in dilute HCl. To successfully cement all Pd from an acidic solution, the PH must be adjusted up. From my own observations, the less reactive a metal is, the harder it is to drop as an oxide. You can dilute gold solution until the solution has no color but still test positive for gold. All of the less reactive metals exhibit the same behavior. In an electrowinning cell, the solution entering the cell has very little dissolved metal initially.


You are right. I have tried this standard procedure early on. Main problem with this stubborn feedstock is very low Rh content. It is very difficult for me to "enrich" Rh content for example to 20% (which could we sell) without loosing like 50% in the process. I am certain that it could be done properly, but the NH4Cl step and also DMG or chlorine Pd precipitation drag also a good portion of Rh salts to the precipitate. I studied many papers on the Pt drop subject, also read whole bunch of information here on the forum, mainly from the experts in the field, like Lou or 4metals. Along the other refining stuff that i need to do, i have little time to move with this material forward.

Currently, small testing is undergoing - which raised from observation, that Pt is relatively soluble in nitric acid, when finely divided. 
Cementation of another PtPdRh solution on zinc formed nice, easy settling precipitate of PGMs. Unfortunately, prolonged boiling in nitric acid shown that reaction very quickly reach equilibrium point, when no more metals are dissolved. Platinum and palladium were dissolved, Rh staying in the precipitate. But it was slow and results were nowhere "usable", as the reaction didn´t reach full dissolution of PtPd anyway.
Equipped with proper gear, we prepared two buttons of PtRh material "inquarted" with copper and aluminium, respectively. PGM content 20%. Just to test this out. No base metals, just PtRh alloy and copper or aluminium.

Theory was to dissolve them in nitric or NaOH, leaving very active particles of PGMs, which could then be leached with nitric to get rid of the majority of Pt. Just enough to pass that 20% mark on Rh, as we could recover sellable Rh. Dissolving the copper "inquarted" button in nitric acid unfortunately produced so fine nanoparticles of PtRh, that they refuse to settle even after a week. Flocculants arent of any help (at least what i have in hand). So i am aware of putting the second Al "inquarted" button to NaOH solution, as it will likely produce the same result. 
Now figuring out what to do with this route, if to completely abandon it, or try one more time.
We concluded with any route employed, the main problem will be separation of Pt and Rh from this mix. 

I was never "***ked up" so badly by chemistry in my life (doing high end chemistry for 8 years now)  after these experiences, i start to think that it will be unaviodable to conduct hydrolysis on this stuff in some step. Another thing, which i never done before. Also, i dont know if it is even possible to conduct the hydrolysis on such impure mix of PGMs (i can get rid of base metals easily).

Maybe one more question: 
It is possible in some way to drop Pt and Pd simultaneously with saturated NH4Cl solution and chlorine gas ? This could possibly eliminate two steps of precipitation/filtration, maybe lowering the loss of Rh locked up in the precipitate to somewhat lower percentage. In my position, i have no big benefit/profit from refining Pt and Pd to the pure form (eg 99,9%). My objective is only to produce some reasonably enriched Rh fraction, where i could get paid for Rh. I also want to avoid the manipulation of large quantities of PGM salts to minimum due to hazards, so maybe 1-5% of extra profit on fully refined stuff don´t outweigh the potential risks.


You mentioned, that Rh is soluble in concentrated HCl even without oxidant. This is very interesting observation, thank you for pointing it out 

Thank you for your reply.
orvi


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## Geo (Dec 11, 2021)

It can be done in one step but then you would have to reduce and refine the Pd and Pt separately. After the addition of NH4Cl, it is simple to filter the salt out and then add the chlorine gas for the Pd. In my case, I add pool chlorinator powder to generate the chlorine gas. The palladium ammonium chloride is stable in solution until chlorine gas is introduced and then converts to red (NH4)2PdCl6. The process I do is quick and dirty. It is not perfect but it effectively separates the metals. There will be cross contamination of elements in each phase. This is recovered by cementation and collected until enough to process is gathered.


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## orvi (Dec 11, 2021)

Geo said:


> It can be done in one step but then you would have to reduce and refine the Pd and Pt separately. After the addition of NH4Cl, it is simple to filter the salt out and then add the chlorine gas for the Pd. In my case, I add pool chlorinator powder to generate the chlorine gas. The palladium ammonium chloride is stable in solution until chlorine gas is introduced and then converts to red (NH4)2PdCl6. The process I do is quick and dirty. It is not perfect but it effectively separates the metals. There will be cross contamination of elements in each phase. This is recovered by cementation and collected until enough to process is gathered.


Thank you for the valuable information. Do you measure some quantity of NH4Cl based on expected ammount of PGMs or just dump in good excess of it (sat. solution) ? I am asking because too much NH4Cl can also cause the drop of other PGMs and junk with hexachloroplatinate precipitate (at least what i read about it and observed in my first trials).

If i dont bother with PtPd mixture to say first (i will end up mixing the two anyway in the final melt to sell them), is there any culprit to process platinate and palladate salts (precipitated both together) to PtPd metal alloy ? I do not intend to refine them, as this will cause a lot of hazardous work for very little profit. If i have them separated in close to pure form (eg 95-98%) by means of two stage precipitation as you do, other element (traces of Pt in Pd fraction) would be considered as impurity at selling, thus lowering the value of whole lot.

What is the composition of pool chlorinator you mention ? I think you mean calcium hypochlorite. Here, it is obtainable, and I think about using it instead of setting up chlorine generator from TCCA/HCl - calcium in chloride solution shouldn´t be a problem (?). One option was to use chlorate, but i don´t quite like the possibility of ClO2 popping and splashing PGMs to me and whole fume hood.

Yeah, i look for something like this  rough and straightforward. I would be pleased to have enough time to play with this in more scientific way (that´s what i am used to do in my "real" work). Time for "educated giving-up" on this was while ago. Now i am all into this (unintetionally) and i must somehow scavenge the values from it. Luckily, time is not the big issue, I am not in hurry.

I will post here if any usable result (positive or negative) come out of this situation.
Appreciate your responses.
orvi


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## Geo (Dec 11, 2021)

Trichloro-s-triazinetrione in powder form.
Sodium hypochlorite in powder form will work as well but commercial bleach will dilute the solution.


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## Geo (Dec 11, 2021)

Ammonium chloride in a saturated solution is used to drop both Pt and Pd with addition of chlorine gas. The solution is also used as a rinse to wash the recovered salt. If you use water, it will dissolve some of the salt. Since an excess of NH4Cl is needed, the saturated solution can absorb very little extra salt. It is just natural to use the same solution to rinse the solution from the precipitated salt.


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## orvi (Dec 13, 2021)

So, after a long time I have something new with this refining/learning venture. And maybe worth sharing with community, as these findings could be usable in some way  kind of. This time, training on model situation/hypothesis.

As I explained above, we hypothesize about "inquarting" PGMs with copper or aluminium, and then etch base metals out and leach the remaining PGM precipitate with nitric acid in order to dissolve Pd and Pt, hopefully leaving Rh as insoluble mud.

