Dropping pt

[67eod]

Hi,
I am stuck again. I have 3 gals of hcl/cl that show a high content of pt with stannus cloride, bright orange that does not fade afer 24 hours. I have tried dropping it with zinc powder, the result is a rapid foaming that stops after a minute or so and then a few black particles in the flask. The s/c test still shows pt in the solution. Question 1. How much zinc powder per gal of solution?
Question 2. What color will the pt be when it drops out?
Question 3. What else can be used to drop pt from hcl/cl solution?
This pt came off from some very old boards that also had a good amount of gold on them. I got the gold out with B/D.
:?:
Bob

 

[Lou]

Evaporate it down to a concentrated syrup. It will be a deep blood red. Then you can add zinc, or preferably, ammonium chloride to precipitate out the canary yellow ammonium hexachloroplatinate salt.

 

[4metals]

If 3 gallons is too much to concentrate as Lou suggests, cement all of the PGM's with copper, be sure to agitate (an air bubbler works well) and leave the copper in at least 8 hours. You should no longer get a positive stannous for Pt. Decant the waste liquid and filter the solids. Roast and digest in A/R and process for Pt as Lou suggested.

 

[lazersteve]

Another alternative to both Lou and 4Metals excellent suggestions is to raise the pH of the solution using soda ash (raise to around pH 4) and try your zinc again.

Add zinc in small amounts until the solution turns a dark gray-black color that clears as the black mixed PGM powder settles to the bottom. Pour off the clear solution (sometimes slightly green) as soon as the mossy powder settles as the black powder will sometimes redissolve if left in the solution too long.

Since you are using zinc powder (I'm assuming it's 200 mesh or less) it most likely contains Cab-O-Sil (silicon dioxide - sand ) added to allow shipment of the fine mesh powder. The Cab-O-Sil will report in your PGMs and you must redissolve the black powder and filter to remove it after the PGMs are zinced out.

Since I learned of the Cab-O-Sil, I started using zinc turnings. You can find them for cheap on my website. They contain no Cab-O-Sil and will work better than the fine mesh zinc.

Steve

 

[samuel-a]

67eod

i'm using Aluminum from heat sinks to drop mixed PGM's out of solution, and it's working great, like the zinc.
the black powder that precipitate looks axactly like on steve's video when he used zinc.

the solution can take up alot of Al, so don't over do it, just until the solution is clear to lite pale green.

 

[4metals]

Copper, zinc, aluminum, we're working our way up the Electrochemical potential chart here and you should consider each of these metals displaces the metals beneath it on the chart. Beneath copper are the precious metals and mercury, beneath zinc are iron, lead, tin, nickel, and chromium (trivalent), below aluminum are all of the above plus chromium (divalent), and titanium.

Our goal is to end up with our precious metal concentrated with as little other metals as possible. sure zinc works well, as does aluminum. Heck you can see it working. But they're working on more metals than you're bargaining for and you'll have to clean up the concentrates before proceeding. Just keep that in mind.

Interesting about the Cab O Sil, something to do with dusty shipments? Probably another after effect of the anthrax scare of 2001.

 

[lazersteve]

Copper, zinc, aluminum, we're working our way up the Electrochemical potential chart here and you should consider each of these metals displaces the metals beneath it on the chart. Beneath copper are the precious metals and mercury, beneath zinc are iron, lead, tin, nickel, and chromium (trivalent), below aluminum are all of the above plus chromium (divalent), and titanium.

Our goal is to end up with our precious metal concentrated with as little other metals as possible. sure zinc works well, as does aluminum. Heck you can see it working. But they're working on more metals than you're bargaining for and you'll have to clean up the concentrates before proceeding. Just keep that in mind.

Interesting about the Cab O Sil, something to do with dusty shipments? Probably another after effect of the anthrax scare of 2001.

Excellent point about the activity series, zinc is best used when you have a relatively clean solution of a large volume which contains salts that would precipitate out if the solution were concentrated. It's a quick way to push your values out (along with some contamination) as long as you are willing to do the clean up work on the resulting powder. Luckily most of the base metals below zinc are easy to dissolve off of the PGMs using HCl or H2SO4.

I've used copper and aluminum both on occasion and I don't like the slimes that come with the aluminum process and with copper the PGMs tend to adhere to my copper very strongly.

I believe the Cab-O-Sil is included to reduce the spontaneous ignition hazard associated with fine mesh powders.

I use zinc to clean up relatively dilute solutions of PGMs with little to no contamination. I also use zinc to precipitate mixed PGMs from HCl-Cl leaching solution of catalytic converters because dehydration of the solution leads to large amounts of sodium chloride crystals.

Steve