First Post and Introduction

[Kharsa]

Hello everyone!

I stumbled upon this forum as I was researching a little bit further into the refining of precious metals and I was surprised/excited to find such a community.

Basically, a quick introduction of myself, I am currently working with my father, who has been in the gold refining business for over decades and we are currently running a gold refinery with the capacity of refining anywhere from 500kg to a ton of gold a day.

On a quarterly basis, we recover big amounts of sludge from the treatment of chemicals before their disposal, so that we are sure no metals whatsoever are being disposed with the chemicals. This sludge usually contains all the metals other than the silver and gold that we have recovered during our refining process which includes PGMs (mainly platinum and palladium), but in very small quantities relatively (which add up eventually). We end up sending this sludge abroad in order to have it further processed and have the PGMs recovered, but this process costs a lot, takes a lot of time, and effort.

I plan on building an extension to the system, so that I can recover platinum and palladium as well after recovering the gold and silver. So I would like to know what additional steps I should be taking in order to implement this. Should I be looking to precipitate the platinum and palladium after precipitating the gold? If so, what is the procedure to precipitate them from aqua regia after precipitating the gold. I am looking for some in depth information regarding this topic, and I would be interested in any related posts you guys can refer me to.

P.S. My background is in engineering not in chemistry, so it might take me a while to adapt to the community.

- Kharsa

 

[nickvc]

Welcome to the forum Karsa.
Most small refiners cement their spent solutions with copper using aeration to keep the solution moving to recover any trace values from their solutions which is a cheap and fairly efficient process to recover them.
There are products available which scavenge spent solutions for values Johnson Matthey has a product called scopex but I’m unsure of it’s cost but apparently it will recover values to an almost zero remaining degree and if as you say you are a large refiner I’m sure they would be happy to discuss your needs.
Be aware refining and recovering PGMs comes with a whole load of extra health risks compared to gold and silver refining so you will probably need a separate and dedicated area to do this and have your staff aware of the risks.

 

[Kharsa]

Welcome to the forum Karsa.
Most small refiners cement their spent solutions with copper using aeration to keep the solution moving to recover any trace values from their solutions which is a cheap and fairly efficient process to recover them.
There are products available which scavenge spent solutions for values Johnson Matthey has a product called scopex but I’m unsure of it’s cost but apparently it will recover values to an almost zero remaining degree and if as you say you are a large refiner I’m sure they would be happy to discuss your needs.
Be aware refining and recovering PGMs comes with a whole load of extra health risks compared to gold and silver refining so you will probably need a separate and dedicated area to do this and have your staff aware of the risks.

Thanks nick.

We currently have a whole treatment system to recover all the metals from the solution and have it neutralized and tested afterwards as it is mandatory before the municipality can collect the solution from us. Usually, all of these metals get stuck in the filter press and end up in the form of sludge which I believe is similar to the cementing process you have mentioned but on a larger scale.

I will definitely take a look at the products that you have mentioned for scavenging the spent solutions, but as a refinery, I would hope to be able to get pure platinum and palladium, so I would have to separate each on its own without the rest of the metals.

Of course, we have enough space that we would like to dedicate for recovering/refining PGMs, and are already implementing all safety measurements for our employees as even our current processes already prove to have risks if mishandled.

- Kharsa

 

[nickvc]

How are you getting the metals from solution ?
If you are dropping all the metals then you will have large volumes unlike using copper cementation which will only drop metals above it on the reactivity series so much less metals and volume .

 

[Kharsa]

After recovering the gold and silver from the solution, testing it, and transferring it to a holding tank before the treatment starts, we add zinc powder to precipitate the rest of the metals. Would you suggest for example, dedicating a tank first and adding copper powder (if I understood correctly) in order to precipitate the rest of the precious metals and then moving it into another tank and using zinc powder to precipitate all the other metals since it is way high up on the activity series?