So, two alloys were prepared (aiming on 20% PGM content - roughly accomplished), but this time just PtRh, without Pd (no pure Pd in hand unfortunately). As the platinum will be more tough to dissolve, it should be good quantification of result anyway. Dont mind other elements measured, our XRF starting to be confused a little 



First, copper alloy was etched with nitric acid (65%). From the first few ml of acid, it was quite obvious what is gonna happen  copper dissolved without issues and also without reqirement for heating - to the black "solution". Precipitate thus formed was so fine, that it refused to settle (whole week settling time). Some bigger particles make it to the bottom, but no progress was seen afterwards. Two different flocculants were tried with no success, and similar result was obtained also with centrifuge. Centrifuge tho produced a small ammount of relatively usable "solid" residue. I was affraid of something like this happening, but it is what it is.


Supernatant (after centrifuge) was measured by XRF to reveal that significant portion of Pt was in solution. But it is important to mention, that solution was full of nanoparticles of the PtRh, so the result is only informative. Also, Os and Au certainly aren´t present, our XRF gun need some understanding for fiction results 


This approach could be valuable for quick dissolution of these metals (mainly Pt), maybe in AR (as Lou suggested in one thread), but this precipitate would be very painful to deal with. No filtration recommended, as it would likely fail completely  It is what it is, lesson learned.

Next, Al+PGM alloy was dissolved in 20% NaOH solution. This time i was pleased by the results from the beginning. 


Reaction was very robust, but not going out of control so quickly, as plain Al would behave. Cooling with water bath and cautious addition of more NaOH is required. Precipitate of PGMs was this time very compact, yet fluffy. Heavy, readily settled to the bottom of the beaker. Precisely what I was looking for the next experiments. But, reality shows if it serves good for the nitric leaching step  Hopefully, grain size and crystal structure will help us.


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## arthur kierski (Dec 14, 2021)

orvi said:


> Oi
> por um longo tempo, temos um problema bastante complexo sentado em nossa oficina de refino. Solução contendo aprox .:
> 34% Pd
> 9% Pt
> ...


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## Yggdrasil (Dec 14, 2021)

?


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## arthur kierski (Dec 14, 2021)

arthur kierski said:


> i would do the folowing---1-cement with copper--the powder from cementatio,dissolve with nitric,making a solution,with pd---the powder left use hcl+peroxide,the liquid will contain pt and the powder left is rh--now ,treat the solutions with the reagents like dmg for pd and the platinum solution with nh4cl--the rh ,purifies your way


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## Yggdrasil (Dec 14, 2021)

Hi sa dugay nga panahon kami adunay usa ka medyo komplikado nga problema nga naglingkod sa among refining workshop. 
Solusyon nga adunay gibanabana nga: 
34% Pd 
9% Pt 
2% Rh 
ang uban mga base nga metal, kasagaran Fe, Co, Ni, pipila ka mga timailhan sa Pb, walay Ag o Au. 
Ang mga metal anaa sa porma sa mga chloride sa AR nga solusyon nga gigamit. Tino nga adunay pipila ka nitric. Ang among tumong mao ang pagbawi sa gipadato nga tipik sa rhodium, labaw pa sa 50% sa masa mahimong talagsaon, tungod kay kami nagtrabaho uban sa daghan niini nga materyal. 
Dugang pa, ang Pt ug Pd fractions dili kinahanglan nga super puro, ug ang mixed PtPd fraction mahimong igo. Nagbasa ako usa ka hugpong sa mga mantalaan, mga thread sa forum ... 
Ug nakamugna ako usa ka plano sa DIY kung giunsa ang pag-atubang sa problema: 
1. Ipagawas ang Pd nga adunay DMG - Rh enrichment solution, sa pH ca 3 kinahanglan nga dili daghan ang Ni co-precipitation, pero kung naa, dili kini dako nga problema. 
2. buhian ang dili putli nga Pt nga adunay NH4Cl uban ang pipila ka bahin sa Rh isip kontaminant 
3. nahabilin nga mga halangdon nga metal, semento sa usa ka butang (Zn, Fe?) 
4. calcination sa dili putli nga ammonium hexachloroplatinate ug pagtunaw sa nahabilin nga metal nga espongha ngadto sa NaHSO4 
- o leaching sa Rh uban sa H2SO4 
- unsa nga paagi ang mas maayo? 
o aduna bay mas maayo nga paagi kay niini? 
5. halangdon nga mga metal nga gisemento sa leaching sa susama nga paagi sama sa ibabaw. 
Wala akoy daghang kasinatian sa kini nga natad, apan ako adunay daghang praktikal nga kasinatian sa chemistry sa kinatibuk-an. 
Tingali kulang ako usa ka punto o nasayop ako sa usa ka paagi ... 
Ang akong pangutana mao: 
mahimo ba kini? 
Labing maayo nga pangutana: 
unsa ang imong sugyot? 
sa unsa nga paagi kini mahimo nga mas maayo / mas episyente? mahimo pa ba? 
Salamat daan sa imong opinyon.


Google translate makes wonders


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## Yggdrasil (Dec 14, 2021)

Hi
for a long time we have a rather complex problem sitting in our refining workshop. Solution containing approx.:
34% Pd
9% Pt
2% Rh
the rest are base metals, mostly Fe, Co, Ni, some traces of Pb, no Ag or Au.
Metals are in the form of chlorides in the AR solution used. Certainly some nitric is present.
Our goal is to recover the enriched fraction of rhodium, more than 50% by mass would be fantastic, as we work with a lot of this material. Furthermore, the Pt and Pd fractions do not need to be super pure, and the mixed PtPd fraction would be adequate.

I read a bunch of newspapers, forum threads... And came up with a DIY plan of how to deal with the problem:

1. Release Pd with DMG - Rh enrichment solution, at pH ca 3 there should not be much Ni co-precipitation, but if there is, this is not a big problem.
2. release impure Pt with NH4Cl along with some part of Rh as a contaminant
3. rest of noble metals, cement on something (Zn, Fe?)
4. calcination of impure ammonium hexachloroplatinate and melting the remaining metal sponge into NaHSO4 - or leaching of Rh with H2SO4 - which approach would be better? or is there a better approach than these?
5. noble metals cemented with leaching in a similar manner as above.

I don't have a lot of experience in this field, but I have a lot of practical experience in chemistry in general. Maybe I'm missing a point or I'm wrong in some way...
My question is: will it work?
Best question: what's your suggestion? how could this be done better / more efficiently? is it even possible?

Thank you in advance for your opinion.

And now in English 

Please post in English. It is an international forum and English reach most members.

Regards Per-Ove


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## Geo (Dec 14, 2021)

Just as we refine gold twice to improve quality, PGM's from the same process. The fastest process is to precipitate Pt with NH4Cl. Filter out Pt salt. Precipitate Pd by adding chlorine gas or other source. Precipitate Rh with cementation. All three will be contaminated. Reduce the salts in your preferred method. Refine a second time taking more care or using different precipitants.


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## butcher (Dec 14, 2021)

_Authur Kierski our well-known member is still having trouble with the new forum, I do not understand the problem but it may have something to do with translating his messages._

Arthur posted above:
_Hi
for a long time, we have had a pretty complex problem sitting in our refining workshop. A solution containing approx.:
34% Pd
9% Pt
2% Rh
the rest are base metals, mostly Fe, Co, Ni, some traces of Pb, no Ag or Au.
Metals are in the form of chlorides in the AR solution used. Certainly some nitric is present.
Our goal is to recover the enriched fraction of rhodium, more than 50% by mass would be fantastic, as we work with a lot of this material. Furthermore, the Pt and Pd fractions do not need to be super pure, and the mixed PtPd fraction would be adequate.

