Unlocking palladium from AgCl - or better separating technique ?

[orvi]

I recently acquired around 80g of silver-palladium alloy contacts with approximate 20% Pd content. I intend to refine them by dissolving in nitric acid and then dropping the silver with salt water. Palladium would be then reduced with formate.
But, when dropping AgCl from palladium containing solutions - it always lock some Pd int othe AgCl. It is then "dirty", brownish coloured, and it cannot be easily washed out with water or dilute HCl out from the precipitate.
What could help to wash it out ? Should I just let it stirr for few days with dilute (like 3-5%) HCl, or is it because I added it too quickly without vigorous stirring (palladium chloride hypothetically formed, which is of low solubility in water) ?

 

[4metals]

For a small quantity like you have can you drop the Palladium from the Silver Nitrate solution with Dimethylglyoxime? Then drop the Silver last.

 

[orvi]

For a small quantity like you have can you drop the Palladium from the Silver Nitrate solution with Dimethylglyoxime? Then drop the Silver last.

I have some quantity of DMG available, but I do not have proper setup to incinerate the complex. And it always end up in Pd loss after incineration :/ at least for me. I do not know what is the "usual" loss, when incinerating DMG complex in the air as it should be done, but for me it was always in range of %´s. Not actually lost, I recovered it from the refractory wool, with which the crucible was covered... But anyways, another trouble.

But if the precipitation of AgCl would behave like it always did, I wouldn´t have much more choices. I wondered about re-processing the AgCl... But my tired brain does not came to any solution, other than re-making metallic Ag and then redissolving and redropping it, leaving leftover Pd in solution. Redissolving AgCl in ammonia does not get me much further, as palladium also redissolve to amino-complex. And DMG does not work well in basic enviroment.

 

[snoman701]

But if the precipitation of AgCl would behave like it always did, I wouldn´t have much more choices. I wondered about re-processing the AgCl... But my tired brain does not came to any solution, other than re-making metallic Ag and then redissolving and redropping it, leaving leftover Pd in solution.

It would, but you will effectively reduce the concentration of Pd in the remaining supernatant by a substantial amount. Once to that point (a second crystalization of AgCl, conversion back to Ag) the remaining Pd is likely within the realm of what a silver cell will effectively separate.

 

[Yggdrasil]

I recently acquired around 80g of silver-palladium alloy contacts with approximate 20% Pd content. I intend to refine them by dissolving in nitric acid and then dropping the silver with salt water. Palladium would be then reduced with formate.
But, when dropping AgCl from palladium containing solutions - it always lock some Pd int othe AgCl. It is then "dirty", brownish coloured, and it cannot be easily washed out with water or dilute HCl out from the precipitate.
What could help to wash it out ? Should I just let it stirr for few days with dilute (like 3-5%) HCl, or is it because I added it too quickly without vigorous stirring (palladium chloride hypothetically formed, which is of low solubility in water) ?

Have you tried Nitric?
Wouldn’t that redissolve the Pd?
Or do you think the Pd is locked in?

A friend had a similar problem with Gold. When he dropped the AgCl it became dirty brown.

He put it in AR and it became white as snow again. He have no analytic equipment so it is based on plain observation and estimation.

 

[orvi]

It would, but you will effectively reduce the concentration of Pd in the remaining supernatant by a substantial amount. Once to that point (a second crystalization of AgCl, conversion back to Ag) the remaining Pd is likely within the realm of what a silver cell will effectively separate.

Yeah. It isn´t big ammount of material, so if something goes bad, it wouldn´t be an issue to just reduce all dirty AgCl back to metallic silver and start all over. But I wanted to know if there is some hack or anything for washing it.

OwlTech has one video, where he was parting silver and palladium by hydrolytic precipitation. Also nice route - to PdAg nitrate, he was adding potassium hydroxide until the solution loose colour - Pd precipitated as hydrated oxide alongside with some silver. Then he filtered the mainly Pd hydroxides, and washed the cake with concentrated HCL - this liberate Pd to the chloride solution and remains of Ag convert to AgCl. Solution could be then diluted to squeeze out some extra AgCl, and filtered -> reduced.

 

[Aurumlife]

I recently acquired around 80g of silver-palladium alloy contacts with approximate 20% Pd content. I intend to refine them by dissolving in nitric acid and then dropping the silver with salt water. Palladium would be then reduced with formate.
But, when dropping AgCl from palladium containing solutions - it always lock some Pd int othe AgCl. It is then "dirty", brownish coloured, and it cannot be easily washed out with water or dilute HCl out from the precipitate.
What could help to wash it out ? Should I just let it stirr for few days with dilute (like 3-5%) HCl, or is it because I added it too quickly without vigorous stirring (palladium chloride hypothetically formed, which is of low solubility in water) ?