- Kharsa

 

[nickvc]

Yes copper powder would work but you will need vigorous agitation as PGMs are notoriously hard to cement , using thick copper sheet hung in the solution with the solution moving would be better in my opinion but others may well chip in with advice .

 

[Kharsa]

Yes copper powder would work but you will need vigorous agitation as PGMs are notoriously hard to cement , using thick copper sheet hung in the solution with the solution moving would be better in my opinion but others may well chip in with advice .

That is actually a very interesting idea! We do have agitators installed in all of the tanks so that should not be an issue at all. I think I will take a sample from the solution and experiment with it on a smaller scale and see how it goes before implementing it. Thanks a lot for the advice!

Any other advice is most welcomed of course.

- Kharsa

 

[nickvc]

You may find you recover some more gold and silver along with the PGMs which would be a nice bonus.
The other thought I had was depending on the percentage of copper you have in the mix , you need 95%+ in reality, you could melt the powder and run the bars through a copper cell and collect any values from the slimes , plus you would have pure copper to sell .

 

[kurtak]

Nick is absolutely right - you want to first cement with copper to recover any PGMs as well as any trace of gold that got past the original gold precipitation

Once you have recovered your PGMs (& any trace of gold) you can then go to the zinc cementing as you are currently doing

As Nick pointed out - cementing the PGMs can be somewhat problematic --- if not done right

Here is a thread that discusses the problems you will encounter when cementing PGMs (with copper) & how to overcome those problems thereby allowing you to bring down a relatively to very clean end product

https://goldrefiningforum.com/threads/fuzz-button-interconnects-need-some-advice.22203/
Kurt

 

[Kharsa]

Nick is absolutely right - you want to first cement with copper to recover any PGMs as well as any trace of gold that got past the original gold precipitation

Once you have recovered your PGMs (& any trace of gold) you can then go to the zinc cementing as you are currently doing

As Nick pointed out - cementing the PGMs can be somewhat problematic --- if not done right

Here is a thread that discusses the problems you will encounter when cementing PGMs (with copper) & how to overcome those problems thereby allowing you to bring down a relatively to very clean end product

https://goldrefiningforum.com/threads/fuzz-button-interconnects-need-some-advice.22203/
Kurt

Thanks for the answer Kurt. I would like your take on my thought process.

After precipitating the gold from the aqua regia, I can pass all the solution to a different tank, use ammonium chloride to precipitate the platinum, then move the solution to another tank and use sodium chlorate to precipitate the palladium. Finally, I can take the solution and use zinc powder as I currently do in order to take the rest of the metals out of the solution.

Do you think that this would be possible considering the platinum and palladium would be sometimes <=1%? Would I be able to precipitate them from aqua regia use ammonium chloride and sodium chlorate and get pure platinum and palladium? If yes, in what form would the platinum and palladium be after precipitation and what would be the required steps in order to convert them into metal again?

I was thinking that precipitating them from the solution would shortcut the cementing process, but I am not sure if it can work this way.

 

[nickvc]

From what I understand PGMs precipitate the best from concentrated solutions so I fear that your plan will not work as well as cementation, please bear in mind I have avoided working too much with PGMs due to the hazards involved so maybe someone with more experience will chime in.

 

[Kharsa]

From what I understand PGMs precipitate the best from concentrated solutions so I fear that your plan will not work as well as cementation, please bear in mind I have avoided working too much with PGMs due to the hazards involved so maybe someone with more experience will chime in.

That is exactly what I am wondering about. If it would be impossible to precipitate such low quantities from large amounts of solution, then maybe cementation would be the better option.

Also, what would you consider as "concentrated" solution to make it worth precipitating the PGMs directly after gold precipitation instead of cementation? 30%+ of PGMs in the solution? Maybe a little bit less or more?

 

[nickvc]

Again this is from memory and reading but the higher the concentration the better the result for precipitation but for cementation the concentration matters little, exposure of all the solution to the copper is what matters and avoiding coating the copper with the PGMs which will happen without good agitation.

