Electrochemistry Ag Pd Pt Anode ?

[samuel-a]

At the moment i'm not electrochemically experimenting with this type of alloy but might get the chance to do so on small/medium scale.


The alloy propositions are as follow: Ag 89.1% , 9.1% Pd 1.8% Pt (with possible deviation of +- 0.2%)

With your experience, would it be feasible introducing it to silver nitrate electrolyte?

 

[rusty]

At the moment i'm not electrochemically experimenting with this type of alloy but might get the chance to do so on small/medium scale.


The alloy propositions are as follow: Ag 89.1% , 9.1% Pd 1.8% Pt (with possible deviation of +- 0.2%)

With your experience, would it be feasible introducing it to silver nitrate electrolyte?

Bring add more silver to your anode, ideally bring it up too 95 percent or slightly higher.

 

[Harold_V]

It will part, but you're likely to have problems with slimes adhering tightly to the anode, requiring hand scraping to expose silver. You also risk cross deposition of palladium, and depletion of silver nitrate, so keep a close watch on the slimes.

If you find you struggle parting the material, you might consider toughing it out until you have completed the parting, then part the crystals a second time, with a change of filter cloth and electrolyte . No need to melt them, simply place them in the basket with a candlestick contact and allow them to part once again. An anode place on top does no harm, and keeps the candlestick out of the electrolyte. That way you'll eliminate the traces of palladium that are deposited. I used that very method when I processed the waste materials from my years of refining, which were heavily laden with platinum and palladium.

Harold

 

[samuel-a]

Thanks Rusty and Harold for the pointers.

I guess i could, at some point raise the Ag levels in anode for the initial parting to help prevent the "passivation" .

 

[Lino1406]

Bear in mind that dealing with
AgNO3 is dangerous

 

[lazersteve]

Hoke mentions using sulfuric acid to dissolve silver. This should leave your Pd and Pt behind as black sponge.

Steve

 

[samuel-a]

I will try that Steve and report back.

Thanks.

 

[Alchymist]

Sam,
The sulfuric acid needs to be concentrated and very hot (near BP), because of low soluability of Ag2SO4 at room temp. and it will probably allso dissolve some Pd.
-Peter

 

[Sucho]

Yes, it is highly possible that Pd will go into solution.Pd dissolves easily in dil.sulfuric and potassium persulfate.also in electrolysis, from Pd conc. Of 1 g/dm3 in electrolyte Pd codeposition is measurable in range of 0.00X % and raises exponentially

 

[Geo]

ive tried hot sulfuric on silver plated copper pins, and even though i got a reaction and some stripping did occur, when i pulled the pins out there was still a light layer of silver on them. is just the silver plating back to the copper before i could get them out of the acid or was it just an incomplete process? im worried about dissolving copper and fouling my acid.

 

[goldsilverpro]

ive tried hot sulfuric on silver plated copper pins, and even though i got a reaction and some stripping did occur, when i pulled the pins out there was still a light layer of silver on them. is just the silver plating back to the copper before i could get them out of the acid or was it just an incomplete process? im worried about dissolving copper and fouling my acid.

The old standard method of stripping silver plate from copper is to use a 95% conc. sulfuric/5% nitric solution at 180F (82C). The percentages are by volume. The nitric provides the needed oxidizing power. This formula is found in most plating books. However, platers are only interested in recovering their copper parts without damage so they can be re-plated. Therefore, there is no mention in these books on how to get the silver out of the solution. I've used this same stripper many times at room temp. It's much slower (and much safer!) when it's not heated but it works pretty well if the silver isn't too thick. Any addition of heat will speed it up proportionally. Keep water out of the solution or it will start attacking the copper.

After stripping a bunch of material it will slow down. When it does, the very careful (full face shield and gloves) addition of a little more nitric will perk it up. I try to get as much silver dissolved in it as possible before recovering the silver. To get the silver, the solution must first be diluted and then the silver is dropped out as a chloride with HCl or salt. I would first dilute it down to 20%, or less, with water. Anything stronger will probably chew up the filter paper. When diluting, to avoid splattering and the great possibility of getting burned, always add the acid to the water and not the other way around! After diluting, you might try cementing the silver instead (Cu, Fe, etc.). I haven't tried that. I always went the AgCl route.

 

[Geo]

great. thanks for the info GSP.

 

[Alchymist]

Sucho, good info about Pd codeposition.

GSP, yes, the 95/5 H2SO4/HNO3 mix is perfect for recovery of silver from plated copper and even brass parts. Many years ago I tried it on a huge load of high voltage fuses. There were several types, but all of them had long porcelain tubes filled with sand, and a silver wire or foil as the fuse element. The terminals were made of heavily silver plated copper or brass, screwed into the porcelain with silver plated brass screws. A friend and I made a deal with a local scrapyard, that we could buy several metric tons of them, take them apart, and keep the silver, and then return the copper plus brass for the same price. We took them apart, and recovered around 2 Kg of pure silver wire/foil. The terminals was dipped in the 95/5 mix (we did it at around 80 °C) for maybe half a minute. After a flush, the copper and brass parts were nice and shiny. We also went the AgCl route, and got around 3 Kg of silver from the spend solution.
One word of caution: This mix is VERY nasty to skin and clothing (especially at 80 °C), and it makes a violentl reaction with water. I noticed at that time, that after many hours of work, I payed less attention to the dangers, and started to treat the solution like if it was water. This is a typical human behavior, but very dangerous. If you are a pro, you have learned to take precautions, but if you are doing it as a hobby, it becomes dangerous after some time, when you start to relax. We didn't have any mishaps, but we had to remind ourself about the dangers over and over.

-Peter

 

[lazersteve]

Sam,

As with all reactions involving metals reaction speed is proportional to the surface area. If you could roll the material into a thin foil or granulate to fine particles, you will have an easier go at it.

Steve

 

[samuel-a]

Thanks Alchymist , Sucho and Steve.

I'm fine with some of the Pd and/or Pt being dissolved, as long as we are talking traces. As far as i know DMG will ppt any Pd(II) species in acidic conditions, so i'll test the solution once Ag is out.

Since silver and sulfuric does not form water to accommodate aq Ag2SO4, i reckon i should try multiple samples at different acid concentrations ranging from 70% and up to 98% to see with my own eyes which works best. I can already "see" the tricky part where Ag2SO4 will start crystallizing back as soon as heat is removed...

I have a rolling mill, so rolling the samples flat is done easily.

 

[Lou]

Just be sure not to use a DMG solution in ethanol when you're removing palladium from a silver nitrate in nitric acid solution.



I have a parting cell for high palladium silver anodes. We'll run an anode that is 8-10% palladium, 2-5% Au with traces of platinum, cobalt, nickel. At 70 g/L Ag+ concentration the silver crystal will be 999 fine (better in fact) for about 20 ounces deposited per liter of electrolyte used. Any more than that and the silver crystal will have palladium co-deposition in the form of darker gray crystals that are not mirror shiny. This occurs at about 2 g/L with less than 0.5 M HNO3 in the system. The bulk of the palladium (about 90% of it) ends up with the gold in the anode bag.

The palladium can be quantitatively removed by the addition of a saturated solution of dimethylglyoxime in hot dimethylsulfoxide. Alternatively, there are several nuclear grade resins that will leave the silver but go after palladium, nickel, and copper. Unfortunately, palladium has such an affinity for the functional group on the resin, it is not easily eluted off the resin.

 

[samuel-a]

Thanks for sharing Lou.

p.s. - I'm using DMG dissolved in NaOH.
When both Ni and Pd are in solution, the test drop turns pinkish red at first, but soon re-dissolved and yellow ppt form.