palladium reduction

Geo · Jun 27, 2016

I am in the middle of reducing the volume of palladium chloride I have stored. I have been reducing the solution by evaporation until it changes from red to almost black. I have about 500mL of this black palladium chloride. I am just now getting some NO2 formed in the evaporation. My problem is, I am getting some blood red crystals formed in the solution. Have I evaporated the solution too far? It is a nice clean solution with little contamination. These red crystals are slow to dissolve in water and the solution is bright red once dissolved.

I do understand the dangers of concentrated palladium chloride because I have been studying on it for over a year and decided to try and precipitate what I have stored and calcine it. I will be using a chlorine generator to bubble chlorine gas through the solution. When do I know it is evaporated low enough? If I am getting solid crystals of Pd salt, it should be ready or no?

nickvc · Jun 28, 2016

Geoff never done this but I'd say if your getting crystals you have gone too far, the material needs to be in solution to precipitate it, I know you know the dangers but be ultra careful with that solution and any gases or salts from it.
We're it me I would simply cement it out that way you have no salts to worry about especially if it is just a Pd solution with no other values, then rinse and melt the Pd blacks, much simpler and safer I'm my opinion.
If your doing this out of scientific interest then ignore my opinion and be safe.
Further opinion ask Lou :idea:

4metals · Jun 28, 2016

Dilute it until the solution has no more crystals and filter out any PdO which may be in there, that has to be roasted and re-dissolved.

De nox all solutions.

Then add an equal volume of saturated ammonium chloride to your starting liquor followed by sodium chlorate to drop your Palladium as Palladium(II) ammonium chloride. The salt is hygroscopic and the dry (dessicated) salt weight multiplied by .37431 will tell you how much Palladium is present.

I often will dry and weigh the salt to settle an individual processing lot and accumulate enough salts before reduction to metal.

nickvc · Jun 28, 2016

Or 4metals

Geo · Jun 28, 2016

Thank you Nick and 4metals.
I have the chemicals needed. I evaporated the solution in a fume hood and handle everything with thick rubber gloves. I wash my gloved hands in a basin before taking them off. I wear eye protection and an apron. I am trying to be as careful as I can be.
So dilute until the crystals dissolve and filter. Add an equal volume of saturated solution of ammonium chloride and then add sodium chlorate to drop the palladium(II) ammonium chloride.
This is the first time I am trying this process. There is a lot of Pd in the material I deal with. I want to get the best price I can get for it.

Thanks again for the information.

nickvc · Jun 28, 2016

Geoff I doubt whichever route you take the payout will be any different percentage wise, I'd stick to cementation and a simplish melt, if you need an assay on the bar my mates in the UK will do it for about $20 or less and they are quick.

4metals · Jun 28, 2016

There is always a chance you may have Platinum in there as well, one way to get it is to leave the solution sit after the ammonium chloride addition and it will drop out of solution. If it is not much it may take overnight. Then filter and collect the Platinum as Ammonium chloroplatinate.

No sense giving away your Platinum for Palladium prices!

Geo · Jun 28, 2016

So as soon as I added the ammonium chloride solution, this yellow precipitate fell out of solution. I am assuming it is platinum. I would have argued that platinum is not used in electronics, I guess I would have been wrong. Thanks again for the information.

4metals · Jun 28, 2016

Considering the difference in price between Platinum and Palladium, I would consider that color Happy Yellow!

The yellow powder, dried and weighed, is 43.95% Pt by weight.
Pt factor as ammonium chloroplatinate .4395 (Platinum ammonium chloride)

So considering the difference in percentage of metal per ounce of salt and the price difference, happy yellow is a good description.

Geo · Jun 29, 2016

Okay, complete failure. After filtering the yellow salt out of solution, I placed the 1000 mL beaker with roughly 600 mL of solution in my catch pan and started adding sodium chlorate. There was a nice brick red solid precipitating out. I waited a few minutes and added some more. About a half teaspoon each time. I waited for another five minutes and added some more. I noticed a blocky looking salt forming on the bottom of the beaker. After some time, I added the last of what I was going to add and closed everything up and went inside. I am still shaking thinking about it. I was getting ready for bed and I heard a pop. Loud pop from outside. I was afraid it had something to do with the beaker and the strange salt. I got dressed and went out slowly, not know if a cloud of chlorine gas was waiting. Nope, no cloud. I walked out to the fume hood and there was the Pd solution everywhere. Dripping from everything in the fume hood. The beaker had exploded. The catch pan had a little in it but the majority was everywhere else. And I had been standing right in front of it not less than fifteen minutes before. No heat, no flame. I just closed everything back up and decided that I had had enough excitement for today and I will clean it up tomorrow. Win some, lose some. At least it was my own material.

nickvc · Jun 29, 2016

Geoff do you think it was an exothermic reaction?
Whatever the cause we need to find out as that could have been so much worse and I'd hate anyone following the thread to have the same thing happen but be standing in front of the beaker!

