pgm and gold refining from rich and possibly complex leach

[lazylightning]

Howdy Folks!

I'm new in these here a parts and was a wonderin if anyone would help me. I've got this leach which should be rich in all pgms in high quantities and perhaps gold and any or every other kind of contaminant as well. First of all I will bubble some air through the solution which contains nitric acid, the air stream will carry out the Oso4 through some bubbling cylinders with 25% KOH solution to absorb it for later extraction with ethanol(so the overall volume is 5% ethanol for optimum precipitation).

My question is, when I raise the heat on that aqua regia laden with platinum group metals, but already stripped of Os, will the other pgm's distill off with the nitric and HCl? A colleague of mine seems to have heard this before, however he is not sure. If it does not then I may simply evaporate off that AR without having to worry about catching it with distillation.

I can't simply neutralize the solution before the burn off since the ammonia nitrate is added to the HCl liquor before the burn off as a condition to avoid complex chemical changes during the burn off which is also mandatory at this stage. Obviously there is an excess of ammonia nitrate added and not just to make nitric acid in the HCl. Reduction burn off will be in an atmosphere sealed stainless steel vessel so acid should be gone before hand.

Also before burn off, I should be sure that any aluminum is removed if it existed in the solution. Does anyone have an idea how to remove it or even test for aluminum?

Thanks in advance!

Best Regards,
Paul

 

[lazylightning]

So what I got is lots of everything in there, that I need to get out. My girlfriends grandfather was repressed by the Georgian gangster and Soviet dictator and sent to work in Siberia in the 40's and 50's, gulag. So what was going on was that these millions of repressed people, many of which were members of the intelligentsia and just plain smart professional people made it a custom to take revenge against their captors. They trashed from 50-75% of the gold and plats they were mining. This was done to make sure that they weren't going to the Soviet state.

The Soviet Sate didn't really notice the difference because Siberia is so full of pm's that the part they got was quite alot too. So my girlfriends grandad was released/rehabilitated after Stalin died and in the 70's during a trip to Siberia snatched a couple of sacks of material from a waste site that he had made during his service at a gold and platinums site. He had always said that he put enough pm's into that waste to make it very rich material. I've also heard from other experts in the gold field that the old sites can still be loaded with pm's because either the diggers shoveled it off to the side to be left behind or it was thrown into or washed out with the waste by people of soul.

Her grandad, in the heavenly kingdom, had tried for years to get some out, but there are problems with this stuff because all of the shit that it was mixed with. Now I'm getting ready to give it a try, so I'll have plenty of more questions coming.

Has anyone ever worked with solvents and absortion columns before?

 

[Lou]

Yes, yes, and yes.


You've got me interested in it.



You seem to be on your way if you've figured out that you want to make potassium (per)osmate from OsO4 to prevent killing yourself. And then it is an easy reduction with MeOH or EtOH. Just don't forget that Ruthenium is chemically a twin to Osmium, and even more dangerous when it's +8 oxidation state because it is even more volatile! milligrams will kill you.

Personally, I would do just as you are--roast everything with excess oxygen. This will remove the volatile Ru and Os tetroxides. What you are left with (if you take it really hot) is rhodium (III) oxide, Rh2O3, PdO and PdO2, and Pt metal (Pt won't oxidize). If it were me, I would dissolve away the Rh2O3 and Pd oxides (should dissolve reasonably well with heating) with HCl giving you the acid salts of these metals. These can then be precipitated a variety of ways, or reduced with ammonium formate as is. I'd suggest a second refining operation on it. With respect to the platinum, it should be contaminated by iridium. Dissolve all in near boiling aqua regia with some H2O2. That should get the iridium in if it's fine powder. If it's lumpy, forget about it. Either way, precip. the ammonium (+4) salts and reduce with either formate, borohydride, or hydrazine routes.


This is assuming your ore isn't high in alkali halide salts--these will attack all but iridium with quite some vigour at high temperature.



Sorry I have to be brief, I've got to head out the door! All for now!

 

[lazylightning]

Thanx for the advice! Actually I'm going to get the Ru out by bubbling chlorine through it while in a hypochlorite solution. As I understand it really gets in the way of precipitation. With the Os and Ru safely and simply removed, then I will reduce it with a burn but with no oxygen. I don't really want to get oxides. That could be very problematic. Also this stuff is screwwed up already and terrible alloys that can't be seperated are forming for some reason. So, I've been told it needs to be burned down at 4-500 C with no oxygen or air getting in. Base metals will wash or dissolve off with HCl and then what I have (probably Pd,Pt,Rh,Ir) will be dissolved completly by aqua regia and then I can try to dissolve something. Before I burn it down I need to get out some of the other bad stuff that usually gets in the way because something is going on here during the burn off process to make unseperatable brittle white alloys with magnetic properties. If I try to precipitate before burn off nothing will come out.

I've been told that I must get the aluminum out at a minimum or it will create complex refractory bonds that will rob me of my plats. I think some other things may be there that are doing the same. Everything from Te to As and many more are known to completely get in the way of the pgm precip. process.

