Platinum purification issues

[yacht252002]

I am working on adding the Platinum and Palladium refining into my current Au&Ag refining process these days, and I have a few questions about the purification of platinum.
My materials are usually Gold 50%, Ag 10%&lower, Pt/Pd, a lot of copper
My steps are:
1. Aqua regia dissolving, remove Ag.
2. SO2 drops the gold.
3. Check the solution by ICP to see if any leftover gold, and find out the range of Pt/Pd (usually around 1000-6000ppm)
For the Pt/Pd refining, I basically followed the “Refining Precious Metals Wastes by CM. Hoke” book by the steps below:
1. Add NH4Cl powder to the solution, based on 1g Pt/Pd with 2g NH4Cl.
2. Let the precipitate (Pt salt) settle down, remove the supernatant (solution A) for Pd refining.
3. Purify the yellow Pt salt.
4. Add sodium chlorate to solution A to drop out Pd
5. Purify the red Pd salt.
Now my questions are:
1. After I get the yellow Pt salt, I use NH4Cl solution (3g NH4Cl in 600ml) to wash several times, then filter the salt and put them in the furnace to make Pt powder. The problem is I have to do this purification at least 4-5 times in order to achieve the 99.95% purity, but based on the Hoke book, it could be done by 2 times. Are there any tricks at washing?

2. I tried to wash the Pt salt with the NH4Cl solution more to reduce the refining cycle number. It looks like helps a little bit, I can drop the cycle from 5 times to 3 to 4 times to reach 99.95%. But I noticed that more and more Pt lost with the wash, if I do 5 times wash for each refining cycle, I could lose up to 20% of Pt per refining cycle. For example, for one experiment, I used pt salt which should have 3.4g of Pt at the beginning, after the first refining cycle, the Pt powder is only 2.7g. This number was down to 2.1 after the second cycle and finally to 1.7g at the end of the third cycle. I did notice that every time the washing solution becomes yellow in color, and I know there will be always a loss but I am not expecting that much. How to decrease the amount of the lost Pt in order to increase the refining rate?

3. This is the NH4Cl that I bought:

https://www.amazon.com/Alpha-Chemicals-Ammonium-Chloride-NH4Cl/dp/B004V9UQ14/ref=asc_df_B004V9UQ14/?tag=hyprod-20&linkCode=df0&hvadid=167139575215&hvpos=&hvnetw=g&hvrand=14257485731252429006&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9005444&hvtargid=pla-306024084888&psc=1

I noticed that when dissolving them in DI water, the solution looks a little cloudy(white), as I understand it means the NH4Cl is not pure enough that I need to filter it. But will that affect a lot to refining process?

Thanks

 

[Lino1406]

Why using 3g NH4Cl/600ml solution and not saturated solution?

 

[yacht252002]

Why using 3g NH4Cl/600ml solution and not saturated solution?

Thanks, Lino.
Good question. That is actually a good point. So at room temperature, the NH4Cl saturated solution should be around 380g/L, right? Based on this diagram from the internet.

https://socratic.org/questions/what-is-the-mass-of-nh-4cl-that-must-dissolve-in-200-grams-of-water-at-50-c-to-m

Based on the Hoke book, we could also use 15-20% NH4Cl solution. Do we know which one works better for washing? The 15% or saturated?

That's maybe one of the main reasons for the Pt loss.

 

[g_axelsson]

I have no experience myself from PGM refining, but everything I've heard about it is that you want to work with as high concentration as possible just because the PGM salts are slightly soluble. Washing with saturated and cold solutions also lower solubility.

Having an ICP at hand is a wonderful tool, you could easily check the liquid from the wash to see where the PGM goes.
It's on my want list.

Göran

 

[yacht252002]

I have no experience myself from PGM refining, but everything I've heard about it is that you want to work with as high concentration as possible just because the PGM salts are slightly soluble. Washing with saturated and cold solutions also lower solubility.

Having an ICP at hand is a wonderful tool, you could easily check the liquid from the wash to see where the PGM goes.
It's on my want list.