I read a bunch of newspapers, forum threads... And came up with a DIY plan of how to deal with the problem:

1. Release Pd with DMG - Rh enrichment solution, at pH, ca 3 there should not be much Ni co-precipitation, but if there is, this is not a big problem.
2. release impure Pt with NH4Cl along with some part of Rh as a contaminant
3. rest of noble metals, cement on something (Zn, Fe?)
4. calcination of impure ammonium hexachloroplatinate and melting the remaining metal sponge into NaHSO4 - or leaching of Rh with H2SO4 - which approach would be better? or is there a better approach than these?
5. noble metals cemented with leaching in a similar manner as above.

I don't have a lot of experience in this field, but I have a lot of practical experience in chemistry in general. Maybe I'm missing a point or I'm wrong in some way...
My question is: will it work?
Best question: what's your suggestion? how could this be done better / more efficiently? is it even possible?

Thanks in advance for your opinion  
More about this source textSource text required for additional translation information
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## orvi (Dec 14, 2021)

Geo said:


> Just as we refine gold twice to improve quality, PGM's from the same process. The fastest process is to precipitate Pt with NH4Cl. Filter out Pt salt. Precipitate Pd by adding chlorine gas or other source. Precipitate Rh with cementation. All three will be contaminated. Reduce the salts in your preferred method. Refine a second time taking more care or using different precipitants.



I make small test runs (4) in the bigger testtubes now. Owner gets excited about this approach (because previously we observed no Rh leaching to nitric), but i am slowly loosing my "amazement"  from beginning as we used the PtPdRh cemented mix, nitric only leached out portion of Pt and Pd, Rh left in precipitate.
I do not understand it, but now it also eaten up Rh... after only 16 hours at low heat  ...broken XRF, some troll who add HCl to our nitric, i don´t know. More and more strange results.

As this experiment will be over, best chances are that i go with approach you suggest. 
If some significant portion of Rh gets stuck in Pt NH4Cl drop, i will consider bromate hydrolysis to scavenge the Rh.
If Pd portion drag significant ammount of Rh... Hmmm... This will be more complicated 

Overall, we wanted to base our preliminary research on initial findings, but now, reconsidering the results... Very likely we will come back from reinventing the wheel to standard approaches


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## orvi (Dec 14, 2021)

_"i would do the folowing---1-cement with copper--the powder from cementatio,dissolve with nitric,making a solution,with pd---the powder left use hcl+peroxide,the liquid will contain pt and the powder left is rh--now ,treat the solutions with the reagents like dmg for pd and the platinum solution with nh4cl--the rh ,purifies your way"_

I had considered this approach and very similarly, I replicated this procedure one time, but obviously i have made some mistakes with precipitations - i lost practically more than 50% of Rh to the ammonium hexachloroplatinate and Pd(DMG)2 complex.

After this researching, one of my next attempts will be something like this, but this time more prepared, well educated about all the right parameters of each precipitation, and hopefully we get some usable outcome


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## Yggdrasil (Dec 14, 2021)

butcher said:


> _Authur Kierski our well-known member is still having trouble with the new forum, I do not understand the problem but it may have something to do with translating his messages._
> 
> Arthur posted above:
> _Hi
> ...


Hi Butcher.
What surprises me is that when these translation issues happen, the OPs don't seem to notice. 
Is this some kind of forum software thing?
Or don't they reread what they posted after posting?
In retrospect I see that l should have added some additional text around the translations, sorry about that.
I really don't like posting long posts from my phone.

Regards Per-Ove


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## Geo (Dec 14, 2021)

Have you tried reducing Pd with formic acid? I have not read that formic acid will reduce Rh. I have reduced formic acid for Pd and it seemed to do a good job. Once the metallic salts are reduced, there is no chance to mistake it for something else. It normally reduces to heavy, dark to black powder. If am not mistaken, the formic acid will reduce the Pd but not Rh, leaving it in solution.


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## Geo (Dec 14, 2021)

Or, the Rh stays in salt form and can be dissolved with boiling water.


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## goldandsilver123 (Dec 15, 2021)

Why don't you try some purolite resin (9140 or 9200) to absorb just the PMs and when you have more mass you can try to separate them.



Geo said:


> Have you tried reducing Pd with formic acid? I have not read that formic acid will reduce Rh. I have reduced formic acid for Pd and it seemed to do a good job. Once the metallic salts are reduced, there is no chance to mistake it for something else. It normally reduces to heavy, dark to black powder. If am not mistaken, the formic acid will reduce the Pd but not Rh, leaving it in solution.


Formic does reduce rhodium:








Looking for reductant option for rhodium chloride solution


I've around 40 g of rhodium in less than 1 L of solution, I'm looking for options on reductants. I've used NaOH and formic acid in a small portion of rhodium solution, but the precipitate isn't good. It filters well by gravity but using vacuum filtration drags the precipitate down. There's...




goldrefiningforum.com


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## orvi (Dec 15, 2021)

goldandsilver123 said:


> Why don't you try some purolite resin (9140 or 9200) to absorb just the PMs and when you have more mass you can try to separate them.
> 
> 
> Formic does reduce rhodium:
> ...


good idea, i didn´t considered resins yet


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## orvi (Dec 20, 2021)

Okay, idea with leaching platinum from high surface area PtRh blacks (from "inquartation" with Cu or Al) was given up. In all samples, rhodium tend to also slowly dissolve. Dissolution rate of platinum is higher, but it very quickly reach equilibrium in 65% nitric, and no more dissolves even after prolonged heating. PtRh black from Cu inquartation/dissolution is very active, does not settle over time, and rhodium is dissolved relatively quickly.
PtRh black from Al inquartation is very compact and easy to work with. But also here, Rh slowly dissolves into the solution.
Nitric acid used was p.a. grade 65%, and both procedures were conducted with exclusion of chlorides.

Next, I will focus on perfecting classic sequence of NH4Cl Pt drop, followed by NH4Cl/"Cl2" Pd drop (after Christmas  ). 
I will probably try to follow an article (listed below), where authors pointed out some good points in terms of temperatures, concentrations of HCl and NH4Cl ammounts and reaction times.

My aim is not to obtain the best yield of Pt salt, but to loose as little Rh as possible in the precipitated Pt ammonium salt. Some rational compromise 

I read whole bunch of threads here on this classic sequence, but it seems to me that procedures vary from user to user in terms of concentration, precipitation temperature, HCl content, ammount of NH4Cl used and mostly by contact time of formed precipitate with mother liquor.
In many articles I read that contact time should be minimized due to unwanted "reversed hydrolysis" (precipitation of Pt salt reform HCl in the solution) of other PGM chlorocomplexes, which cause unwanted drag of other PGM salts with ammonium chloroplatinate. 

Any suggestions are very appreciated.


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## orvi (Jan 7, 2022)

So I am back. I was elaborating Pt NH4Cl drop on two samples of PGM solutions - one containing base metals (heavily polluted, up to 50%), the other was clean PtPdRh solution.

As in the accessible literature aren´t much information about exact procedures, i was just making it from the best assumptions i had. I tried to follow the article above, but it failed to deliver results which I could work with.

Denoxxing was done by two times boil down the solution to the viscous liquid (refilling with fresh 35% HCl after first boil-down). After HCl evaporation to temperature of 150°C, whole mixture started to form viscous semi-solid goo. As i realized it, i took it off hotplate and let it cool, then try to redissolve the formed precipitate, but it was too late, good portion of precipitate did not make it to the solution... Filtration was near impossible, so i stopped the experiment and started with fresh sample.