If anyone knows at least how to get the Aluminum out, that will be a great step in the process of "elimination" to figure out what's screwing the batch so badly. If I still have probs. after the aluminum is gone or proven not to be then I can move on, otherwise I won't be using my head and random shots in the dark can be compared to all kinds of unpleasant sensations ;D

 

[Lou]

I don't know who told you that your metal will be lost due to ''refractory bonds''. This is chemistry here, not physics--your metal is not going anywhere. Things may get more difficult, but as far as I'm concerned, if this is a concentrate and at today's prices, it is well worth your time to go after values.

There are a bunch of options available to you.

Aluminum is easily removed with HCl, same for pretty much all of the base metals. Some peroxide may help.

I should mention this, you do want to crush it to a fine powder, taking care not to breathe any of it. You SHOULD roast it under oxygen at high temperature.

Let's say I were in your position, and had to contend with a concentrate that had every PGM in it, but it was contaminated with Nickel, Arsenic, Cadmium, Sulfur, Tellurium, and Iron and of course silicates.

I have several options to deal with this, ranging from fusions, to smelting, to roasting.

I don't like doing fusions, I don't mind smelting, but I really think roasting it is clever because it accomplishes more: Ican remove the Os and Ru from the system, and these can be effectively distilled, or reduced together and reprocessed. At the same time, all the Sb, Se, Te, and S would be gone, while Fe, Co, Ni, Cu, and others would be easy to dissolve oxides.
I would then be left with the unchanged Pt, Ir, and Rh. Pd, Ag will go into solution (the Pd will oxidize) with the base metals oxides. Test for them and then pursue them if I deem it worthy.

 

[lazylightning]

Thanks again! I agree that the roasting is easiest. I've been led to believe that the roasting is done to break down the sulfides. I read a patent that stated that the sulfides were more easily broken down at lower temperatures in the presence of moisture. I just put my fine powdered(silk screen sifted) in a stainless steel pan with water and put it on an electric eye on high all night under the hood with asbestos carton on the lid to keep the heat in. I think it got plenty hot cause when I took the pan off in the morning it smoked my glove and the newspaper I put it on almost caught on fire, had to move it onto the asbestocarton quickly (no handle on pan). Not much oxygen for it but I guess the moisture had some oxygen in it. Actually before roasting I had already let it sit overnight with HCl to leach out iron and other base metals. Then I washed it several times, and it reeked of sulphur. Then I roasted it several times starting wet and now the smell of sulphur is almost unoticeable. Since our electric meter was stolen the communal services can't get around to installing a new one and we pay a flat rate for electricity. I always make sure I get my moneys worth ;D

Now after preleaching and roasting I will load her up with AR and simmer for several hours. I've been advised to add potassium chloride to the acid before ever adding a multimetal ore with plats. It's supposed to sequester the iron and Os which should help avoid disastrous complex bonds from forming.

Since I don't have the burning reactor ready, I can only do the Os and Ru removal with bubbling. The Os is so easy cause in the AR all you have to do is bubble air through it at 85C and in the prescence of nitric acid it just flies away. I already have the main bubbling reactor for the pregnant AR ( a large glass condenser) and three specially made bottles with burets in lids for capturing in KOH solution. For bubbling the Ru out of a hypochlorite solution I'll need a source of chlorine gas to bubble through it. I'm still thinking on that one.

The burn off reactor for burning it down without any contact with air should be fairly easy to make from a stainless pot with lid, asbestos carton for insulating walls and an electric eye.

Then I've been led to understand that I will be able to succesfully wash the remaining residue and then redisolve it and use conventional means of seperating the Pd, Pt, Rh and Ir. I haven't decided which way to go with that and I'm all open for suggestions.

What I'm concerned about is how to remove any aluminum that is already dissolved in the AR together with the plats. How can I precipitate the remaining aluminum without precipitating any of the plats. There must be some remaining aluminum in the micro pieces of plats that will dissolve later in the hot AR. So some aluminum will be there anyway. How could I get rid of it. I've been warned that it will cause great problems during the burn off process. Many other contaminants that were contained in the micro peices of pgm will be freed up into solution along with the pgm's. The preleach I did just helped me get rid of alot of the base metals, but not all of them because some of them are trapped inside of the pgm micro fragments/pieces.

 

[Lou]

I should warn you that Ru, Ir, and Rh are practically insoluble in aqua regia.

Ru and Os can easily be ''distilled'' off by heating to about 250*C with a flow of oxygen. Heat it up further and you'll lose the volatile metal oxides.

I don't know the nature of your ore, but I don't think aluminum will cause problems.


If you suspect the values are encapsulated in some refractory oxide or perhaps alloyed with base metals, I suggest you melt it all with a collector of some sort. Part it with nitric acid and you'll be left with your metals all concentrated as a residue.


Lou

 

[lazylightning]

"Ru and Os can easily be ''distilled'' off by heating to about 250*C with a flow of oxygen. Heat it up further and you'll lose the volatile metal oxides."