Göran

Thanks, Goran. I tried saturated NH4Cl in the past two days, the results are great. The problem is, I am run out of NH4Cl powder already LOL.

 

[FrugalRefiner]

Keep the wash solution cold too. As Göran said, it lowers the solubility of your platinum salt in the washes.

I do urge anyone who reads this thread to understand the toxicity of the platinum salts. Everything we do is dangerous, but platinum is another level.

Dave

 

[nickvc]

Dave it’s not just platinum but PGM salts in general I believe but I’m sure Lou can confirm this, I know palladium salts can be highly toxic.

 

[yacht252002]

Toxic because it will release Cl2 gas when burn? Or are there any other reasons?

 

[Lou]

Toxic because, in some individuals, it causes a progressive irreversible allergy that may lead to idiopathic fibroses of the lung which is more or less...fatal.

 

[yacht252002]

Toxic because, in some individuals, it causes a progressive irreversible allergy that may lead to idiopathic fibroses of the lung which is more or less...fatal.

Oh boy, gonna start to use double gloves lol

 

[FrugalRefiner]

It's not just gloves. You need real fume control and full PPE.

Once you dissolve platinum, you're dealing with platinum salts in solution. If you dry them, the danger of airborne particles rises dramatically. Freechemist lost his life to the hazard, and he dealt with them professionally. Others have been sensitized to the point where they can't be anywhere near them, even in solution.

Dave

 

[kurtak]

It's not just gloves. You need real fume control and full PPE.

Dave it’s not just platinum but PGM salts in general I believe but I’m sure Lou can confirm this, I know palladium salts can be highly toxic.

I was going to comment (about the dangers of PGM refining) assuming that yacht252002 was just another one of our MANY hobby refiners & therefore - for safety reasons would be better served to simply recover his PGMs by way of copper cementing (hobby level stock pot process)

However - before posting a reply - I decided to look at his other postings & found he only has one other thread from back in 2017

:arrow: Why add free acid in Ag cell?

So clearly yacht252002 is not just another hobby refiner but in fact works for (&/or maybe owns &/or maybe has a vested interest) in a large scale refinery --- so we can assume (if not actually figure) that he has "all" safety protocols in place to (at least) set up &/or pursue adding PGM refining to his refining process

Although I "played" with refining PGMs - I "soon" found that at my level of refining I was better off to simply recover rather then refine the PGMs that came out of my gold/silver refining --- therefore I can't really help with advice concerning actual refining

Sadly - most of our real pros (other then Lou) that could give real advice have ether passed on or moved on with their personal lives

I "think" we can "assume" that yacht252002 is "at least" seeing enough PGMs coming out of his gold/silver refining to at least "consider" adding PGM refining to his current refining circuit(s) --- so the question is - is that true or not ? (enough PGMs to make the pursuit of actual refining worth while)

Therefore yacht252002 - if you don't provide more details about you refining operations you are likely to get nothing more then "hobby" refiners advise - whereas with some real details you "may" get some real "pro" advise --- IMO

Kurt

 

[butcher]

Some metals are needed by the body to function, but in larger quantities just like water can dangerous or poisonous to our systems.

Some metals our body may not absorb very well, but our body may absorb the salts of these metals more easily becoming more poisonous to us, like the chlorides, many medicines are made with HCl to be more soluble in our systems, so a metal that normally may not be a problem to handle may become much more soluble and dangerous to our system as a salt of those metals.





https://ipa-news.com/assets/sustainability/IPA_Guidance/Chapter%206_PGM_Guide.pdf

