No rush Kurt, thanks for the updates though.
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- Thread starter Kharsa
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Yes you are right, mercury is used in the amalgamation process in order to make the doré bars which we receive from the mines for refining, so I would expect it to precipitate with the PGMs, but the purpose of cementation is just to increase the concentration, not really recover pure PGMs, so it should not be an issue as the next procedure would be to refine them.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 juiceExcept 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
From what I have read in Frugal's post (When In Doubt, Cement It Out), I might try to make a similar system on a smaller scale to see how efficient it is. Apparently, using a similar method will help avoid having the surface of the copper covered so that it the precipitation will not stop. If it does work as intended, it wont be an issue to make it on a larger scale once the concept is clear.
I understand that there will always be some secrecy, it was quite similar around 30 years ago when we first started refining gold. It took quite a bit of experimentation in order to achieve perfect results and optimize the system on such a large scale. So I am sure, it will be the same case with refining PGMs right now. We do have a laboratory where we usually do extensive experimentation before moving onto a larger scale as the costs and risks are quite high in moving on with such a project blindly.
My main focus right now is Pt and Pd, as for the rest such as Rh, that might be for some other time in the future maybe. I have done my calculation and it might not necessarily be worth it if my plan was to only recover Pt and Pd from my solutions. But, I do always receive inquires about refining big quantities of Pt and Pd in high concentrations, which is when I would add the rest of my cement to refine with as some kind of an added value.
kurtak
Well-known member
Kharsa
Thank you for the compliment - however - when it comes to the PGMs I am limited in the refining of them (though I have "played" with it)
The chemistry set of skills/knowledge for refining PGMs (if/when the PGMs are mixed PGMs) is far greater then that for refining gold & silver & is beyond my skill set which is why I have for the most part simply recovered my PGMs by way of cementing them from gold &/or silver solutions that also contained the PGMs (after first recovering the gold/silver of course)
My point being I am not really the one to help with advice on the refining of mixed PGMs
Recovery (by cementing) is another story --- which is why I asked -----------
To which you replied -------
Per the bold print - we still need to know what is meant by mainly PGMs - & other metals
As the saying goes in refining - garbage in garbage out - meaning if you have a lot of garbage (base metals) in a solution of PMs (Precious Metals) the more likely you are to have drag down of the garbage when you precipitate the PMs --- this is especially true with PGMs
PGMs chemistry is much more complicated then gold/silver chemistry - meaning it is easier to selectively precipitate gold & silver to a high purity from dirty solutions then doing so with dirty solutions containing PGMs
In other words - in PGM chemistry there is more of a tendency to have drag down of other metals & (at least as I understand) not just base metals but "some" drag down of PGMs themselves when trying to separate them - which is in part why "refining" PGMs is more costly & complicated then refining gold/silver
In other words - as an example (at least as I understand) in say a solution of Pt & Pd (&/or other PGMs) when you go to selectively precipitate the Pt you are likely to get some drag down of the Pd so you will likely need to do a second refine of the first precipitation to reach the target 999 purity --- again - part of why PGM refining is more costly then gold/silver refining (as I understand)
The point being the cleaner the PGMs going into solution the better --- which brings us back to the cementing of the PGMs from your solutions after you have recovered the gold & silver
So back to the question -----------
We still need to have at least a rough idea of what is meant by mainly PGMs & what is meant by other metals as in a rough idea of the percentage of the PGMs compared to the other metals & for that matter what those other metals are (some metals have more of a tenancy to drag down then others)
I ask because that can make a difference in whether cementing with copper is actually needed - or - if cementing with zinc (as you are currently doing) is good enough
In other words - IF (the BIG IF) your end goal is to actually refine the PGMs - the other metals may not be in significant high enough amounts to need copper cementing
Copper cost (about) 3 - 4 times more then zinc - so cementing with copper instead of zinc will cost 3- 4 times more --- therefore - unless the other metals are so high as to be problematic in the refining of the PGMs I would stick to cementing with zinc rather then copper
To put it in perspective - when I was leaching catalytic converters for the PGMs besides the PGMs going into solution metals like iron, manganese, nickel & copper would also go into solution - but those base metals where not high enough to be of concern (15 % or less) so cementing them (the PGMs & base metals) with zinc was not an issue
On the other hand - when leaching certain electronic scrap (such as CPUs &/or ceramic ICs etc.) beside gold & PGMs going into solution LARGE amounts of other metals like iron, copper, nickel, cobalt etc. go into solution - so - after dropping the gold you end up with a solution HIGH in the base metals & low in PGMS (plus/minus 10% PGMs) so cementing with zinc would bring down all the base metals along with the PGMs & therefore whereas cementing with copper would bring down mostly the PGMs with some copper contamination (1 -2 %) & maybe (or not) some very small traces of the other base metals
Hope that helps
Kurt
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kurtak
Well-known member
First of all I find it hard to believe anyone is actually using mercury to recover gold from large scale mining operations as that is really a very old method for recovering gold - there are now much better methods for gold recovery
That said - even if the mines are using mercury for gold recovery there should be no mercury ending up in your dore - that is assuming the mine(s) would first be retorting the amalgam to recover the vast majority of the mercury for re-use --- any "trace" mercury in the gold after retorting "should" go off in the melting/smelting
Kurt
This is true. Proper smelting/melting will drive off most of the mercury. Sometimes the traces of it alloy that way it just won´t evaporate during quick smelt/melt, but it is minor.