This time, when starting the sequence of denoxxing boil-down, I added 2,4 molar equivalent of NaCl (to PGMs present) to the solution, which prevent the salts from decomposing at elevated temperature. It worked as expected, and I was able to stripp all the HCl present, forming crispy red-brown solid at the end of denoxxing step.
The formed solid readily dissolved in water without leftover solids.
For experiment, I was using 2g of dissolved PGMs containing roughly 51% Pd 42% Pt and around 2,5% Rh.

I diluted the solution to total volume of 10 mL, then according to the article heat it up to 60°C (best temperature I figure from their graphs in terms of purity and recovery intended) and measure NH4Cl saturated solution in a way that final concentration of free NH4Cl does not cross 0,5 M (molar) - also get this number from the table in the publication, showing that after 0,5M mark, complexes tend to be less soluble in general for all PGMs. I used around 0,75 grams, from which 0,47g was calculated stechiometry, 0,31 was excessive. Given the solubilities of Pd and Rh NH4 complexes, this excess in theory should not bother them to coprecipitate... (well, I was clearly wrong).
According to the article, i did not mix the precipitated powder too long, so after few minutes i filtered it and wash it with 150g/L NH4Cl as was mentioned in the article (used 10 mL + 2 mL of it).

Only to find out that dropped ammonoplatinate is only 93,6% Pt. Also contained around 4% Pd and 2% Rh...
Mother liquor contained in terms of PGMs only 1% Pt.

After it was done, I realized few mistakes and misconceptions i did and have.
When using the NaCl method for denoxxing, there is no way to form partially hydrated PGM complexes, which authors of article mentioned to be beneficial for the precipitation. Also, maybe I should not use excess NH4Cl and dont rely on theoretical values of solubility.

*My questions to you, more skilled PGM refiners, are:

1.* when dropping (NH4)2(PtCl6), how much NH4Cl (stechiometry) do you use when refining platinum from the mixtures containing lot of PdRh ? Should I use stechiometric ammount or excess... less than stechiometry ? My aim is some rational compromise between purity and recovery, so the process is of any use. Say when 90% of Pt will drop with minimal other PGM, i would be happy. What do you suggest ?

*2. *how long you routinely stirr the suspension of formed solid ammonoplatinate ? in the article, folks wrote that contact time between suspension and mother liquor should be kept minimum. But it was more likely for their case, taking the advantage of slow reverse hydrolysis of PGM complexes, when HCl is formed during the drop.

*3. *what temperature you use to precipitate NH4 Pt salt from solution ? also, it was heavily discussed in scientific literature, but no practical implications can be found on real world material examples - like mine canister of dissolved PGMs.

*4.* does sodium content (not negligible) inevitably present from using NaCl for proper denoxxing and driving off HCl mess the whole process ? I mean if it could mess up the solubilities of PGM salts, as the solution will be more saturated with chlorides. Could it be done this way with NaCl content or I should abbandon it and try to proceed in another way ?

*5.* I used rough concentration of 85g Pt / L for the drop of ammonoplatinate. Considering there is also other PGMs which could coprecipitate more likely if it was more concentrated. Do you think the solution should be more diluted when dropping Pt from such excess of other PGMs ?

I will be very happy if you could shed some light into this problem. I know that maybe I am asking for secret informations as the refining of PGMs is well hidden from the ordinary small refiners as I am - but I tried  any information will help.
Thank you
Orvi


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## goldandsilver123 (Jan 7, 2022)

With your denoxxed solution of Pt, Pd and Rh, I would raise the pH to 10 with a mixture of sodium hypochlorite and sodium hydroxide. You need to keep the solution really oxidizing. Pd and Rh will ppt as hydroxides, the filtrate will render you pure platinum >99.9%.

The Pd and Rh can be recovered from the hydroxides.

My experience is that ppt with NH4Cl will always drag Rh. And I see on Pt from other refineries Rh and Ir contamination on their "pure 99,99% "platinum products


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## orvi (Jan 7, 2022)

goldandsilver123 said:


> With your denoxxed solution of Pt, Pd and Rh, I would raise the pH to 10 with a mixture of sodium hypochlorite and sodium hydroxide. You need to keep the solution really oxidizing. Pd and Rh will ppt as hydroxides, the filtrate will render you pure platinum >99.9%.
> 
> The Pd and Rh can be recovered from the hydroxides.
> 
> My experience is that ppt with NH4Cl will always drag Rh. And I see on Pt from other refineries Rh and Ir contamination on their "pure 99,99% "platinum products


As high as pH 10 ? Interesting. I always read that it is extremely pH sensitive, any kind of "hydrolysis" type reaction with PGM. Most of the guys getting it to the pH 7.5 - 9. 
When you are saying that you could go as high as 10, that would simplify the proces by order of magnitude. 
Thanks for the advice


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## Abdoulapapatte (Jan 27, 2022)

hello orvi little question what do you think about the use of potassium persulfate know that it melts at 180.
and it dissolves the rhodium  if it can help you 
I hope you have managed to improve your process in the meantime.
I think you should have no more problems with pd and pt and have good racial %.
what are your best pt pd and rh ration that you have measured in solid (powder mud, until now?)
courage you are on the right track. it's good what you do if you want i give you an answer in mp. 
for me the closest to my way of doing is geo, 
you should also know that after the Nh4Cl episode and the release of platinum, 
yes we can use chlorate, I didn't know that there was a risk of splashing, technically potassium chlorate produces a purer salt theoretically, then by evacuating the remaining liquid with hcl we can recover the rhodium


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## orvi (Jan 27, 2022)

Abdoulapapatte said:


> hello orvi little question what do you think about the use of potassium persulfate know that it melts at 180.
> and it dissolves the rhodium  if it can help you
> I hope you have managed to improve your process in the meantime.
> I think you should have no more problems with pd and pt and have good racial %.
> ...


Thanks for the support, but we did not manage to separate it and needed to pass the bulk metal further. Sad, but life goes on 
What I learned is fact, that with simple textbook separations, you can´t do it with that low percentage of metal you are aiming to salvage. At least, I cannot do it.
Every time I´ve attempted to follow some published procedures, it gives me poor resolutions and bad separations. Things aren´t 100% efficient and basically, you are just producing enriched fractions  at least, i was producing enriched fractions. 

It will be possible to go with two-step rafination, for the first pass, enrich the Pt and Pd above 93-95% with NH4Cl or KCl method, and then refine the Pt and Pd to squeeze the last traces of Rh out (best with hydrolysis for Pt). Create enriched mix of PtPdRh, and if it is not on the sellable side, go one more time.
But this procedure will be labor intensive, and with my current health issues, not possible


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## Abdoulapapatte (Jan 27, 2022)

don't feel defeated at 2 minutes of victory


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## Yggdrasil (Jan 27, 2022)

Abdoulapapatte said:


> ne vous sentez pas vaincu à 2 minutes de la victoire


Kan ikkje du være så snill å skrive på engelsk?


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## Abdoulapapatte (Jan 28, 2022)

hi orvi 

I would like to recommend these videos, they are very high quality and illustrate your situation perfectly.

You start with plain water, so before the first step you either concentrate your solution and boil it.

You evacuate the water in vapor and you concentrate your concentrations of pgms. then when the solution is ultra concentrated, and quite dark, you dilute by adding hcl to eradicate hno3, you evaporate, you concentrate and you put back hcl a second time.