https://www.google.com/search?q=health+danger+of+pgm+metals+and+its+salts&sxsrf=ALeKk02FOVvqhUNlA0I3UPLm61vCD_mdCg%3A1617373447690&source=hp&ei=BylnYIXdJ8ic-gSSzZy4Ag&iflsig=AINFCbYAAAAAYGc3F5yqO0KW96g6KcuBanjatmeJsdit&oq=health+danger+of+pgm+metals+and+its+salts&gs_lcp=Cgdnd3Mtd2l6EAM6BAgjECc6CgguEMcBEKMCECc6BQgAEJECOggIABCxAxCDAToLCC4QsQMQxwEQowI6BAgAEEM6CggAEIcCELEDEBQ6BgguEAoQQzoHCAAQyQMQQzoCCAA6BQgAELEDOgoILhDHARCvARBDOhAILhCxAxCDARDHARCjAhBDOgsILhDHARCvARCRAjoICC4QxwEQrwE6BwgAEIcCEBQ6BQgAEMkDOgYIABAWEB46CAghEBYQHRAeOgUIIRCgAToFCCEQqwI6BwghEAoQoAFQxDxYu4UCYI-LAmgAcAB4AIAB5wKIAaMrkgEINS4zMy4xLjKYAQCgAQGqAQdnd3Mtd2l6&sclient=gws-wiz&ved=0ahUKEwjF_MPO4d_vAhVIjp4KHZImBycQ4dUDCAk&uact=5

 

[nickvc]

To be honest unless you have an out for the refined PGMs I would still recover and sell, by an out I mean a buyer who will pay over spot or very close to spot for the metals, many refiners will not pay out much more for PGMs in a refined state than as an assayed bar so the question is simple, is it worth the extra risks and costs involved, if it is as Kurt advised give us more details and let’s see if anyone can help which I’m afraid keeps me out of this thread as I have no experience of refining PGMs and want to even less.

 

[yacht252002]

It's not just gloves. You need real fume control and full PPE.

Dave it’s not just platinum but PGM salts in general I believe but I’m sure Lou can confirm this, I know palladium salts can be highly toxic.

I was going to comment (about the dangers of PGM refining) assuming that yacht252002 was just another one of our MANY hobby refiners & therefore - for safety reasons would be better served to simply recover his PGMs by way of copper cementing (hobby level stock pot process)

However - before posting a reply - I decided to look at his other postings & found he only has one other thread from back in 2017

:arrow: Why add free acid in Ag cell?

So clearly yacht252002 is not just another hobby refiner but in fact works for (&/or maybe owns &/or maybe has a vested interest) in a large scale refinery --- so we can assume (if not actually figure) that he has "all" safety protocols in place to (at least) set up &/or pursue adding PGM refining to his refining process

Although I "played" with refining PGMs - I "soon" found that at my level of refining I was better off to simply recover rather then refine the PGMs that came out of my gold/silver refining --- therefore I can't really help with advice concerning actual refining

Sadly - most of our real pros (other then Lou) that could give real advice have ether passed on or moved on with their personal lives

I "think" we can "assume" that yacht252002 is "at least" seeing enough PGMs coming out of his gold/silver refining to at least "consider" adding PGM refining to his current refining circuit(s) --- so the question is - is that true or not ? (enough PGMs to make the pursuit of actual refining worth while)

Therefore yacht252002 - if you don't provide more details about you refining operations you are likely to get nothing more then "hobby" refiners advise - whereas with some real details you "may" get some real "pro" advise --- IMO

Kurt

Kurt, you are right. I am a chemist who is working in a small refining company, started with the QC lab then to an R&D position. Since I am working in the lab, PPE and hood are not an issue for me.

Now I am working on the project which, like you said, adding PGM(only Pt/Pd so far) refining in our current Gold/Silver refining system. We have quite a bit of Pt/Pd that we are currently using Zn to drop. However, there are a few issues that make me want to do the Pt/Pd refining by ourselves:

1. The Zn dropped Pt/Pd powder only contains 1-5% Pt/Pd. Rest are all Zn and Cu. To send these out to do refining costs us a lot, especially about shipping/insurance.
2. We are purchasing pure Pt/ Pd from JM for our alloys. So why not make our own?

Of course, I just started this project, everything is on small scale right now. There are still a lot of issues in the process that I am trying to figure out.

 

[nickvc]

Instead of precipitating with zinc have you thought of cementing the PGMs on copper, it’s not as simple as silver but there are a few good threads with good advice, Kurt posted about it a few days ago, while not getting pure product you will get a much higher percentage of PGMs and from the little I understand of refining them they need to be in high concentration to get reasonable results and if you decide to sell on it will be cheaper to move.
If you are using reasonable quantities of Pd and Pt have you asked JM about a metal account where you put in scrap or bars and receive pure metals in return, this is usually a fair amount cheaper than selling the scrap or bars and then buying the metals.
I’m not sure of the costs of producing high grade PGMs but I gather it needs fairly specialized equipment, if you have serious quantities to deal with then it may well pay.

