Palladium recovery from monolithic capacitors

Hi guys

I have been looking on here for a complete step by step method to recover Palladium and if present Silver from monolithic capacitors. I have seen the slide show but like it says there are no details given and read through stacks of post listed on the forum and have used several search headings before posting this question. I have seen several posts on different ways from dropping with zinc or aluminum to ammonium chloride. I haven't seen how you recover the silver after the first boiling in HCL to remove the ceramic.
The reason I ask is that I have several kilos of capacitors and would love to have a go at trying to get Pd sponge. I have done several batches of gold from different sources and would like to try something a little more challenging but like I said I am having trouble finding a guide in which I could follow to try to limit my risk of messing up, as you guys know that it takes a while to scrap that many of boards so any help would be fantastic. P.S I hope I posted in the right section.

I will try to help with the chemistry of this but be aware I have never worked on this material.
I'm not too sure that boiling In HCl will remove the ceramics but I could be wrong.
If the items are made up of layers of silver, palladium and ceramics which acids can access I'd suggest going straight to nitric as it will dissolve both of the metals you are after, if you use HCl first you are going to have to incinerate or you will create silver chloride which will possibly interfere with the recovery.
If you can use nitric straight off then you simply have to make your choice of which way you wish to recover the values.
You can cement with copper which will remove the silver and palladium which then will need putting through a silver cell to recover the individual values.
Or you can add HCl or salt to create silver chloride and filter the Pd bearing solution off and then cement with copper to recover your Pd.
I personally always advise to avoid PGM refining unless you have the right equipment and knowledge due to the toxicity of the salts.
If my thinking is wrong I'm sure someone will tell me fairly quickly 8)

Just a small addition, the tin from the solder could make quite a mess if you go straight to nitric. I think that most people doing MLCC the chemical way start by removing solder in a HCl bath. (at least I did the two times I processed MLCC:s)

Then after either incineration to drive off the HCl or only washing to nitric acid. If you don't incinerate you will form some silver chloride but not that much that it affects the rest of the process.

Sam has a tutorial on his website where he goes HCl and then to Aqua Regia.
http://www.goldnscrap.com/index.php/others/87-recovering-palladium-and-silver-from-monolithic-ceramic-capacitors-part-1
http://www.goldnscrap.com/index.php/component/content/38-searchresult/searchresult/69-recovering-palladium-and-silver-from-ceramic-monolithic-capacitor-part-2
And the youtube slideshows https://www.youtube.com/watch?v=FWftjRnNrNw

I used a slightly different approach with HCl and then nitric acid.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=18564

Göran

Goran

When using your method
1. Soak the MLCC:s in hydrochloric acid to remove tin, lead and other base metals. As I didn't heat it I just left it in acid for several days before switching to new acid. Stopped it when it seemed there were no more reaction. Eventually many of the MLCC:s breaks up into separate metallic foils but it can take a week or longer.
2. Wash and decant the broken down MLCC:s with water to get the chlorides and HCl out, quite some foils in it.
3. Add NaOH to transform any AgCl that formed in the HCl treatment into Ag2O. I don't know if this is necessary or even works.
4. Wash and decant off the NaOH solution
5. Add nitric acid to dissolve the silver, silver oxide and palladium. Some chlorides will remain but they get locked up in silver chloride that forms.
6. Filter off the dissolved values. I decanted and filtered. It was apparent that there were some silver chloride in the reaction vessel as the filter clogged up with silver chloride that turned purple.
7. add NaCl solution to the filtered tea colored solution, it precipitates the silver as white silver chloride. Stop when additional NaCl doesn't make any precipitation.
8. Decant and filter off the palladium solution, I reused the filter from above as it caught all silver chloride. Multiple washes was used to get most of the palladium out from the silver chloride.
9. Treat the silver chloride with NaOH and sugar to get silver powder.
10. Add zinc shavings to the palladium solution to cement out the palladium.
11. Decant off the liquid from the cemented palladium and then wash it with HCl to remove excess zinc and eventual base metals that the zinc precipitated.
... collect, dry and weigh the result. The fluids goes to the proper stockpot and the metal powders are put into respective storage beaker with other powders awaiting final refining when I have enough to do it.

Do you heat your Palladium solution to remove excess nitric before adding the zinc.

I don't think I denoxed the solution before adding zinc, but later I learned that cementing is better done with just a little bit of acid in the solution. It keeps down the amount of zinc needed. A bit of acid is okay though as it keeps the zinc shavings surface fresh for cementing.

Today I would add HCl instad of NaCl as it would keep down the amount of metal salts in solution and make it possible to denox with less volume of solution.

Even if you find a method here on the forum you should research every step in it so you understand what to expect, what can go wrong and what to do to save the process if it does.
Things will go bad when you least expect it. The batch I wrote about went well but the one after that just became a large mess that I still haven't recovered all metal from.

Göran

I think I said it before, I really like Göran's mlcc method. Once I will try this,

I thought of removing the chlorides completely before using HNO3. I believe any chloride will hold some silver insoluble - just an assumption, thinking it is some kind of equilibrium.

