goldsilverpro said:
Note: It is much easier to dissolve the DMG in alcohol or an NaOH solution than in water. However, the water solution is best for testing because it's more sensitive than the others.
I'm no chemist but, since you're trying to reduce those metals, it wouldn't be good to add an oxidizing chemical. It seems to me, it would be a tug of war, the copper trying to reduce the gold, etc., out of solution, and the chlorine trying to re-dissolve it.
Right on both accounts GSP - In fact your Pd will stay &/or go back into solution without the oxidizer the HCL alone is enough to keep/put back the Pd into solution
HCL will not dissolve a solid piece of Pd metal but when it is finely divided HCL alone will - I found this out when processing CATs - the Pd (or at least some) would go into solution as soon as I added the HCL to the combs & before I added the CL (oxidizer)
Also I just got done working on recovering the PMs from last years anode slimes (this was my first go at anode slimes)
After I incinerated them I did a nitric leach to get the remaining silver & of course some Pd went with that which I dropped with DMG (prepared with NaOH)
The next leach was AR (hot) to get the Au & PGMs with the plan to use copper to cement out the values to then be refined - what happened was interesting
I put the AR on the hot plate & turned it up to setting 4 - when it got relatively warm I dropped in my copper & the Au & PGMs started to come down out of solution - as expected - so I let it sit on the hot plate to do its thing for about 4 or 5 hours --- at which point I came & did a stannous test which showed there was still some Pd (kind of a lite to mid green on the swab) along with a trace of Pt (just a bit of orange) & the solution was showing good blue with just a hint of green --- so I left it on the hot plate & came back to check on it about 1&1/2 hours later - my solution had gone back to a blue/green & my stannous test showed heavy Pd green - almost black
I had my Au & at least most of the Pt in the bottom of the beaker & crusted on the copper --- but the Pd (& likely some Pt) had gone "back" into solution
That's when it dawned on me (from my CAT leaching experience) you can't really cement Pd from a solution that has HCL in the mix - The HCL puts the "
finely divided" Pd back into solution --- & because HCL also does not dissolve copper
So (at least the best I can figure based on this out come) is that with AR - when you first start to try to cement PGMs using copper they will come down out of solution as long as the ion exchange with the nitric is taking place (copper going into solution - PGMs coming out) but once the nitric is saturated with copper the HCL goes back to work on the Pd putting the Pd back into solution
So what I did was filtered the Au & Pt from the AR that was once again loaded with Pd (as well as Cu & likely some Pt) was cement it with zinc --- because this of course was heavy in copper I then treated it with "
hot" nitric - & because I am low on DMG instead of dropping the PD out of a nitrate solution with DMG I cemented it with copper which needs to be done hot other wise the Pd will passivate the copper & slow the ion exchange way down
So at this point of working on my anode slimes I have my silver removed (& most other base metals) - have parted the Au out (nice little 11 gr bar) & have my PGMs recovered (about 57 gr PGM black) that of course is contaminated with Cu & trace ? base metals
Kurt