I thought about actual gold concentrate in terms of gold dust/flakes concentrated in the processing to the point where is not much junk mixed in them. Raw natural gold often contain few % of mercury. Just didn´t noticed the word "dore" in the main text or forget about it somehow.
Even though you believe it is beyond your skill set, you never really know how valuable some of the information you offer might be. Little bits and pieces here and there from a couple of people might help provide a base to work on and further experiment.
I can not really provide you with exact numbers, I personally do not have the capability of performing ICP myself. Many laboratories that I have visited around here tend to perform ICP but neglect all precious metals out of their results except silver as the "standards" for the other precious metals are quite expensive for them. That is what they say at least. However, when we do end up sending the waste abroad every quarter for treatment, they perform ICP on the waste and do end up recovering quite a bit of platinum and palladium which leads me to believe that the impurities in the gold we receive is mainly PGMs. I would definitely have to go through the reports to get exact numbers as this is just from memory.
When it comes to gold and silver, this does not seem to be the case for us at least, we do not have any issues refining high and low purities of gold and silver and having them precipitated without any other base metals. For PGMs though, and after reading on the complexity of refining it, I imagine that it would be a pain if the solution had lots of base metals. Takes us back to the point where PGMs should be in high concentration before refining.
I have read that some people are actually refining more than twice in order to reach the target purity which like such a hassle.
This is definitely something to think about right now, especially since the prices of all the other metals have increased significantly over here in the past year. I think the right approach here would be to send at least a couple of samples for ICP abroad to get a good estimate of the average percentages of the other metals compared to the PGMs and find out whether using copper to cement would be worth the extra cost or not.
After all, the best solution might be just to keep on sending the waste abroad instead of recovering it and refining it, but I have to study it from all perspectives before judging.
Thanks again.
Kharsa
Honestly speaking, we do not involve ourselves much on the mining side as I believe that it is on its own a whole other field. So, I personally, am not up to date or experienced much on all of the methods used in operations of extraction of gold.
As I have mentioned before though, the local ICP that we do every once in a while to the waste solution shows all the metals in the solution including silver but excluding the rest of the precious metals. The results always show traces of mercury in the solution. Again, I can not currently provide numbers as I would have to refer to the reports first, but mercury is definitely in there and I assumed that it was from the process of recovering the gold.
Kharsa
You needn´t to start big. You can build up steadily. First thing would be precipitation of any precious metals using copper - that would bring you metal cement, where all possible values will be entrapped. Traces of gold, silver and also the PGMs.
I know the copper is somewhat more expensive than zinc and not to say iron, but with copper, you get fairly clean PM mud to later work with. And as we do not expect huge ammounts of values, this wont be very much of copper. If you take into consideration the cost of copper against the value of recovered platinum and palladium, it is very very small fraction. Even on large scale.
Copper with molar weight around 63 and Pt ca 195, Pd ca 106... Being tetravalent and bivalent... Theoretically you will need little less weight in copper to precipitate PGMs present. Depending on the process, you will have say trace active oxidant in the solution, some oxygen would make it to the solution despite closed vessel... If it would be as much as 4 times the ammount of copper theoretically needed, still it is a tiny tiny fraction of the values recovered.
That tiny extra cost will give you advantage of producing quite pure PM mud to later work with.
If you opt for zinc, any iron, tin, lead, copper, nickel will also precipitate from the solution. Making your operation more lengthy, as the values will be quite diluted and there would be probably need of second refinement of the mud.
You can totally stop there, and just collect and melt the resulting mud. And sell it as mixed PGM enriched alloy. You squeeze some good money from the juice with practically minimal input effort and cost. And you minimize the possibility of contact with irreversibly and incurably toxic PGM salts (mainly Pt salts).
If this would work for you, you can then proceed further and try to elaborate some viable refining process to separate Pt and Pd. As it was said there numerous times, it is far more complicated and empirical field than hanging copper bar into the tank of liquid
But certainly doable. Depending on impurities present (I think you should make a sample of metal cement with either Cu and Zn, and get it at least XRFed to know what will go out), the outcomes from one refining cycle will vary.
Main problem is you never get full separation of the metals one from another. Mixed fractions will arise from refining, which should be processed, prolonging the process. Also, with one pass, the purity is not likely to be more than 99% with basic methods. Say you produce 96% Pt and 98% Pd, there would be 4% of mainly Pd in your platinum and 2% of mainly Pt in your palladium. Many refineries observe this low ammount as impurities and not pay any money for them. So you will need second refining cycle for both of them. Labor cost, protective gear, more waste created, chemicals needed... Against the profit you can possibly squeeze out of throughly refined metal. Need to be carefully calculated
At present you are zincing your spent solutions to remove most of the metal contents which is why it’s not feasible to recover and refine the PGMS but if you cement using copper you will only recover PMs and a little mercury which can be removed by using a retort, as you mention the cost of copper is increasing so after cementing your solution for values you could then add steel to cement the copper which I think will also scavenge any PGMs left in the solution , if you use that copper for cementation you get free copper and a small bonus of any PGMs that cemented with the copper.
As Kurt mentioned a full read out of your metal waste would help us help you to find a process that fits your needs.
As Kurt mentioned a full read out of your metal waste would help us help you to find a process that fits your needs.
kurtak
Well-known member
I sure would like to see Lou chime in on this !!!
resins like scopex "might" be your best option
Kurt
resins like scopex "might" be your best option
Kurt