Good to know! I'll get that Os off seperately first with the bubbles through the solution in the presence of nitric acid, that's really easy. I'm thinking about sending the stream directly through some 95% ethanol instead of the KOH solution. That way I'll get OsO2. I suppose they don't do so on industrial levels because of the expense of blowing off extra alchohol.

As far as overheating it and losing some values as volatile oxides, I plan to seal her up for the burn off. So I'll boil off the acid and water and when its boiled off I'll wash/move it to the stainless burning vessel, get the residue just dry with moderate heat. With all the moisture gone, I'll seal her up and bring the heat up to 450C, there should be no problem with pressure buildup. Since there will be no oxygen inside, there shouldn't be any oxidization occuring and with it sealed up, nothing will get out of the vessel anyway. Then later I can just give it an HCl bath to get rid of the base metals. It's not platinums as usual or I wouldn't have to do the burn off procees which is for breaking undesirable bonds between the platinums and other things including H2O. It's during this burn off process, which will bring the plats into the conventional world of refining, that there can be some problems with the aluminum. Otherwise the plats may refuse to obey known laws and I may never see them except through a long spectrographical burn in an argon column...lol.

 

[lazylightning]

I should warn you that Ru, Ir, and Rh are practically insoluble in aqua regia.

Ru and Os can easily be ''distilled'' off by heating to about 250*C with a flow of oxygen. Heat it up further and you'll lose the volatile metal oxides.

I don't know the nature of your ore, but I don't think aluminum will cause problems.


If you suspect the values are encapsulated in some refractory oxide or perhaps alloyed with base metals, I suggest you melt it all with a collector of some sort. Part it with nitric acid and you'll be left with your metals all concentrated as a residue.

Lou

Hi Lou!


I've been quite busy for a while and now I've got some news and new questions. The more we find out, the more questions appear.

So instead of using the burn off technique which is problematic on my 15th floor balcony, I decided to try the electroprecipitation of sulfides process. The HCl was neutralized with copius amounts of sodium metabisulfite concentrated solution. There was no Nitric acid in it and the hazard sheet says that sulfur dioxide explodes violently when in contact with nitric acid. If you have AR then I don't recommend trying it. The solution is neutralized when no more sulfur dioxide gas forms. The solution becomes somewhat sulfuric acidic in content and is more conductive for electroprecipitaion. Ammonia sulfate is added generously to help move the pgm's to sulfides and for producing more hydrogen at the negative electrode to help the process too. Using an inert graphite positive electrode and a negative electrode made of a long vertical strip of stainless steel for convection(don't get those electrodes too far apart or you'll burn up you power supply( 6-20 volts to 20 amps), the sulfides of pgms and base metals precipitated(not plated) as a black residue on the negative stainless electrode and the bottom of the reactor/jar. Positive electrode should be in a polyester sheath to keep any graphite out of the solution.

My question is, regarding the refining of those sulfides. It has been recommended to me to treat them with a "weaker" nitric acid to get out the base metals and then go after the Rhodium with Aqua regia. I am supposing that is because the Rhodium will not dissolve in the Aqua regia and perhaps the Ru and Ir too(as you mentioned). Then I will just have to remove the Ru and seperate the Ir from the Rh.

What concentration of "weak nitric acid" would you recommend for removing the base metals?

What concentration/proportions of acids should I use in the Aqua Regia for removing all the rest except for the Rh and perhaps Ir and Ru if they are also going to stay with the Rh? I have 70% nitric and 40% HCl. Should I heat it or will the sulfides of Pt, Pd, Os, and perhaps Au dissolve in cold AR, so as to not risk losing any of the values of Rh. I can leave it in cold AR for days or a week if neccesary.

Paul

 

[Lou]

That whole ''sulfide electroprecipitation'' seems dodgy to me. You also shouldn't be doing this anywhere near a city or other people. Please find somewhere else.


Granting that you did obtain sulfides of all of those metals, you're still at square one so to speak--all you accomplished was separating out the metal from the gangue.

Adding any sulfide to an acid is asking for trouble, and possibly a very smelly death. Unless you're out to make a horrific rotten-egg smelling plume of H2S that is sure to stink up a large area (it's detectable in low ppb), don't try to dissolve your sulfides. Rather, put them in a pan and roast them to burn off the sulfur as sulfur dioxide which is more benign. Bear in mind that any Ru and Os will still volatilize when the sulfur is burned off, so take precautions to recover the metal.

Do that and then we'll talk wet chemistry.

 

[lazylightning]

Thanks for the tip about the danger of dissolving sulfides in acids. I'll take er all out in the country for this stuff.

What about catching the Ru and Os coming off along with the sulfur dioxide in a solution of alchohol or KOH? Is sulfur dioxide strictly a gas that will not precipitate into any solid forms in that solution along with the Os and Ru? After what I read about it, I wouldn't want to get any into some nitric later when I redissolve that Ru and Os and pass air through it to selectivley remove the Os.