 

[kurtak]

After precipitating the gold from the aqua regia, I can pass all the solution to a different tank, use ammonium chloride to precipitate the platinum, then move the solution to another tank and use sodium chlorate to precipitate the palladium. Finally, I can take the solution and use zinc powder as I currently do in order to take the rest of the metals out of the solution.

I don't have a lot of time to post today - that said - again Nick is absolutely right - you can not precipitate Pt & Pd with ammonium chloride & sodium chlorate unless the solutions are very concentrated solution

when precipitating Pt & Pd with those chems it precipitates the Pt & Pd as "salts" of those metals - those salts are actually quite water soluble

so not only do the solutions "need" to be "high" concentration of the metals but they also have to have little to no water in them --- the salts also (once precipitated) then still need to be reduced from salts to metal --- & for what it is worth the salts of PGMs are quite carcinogenic so safety precautions when working with them are important

Thinking about this & before moving forward with more advice we need to back up a bit

You are working with LARGE amounts of gold that also contain silver & PGMs - that's what we know

What we don't know is what other metals are involved &/or in what (roughly) percentages ???

Metals such as copper, nickel, zinc etc. etc. ???

Kurt

 

[Kharsa]

Again this is from memory and reading but the higher the concentration the better the result for precipitation but for cementation the concentration matters little, exposure of all the solution to the copper is what matters and avoiding coating the copper with the PGMs which will happen without good agitation.

Yes, I have actually checked out some other threads and they all say that the solution should be in high concentrations of PGMs before trying to precipitate them for it to be efficient. I have also read that cementing with copper is not as simple as cementing with zinc and the proper steps need to be taken in order to avoid the hassle.

 

[Kharsa]

I don't have a lot of time to post today - that said - again Nick is absolutely right - you can not precipitate Pt & Pd with ammonium chloride & sodium chlorate unless the solutions are very concentrated solution

when precipitating Pt & Pd with those chems it precipitates the Pt & Pd as "salts" of those metals - those salts are actually quite water soluble

so not only do the solutions "need" to be "high" concentration of the metals but they also have to have little to no water in them --- the salts also (once precipitated) then still need to be reduced from salts to metal --- & for what it is worth the salts of PGMs are quite carcinogenic so safety precautions when working with them are important

Thinking about this & before moving forward with more advice we need to back up a bit

You are working with LARGE amounts of gold that also contain silver & PGMs - that's what we know

What we don't know is what other metals are involved &/or in what (roughly) percentages ???

Metals such as copper, nickel, zinc etc. etc. ???

Kurt

I appreciate your replies, you seem quite knowledgeable.

So, considering that the solutions are quite low in concentration of PGMs, then from what I have understood is that I would have to perform cementation with copper and leave the residue aside, for later refining with ammonium chloride and sodium chlorate. Now you have mentioned that when if I precipitate pt and pd using ammonium chloride and sodium chlorate, the result would be the "salts" of those metals, but what would be the result in the case of cementing using copper?

Also one more thing, is there are sort of reliable source of information where I can dive deep into this topic with? Some source of information about refining pt and pd, reducing them from salts to metal, and the whole process in general?

Regarding your question at the end, unlike the rest of the forum members, the gold we refine is usually coming from mines. That type of gold is usually in high purities with the rest being silver. So an XRF would give us a result of lets say 90% gold and 9-10% silver. XRF can only be so accurate though, so using ICP, we would notice that there is around 1% (usually less) of other metals which tend to be mainly PGMs. It might not seem as much, but considering every month we refine a couple of tons, it would definitely add up and is worth it to go through a process to try to recover at least pt and pd and refine them every once in a while.

- Kharsa

 

[nickvc]

The best resource for most refining processes is here so check out any threads covering PGM recovery and refining, we have very few hands on experts with the subject but anything Lou posts is from personal experience, there are a few others but reading the threads should inform you who knows the ins and outs of the processes.

