Palladium, did I do this right? or what did I do?

[jewelerdave]

This is only for the experts so please only respond if you know and are not guessing.

I have previously separated my palladium bearing scrap to send into a larger refiner for processing. However I decided to try it myself.
Out of five ounces of bench sweeps processed with AR I was able to recover just over 2ounce of fine gold...about normal for the mix of scraps I do.
this one had a bit more palladium White gold contained.


After the AR treatment the solution was brown rather than the normal emerald green I usually get when doing scrap gold. I am going to assume this is the palladium doing this?

After pulling the gold I re concentrated the brown solution from about a gallon to about 1000 ML and I got a red froth on top and some in the bottom of the beaker, and my solution had turned green. What happened here as I did not add any ammonia Chloride yet.
I added a little ammonium chloride to be safe and the result was the same.

I filtered off the red froth and sludge on the bottom, I have the solution boiling down some more to make sure I got it all but when I melted the red stuff I recovered about 1/4 ounce of shiny gray metal that looks identical to some of my pure palladium stock.

It reduced down a lot, the red salt was very light, and it condensed down quite a ways when I melted it. Does this palladium salt have a large volume? Id didnt need any flux, or did I burn something away?

My question is.
Is this my palladium? or is it nickel from white gold?

Is this a way to recover palladium?

Is this going to be at least 99% pure so that it can be reused in jewelry?

I have posted a picture below.

 

[Lou]

I'm still not exactly quite sure of what you did, only am I sure that you did it incorrectly and that I have covered this in detail before on this forum. Once again:

Palladium is remarkably simple to process if you know what you're doing.

When you dissolve palladium up in aqua regia you will form H2PdCl6 which is a brown (actually it's quite yellowish on dilution) color. Your first thing to do is to drop the gold after everything has been sufficiently deNOxed (removal of nitric). After that you will have a solution containing either nickel or palladium, or a mixture of both depending on the source of the scrap. The nickel will be green, and the palladium brown. For 5 ounces of metal, evaporate down to about 500 mL of syrup. It will be heavy. Then heat this to blood temperature or perhaps a warm bath. Then either add a couple crystals of sodium chlorate or bubble in chlorine gas (bleach would probably also substitute in lieu of the others). Add in a saturated solution of hot ammonium chloride and you'll see an immediate precipitation. Place this in an ice bath and you will see a brick red, flocculent precipitate which is somewhat voluminous. This is your ammonium hexachloropalladate; filter this and rinse with cold saturated ammonium chloride solution and vacuum filter it (you'll be all day otherwise) onto a frit. This can be reduced many ways, but given your limited access to the more normal routes and probable lack of equipmen, you can reduce with heat. The salt will break down into ammonium chloride, and eventually HCl gas (look for white fumes). You do not want to use a torch!!!! Doing so will cause loss of values upon heating, they will go up as a gray smoke. Instead, put them in a shallow porcelain dish and heat from below and let it smoke. After no more gas or 'smoke' comes off, you'll be left with Pd sponge. Dissolve this up again and repeat the procedure and your Pd will assay 99,95% pure.

You do not ever need to have a gallon of volume for 5 ounces of scrap, no matter what type of scrap. Work in small volumes or you will throw money away.

As for your button, that is Pd. It's quality is dubious at best just based off your procedure and something about it doesn't look right. Anyway, you probably got some of it, but I'll bet not all of it. Remember, nickel oxidizes readily, Pd doesn't oxidize at its melting point because its oxide is unstable, much like that for gold and silver, both of which do not oxidize if they are pure.

If you're a visual learner and you want to learn a wee bit of chemistry and see this done by a chemist in an obviously professional lab (also instructions for platinum), please see this link:

http://www.sciencemadness.org/talk/viewthread.php?tid=9721&page=1#pid113781

Lou

 

[jewelerdave]

Thank you, I know what I did wrong as well as right. It just surprised me to the flocculent precipitate which is somewhat voluminous came about while the solution was reducing.
The reason I had about a gallon to reduce down was mostly from rinsing the gold. The batch started out as 1000 ML of AR on bench sweeps.
I get some more volume from rinsing the sweeps with water.
I get more volume from the addition of the Urea in water
and more volume from the addition of SBM in water added to drop the gold.
Then I get more from the rinse of my precipitate with HCL and water.

I put it all into the same jar, then boiled it down to re concentrate.

This is when the flocculent precipitate showed up during the reduction stage when it was back down to 1000ml

It was filtered then rinsed with HCL and water.

So recap I should have at this point gently heated it to drive off ammonium chloride and HCL to make a sponge, then redissolved in AR
to repeat?
what is keeping the Pd Sponge from being pure? or is it for industry standard?
My reason for asking is the alloy is then going to be used as jewelry alloy where only the gold content matters and not the palladium, the palladium is only used as a whitening/graying agent in the alloy. 18% to 22% palladium 58.5% gold the rest hardening alloy of copper/silver.

