No ascorbic acid.
In my book basic means the 3 primary mineral acids (preferrably in their "dry" forms), a base of your choice, and SMB for chemicals. Add to this list a few fundamental lab tools (pH paper, beakers, funnels, and filters) and you too can produce "high" purity Pd with minimal effort and cost.
At $250+ a kilo DMG is a dead end for the refining of Pd, not to mention the unwieldy nature of the massive precipitate it forms. It's great for testing, but stinks (in more ways than one) from a recovery/refining perspective. After spending thousands of USD on DMG using it all in my Pd recovery processes (just as Kevin demonstrated above) I hit the books and found a much simpler and direct method that is both elegant and economical. Lastly, despite the accepted idea among the masses that DMG is solely selective for Pd, I can tell you first hand experience (and back it up with numerous photos) that it is not unless the reaction conditions are properly controlled. Drag down and entrapment are two major downsides to using DMG for Pd on any scale above a few grams.
Formic works when all the conditions are controlled properly, but isn't required as it forms in situ in many instances as an intermediary. It's one of those fun to try methods (been there done that), but from the standpoint of ease of use and the most direct route from soup to nuts...formic is out in my lab.
I'm still not entirely sure why PGM recovery and refining techniques have "evoled" to their currently accepted methods, but I can assure you all the whoopla surrounding them is more of a method of obstruction than good sound ends to the means of producing relatively pure PGMs. That's not to say the currently accepted techniques don't work, but they are not required to obtain PGMs of an acceptable sellable purity. Additionally, the proclaimed hazards of PGMs and their toxicity are real and perhaps this is one contributing factor as to why the more direct methods have been brushed under the proverbial rug by history. If something is made out to be complicated and difficult, few will attempt it, let alone unlock the secrets it holds.
Sorry for the long winded reply. This is a subject that I have literally devoted years of my life researching and discovering for myself here in my humble lab so it is dear to me.
Steve
I work with Pd a lot now. My first and biggest variable of concern is time. I refine Au and Ag materials (various common and totally uncommon feeds, different processes etc...) and also quite a bit of PGMs (mainly Pd and Pt, less Rh, in the future maybe Ir - which I only collect as enriched fractions for now).
Yet very unplesantly looking, I still use AR for kilos of pins/transistors/plated stuff and mixed Au e-scrap, lye/sugar for silver (but moving forward to iron cementation slowly) and mainly formic/DMG for Pd - sometimes DMG. Ladden with lots of pyrometallurgy for complicated matrixes and oxidative/evaporation cleaning of PGM alloys from Cd,Sn,Pb and Bi at very high temperatures.
It may sound completely nuts, but with dirty, mixed, complicated and non-homogenous materials I didn´t found better approaches suited for me (yet).
And I had quite a venture with PGMs (few posts from me regarding separation of low Rh from PtPd etc...). I tried unhealthy ammount of various precipitants, SX, hydrolyses, reducing and oxidizing agents... From old NH4Cl to very interesting precipitants like mercaptobenzothiazole, SX with standard and also very uncommon solvent mixtures, various alterations of classic NH4Cl platinum drop, fractional crystallization of Na2PtCl6 contamined with Rh (relatively nicely working technique, but a bit tiring - altough done in very low volume/quantity ratio) etc... Combined hundreds of hours of doing "private" research with real samples and "made out" samples from pure PMs to prove the concept. Surely, big guys are doing better, more smoothly and nicer. But I didn´t have the ability or luck to find better working conditions for established feeds I currently have.
And despite all this, I still use DMG as precipitant of choice for bulletproof and very sharp separation of Pd from other PGMs/BM starting "soups".
250+USD/kg DMG is from local vendors - which get it from China for less than 80USD/kg - and I am getting DMG directly from China for that 80USD/kg. With like 8-10 component liquid soup of PtPdRh and you name what base metals, I get 99,8% Pd in less than one day to the ingot. Smoking loss of Pd can be minimized below 0,5%, and you catch all on the mineral wool plug (later toss to the MLCCs melt to recover the Pd, so overall no loss). Filtration of big batches is relatively horrific looking, but nothing that bad if you have setup for filtration of big volumes conveniently.
So that´s it. Not very nice and "refined" technique, but put on the sheet of paper - cheapest I currently have in hand in terms of material costs, labor time and efficiency/result delivery (combined). DMG to remove Pd out (after slight pH adjustment to positive numbers), two boiling hot, slightly acidic washes, one controlled pyrolysis/incineration and you have very nice Pd sponge in hand. If I do not need to go with DMG, I am more than happy to proceed without it.
I assume you clean the Pd by hydrolytic precipitation of base metals (raising pH), leaving pure Pd solution, which is then reduced to Pd. Just my thought, how I would do it with chemicals you mentioned. I also tried this - but as I am always dealing with AgPd alloys, silver removal is essential before Pd cleaning. Hydrolytic separation of silver and Pd work - but I never achieved desired goals with it (not sharp in my hands). So anyway, silver need to be removed beforehand and Pd is then dropped. Maybe there is some trick to better pack the gooey BM hydroxide cake formed, but for me it was always tedious using easily accessible coagulants/flocculents and filtration (high retention in cake). So while I needed to boil the pot anyway, formate is the easiest method to perform next. And also that is the method type I like, you set it for boiling and let it be for several hours, doing other jobs and Pd just settle to the bottom when you arrive back to it. No further care
But I very like your approach to things, elaborating new practices is essential thing to move further. And also reviving old techniques for convenience
like peroxide for gold dissolution
As a professional chemist, I cannot agree more.