* ,1) if now you have 100 liters, add zinc, added with zinc (or cu) and precipitate the pgms *

hno3+hcl from dissolving pgms------> boil-----> evaporate ( pgms concentration)-----> add hcl 

-----> boil and insert the solution again then you get to this stage, note all the tips in the video.



*2) after applying the platinum sponge ----> reduction in its metallic form by ammonium formate *



*3)Then separation of palladium:*

 

*3.1) add ammonium chloride again in small quantities, add also *

kclo3 (potassium chlorate or NaClO3 (sodium chlorate works better). -----> boil 

the red concentrate-----> red precipitate will be palladium , the rest of the highly concentrated liquid will be rhodium .

*3.2 rinse with HCL or with a 10% ammonium chloride solution (pd salt will not dissolve)

4 turn the palladium sponge into metal:*



dilute palladium precipitate with water ------> boil ------> ammonium formate----> Pd metal

*5) precipitation of rhodium in its metal form :*



THE OLD ZINC TECHNIQUE ------> will not dissolve in aqua regia 

*6) another observation *

to refine rhodium easily it is necessary to prepare it (make it etchable):

two videos not to be underestimated :









Rhodium refining secrets.







www.youtube.com





https://www.youtube.com/watch?v=2gzzCDHtvzE&t=6s (precipitation with alcohol)



I hope that it helped you, I wonder if the stoichiometry is really important, I know well that Nh4cl can precipitate platinum and palladium at different precipitation times 

1)platinum -----> precipitates-----------time-----> palladium precipitates

bye


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## orvi (May 18, 2022)

Abdoulapapatte said:


> hi orvi
> 
> I would like to recommend these videos, they are very high quality and illustrate your situation perfectly.
> 
> ...



Yeah, I know and we tried these easy and straightforward approaches in the beginning, but we have limited time, and we cannot afford to scavenge PGMs from all feeds back together and re-refine all fractions to get values to the two piles.
I am still working on the subject, with little pauses.


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## orvi (May 18, 2022)

So, after long time two new things were tested, with partial success in one way.

I had an idea... Wacker oxidation (org. chemistry) uses PdCl2 as catalyst together with CuCl2 as co-catalyst. In the reaction, CuCl2 is able to oxidize Pd to PdCl2 and it reduce itself to CuCl. So I give it a go with my PGM mix cemented on zinc powder.
Composition roughly 50% Pd 43% Pt 2% Rh. For 2 grams of the PGM powder, I used 1 g of CuCl2x2H2O and 2 x the ammount of HCL needed to make chlorocomplexes from all PGMs. Stirred for 2 days. Found that CuCl2 etch all PGMs in cemented form, Pd mostly, Rh is going also quite fast, with Pt as least reactive to these conditions.
Solution transitioned from blue-green (from copper) to dirty-green-yellow to nearly black-brown. More than half of the PGM charge dissolved to the solution, but I didn´t measured the remaining powder exactly - I just calculated it from XRF readings ( I knew how much CuCl2 and PGMs I used, so I know the composition of the solution).

It may be a valuable info for anyone trying to cement or dissolve PGMs easy way from various sources. I must point out, that I do not know how PGMs would behave in form of plating or wire etc...

-------------

*Optimization of Pt drop with NH4Cl*

After previous failure, I decided to follow instincts rather than scientific papers without any exact procedures given - this particular thing can get me quite upset. Lots of papers without exact procedure given, limited numbers and unclear experiments. So I planned my own one, tuned by experience from the first time drop.
I used roughly 2,17g PGMs in solution, *50%Pd42%Pt2+%Rh with just a 1% base metals*, mainly zinc and touch of copper.
*To this solution (7,5 mL) I added NaCl *(1,79 g) corresponding to the stoichiometric ammount needed to form Na-PGM salts on heating - denoxxing. As salt do not dissolve well in solutions full of chlorides, I added just enough water to completely dissolve the salt at boiling point. This is important, because if salt remain undissolved, chlorocomplexes start to liberate HCL and on redissolution, opalescent liquid with precipitate is obtained, which need additional HCL to redissolve = more chlorides = less selective drop.

*After complete evaporation to crispy solid*, I added water (20 mL) and dissolve the solid to semi-clear solution. Some HCL was used to correct the pH and allow the solids to enter the solution (less than 0,5 mL). Solution was acidic after this operation (*pH 2-3*).* I measured just stoichiometric ammount of NH4Cl needed for Pt drop* (0,501 g) and dissolved in minimal water.

I added NH4Cl solution in one portion to the clear, stirred solution of the PGMs at room temperature. I wash the small beaker (used for dissolving NH4Cl) with little water to quantitatively transfer NH4Cl to the reaction. Stirring was continued for 40 minutes.* Total volume of the solution was 32 mL, so after adding all ingredients, PGMs concentration in solution was 70g/L - so Pt content was 29,4g/L.*

Filtering the precipitate and washing the cake 2x10 mL of 5% NH4Cl resulted in *precipitate of composition:

98,6% Pt 0,80 % Pd and 0,56% Rh (XRF).* Much much better than previous attempt. Cake is also much nicer in color, no orange tinge, no green specs. From that highly "polluted" solution with other PGMs, I think it is not a bad result - correct me if it can be done much better, I do not know since these are my best numbers  

Effectivity of the drop was roughly 80-85% - I correct the number after weighing the ppt in the liquid. 
After filtering the remaining precipitate in filtering flask (due to NH4Cl wash) and XRF measurement of the liquid, *effectivity of the drop was 87%.*
Remaining NH4 platinate precipitated in the filtering flask after washing the cake with NH4Cl. It will be wise to change the filtering flasks before washing to eliminate this problem and allow to re-drop the Pt from mother liquor in controlled way. Since Pt drop isn´t 100% any time, it is easy to calculate NH4Cl left in the solution and adjust the ammount of second addition of NH4Cl to precipitate more Pt from juice, altough with low Pt content, It would probably be quite impure. Or with prolonged stirring in large batch, it would be easy to measure liquid and solid phase to find comfortable point between purity and yield. I will see.
Effectivity is not very good for one-step operation. We need to get at least 90% of Pt out in this operation. I will see if it is possible - to balance purity and recovery somwhere acceptable. If this cannot be accomplished... we need to consider two stage refining of NH4Pt salt :/

Two more experiments are planned - one with stoichiometric NH4Cl and higher concentration of PGMs (120-150g/L, from this Pt 50-63g/L), second with slightly over-stoichiometric ammount of NH4Cl (1,2 x NH4Cl needed) with retained concentration of 70g/L PGMs.


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## orvi (May 26, 2022)

Another failed experiment, but with some interesting things happening:

Theory: 

If Rh is insoluble in nitric acid, and palladium sure is, there could be possibility to resolve these two by making PGM powders and adding HNO3 to them. Then filter the undissolved Rh.

Real life:

I have taken the enriched fraction of denoxed AR solution of PdRh - around 90% Pd 4-5% Rh and ca 3% Pt - mother liquor after Pt precipitation with NH4Cl - total weight of the metals was around 1,0 g. While stirring vigorously, I added zinc powder until all PGMs were dropped. Then added HCl and heated to ca 60°C to redissolve any excess zinc that could be present. After half hour, settled cement (nicely flocculated by the action of ZnCl2) was decanted and repeatedly washed with water (around 4 times). It was clearly visible, that ZnCl2 was slowly washed from liquid - because the precipitate started to fall appart from nice flocculated particles to nearly dust. Last two washes were with distilled water. AgNO3 test on wash water proved that there are no chlorides in solution.

