Purifying Palladium Salt extracted with DMG

[niteliteone]

Lou or FrugalRefiner,
I am fascinated by and interested in learning more about the actual actions and\or reactions of the processes we use here on the forum.
Would you by chance know the name and author of a good beginners Chemistry book or web site where a person can learn enough basic chemistry so these processes will be understandable ???

A lot of the terms used here on the forum are confusing to me since I do not have a chemistry back-ground.

 

[FrugalRefiner]

nitelite,

I don't have any specific recommendations and I don't have anything on my hard drive. I googled beginner chemistry and it looked like you might find something there. Hopefully, some of the other members will have some suggestions.

Dave

 

[kadriver]

Here is a website that is free - the chemistry course is geared towards a beginner with zero knowledge of chemistry. I need to get busy and start this myself:

http://www.ck12.org/student/

kadriver

 

[niteliteone]

Thanks FrugalRefiner and Kadriver. Now I have something to read while taking a break from C.W. Ammen's "Recovery and Refining of Precious Metals 2nd edition" I bought last week.

I appreciate this much
Tom C.

 

[freechemist]

Lou writes:

Pd is one of those metals that it is inadvisable to calcine, especially in quartz. It forms palladium silicides which embrittle the metal.

Where I worked, we analyzed Pd-concentrations of various PM-solutions in HCl quite often by gravimetric determination of their Pd-content, especially in order to validate/calibrate the usually ongoing ICP-measurements. This was done by first precipitating Pd with H₂DMG as [Pd(HDMG)₂], and then calcining the washed and dried precipitate to pure Pd-metal in an unglazed porcelain crucible. We never observed false Pd-results, caused by uptake of silicium from the crucibles.

In a following post (August 25th, 2013) Lou writes:

I am not a big believer in the ammonia treatment of Pd-DMG.
If you must recover via DMG, oxidize away the organic ligand with aqua regia. Then you can proceed as normal. Just trying to dissolve in ammonia is wasteful of reagent, plus, where does the DMG go from the complex. What makes you so certain that you'll get the diammine and not your DMG back?

Like Lou, I don't believe in the ammonia treatment of [Pd(HDMG)₂]. Sure, some of the bright yellow precipitate may dissolve in a big excess of aqueous 10% ammonia, and boiling away the ammonia, together with water, from the solution-phase, lets re-precipitate dissolved [Pd(HDMG)₂].

Dimethylglyoxime, which I prefer to abbreviate as H₂DMG, contains two acidic protons, and thus can form a mono-anion, HDMG^- and a dianion, DMG^2-. It is an only weakly acidic organic compound, and therefor practically insoluble in water, but it can be dissolved in aqueous alkaline solutions, e.g. aqueous NaOH, and, may be, to some extent in concentrated aqueous ammonia.

H₂DMG <==> HDMG^- + H⁺ and HDMG^- <==> DMG^2- + H⁺ or
H₂DMG + OH^- <==> HDMG^- + H₂O and HDMG^- + OH^- <==> DMG^2- + H₂O

The actual active reagent, precipitating Pd, is the mono-anion, HDMG^-, forming the very stable, uncharged complex "inner salt" [Pd(HDMG)₂], insoluble in water, like an organic molecule.

In recovering Pd via [Pd(HDMG)₂], I always preferred calcination to the metal, followed by dissolution in HCl/H₂O₂; HCl/NaClO₃; HBr/H₂O₂, avoiding the use of AR, where ever possible, because of some very nasty boil-over-experiences on dissolving finely divided Pd-metal in HCl/HNO₃.

After my experience, it is neither necessary, nor useful, to oxidize away the organic ligand with aqua regia, and chances are, that a mess results. E.g. Pd stays dissolved, but you don't know, in what form, in which oxidation-state (II, IV?). In addition some quite nasty, small organic molecules may be formed on breaking down H₂DMG in aqua regia.