Refining Platinum: no walk in the park
Chris, Sat Jan 20 2007, 12:07PMI remember there being a thread awhile ago on electroplating platinum, details can be seen here:
Now here's a thread dealing with my efforts and the difficulties and possible solutions to actually refining contaminated platinum scrap into a pure salt or metal. In all the reading I have done on the matter, platinum is melted into shot, and dissolved in aqua regia over the course of at least an hour, and at most several hours. This is done with the aqua regia heated to nearly boiling, as the action of the acid on platinum is minimal at room temperature. The platinum I started with was in the form of foil pressed onto titanium plates. I ground it off with a dremel, inside a bucket with a bag over it so only the very tip of the tool poked in, to make sure everything that was ground off was collected. It is mainly fine powder, with some larger pieces of foil. There should be about 30g or 1 troy ounce total on the plates, by foil thickness measurements, and weight of a sample of known area. At present only about 2/3 of this is ground off, which I have been attempting to dissolve.
The plan is to dissolve all the metal, bits of grinding stone, etc, and convert the resulting chloroplatinous acid to chloroplatinic acid, then that to ammonium chloroplatinate, which is easily decomposed to platinum sponge or powder at 200C. This would be then treated with concentrated nitric or sulfuric acid to dissolve remaining solubles which were either not decomposed, or consist of metals which can be dissolved by such acids. The remaining platinum would then be redissolved, and this process repeated perhaps several times, finally yielding a highly pure platinum salt, or platinum metal which can be electroplated or forged.
The acids I am using are red fuming nitric acid which I distilled at 1 atmosphere from potassium nitrate and sulfuric acid, and fuming hydrochloric acid made by fortifying muriatic acid (32% HCl) with additional HCl generated by NaCl and sulfuric acid. The mix is 3 parts of the latter to one part of the former.
When I first began the process, I left the platinum in the acid for over a month at room temperature; there was almost no reaction at all (I was not aware it was supposed to be heated). Upon boiling that acid off and replacing it with a fresh mix, I heated it in a flask on an improvised mixing device which I have named the "wobblin" after its comical offset rotating motion. The device is fitted with a condenser to re-condense any acid that boils out, and the top is fitted with a diffuser filled with sodium bicarbonate in an attempt to absorb most of the chlorine and nitrosyl chloride produced by the reaction and the decomposition of aqua regia. The success of this approach was minimal, with much of the caustic gas still escaping. The setup was moved out to the shed, with ventilation in place so it won't completely destroy my tools and stuff. Venting it to the outside doesn't work so well either, it just fills the entire neighborhood with caustic fumes; someone will probably think I'm running a meth lab.
There seems to be no easy way to deal with that stuff, maybe I could build a huge diffusor filled with sodium hydroxide or something. In any case, after an entire day of running the wobblin, there is still nearly as much metal as before left in the bottom of the flask. It's difficult to tell how much has dissolved, but the thick blood-like color of the spent solution indicates a significant amount of chloroplatinous or chloroplatinic acid, and insoluble nitrosoplatinic chloride (all deep reddish-brown solids). Yet much metal remains. Upon boiling the liquid down (a horrendous process which I need to find a different approach to), the volume left in the flask even with some liquid is far less than the total volume of dry chloroplatinic acid which should be formed from the platinum that was originally placed into the flask. Either most of it magically disappeared, or only a small portion has dissolved. The metal is in the form of very fine powder and some pieces of thin (0.001") foil, along with titanium metal, and some undercoat of an unknown metal which is possibly nickel, silver, titanium, or some alloy. Should it not dissolve very quickly in hot fresh aqua regia, especially with agitation? Surely it should dissolve much faster than platinum shot. If I didn't know better, I would say either the aqua regia is not effective (unlikely, as it exibits the proper color, fuming nature, and extreme corrosiveness to everything else) or the metal is irridium or tantalum instead of platinum (unlikely due to its ductility, and simply the fact that it was available at a very low price).
I can't imagine what is going on here. Any ideas?
Re: Refining Platinum: no walk in the park
..., Sat Jan 20 2007, 06:03PM
Well, have you considered that maybe there wasn't as much Pt as you originally hoped? It is possible that the layers are like 99% nickle (or whatever sticks to Ti) with a few Pt molecules plated on it.
Perhaps you should try dumping the powder left in the bottom of the jar into some H2O2 and check for bubbles? Very fine Pt powder should go crazy...
Another possibility is that you just hit the endpoint of the reaction, and you need to remove some excess Pt ions for it to continue any further... How ironic, 2 posts in a row deal with my to favorite chem subjects; equilibrium and thermodynamics
..., Sat Jan 20 2007, 06:03PM
Well, have you considered that maybe there wasn't as much Pt as you originally hoped? It is possible that the layers are like 99% nickle (or whatever sticks to Ti) with a few Pt molecules plated on it.
Perhaps you should try dumping the powder left in the bottom of the jar into some H2O2 and check for bubbles? Very fine Pt powder should go crazy...