 

[yacht252002]

Instead of precipitating with zinc have you thought of cementing the PGMs on copper, it’s not as simple as silver but there are a few good threads with good advice, Kurt posted about it a few days ago, while not getting pure product you will get a much higher percentage of PGMs and from the little I understand of refining them they need to be in high concentration to get reasonable results and if you decide to sell on it will be cheaper to move.
If you are using reasonable quantities of Pd and Pt have you asked JM about a metal account where you put in scrap or bars and receive pure metals in return, this is usually a fair amount cheaper than selling the scrap or bars and then buying the metals.
I’m not sure of the costs of producing high grade PGMs but I gather it needs fairly specialized equipment, if you have serious quantities to deal with then it may well pay.

Thanks for the advice. I tried to use Copper powder instead of Zn, the reaction goes super slow, and the result is not good. I am not sure if it's because of the H2SO4(from the SO2 drop gold process) in the solution, maybe I missed something. I will go over the posts in our forum about using copper.

 

[kurtak]

I tried to use Copper powder instead of Zn, the reaction goes super slow, and the result is not good.

yacht252002

Back in 2014 I was also having a problem cementing PGMs with copper (actually before that)

I started refining after I joined this forum in 2011 - between 2011 & 2014 I had saved a fair amount of solutions (stock pot) that contained PGMs from my gold & silver refining - so in 2014 I had enough PGM stock pot solution that I figured it was worth going after the PGMS so tried cementing them with copper but was having nothing but problems

I posted about those problems here -------

:arrow: Fuzz Button Interconnects, need some advice

"One" of the problems was the high copper content of my cemented PGMs (as shown in my second post)

In that thread 4metals came to my rescue & helped my solve the problems I was having cementing my PGMs with copper

Once you understand the problems with cementing PGMs & how to overcome those problems there should be no reason why you can't cement your PGMs with copper & get good results --- it became my go to method until I shut my refining down in (end of) 2018

Here is some more that I have posted about cementing PGMs - based on my experience after 4metals helped me out (in 2014) until I shut my refining down in 2018

:arrow: Cement

Hope that helps

Kurt

 

[yacht252002]

Thanks, Kurt. I actually studied both posts yesterday and restarted my Cu experiment.

I have two questions:

1. I am using 325 mesh Cu, is it good enough or do I have to use atomic Cu powder?

https://www.amazon.com/Copper-Powder-Pound-DELIVERY-Priority/dp/B072TQ5MWY/ref=sr_1_6?dchild=1&keywords=copper+powder&qid=1617718214&sr=8-6

Because I remember you used to use a 75ish mesh one. If 75 works, 325 should work better, right?

2. I am not sure how aggressive the agitation has to be? I am using a stir machine/a big stir bar with the max stir speed right now, and as you mentioned, I started the stir before adding Copper, will you consider that aggressive enough?

Thanks again for the help.

 

[yacht252002]

Unfortunately, the experiment failed.
Here is my solution:

Cu 60,000 ppm
Pt 400 ppm
Pd 1100 ppm
Zn 13,000 ppm
Trace of other base metal

High HCl, high H2SO4, no HNO3.

Totally 400ml solution, I added over 10g of copper powder with an overnight strong stir.

ICP shows before and after adding copper, the only difference is, the Copper concentration increased in the solution from 60,000ppm to 70,000ppm. Pt(400ppm) and Pd(1100ppm) barely changed. White/gray color powder precipitate at the bottom, filtered and tested 99% Cu with barely any Pt/Pd(less than .01%).

Do I need to use NaOH to neutralize the solution before adding copper? Or what do I miss? As I understand, Copper should not react with HCl, and should not react with this concentration of H2SO4. But if it's not the replacement reaction, why copper get dissolved?