Then to the wet powder (in ca 2-3 mL dH2O), I added 2 mL p.a. grade nitric (65%). Then strange observations started. When heated to ca 60-80°C, palladium started to go to the solution - but no gas, no NOx fumes were evolved. Just solution taken more and more brown orange colour and that was all. No single bubble... 

And, as you can guess, everything passed to the solution, leaving small ammount of some black dust in the beaker. After filtering on Hirsch funnel with pre-weighed filter paper, ppt weighed less than 1 mg... 

So, apparently Rh is quite soluble in nitric acid - if finely divided of course.

Time to move on to the more elaborate, but working procedures


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## orvi (Jun 2, 2022)

So, finally we have some methodology which we can actually use. Not perfectly efficient, but it slowly gets us where we want to be 

Theory:

NH4Cl can drop Pt and also Pd oxidized to +4 oxidation state from their chlorocomplexes. Since *solubility of (NH4)2PdCl6 and (NH4)2PtCl6 is greatly dependent from overall chloride content of the solution, NH4+ ion concentration and also HCl content = acidity,* we made few control experiments on selectivity of Pt drop in various conditions. We found (no surprise), that Pd and Rh coprecipitate more in more concentrated solutions. NH4Cl has dramatic effect on selectivity towards Rh. If *overstoichiometric NH4Cl ammount was used on our mixture, percentage of Rh was rising more rapidly than Pd content of the precipitate*.
SO we designed experiment like this - add stechiometric ammount of NH4Cl for Pt *and also Pd*, and then with stirring, oxidize Pd to the +4. This will cause sharp drop in overall chloride content of the solution (since chlorometallates will precipitate out), which could help keep Rh soluble.

Reality:

2,000 g of PdPtRh cement mixture (ca 50%Pd 42%Pt 2,5%Rh) was dissolved in AR. After complete dissolution, stechiometric NaCl was added and solution was evaporated to dryness (at 175°C). Great care was taken to *have enough water in the solution to dissolve all the NaCl* - if some remain undissolved, portion of the PGM-acids will release HCl and become insoluble after evaporation. 
After evaporation to crispy powder, residue was redissolved in water to form clear dark liquid. Volume was adjusted to 20 mL. Then, stechiometric ammount (for Pt and Pd) of NH4Cl was dissolved in 4 mL of water and poured into the stirring PGM solution. 1 mL of water was used to rinse the beaker from NH4Cl.

Then, I set up the chlorine generator from the round-bottomed flask with side tube, connecting to PVC tubing and Pasteur pipette used as bubbler. I filled the flask with two spoons of KMnO4, and attached addition (pressure equalized) funnel filled with 18-20 % HCL (*diluted to 20% because of less HCL drag with generated chlorine*).

Chlorine was then steadily generated and bubbled to the PGM solution. Whole operation took about 30 minutes, during which it was clearly evident that Pd is creating precipitate, as color of the solution faded. This was a very good lead to the endpoint of the precipitation - when the solution does not discolor more for some time, it was over. I let the reaction stirr for another 5 minutes with very low bubbling rate of chlorine, to keep ORP of the solution high.

Then, the suspension was filtered on Buchner funnel, sucked as much liquid as possible (very light red-orange solution), and washed the cake with 2 x 10 mL of 1 M NH4Cl (ca 5% w/w). After second addition, filtrate become colorless.

Filtrate was collected, PGMs were cemented with powdered zinc *to obtain 120 mg of fluffy, flocculated black powder*. XRF measurement revealed that *it contain 28% Rh, 35% Pd and 15% Pt.* Filter cake measurement revealed 59% Pd 39% Pt and around 1% Rh, which roughly correspond with weight comparisons of feed and zinc-ed filtrate.* So we managed to concentrate 67 % of Rh to the enriched fraction, which we can sell. *

If the selectivity remain the same when we redissolve the NH4 salts precipitates and do the second drop of PtPd, we could squeeze 89% of Rh to the enriched fraction. We will see how this second dissolution-redrop sequence will go. 

But for now, I am buying a bottle of champagne  and I pop it when we get the Rh to the vial


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## orvi (Jun 2, 2022)

Some photos of setup and cake+filtrate


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## Swissgoldrefiner (Jun 2, 2022)

orvi said:


> Some photos of setup and cake+filtrate


Nice job...but what's the aim of increasing the % of Rh? As you mention, you dont want get 99.9% of each metal...So that mean you will end up with giving the concentrate to a refinery or i miss understood?
Otherwise it's because you like the scientific challenge? 
I mean if i was you...i will probably send it like this to refinery...except if that's to have fun and/or scientific challenge.


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## Golddigger76 (Jun 2, 2022)

I assume he's trying to come up with a way to recover enough rhodium % to meet a minimum to be able to sell without very expensive and complicated reactor and supporting equipment plus it's a highly guarded secret by most of those who are currently doing it now.. we know it can be done and they will throw you a bone here and there but they had to learn the same way Orvi experiments. I don't think that I would be so quick to hand out a method that took me a year of working on it to figure out either.
Obviously rhodium is a very expensive metal, complicated to refine, and if you can get 67% rhodium out of your pgm solution without that equipment the Pt and Pd are the bonus metals. Could be having to keep a balance of one metal to hold another in solution ?
I am no expert on PGM'S, still learning palladium and platinum but Rhodium is still way over my head. He's refining catalytic converters and along with that comes the Rhodium.
I have a nice pile of converters waiting for me to get more educated before I try and that's mainly because my waste is still going to have the Rh left in it if I only can recover the palladium and platinum. That would be a damn shame since rhodium is around $15,500 per ounce right now and I don't desire to keep the waist in storage until I get around to figuring it out so for now those converters are a safe form for keeping them.


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## orvi (Jun 3, 2022)

Swissgoldrefiner said:


> Nice job...but what's the aim of increasing the % of Rh? As you mention, you dont want get 99.9% of each metal...So that mean you will end up with giving the concentrate to a refinery or i miss understood?
> Otherwise it's because you like the scientific challenge?
> I mean if i was you...i will probably send it like this to refinery...except if that's to have fun and/or scientific challenge.





Golddigger76 said:


> I assume he's trying to come up with a way to recover enough rhodium % to meet a minimum to be able to sell without very expensive and complicated reactor and supporting equipment plus it's a highly guarded secret by most of those who are currently doing it now.. we know it can be done and they will throw you a bone here and there but they had to learn the same way Orvi experiments. I don't think that I would be so quick to hand out a method that took me a year of working on it to figure out either.
> Obviously rhodium is a very expensive metal, complicated to refine, and if you can get 67% rhodium out of your pgm solution without that equipment the Pt and Pd are the bonus metals. Could be having to keep a balance of one metal to hold another in solution ?
> I am no expert on PGM'S, still learning palladium and platinum but Rhodium is still way over my head. He's refining catalytic converters and along with that comes the Rhodium.
> I have a nice pile of converters waiting for me to get more educated before I try and that's mainly because my waste is still going to have the Rh left in it if I only can recover the palladium and platinum. That would be a damn shame since rhodium is around $15,500 per ounce right now and I don't desire to keep the waist in storage until I get around to figuring it out so for now those converters are a safe form for keeping them.