Another possibility is that you just hit the endpoint of the reaction, and you need to remove some excess Pt ions for it to continue any further... How ironic, 2 posts in a row deal with my to favorite chem subjects; equilibrium and thermodynamics
Re: Refining Platinum: no walk in the park
Bored Chemist, Sat Jan 20 2007, 06:30PM
Sorry to spoil the fun but that's not really an eqm reaction. The other products of the Pt + Aqua Regia reaction are gases so they leave. This would destroy any eqilibrium.
BTW, finely divided just about anything will catalyse the decomposition of H2O2.
Bored Chemist, Sat Jan 20 2007, 06:30PM
Sorry to spoil the fun but that's not really an eqm reaction. The other products of the Pt + Aqua Regia reaction are gases so they leave. This would destroy any eqilibrium.
BTW, finely divided just about anything will catalyse the decomposition of H2O2.
Re: Refining Platinum: no walk in the park
Chris, Sat Jan 20 2007, 07:50PM
Finely divided nickel (or anything besides irridium or tantalum) should dissolve rapidly in aqua regia. Also, as Bored Chemist noted, nickel is catalytic to H2O2 as well. The outer layer of foil has undergone some testing to determine if it's platinum as well. After being heated to white heat with a torch, and exposed to concentrated nitric and sulfuric acids, it remains untarnished, and the bare metal rapidly decomposes 3% H2O2. Also by weighing a small rectangular sample of the foil and measuring its thickness (not super accurate but good enough), it has a density of around 20.
Chris, Sat Jan 20 2007, 07:50PM
Finely divided nickel (or anything besides irridium or tantalum) should dissolve rapidly in aqua regia. Also, as Bored Chemist noted, nickel is catalytic to H2O2 as well. The outer layer of foil has undergone some testing to determine if it's platinum as well. After being heated to white heat with a torch, and exposed to concentrated nitric and sulfuric acids, it remains untarnished, and the bare metal rapidly decomposes 3% H2O2. Also by weighing a small rectangular sample of the foil and measuring its thickness (not super accurate but good enough), it has a density of around 20.
Re: Refining Platinum: no walk in the park
Hazmatt_(The Underdog), Sun Jan 21 2007, 07:25AM
If you want to get rid of metals other then the Pt, I would suggest looking into something like Nitric BiFlouride. We use it for Ti deox, so it strips down Ti like nothing you would ever imagine. HOWEVER, I want to be very clear about this now, Flourides and Biflourides are VERY dangerous. Working with HF, or other corrosive flourides can lead to severe burns, and possibly loss of fingers or bone.
I would look into a Nitric Biflouride mix, but I'm just giving you the 'heads-up' that its not something to mess with if you're ill-equipped.
Hazmatt_(The Underdog), Sun Jan 21 2007, 07:25AM
If you want to get rid of metals other then the Pt, I would suggest looking into something like Nitric BiFlouride. We use it for Ti deox, so it strips down Ti like nothing you would ever imagine. HOWEVER, I want to be very clear about this now, Flourides and Biflourides are VERY dangerous. Working with HF, or other corrosive flourides can lead to severe burns, and possibly loss of fingers or bone.
I would look into a Nitric Biflouride mix, but I'm just giving you the 'heads-up' that its not something to mess with if you're ill-equipped.
Re: Refining Platinum: no walk in the park
ragnar, Sun Jan 21 2007, 08:39AM
I don't think Chris needs to know this, but other readers might:
http://en.wikipedia.org/wiki/Hydrofluoric_acid
ragnar, Sun Jan 21 2007, 08:39AM
I don't think Chris needs to know this, but other readers might:
http://en.wikipedia.org/wiki/Hydrofluoric_acid
wrote ...
Symptoms of skin exposure to dilute HF are not felt immediately, but exposure of less than 10% of the body to it can be fatal, even with immediate medical treatment. Highly concentrated solutions may lead to acute hypocalcemia, followed by cardiac arrest and death, and will usually be fatal in as little as 2% body exposure (about the size of the sole of the foot). This substance is extremely toxic and has the capacity to kill upon exposure rather than simply damage skin and eyes. It should be handled with extreme care, beyond that given to hydrochloric, sulfuric, or other mineral acids.
Due to low dissociation constant, HF can penetrate tissues quickly like a small non-polar particle. Hydrofluoric acid which comes into direct contact with the fingers can severely damage or destroy the tissue underneath the nail without causing any damage to the nail itself. It is this ability to cause little harm to outer tissues but considerable harm to inner tissues which can produce dangerous delays in treatment of hydrofluoric acid exposure. Once the pain starts, it is out of proportion to the burns produced. Patients often describe the feeling as if they have struck their fingers with a hammer. HF that penetrates under the skin causes later development of painful ulcers, which heal slowly.
Symptoms of skin exposure to dilute HF are not felt immediately, but exposure of less than 10% of the body to it can be fatal, even with immediate medical treatment. Highly concentrated solutions may lead to acute hypocalcemia, followed by cardiac arrest and death, and will usually be fatal in as little as 2% body exposure (about the size of the sole of the foot). This substance is extremely toxic and has the capacity to kill upon exposure rather than simply damage skin and eyes. It should be handled with extreme care, beyond that given to hydrochloric, sulfuric, or other mineral acids.
