I don't reclaim automobile catalytic converters, but I will refine reclaimed concentrates from them, so I suppose that is what you'd want to see and try your hand working with the platinum group.
Your best and cheapest bet might be to purchase 10 g bars of platinum and palladium and dissolve them. I can send you some Rh since you won't find that material in small quantities for anything close to sane.
Try dissolving said bars in aqua regia, cold and hot. Weigh the bars after a period of time. You can get how many mg of material will dissolve per hour per square centimeter at a given temperature and concentration of reagents. You'll notice an increase in rate of dissolution as the surface area/volume ratio increases. You'll notice a decrease in rate of dissolution as the solution becomes more concentrated with values. Plenty of things that you must find out yourself because it won't be in the literature
I'll level with you: most PGM refining (especially for Rh, Os, Ir, Ru) is done at the bench in fume hoods. That's how I've always done it. It's not done on grand scale like it is for gold and silver. It simply isn't done that way regardless of the company. Platinum heats are small heats. If one refined only gold and silver but was never serious about platinum metals, he'd be in for a surprise when he tours refineries doing only PGMs. They're much lower volume and much more involved in processing. The chemist's tools in dealing with platinum and her sister metals are flasks ranging from 1L to 22L and batches in the several hundred ounce range (or less). Why do you think refining charges are so high on platinum, let alone rhodium? Much more labour involved, takes longer to dissolve, precipitations aren't 100% efficient, reductants aren't selective, and so on! There is no place for 5 gallon buckets like in gold or silver, let alone electrolytic cells (point conceded that rhodium can be electrorefined quite nicely in some situations). Gold (and silver) are refined by technicians, for one having technical knowledge may be competent. Refining various members of the platinum group, well that requires skills not needed for gold and silver. I realize that sounds terribly elitist, but how many people honestly prepare their own osmates and ruthenates? Calcine their own rhenium? Make purpereosalt out of rhodium? The explosive double nitrite of diammine platinum (II)?
As far as that method I gave you goes: yes, it will scale. But it's all lab scale!!! I wrote that method (and included approximate times) to give you an idea how quickly it might be done in a general circumstance by one who knows his business. It's not how I would do it. Keep in mind though, what you're doing is very very small volumes at tens of grams. You will be very, very hard pressed to find anyone who will seriously tell you how they do it on large scale with all the specifics and hold your hand through the process. Why? Because that is developed by the company and their chemists and stays in the company. You're also not a chemist, so learning this will be irksome. Generalities are published in the literature and IPMI proceedings. It's fairly secretive. Even Raleigh Gilchrist himself (who you had better be reading) makes a great note of it in his splendid review on the platinum group metals and their processing:
"The chemical engineering problems in connection with the refining of platinum
are of a specialized nature, with the result that experience in other fields is not
always directly applicable. Moreover, the tradition of secrecy in the platinum
industry up to the present has prevented refineries from pooling their experience
except in a very general way. This state of affairs is in marked contrast with
what is known about the plant and processes for the refining of silver and gold.
Because of this tradition of secrecy concerning, particularly, the wet processes
used for refining crude platinum and platinum concentrates, very few details
find their way into the literature. The processes used for commercial refining,
once the platinum metals have been concentrated to a point where wet processes
apply, probably differ very little. The scale of operation is small; even the refining
of platinum is frequently described as large-scale laboratory work, and the
refining of the other metals of the group is on a still smaller scale."
Gilchrist, Raleigh. Chem. Rev., 1943, 32 (3), p 295.
Very little has changed save for induction melting, instrumentation, S/X and perhaps some finer points in the aqueous chemistry. One thing that has certainly remained the same: people who refine platinum group metals do not like newcomers. They will not like you refining them. They don't like those who talk about refining them (incidentally, Gilchrist was well respected for his chemistry, not for his mouth). There are not many names in the game so to speak and most roads lead to Rome. Ponder that when you go to sell your first 10 ounces of fine metal!
Good luck to you.
EDIT: by decant, I mean to pour off or siphon away without disturbing the precipitate. It requires a steady hand. As you will come to learn, should you persist in your PGM work, chemistry is as much a trade as carpentry, and requires intimate knowledge of which tool to use to accomplish a given task. In some ways, it reminds me of football for it requires strategy, and the risk of physical harm is quite real.