 

[kurtak]

Kharsa

Thank you for the reply - I do not have time to respond today - I will try tomorrow - if not tomorrow will do so Saturday as Saturday is when I am off from my regular job

Kurt

 

[orvi]

I appreciate your replies, you seem quite knowledgeable.

So, considering that the solutions are quite low in concentration of PGMs, then from what I have understood is that I would have to perform cementation with copper and leave the residue aside, for later refining with ammonium chloride and sodium chlorate. Now you have mentioned that when if I precipitate pt and pd using ammonium chloride and sodium chlorate, the result would be the "salts" of those metals, but what would be the result in the case of cementing using copper?

Also one more thing, is there are sort of reliable source of information where I can dive deep into this topic with? Some source of information about refining pt and pd, reducing them from salts to metal, and the whole process in general?

Regarding your question at the end, unlike the rest of the forum members, the gold we refine is usually coming from mines. That type of gold is usually in high purities with the rest being silver. So an XRF would give us a result of lets say 90% gold and 9-10% silver. XRF can only be so accurate though, so using ICP, we would notice that there is around 1% (usually less) of other metals which tend to be mainly PGMs. It might not seem as much, but considering every month we refine a couple of tons, it would definitely add up and is worth it to go through a process to try to recover at least pt and pd and refine them every once in a while.

- Kharsa

In your situation, after precipitating bulk of the silver and gold, as it was said numerous times - copper cementation is the simplest and most effective way to recover any PGM present in the solution. It will also precipitate any mercury (often found in mining concentrates, so bear it in mind).

PGM precipitates tend to adhere on the surface of copper and with doing so - they cover the whole surface of the copper, blocking the access of solution to fresh copper surface.
Agitation or aeration is therefore needed to continously remove particles of PGM from the copper surface. And it should be moving the solution quite a bit, and it take some time to completely precipitate the values.
Also, be aware that you will find some % of copper in your PGM precipitate. Not high, but it will flake off with PGMs during cementation.
If you have overhead stirrer in the reactor, you will be fine with it. Just test it in smaller setup, observe how it will go.

As you will dive deeper into the subject, you will encounter a lot of secrecy and missing information about refining platinum group metals. Few big refineries in the world refining this material are doing very well hiding the protocols and systems used. Smaller refiners have very similar approach, as not many people in the world know the right procedures to produce pure PGMs - this way, new competitors are more likely to fail. General principles of separation - like you said - NH4Cl, chlorate, hydrolysis etc. are well known. But exact procedures are somewhat hidden, with few exceptions.
I recently tried to concentrate and separate PGMs from very similar solution as you are dealing with. I personally failed to separate mixture of PtPdRh efficiently enough. Concentrating the PGMs is not an issue tho, if you once establish your copper cementing apparatus. Getting them separated is completely different story
Lot of inconveniences, unpleasant findings about reactivity/unreactivity, incomplete precipitations, issues with low purity final products... Refining PGMs is much more difficult than refining gold or silver. And also much more hazardous and toxic. But if you have only Pt and Pd, it is whole lot simpler than having three of them in the juice Except few procedures, in PGM refining, any separation could be characterized more as "enrichment" not "isolation".

In your situation, I will do very thorough calculation - if it is worth your time/money/investigation/health etc. to refine the obtained PGMs. If it is worth premium on the pure 99,9% Pt or Pd (if you can get premium on 3N pure metal), or it will be wise just to sell PtPd alloy and circumvent all the trouble for a few % lower payout

 

[Kharsa]

The best resource for most refining processes is here so check out any threads covering PGM recovery and refining, we have very few hands on experts with the subject but anything Lou posts is from personal experience, there are a few others but reading the threads should inform you who knows the ins and outs of the processes.

I have been lurking around and I have found quite a bit of useful information all around. I have also stumbled upon Frugals post about cementation (When In Doubt, Cement It Out), which I might experiment around with and try to see where I can reach with this whole PGM refining.