Delicious
Digg
Reddit
Facebook
Google
Yahoo
TechnoratiPGM refining question
Hey folks! I'm fairly new to the forum, but I do so hope someone can help me out. I've been recycling some old catalytic converters and reclaiming the platinum group metals. Well, I haven't done it myself yet... I've collected them up and sold them to companies who recycle them. However, I'll make more money if I do the chemistry of it myself.
I looked over the website pretty well and several other places online. I've talked to some folks, but no one experienced with the reactions involved. Well, here's a quote of what it says on the website:
"Preliminary treatment of the ore or base metal byproduct with aqua regia (a mixture of hydrochloric acid, HCl, and nitric acid, HNO3) gives a solution containing complexes of gold and palladium as well as H2PtCl6. The gold is removed from this solution as a precipitate by treatment with iron chloride (FeCl2). The platinum is precipitated out as impure (NH4)2PtCl6 on treatment with NH4Cl, leaving H2PdCl4 in solution. The (NH4)2PtCl6 is burned to leave an impure platinum sponge. This can be purified by redissolving in aqua regia, removal of rhodium and iridium impurities by treatment of the solution with sdoium bromate, and precipitation of pure (NH4)2PtCl6 by treatment with ammonium hydroxide, NH4OH. This yields platinum metal by burning."
It's obvious to me that in the step where the Pt and Rh are seperated that the actual compound is SODIUM bromate, not SDOIUM. Of course that's a typo. But it doesn't say what happens when you add this to the solution. Will I get a Rh bearing precipitate that I'll need to collect? Will it 'lock' the Rh in solution so I'll have to add steps later to remove it? Anyone know?
The page on Rhodium itself isn't much help either. It says, "preliminary treatment of the ore is required to remove silver, gold, platinum and palladium." Then it says you do some other stuff to remove the Rhodium itself from the solution.
Anyone who can give me some advice is welcome to. I'd hate to lose that Rhodium in my solution because it comes out at $1275 per ounce -- that's even higher than platinum. And as it is, if I don't seperate them all out, I'll get jipped by my refiner. They'll pay for the platinum and call the rhodium an impurity, or they'll pay for the rhodium and call the platinum an impurity.
did you notice that is how the "ore" is treated. A finished product is a far cry from an ore! The honeycomb structure is corederite if I recall....an alumino-silicate of some sort. Knowing this,
I would be worried about 2 things.
#1 will the nasty acid dissolve any of the corederite (Si, Al, Mg, and probably some other impurities)
#2 concentrated nitric acid can be hard to come by, and over in the US, I'm pretty sure its a monitored chemical as its necessary for most explosives production.
if you can get nitric, and the corederite doesn't react, I would bet your product is pretty darn pure Pt. There might be some Pd purposely put in the alloy, you'll have to look that up. I was always under the assumption its a pure Pt coating on the surface. Let me know if its an alloy, as I'm curious myself
by the way, oxygen sensors also have a Pt coating, which serve as electrodes on both the reference and sensing side. The actual electrolyte is ZrO2 (white), which won't dissolve in the acids. You might pick up a few miligrams of Pt there as well
Hey thanks a lot for the reply! I appreciate it!
Well, as I understand there is Platinum, Palladium and Rhodium in a catalytic converter, in varying amounts. I don't know if they are actually alloyed persay, or if they are different layers of plating, or what. Somehow people figured out that the three metals seem to work more effectively together than any of them would on their own. I think of it kind of like the nitric and hydrochloric working together to disolve gold, even though neither will do it on it's own.
Everyone who made cars made their own converters so the various makes are each slightly different. Apparently import cars are the hot ticket. Plus, the contents vary depending on economic factors too -- if the Pt price is way up and Pd is way down, they're likely to have more Pd and less Pt. Of course that probably only matters to a degree, so as not to throw off the 'synergistic' effects of the trio. For instance, on the assembly lines in the next month, they will probably be mostly palladium, which is about 1/4 the price of Pt and 1/6 that of Rh right now.
I'm not sure what all is in the actual rest of the converter. I was thinking of it as more of a 'base metal product' than an 'ore', but that's picking nits I say. Anyway, I know that it's some sort of ceramic, but no more. I thought of just trying to use a strong acid to eat the ceramic out from under the plating, making sure to use an acid that wouldn't dissolve the plating along with it. But then I'm still left with a mixture of metals instead of each being separated so that I net the most profit. Plus if I can find out how much of each metal is in each typical kind of converter, I'll know which ones to look for in particular.
And the nitric is tough to find. No stores I've been to have had any, though I found several places for concentrated HCl with ease. Several places have sent me catalogs at my request, but I haven't tried to place an order for any chemicals yet (don't want to spend money until I know exactly what I have to do). I don't think they would turn me away, especially this one place that deals in the metal plating industry, but with terrorism and stuff now, who knows?
I also found a product that is supposed to take the place of the nitric in the aqua regia. It was designed to make GOLD refining safer, and it works supposedly, at least for refining gold (and they offer replacement products for precipitants as well). I don't know if it will work for the platinum and stuff or not. I sent the advertiser a message, but no reply yet. Maybe they're trying it to find out if it works? :wink: On a side note, the the nitric-acid-substitute will precipitate the gold out, BUT if you add too much, and there's no gold left in the solution to precipitate, THEN it starts working on the baser metals like copper. There's a color change in the precipitate as well. Al and Mg dissolve in either acid, and make lots of soluble compounds, so they may just remain in solution. I know I can test the solution with stannous chloride test solution to determine if it has gold, platinum, palladium, or rhodium (and probably others) based on the different colors it turns, so at the very least, I can tell when nothing I want is left in the acid.
The problem with the platinum metals is that small amounts of one can often greatly affect the chemistry of others; you might consult C.M. Hoke's Refining Precious Metal Wastes. I think it was published ca 1982.
Also useful is Gajda's Gold Refining which has an extensive section on precipitating species from aqua regia; the solute is typically deep green if there is extensive Fe or Cu in the solution; otherwise, Au gives a deep yellow color not unlike urine; a deep red suggests Pd or Rh in the mix. A friend of mine used to do this with old mainframe computers; usually the metal is redissolved in aqua regia one more time to further refine it, but that was because in electronics there was Pb or Sn (from solder) which contaminated the Au.