This issue started way long ago. And yes, it seems irrational to just enrich, not refine completely. But as Golddigger76 said, our buyer of PMs have minimum ammount requirement of 15% for Rh to be sellable. From the point that there are thousands of other buyers in the world that account for Rh also in 0,6-2,5% range (what we have in the feed) - yep, it is true. But my boss have long term relationship with his PM buyer, so I was given a task to enrich fraction with Rh to squeeze some more bucks out of the PGM melt. He probably has his own reasons to stick to that specific buyer despite all the trouble. This I do not know, and it is completely up to him.

This whole secrecy, hidden information... Whole another world of immense knowledge is hidden completely from our eyes and made secret just because money. I understand the logic behind it, but personally I do not agree with this. I learned huge ammount of things here on the forum, and I am now maybe giving a little bit of it back. Everywhere is only stated use NH4Cl, oxidize the Pd with chlorate. Nowhere is enough informations for the methods hundreds of years old. So I shared my experiences, which can be valuable as lead for other beginners to avoid some mistakes that I made.

As to the method and sharing it with others... This is a very specific problem, I faced. I do not think there are many refiners who enrich catalytic PGMs that way the Rh is past 15%. Also, I do not feel that I would be able to refine the Rh efficiently to 99+% without few years of trying. We get the smelting right, we get every percent of PGM out of matrix very efficiently. And that took eternity to do right way with limited equipment and furnance temperature.

I am just an organic chemist doing my PhD, I do not want to make a refining career. It is just a little bit more than a hobby for me. Very exciting field. So I play with expensive toys


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## Golddigger76 (Jun 3, 2022)

The information you've provided us with is 100% priceless, hopefully someday l will be able to have half of the incite of you. 
We are still learning our lessons based on Hoke's books and in all of the time that has passed since it was written I have a feeling that a few someone's have found new ways that would blow our minds. Either way I enjoy learning new techniques regardless of if I will ever need them or not so thank you for sharing what has and hasn't worked for you !!


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## Golddigger76 (Jun 5, 2022)

Orvi 
If you don't mind me asking are the industrial cats by chance from big diesel engines ?


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## orvi (Jun 6, 2022)

Golddigger76 said:


> Orvi
> If you don't mind me asking are the industrial cats by chance from big diesel engines ?


I doubt it, but more probably these are catalytic beds used in industry for various reactions. Composition of the ceramic do not correspond to the catalytic converter like matrix.


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## Mdctr (Jun 10, 2022)

orvi said:


> This issue started way long ago. And yes, it seems irrational to just enrich, not refine completely. But as Golddigger76 said, our buyer of PMs have minimum ammount requirement of 15% for Rh to be sellable. From the point that there are thousands of other buyers in the world that account for Rh also in 0,6-2,5% range (what we have in the feed) - yep, it is true. But my boss have long term relationship with his PM buyer, so I was given a task to enrich fraction with Rh to squeeze some more bucks out of the PGM melt. He probably has his own reasons to stick to that specific buyer despite all the trouble. This I do not know, and it is completely up to him.
> 
> This whole secrecy, hidden information... Whole another world of immense knowledge is hidden completely from our eyes and made secret just because money. I understand the logic behind it, but personally I do not agree with this. I learned huge ammount of things here on the forum, and I am now maybe giving a little bit of it back. Everywhere is only stated use NH4Cl, oxidize the Pd with chlorate. Nowhere is enough informations for the methods hundreds of years old. So I shared my experiences, which can be valuable as lead for other beginners to avoid some mistakes that I made.
> 
> ...





Hi


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## Mdctr (Jun 10, 2022)

Hi Orvi,
It's good to see there's still some good people in this world!
Id like to take a minute to give you recognition and appreciate your post. I read ALOT I'm not sure the ratio but its probably up there with odds of hitting the lottery to read _honest positivity. It's people like you that give some light at the end of the tunnel for beginners like myself to continue to educate put forth the effort to achieve our own. 
Let someone mention pgms from catalytic converters and o man peoples jaw drops. Yes i just said the c word sorry if I offend anyone. Lol
I will look through what you have posted and look forward to learning what youre willing to share. Thanks _


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## orvi (Jun 11, 2022)

After initial findings of heavy coprecipitation of Rh and Pd together with Pt, I started to think about why this happen. Solubility of Pd and Rh ammonium chlorocomplexes should be high enough to keep everything in solution, and with prolonged stirring, equilibrium should be established and theoretically, pure (NH4)2PtCl6 should be obtained.
But there is* one thing which I didn´t realized - cocrystalization and adsorption.* These compounds are *heavily charged complex particles* - and they would have tendency to *adsorb themselves onto the surface of the precipitate. *And since the precipitate of platinum ammonium salt have* vast surface area* - it will have plenty of opportunities to do so. Also, in the ppt, there can be locked Pd and Rh, as the formation of precipitate is immediate.

So, I designed an experiment to prove or disprove this hypothesis. I took (NH4)2PtCl6, of composition roughly 93,6 Pt 2,9Pd and 2,11 Rh - which was dropped earlier in the "research". I divided the cake into 2 portions, weighing 1,00 g each. Then, I prepared *0,25 M solution of NH4Cl* (roughly 13g/L, very diluted in comparison to more than 5M saturated solution) and *added 11 mL to each of the precipitates in the small beakers. One was stirred 15 hours at room temperature, and second was heated to 80 °C for 5 hours, and then co*oled undisturbed to r.t. overnight.

Results were clear - this trituration shown that *Pd and Rh ARE leached to the liquid phase from precipitate*, but *only to some extent*. Room temp experiment yielded 96,7 Pt 2,0 Pd 1,2 Rh precipitate, and 80 °C experiment yielded 97,8 Pt 1,3 Pd 0,9 Rh precipitate. It was clear, that even in practically very diluted solutions, PGMs tend to stay adsorbed onto the solid phase, possibly due to some electronic effects or affinity. Experiment at *80 °C yielded more orange tinted precipitate, despite the fact precipitate washed at 80 °C was purer in XRF reading* - crystals were bigger and probably partially hydrolyzed Pt species, not full hexachloroanions...
This is due to the fact that at 80 °C, Pt salt has much greater solubility in water, and *thus it was crystallizing from the solution in bigger crystals = lowering the surface area of the precipitate* = minimizing possible adsorption.

On the photo, right Petri dish and beaker correspond to 80°C experiment, on the left, room temp. experiment.

As this operation has some potential in cleaning the precipitated Pt salt from some limited ammount of PdRh, it shown very clear where lies the problem with NH4Cl precipitations of platinum from HCL solutions.


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## orvi (Jun 11, 2022)

So next, I thought about how to minimize the adsorption of Pd and Rh chlorocomplexes to the Pt precipitate. Logically, there are *two obvious things that could be done - change or alter the surface charge of particles or solution*, so the other ions do not want to adhere on the surface of the particles. *Or, simply lower the surface area available for this to happen*. Since I am not very into surface chemistry mambo-jambo, I tryied the classic way - crystallization.

*It should be said that ammonium platinate does not have great solubility in water*, even at boiling point (tables state 33,6g/L), but gradient for crystallization is very pleasing - depending on source - 1-5g/L at room temperature. *So effectivity of crystallization should be good.*

I picked 1,65 g of impure (NH4)2PtCl6 containing 96,2 Pt 2,58 Pd 1,19 Rh, and certainly traces of NH4Cl from washing steps.