Due to low dissociation constant, HF can penetrate tissues quickly like a small non-polar particle. Hydrofluoric acid which comes into direct contact with the fingers can severely damage or destroy the tissue underneath the nail without causing any damage to the nail itself. It is this ability to cause little harm to outer tissues but considerable harm to inner tissues which can produce dangerous delays in treatment of hydrofluoric acid exposure. Once the pain starts, it is out of proportion to the burns produced. Patients often describe the feeling as if they have struck their fingers with a hammer. HF that penetrates under the skin causes later development of painful ulcers, which heal slowly.
Re: Refining Platinum: no walk in the park
Hazmatt_(The Underdog), Sun Jan 21 2007, 08:49AM
Which is why we work with BiFlourides bp, and not HF directly.
Hazmatt_(The Underdog), Sun Jan 21 2007, 08:49AM
Which is why we work with BiFlourides bp, and not HF directly.
Re: Refining Platinum: no walk in the park
Bored Chemist, Sun Jan 21 2007, 11:45AM
The distinction between HF and bifluorides is a bit academic, particularly in the presence of other strong acids.
Bored Chemist, Sun Jan 21 2007, 11:45AM
The distinction between HF and bifluorides is a bit academic, particularly in the presence of other strong acids.
Re: Refining Platinum: no walk in the park
Hazmatt_(The Underdog), Sun Jan 21 2007, 07:23PM
I have talked about the disassociation with my boss, a chemical engineer and anodizer specifically, and he usually gives a long winded explination that the BiFlouride will not disassociate very much, so the relative HF concentration is very small.
Now if we raised the temprature, and threw in Sulphuric along with the Nitric BiFlouride mixture, then you would certianly increase the HF concentration.
The major point though is that at room temprature the HF concentration is relativily low.
Hazmatt_(The Underdog), Sun Jan 21 2007, 07:23PM
I have talked about the disassociation with my boss, a chemical engineer and anodizer specifically, and he usually gives a long winded explination that the BiFlouride will not disassociate very much, so the relative HF concentration is very small.
Now if we raised the temprature, and threw in Sulphuric along with the Nitric BiFlouride mixture, then you would certianly increase the HF concentration.
The major point though is that at room temprature the HF concentration is relativily low.
Re: Refining Platinum: no walk in the park
Chris, Sun Jan 21 2007, 09:30PM
So what is that? A mixture of nitric acid and ammonium bifluoride or such? If it eats glass like HF does, well, all my labware is made of glass, I don't have any suitable vessels at this time. Not to mention the fact that I would have to buy expensive ammonium bifluoride, as I am not currently set up to synthesize it (a highly dangerous process without fully compatible aparattus, involving hydrogen fluoride). I'm not sure what compounds such an acid mix would yield anyway; I need to end up at some point with an acid or salt that is easily decomposed to metal sponge or powder.
The immediate plan for now is to separate the solution as is from the remaining solids, process the dissolved materials as planned to yield platinum or similar, and go from there with dissolving the remaining metal. If aqua regia really does not act on it at any appreciable rate, I can likely assume it to either contain iridium, rhodium, or... I can't really think of anything else so resistant to acids that would be found as a likely alloying agent with platinum. Tantalum, for example, would be highly unlikely to be present. There are still relatively undissolved pieces of metal foil in the acid, so possibly the foil is not platinum at all, but consists entirely or almost entirely of one of these more resistant metals. Or perhaps I just suck and can't make aqua regia dissolve platinum for some reason. In any case at some point I will need to do some proper assaying to determine what metal(s) are really present. This is an area in which I have almost no knowledge.
Chris, Sun Jan 21 2007, 09:30PM
So what is that? A mixture of nitric acid and ammonium bifluoride or such? If it eats glass like HF does, well, all my labware is made of glass, I don't have any suitable vessels at this time. Not to mention the fact that I would have to buy expensive ammonium bifluoride, as I am not currently set up to synthesize it (a highly dangerous process without fully compatible aparattus, involving hydrogen fluoride). I'm not sure what compounds such an acid mix would yield anyway; I need to end up at some point with an acid or salt that is easily decomposed to metal sponge or powder.
The immediate plan for now is to separate the solution as is from the remaining solids, process the dissolved materials as planned to yield platinum or similar, and go from there with dissolving the remaining metal. If aqua regia really does not act on it at any appreciable rate, I can likely assume it to either contain iridium, rhodium, or... I can't really think of anything else so resistant to acids that would be found as a likely alloying agent with platinum. Tantalum, for example, would be highly unlikely to be present. There are still relatively undissolved pieces of metal foil in the acid, so possibly the foil is not platinum at all, but consists entirely or almost entirely of one of these more resistant metals. Or perhaps I just suck and can't make aqua regia dissolve platinum for some reason. In any case at some point I will need to do some proper assaying to determine what metal(s) are really present. This is an area in which I have almost no knowledge.
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