I would use something funnel-like as the reaction vessel, so I would not need to shift between funnels and beakers. Maybe a flask without bottom (glass wool as filter) connected to a vacuum flask and pump.

Then I would check for tin chloride in the filtrate. As soon as tin is gone, I would stop leaching with HCl in order not to dissolve any palladium.

Followed by converting silver and removing chlorides by hot NaOH washes. Checking for chlorides all the time.

Once no chloride can be found in the filtrate, I would go on with nitric leaching.

Just assumptions.

And I wonder if the solder could be removed by boiling in NaOH alone without the HCl step.... :|

Dissolve lead and tin only!

I think you are overthinking it, Björn.

To keep valuable lab ware locked up for longer times while leaching isn't practical. With a beaker or Erlenmeyer flask you can just put it aside with a stopper, you can run several batches parallel and it's easy to heat if you want to speed it up.
To pour leached material into a filter isn't hard and you could also decant some liquid before adding new acid, getting rid of some of the dissolved base metals. A filter is easily swapped if filtration takes too long while your fiber glass plug would be impossible to swap without emptying the leach vessel.
When filtering I always start with the clear fluid first, then when getting close to the gunk it starts to take time. Starting from the bottom you will clog the filter in no time.

HCl has an advantage (I think) over lye, it also breaks up the ceramics (barium titanate) over time. If lye does that I don't know.
A small amount of silver chloride held back by remaining chlorides from the first bath never concerned me. It was the possibility of passivating the foils that made me wash them in lye. Again, I don't know if it was necessary so some day I'll run a parallel test with two well mixed batches.

Göran

Thanks for the quick replies this has help a heap.

This is the easiest method I've used for smd resistors and MLCC's. I've only done a couple of small batches this way though.

1. Crush MLCC's to a fine powder.
2. Boil in nitric acid. ( I never have had tin problems)
2. Let solution settle overnight.
4. Siphon clear green liquid.
4. Add DMG - Just add white powder to green liquid and mix well. Don't use sodium hydroxide unless you have lots of acid in solution.
6. Filter yellow Palladium salt.
6. Cement Silver or add chloride from now blue liquid.

The ONLY way to recover all your values from MLC is to use a furnace.

Get rid of the tin with a soak in HCl but not to the point of letting them dissolve. Then use a rotary furnace adding a known quantity of silver as a collector. Credit to Lou for this method. Using wet processes is inefficient for this product.

If you must use a wet process, remember that you can do it two ways- - one by avoiding the formation of silver Chloride and dropping the Silver/Palladium mix and using a cell, the other is the polar opposite i.e. make silver chloride and your solution then just contains the Palladium. There are schools of thought for both options and both are described in many places on the forum.

spaceships said:

the other is the polar opposite i.e. make silver chloride and your solution then just contains the Palladium. There are schools of thought for both options and both are described in many places on the forum.

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I myself don't have access to nitrates, so I was thinking about just using HCl to get the silver as a chloride. Save that up until I have enough to convert. The Pd, would be collected in the stockpot with everything else. I'm assuming that HCl/bleach would be enough to do the trick.

Rusty

Hi Rusty

Please give me more information as to how you would be thinking of doing this with HCl/Bleach?

spaceships said:

Hi Rusty

Please give me more information as to how you would be thinking of doing this with HCl/Bleach?

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I was thinking of bleach as the oxidizer. I'm not really certain. Just looking for a way to get the silver as a chloride. I've read it on the forum but can't remember where I saw it. I know that HCl passivates silver, but not certain if anything else should be added, whether H2O2 would help. Been doing a lot of reading, but when I go back over what I wanted to make notes of I can't find it again. A lot going on around here that kind of muttles my brain.

Rusty

Bleach or H2O2 are too weak and slow to be efficient with fine powders at the bottom, even sooner or later Pd might dissolve this would be no joy. Constant stirring could help.

Thank you for the input Bjorn, just trying to find alternatives to the nitrates I'm not able to find. If I can get the silver to become a chloride, I can handle that and store it until I have enough to convert. Convert it until I can be able to sell it or purify it. My only options right now are AP and HCl/Bleach. Still stockpiling at the moment.

Rusty

For efficient recovery, you need to remove the ceramics by smelting; even just plain borax will do the job and no collector is needed if you're willing to give it sufficient time. Aqueous leaching of MLCCs only works if you use a collector resin-in-pulp to pull the Pd values off the ceramic--it is a very clever trick for fetching the last traces that are absorbed to high surface area materials. With smelting, you'll be left with a high grade PdAg/Sn/Cu/Au mix.
Some MLCCs run very well, some run like crap (like the magnetic ones).

Lou said:

For efficient recovery, you need to remove the ceramics by smelting; even just plain borax will do the job and no collector is needed if you're willing to give it sufficient time.

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Ah, that's very good to know. I'm certainly not set up for proper smelting, but for the specific case of MLCCs, would I just be okay with crucible, torch, borax, and perhaps boric acid?