Barren Realms 007 · Jun 29, 2016

It is recomended to the reduction in a cold solution.

4metals · Jun 29, 2016

OK let's get back to basics and see what happened.

How did you generate this concentrate, you said you evaporated solution down to make a concentrate. What solution and how was it generated? Was it nitric to start with or aqua regia?

I did make some assumptions that apparently I shouldn't have. But let's start at the beginning.

Geo · Jun 29, 2016

It started out as AR solution solutions from gold refining. As I would drop the gold, I would collect the spent solutions that tested positive for palladium. I cemented the blacks from these solutions after I have accumulated enough using copper while heated. When I had enough blacks, I would dissolve the powder in AR and drop the gold and store the red solution. At the beginning of this thread, I said that the evaporation was at the point where NO2 was being generated and that red crystals were forming. Would the presence of nitric acid in the solution have caused the explosion?

Geo · Jun 29, 2016

I checked the beaker before I went inside and it was cool to the touch. I was concerned because the reaction was getting strong. There was brick red precipitate both in the bottom of the beaker and floating on top of the solution. I noticed what looked like large yellow and transparent crystals forming at the bottom of the beaker below the red precipitate. My last thought about it was how to separate the two different kinds of crystals.

4metals · Jun 29, 2016

So the cemented values were digested in aqua regia, filtered and concentrated.

I am a little confused about volumes. You started with 500 ml. You added water to dissolve any crystals but no mention of de-noxing, no sulfamic additions I assume. You should always de nox all solutions before dropping the metals, if you were blowing red fumes, you still had active nitric acid. Sometimes dilution is sufficient but it's a crapshoot; de-noxing is always best.

So after diluting the crystal you had what, 600 to 700 ml? Then you should have added an equal volume of saturated ammonium chloride. That would have put you at 1200 to 1400 ml. In the picture you posted of the Platinum drop after the ammonium chloride additions the volume is at 600 ml.

When you add the sodium chlorate to the room temperature solution the palladium drops like a reddish color fine sand, that is what you experienced as well. What I believe the problem was you had free nitric in solution and the solution did not benefit from the 50% dilution with saturated ammonium chloride (did you add it as a powder?) You had a concentrated solution containing free nitric acid and you added a powerful oxidizer, and likely over added. A whole lot of chemistry going on in a small concentrated space!

With chemistry experience is your best teacher, when you see the reaction you are looking for (dropping red sand) and then start seeing a different reaction (the blocky looking salt) you should immediately stop adding the reagent as you have passed the point where the additions are doing what you wanted them to do.

I have never seen sodium chlorate react as you describe but I always work with de-noxed solutions that has been diluted 50% with the solution of ammonium chloride.

Geo · Jun 29, 2016

By the time I had added the ammonium chloride solution, the original solution was at 300 mL. I doubled the volume with the ammonium chloride which brought the volume to 600 mL. That is the solution in the pictures. I did not dilute the solution any farther. It did have nitric acid in solution because it was being evolved when I turned off the heat and let it cool at 300 mL. I didn't denoxx as I didn't know that I needed to. It's a hard lesson to learn. When I first started refining gold, I lost quite a bit to inexperience. I imagine this would be no different..

UncleBenBen · Jun 29, 2016

Well I hate that you lost your palladium, Geo. But I sure am glad you weren't in front that beaker when it detonated!

4metals · Jun 29, 2016

When de noxing solutions by the classical 3 times evaporation process, you evaporate the solution down to a syrup with small sulfuric additions and re-hydrate with HCl and again reduce to a syrup. When you get down to a thick syrup you see the nitric coming off as a red fume, by the third time all of the nitric should be gone.

Very time consuming which is why I prefer sulfamic acid.

I learned something from this as well, I should always list all of the steps and never assume anything.

Geo · Jun 29, 2016

I had thought about using sulfamic acid but didn't because I know that ionized metals can be very reactive. Now I know that it can be used in this process.
Okay, back to the business at hand. Toxic cleanup. Face shield, apron, rubber gloves (elbow length). I will use paper towels to wipe as much of the red salt from the inside of the fume hood. Gather all the items in the hood and wipe them down. These towels will be collected in a bag for incineration. Any glass will be emptied into the stock pot and washed in dilute HCl followed by a water rinse and then soap wash. The inside of the fume hood will be wiped down with dilute HCl and soap wash. The hot plate will be soap washed and the wash water neutralized.
I think I can gather up a large amount of what was in the beaker. I need to pour up what's in the catch pan to see how much of the 600 mL of solution is left. It was precipitating red salt quickly so the solution may not have anything left in it.

palladium reduction

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