# PGMs precipitation



## toja (Sep 25, 2011)

Hi everyone,
For a few weeks I enjoy refining of gold from different electronic waste. 

My question concerns precipitation of PGMs from acidic solutions (HNO3 not present)
Do palladium and platinum precipitate with sodium metabisulphite? I have an impression, that this process occurs, but in noticeable longer time than for gold precipitation. In my opinion Pd precipitates slowly as a very fine black powder (which might escape through filters?). Am I right? What could be the efficiency?

Another possibility to precipitate gold together with PGMs is to use metallic copper. I would use copper powder, as it has great surface per mass unit. This should be followed with careful rinse with distilled water (a few times to remove Cl-), and then with HNO3. The last process would allow to dissolve remaining Cu together with Pd. In precipitate Au and Pt would be present, the mixture quite easily separable. What is your opinion on such process? Copper price is low in comparison to noble metals. I wonder, if Cu process has better efficiency than SMB one, especially for PGMs?

I would appreaciate every comment on these questions.

Cheers!


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## eeTHr (Sep 25, 2011)

toja---

You can find the specific processes for precipitating PGMs by using the search function near the top of the page.

What I would recommend, as an immediate solution to the problem, would be to drop your gold, then test the remaining solution with stannous chloride testing solution (this procedure and resulting color indications, as well as how to make this testing solution, can also be found using the search function). This will tell you if all the gold has precipitated yet, and also if there are PGMs remaining in the solution.

If PGMs are in the solution after precipitating all of your gold, just save the solution until you have the knowledge and chemicals to separately drop them.

If your solution has lots of color, making the stannous test uncertain, just cement the PGMs out with solid copper. Powdered copper will contaminate the precipitated PGMs. Avoid copper tubing because it's difficult to scrape cememted values which may stick to the inside of it. Copper busbar is recommended, but heavy copper wire will work, like size AWG # 0-0 bare ground wire. You can bend it into a flat spiral to get more surface area into the solution (leave spaces between the wires for the cemented metals to fall down through), then bend a hook on the other end to hang it on the lip of the jar or beaker. The spiral should be suspended horizontally above the bottom, so the values will mostly fall off, onto the bottom of the container rather than bunching around the copper and possibly lessening the surface area. This also lets you see if the copper is accumulating values, and if it is, you can knock it against the jar to remove it, usually.

Note: It can take about a week for all the PGMs do cement out. Check it each day, and when it looks like no more has come down, test the solution with stannous chloride to be sure. These precipitations can be very fine black powders, especially toward the end.

Then save the combined metalic PGM powder until you can separate it with refining, as already mentioned above.

There are several threads on the forum for both of the topics you would be searching for, and they are discussed pretty thoroughly. Then if you have specific questions about the processes, just post them, and someone will help you.

You may already know some of this stuff, but I would rather detail it out than leave someone guessing. And it might help others who are entirely new to it, that are reading.


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## Lino1406 (Sep 25, 2011)

SMB would not precip. Pd and Pt


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## butcher (Sep 25, 2011)

Normally if platinum group are involved SO2 gas, sodium sulfite, or SMB are not recomended, ferrous sulfate would be my choice for gold, but then again how much PGM are in solution which ones, is there base metals in solution all of these varibles can change the approach to the process somewhat, I have not acuumulated enough of these metals to give specific advice on them, as I am still learning these.

I feel eeTHr gave some good advice.


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## toja (Sep 26, 2011)

eeTHr, Lino1406, butcher - thanks very much for your answers!

I use the "search" button, but I haven't found answers to my questions.



butcher said:


> Normally if platinum group are involved SO2 gas, sodium sulfite, or SMB are not recomended, ferrous sulfate would be my choice for gold, but then again how much PGM are in solution which ones, is there base metals in solution all of these varibles can change the approach to the process somewhat, I have not acuumulated enough of these metals to give specific advice on them, as I am still learning these.


Does anyone know, why SMB is not recommended, when PGM (in my case Pd, and possibly Pt) are in the solution? Do some complexes form, which make difficult to precipitate metals out with Cu wire? It's really interesting.

I think, I can try use SMB for precipitating gold, an then copper wire for precipitating PGM (rather dilute in my solutions), and collect them for further refining.
My solutions have lots of colour (SnCl2 test is uncertain), so I would rather put copper wire and check if something's left.
Thanks again!


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## Harold_V (Sep 26, 2011)

To my knowledge, you won't have any problems recovering trace elements using copper, regardless of your use of SMB, or not. Frankly, that's the wise way to recover small quantities of the platinum metals, due in part to their resistance to being precipitated from dilute solutions. I did pretty much the same thing, although in my case I did the recovery in the stock pot, using scrap steel. I intentionally recovered traces of copper, which were used, along with other metals that got included, to act as a collector when the material was processed by furnace. Assuming you don't plan to run the recovered material that way, the use of copper is highly recommended. 

One comment I would make---try to not use wire. As it degrades it will become more and more difficult to remove from the solution, whereas a piece (buss bar, for example) would be much easier, and easier to clean as well. Not suggesting that wire won't work---and if you're assured it will be fully consumed it's not a bad idea. 

Harold


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## freechemist (Oct 10, 2011)

Hello toja,

SMB, sodium-sulfite and gaseous sulfur-dioxide will not precipitate Pd and/or Pt from acidic solution. Pt, usually present as Pt(IV) in HCl-solutions, obtained by oxidative dissolution together with nitric acid, will rapidly be reduced to Pt(II), which will no more be precipitated with ammonium (or potassium) chloride. Palladium will form soluble mixed complexes containing halide and, as a neutral ligand, probably SO2. Contrarily, if no halide (or different strongly complexing ligand) and no oxidant, like HNO3 is present, Pd(II) in strongly acidic solution (e.g. sulfuric acid), on heating will be reduced to metallic Pd.
From mixed HCl-solutions with gold, thus only gold usually is precipitated with SMB and/or related reagents. In order to precipitate Pt as ammonium-hexachloroplatinate(IV) after precipitation of gold, it may be necessary to reoxidize eventually formed Pt(II) to Pt(IV).
The best way to precipitate gold from solutions containing significant quantities of Pt and/or Pd, is to use oxalic acid, which will precipitate gold selectively and quantitatively.

freechemist


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