 

[Lou]

Your Pd will have significant nickel contamination hence my recommendation for a second refining. Bear in mind that Pd and Ni serve as the whitening and the hardening agent. Mix the two together in an alloy (say your Pd is 5% contaminated with Ni) and it may make a brittle alloy which would be unsuitable for the gorgeous work you put out. Quite a bit of this is technique driven Dave so I can tell you and show you how to do it however I don't know your skill level.

Gentle heating of your brick red ammonium hexachloropalladate will make a gray powder. Dissolve that up again and go through the whole process. If your torch is somewhat high pressure, it's easy to blow the lighter Pd away (not nearly as heavy as platinum). Sometimes it helps to put wet powder in the crucible and make a small hole in the center (helps steam escape). The wet powder will quickly dry and then sinter under a torch flame and it will not blow away. Of course, if you have an induction furnace that's high frequency and meant for melting sponge, you could just use that

Also, I always avoid the use of urea when dealing with the PGMs as sometimes urea can ''lock'' them up and prevent a truly complete separation. For you dealing with only Pd, it matters little, but for me dealing with Rh, it matters much.


"I put it all into the same jar, then boiled it down to re concentrate."

^^By the way, don't boil stuff down in a jar--you're in for heartbreak when one of those soda lime jars shatters and dumps a very expensive solution all over the place. It even happens to me very occasionally using expensive, professional Pyrex or Schott Duran. Don't let it happen to you.

Also, if you can refine palladium, you can refine most platinum alloys. Ask me how and I will take the time to tell you. Or just refer to that link I provided you with, it's all there.

Lou

 

[lazersteve]

Dave,

Your Pd prematurely precipitated most likely due to nitric in the solution. Palladium in nitrate solutions will precipitate with SO2 (and also with ammonium chloride). This is why DeNoxing is so important. Precipitants require specific conditions to work properly just as acids do.

You should DeNox your solutions better before dropping any PMs. I agree with Lou, urea is not necessary or desirable.

Steve

 

[jewelerdave]

Ok, that does make sence, bear with me as I am a jeweler and not a chemist but I would like to reclaim my PGMs

I typically use Urea to denox, what do you recommend to denox?

I did roll the PD Lump alloy and it did crack, so it is not pure. I would like to make this pure.

 

[lazersteve]

Dave,

To denox simply boil the solution down until it is almost a syrup, but don't dry it out completely. Next add enough HCl to make it a free flowing liquid again. Repeat the process two more times. On the third go around use water instead of HCl, and evaporate until the solution has a nice dark color. With each HCl addition you should see signs of fizzing and some fuming.

After denoxing recover the remaining PGMs in solution by slowly adding soda ash with stirring until more soda ash reacts slowly with the liquid. Add a little, stir, let it react, then add more. Do this in a partially full beaker as the reaction foams and fizzes a lot. As the pH goes up the soda ash reacts less quickly and tends to remain solid longer. Some light colored pasty precipitates usually form when the pH is right.

Now slowly stir in small additions of fine mesh (-200) zinc to the solution. More fizzing and foaming will occur. Let each zinc addition react before adding more. Add enough zinc to change the solution color to a cloudy black or gray color. This black cloud should settle as a fine black/gray powder leaving a nearly clear colored solution. If the solution color hasn't changed dark and the zinc doesn't react add a little HCl to lower the pH and get the reaction kicking again. Go easy on the HCl as any excess only consumes zinc and is wasting both zinc and acid. If the pasty precipitates remain when the color darkens to gray/black add a little water to dissolve them.

Filter out the powder after it settles as letting it sit overnight will allow some of the black powder to redissolve into the solution. Rinse the powder with dilute HCl. If the HCl rinse fizzes and reacts with the powder repeat this wash unitl no more fizzing occurs. Follow all these up with a clean water rinse or two.

This black powder can now be dissolved with hot AR or nitric (along with your impure button) to get everything back into solution. This time around be very mindful of denoxing the solution throughly and everything should proceed in a text book style.

Test your solution and colored powders to be sure you know what you have precipitated. DMG can identify both Pd and Ni in solutions. Here a snapshot of positive tests for each:

Pd + HCl + DMG ( Pd compound is the yellow precipitate):

[img:1079:943]http://www.goldrecovery.us/images/Pd_DMG2.jpg[/img]


and

Ni + NH4OH + DMG ( Ni compound is the pink precipitate)

[img:967:1505]http://www.goldrecovery.us/images/Ni_DMG.jpg[/img]

Steve