Separating Palladium and silver was always somewhat troublesome at recovery stage. Really depends on the fact if one is running a silver cell. I for example decided for myself certain route where DMG is not used at separating silver and palladium at first. I found it unnecessary and expensive. I don't think there is a reagent (except for a sulfur gas, maybe) that would drop Palladium quantitatively from Palladium nitrate, especially with silver being present in big amounts. So I drop silver first. Palladium nitrate when is getting converted to Palladium chloride complex will form transition salt in some quantities (red color). I always finish washing AgCl in weak AR. It’s usually enough to leave a really white looking AgCl. And then Palladium chloride (which might be volumes after all AgCl washes) I patiently just evaporate. From my small experience- its better to work with Palladium when its more concentrated. When it becomes syrupy- add a little HCL and some distilled water. Let it cool and settle. Filter from tiny amounts of leftover AgCl. Then proceed with whatever way you find most suitable to get Palladium: purify further thru > ammonia > impurities hydroxides filtering > HCL Palladozamin precipitation or just reduce Palladium with Sodium Formate from Palladium Chloride. I only use DMG now for: testing solutions for Pd presence, adding DMG to a solutions left after dropping Palladozamine. Everyone decides for themselves. This is the way I have chosen so far. To me it involves the least of steps, volumes of liquids and expensive chemicals.

 

[orvi]

Separating Palladium and silver was always somewhat troublesome at recovery stage. Really depends on the fact if one is running a silver cell. I for example decided for myself certain route where DMG is not used at separating silver and palladium at first. I found it unnecessary and expensive. I don't think there is a reagent (except for a sulfur gas, maybe) that would drop Palladium quantitatively from Palladium nitrate, especially with silver being present in big amounts. So I drop silver first. Palladium nitrate when is getting converted to Palladium chloride complex will form transition salt in some quantities (red color). I always finish washing AgCl in weak AR. It’s usually enough to leave a really white looking AgCl. And then Palladium chloride (which might be volumes after all AgCl washes) I patiently just evaporate. From my small experience- its better to work with Palladium when its more concentrated. When it becomes syrupy- add a little HCL and some distilled water. Let it cool and settle. Filter from tiny amounts of leftover AgCl. Then proceed with whatever way you find most suitable to get Palladium: purify further thru > ammonia > impurities hydroxides filtering > HCL Palladozamin precipitation or just reduce Palladium with Sodium Formate from Palladium Chloride. I only use DMG now for: testing solutions for Pd presence, adding DMG to a solutions left after dropping Palladozamine. Everyone decides for themselves. This is the way I have chosen so far. To me it involves the least of steps, volumes of liquids and expensive chemicals.

I was not that into separating palladium from silver, but vice versa, silver from palladium. I was OK with few% Ag in Pd anyway. I needed sharp separation which concentrated Pd stream and leave somewhat clean Ag stream. As palladium is significantly more valuable and I do not have interest in further refining of both metals (90+ for Pd and 99,5+% for Ag is fine) due to slim finencial benefit and too much hassle involved (of course I know how to do it with both Pd and Ag, but it does not make sense money-wise).

Evaporation was a no-go for me as it just takes too long and wrecks the hood very quickly. DMG is not the best thing for Pd removal, that is for sure, but it nicely works for removing low grade Pd from bulk of solutions whith very high % recovery without need to cement it out (another lengthy and often incomplete procedure).

NH3 and HCL is the standard for smaller operations. That is true with material, which is at least few % in palladium. I often dealt with few g/kg Pd at best, either in pins or in old silver tantalum capacitors. I had both AR solutions or nitric solutions with less than 0,5g/L Pd, which needed to be separaated from bulk of the other PMs (gold in AR, silver in nitric) in order to get money for it. For this purpose DMG was perfect reagent. It was dozen of grams at time (not too much), it did the job perfectly (after killing the oxidizing acid species in AR/free nitric in nitrate silver solutions) without nothing more than stirring and filtering.
For bigger operations, it would need more robust process without DMG i suppose. I did some reactions and reductions with different reagents, and practically solved simultaneous drop of AuPd from AR. But for nitric solutions of low Pd content, I still didn´t found nothing better (overall) than DMG.

 

[Aurumlife]

I was not that into separating palladium from silver, but vice versa, silver from palladium. I was OK with few% Ag in Pd anyway. I needed sharp separation which concentrated Pd stream and leave somewhat clean Ag stream. As palladium is significantly more valuable and I do not have interest in further refining of both metals (90+ for Pd and 99,5+% for Ag is fine) due to slim finencial benefit and too much hassle involved (of course I know how to do it with both Pd and Ag, but it does not make sense money-wise).

Evaporation was a no-go for me as it just takes too long and wrecks the hood very quickly. DMG is not the best thing for Pd removal, that is for sure, but it nicely works for removing low grade Pd from bulk of solutions whith very high % recovery without need to cement it out (another lengthy and often incomplete procedure).

NH3 and HCL is the standard for smaller operations. That is true with material, which is at least few % in palladium. I often dealt with few g/kg Pd at best, either in pins or in old silver tantalum capacitors. I had both AR solutions or nitric solutions with less than 0,5g/L Pd, which needed to be separaated from bulk of the other PMs (gold in AR, silver in nitric) in order to get money for it. For this purpose DMG was perfect reagent. It was dozen of grams at time (not too much), it did the job perfectly (after killing the oxidizing acid species in AR/free nitric in nitrate silver solutions) without nothing more than stirring and filtering.
For bigger operations, it would need more robust process without DMG i suppose. I did some reactions and reductions with different reagents, and practically solved simultaneous drop of AuPd from AR. But for nitric solutions of low Pd content, I still didn´t found nothing better (overall) than DMG.

How about dropping Pd from volumous solution of Pd chloride (after separating Silver as AgCl) as hydroxides. Palladium salts should go for hydrolysis pretty easy, and be converted to hydroxides, especially from clrorides of Pd. Redissolve in HCl or weak AR and this way concentrate the values? And just do Pd reduction from chloride solution with Sodium Formate?!