This was brought to boiling in water, and overall *55 mL were required to fully dissolve the cake to very nice, deep orange liquid*. I suspect traces of NH4Cl in the precipitate could lower the solubility, because in theory less than 50 mL should be enough to completely digest the precipitate at boiling point. Then I *left the beaker on hot hotplate to cool down slowly to room temperature overnight.* In the morning, nice crop of small *very brightly orange crystals* appeared, which were collected on Buchner funnel - *weighing 1,11 g.* XRF shown *essentially pure Pt (99,95% reading, confidently more than 99,8%* due to fact it is measured by XRF handgun).

I attempted to *collect remaining platinum from still quite deep-orange colored mother liquor by adding saturated NH4Cl - but without the success.* *Hexachloroplatinate anions must have hydrolysed* in boiling conditions to mixed hydroxo-chlorocomplexes, thus largely enhancing the solubility in water. So I also added few mL of HCL to the solution in effort to re-chlorate the platinum. And it worked.
*Shifting the equilibrium towards the precipitate of fully chlorinated Pt species is slow, it took few hours, but this is advantageous - slow release of fully chlorinated Pt salt tend to produce bigger crystals = lowering surface area for adsorption. *And by this procedure, I managed to get *additional 0,298 g of yellow crystals with slight green tinge (Rh).* XRF reading was *99,4 % Pt 0,6% PdRh.*

First crop of nice *orange crystals don´t resemble hexachlorocomplex, but more probably partially hydrated aquachloro complex*. So for weight, there will be probably slightly more Pt (since H2O has lower molar mass than Cl) than expected.

Zinc-ing out the mother liquor (very faint coloured solution) gave only 30-60 mg of PGM precipitate with 18% Rh content. Which is spectacular result for me.

With careful addition of just a little NH4Cl and HCL to the hydrolysed PtCl6 mother liquor, it would be possible to go for even better purity than 99,4 % for the next precipitation.

*Clearly, this isn´t industry-friendly process. 33,6g/L resembles just around 15g of platinum metal per liter* of water needed. Working in 5L beaker safely can only accomodate 60g of platinum. But it works. And could be helpful for small scale refiners to achieve good separations 





Satrurated solution on the left and crystals from first crystallization on the right 



XRF of the first crop of crystals. Our XRF is confused and measure Rh and Pd in very small concentrations as Zn, when measuring chloride salts.

So, I am happy  finally, something is working.


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## Mdctr (Jun 11, 2022)

orvi said:


> So next, I thought about how to minimize the adsorption of Pd and Rh chlorocomplexes to the Pt precipitate. Logically, there are *two obvious things that could be done - change or alter the surface charge of particles or solution*, so the other ions do not want to adhere on the surface of the particles. *Or, simply lower the surface area available for this to happen*. Since I am not very into surface chemistry mambo-jambo, I tryied the classic way - crystallization.
> 
> *It should be said that ammonium platinate does not have great solubility in water*, even at boiling point (tables state 33,6g/L), but gradient for crystallization is very pleasing - depending on source - 1-5g/L at room temperature. *So effectivity of crystallization should be good.*
> 
> ...


Have you ever tried melting NH4CL or NaCL03 by itself and adding to solution at room temperature?


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## Yggdrasil (Jun 11, 2022)

Mdctr said:


> Have you ever tried melting NH4CL or NaCL03 by itself and adding to solution at room temperature?


Since NH4Cl melts at 338C that is not possible.


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## orvi (Jun 12, 2022)

Mdctr said:


> Have you ever tried melting NH4CL or NaCL03 by itself and adding to solution at room temperature?


What would be the intention of such melting and addition ? I don´t understand.
Molten sodium chlorate is insanely dangerous oxidant. And ammonium chloride rather sublime than melt.


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## Yggdrasil (Jun 12, 2022)

If time is not of essence, won’t the different salts separate as they crystallize?
At least to some degree.


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## orvi (Jun 12, 2022)

Yggdrasil said:


> If time is not of essence, won’t the different salts separate as they crystallize?
> At least to some degree.


Yes, they would, and quite sharply. But you need to get conditions right. Not too much HCL not too much NH4Cl in second crystallization, slowly and steadily. You obtain two crops of crystals and one mother liquor. If you get it right, you get two crops of xx you can combine and process. With mother liquor, you get what you get. In my case from 2% Rh to 18% Rh as cemented powders.


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## Mdctr (Jun 12, 2022)

Yggdrasil said:


> Since NH4Cl melts at 338C that is not





orvi said:


> What would be the intention of such melting and addition ? I don´t understand.
> Molten sodium chlorate is insanely dangerous oxidant. And ammonium chloride rather sublime than melt.


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## Mdctr (Jun 12, 2022)

Quicker precipitation


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## Yggdrasil (Jun 12, 2022)

Mdctr said:


> Quicker precipitation


It can not be done, if you pour molten Sodium Chlorate at 300+ C into a liquid at say 50C you will have a steam explosion throwing seering hot intense oxidiser all around you.

How do you come up with such Ideas?

Are you sure you don’t mean dissolved and not molten?


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## Allthatscrap (Sep 1, 2022)

Geo said:


> To your solution, add a concentrated solution of ammonium chloride. Amounts and volumes are relative. Add the concentrated solution to the pregnant solution in amounts that are relative to the starting amount of pregnant solution. The ammonium chloride does two important things. First it drops Pt as a yellow salt. This is what you are looking for. Add until no more yellow salt is produced. Second, the ammonium binds with the palladium chloride. This allows the Pd salt to be converted to a solid by adding chlorine gas. The Pd salt will precipitate as a red to dull-red salt. None of this effects the rhodium to any great degree, which remains in the solution. I recover the Rh and can clean it somewhat but have never tried to refine Rh. Be aware that finely divided Rh powder will dissolve in concentrated HCl without an oxidizer. Palladium is difficult to cement from acidic solutions. It tends to dissolve in dilute HCl. To successfully cement all Pd from an acidic solution, the PH must be adjusted up. From my own observations, the less reactive a metal is, the harder it is to drop as an oxide. You can dilute gold solution until the solution has no color but still test positive for gold. All of the less reactive metals exhibit the same behavior. In an electrowinning cell, the solution entering the cell has very little dissolved metal initially.


Hey there geo,
Is this that's so you are still in this forum?


I've appreciated your previous post, slot, I just wanted to see if I could pick your brain a bit aboutPd and it's yellow salt ammonium chloride and which way from there one might choose to go fourth with. Is rendering the red salt a complete action?


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## Yggdrasil (Sep 1, 2022)

Allthatscrap said:


> Hey there geo,
> Is this that's so you are still in this forum?
> 
> 
> I've appreciated your previous post, slot, I just wanted to see if I could pick your brain a bit aboutPd and it's yellow salt ammonium chloride and which way from there one might choose to go fourth with. Is rendering the red salt a complete action?


I think you should hurry slowly. 
Dealing with Gold and Silver is hard enough until you master it.
Dealing with Platinum Group Metals are waay harder and a lot more toxic.
Get confident with Gold and Silver first.


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## Geo (Sep 1, 2022)

I agree with Yggdrasil. Master one thing at a time. The knowledge you gain from studying one element at a time will help you with the next. 

The yellow salt of Pd is obtained by a different method. Ammonium hydroxide is added to palladium chloride solution until the solution has been neutralized. Then an excess of ammonia is added to the pink/flesh colored Pd salt until the salt goes clear of color. Then small additions of HCl will precipitate the yellow salt of *diammine-palladium (II)chloride. *


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