Friends, not sure if my question is in the right section, but since it's about precipitation, and i'm such a noob: :wink:
I have experienced something new
: i was melting my buttons together and noticed triangular crystal patterns in the bottom side of the button, i suspected PGM's.
Redissolving the buton slowly in AR(10 gr of gold in 50ml HCL and about 6 ml HNO3, in small addittions) the button almost dissolved in a closed erlenmyer flask overnight, leaving the reaction on low heat, +\- 50 C.
This morning, there was a small bit of gold left undissolved, and i found a light colored precipitation around the button.
These were small buttons already refined in AR, so silver can be ruled out, since no AgCl formed during earlier AR baths. No lead fell out upon adding ad drop of sulfuric acid. So no lead present.
Is my assumption correct that these are one or more PGM's that fell out onto the gold because of the reactivity series?
If so, would a PGM stockpot be an idea to separate the PGM's from Auric Chloride in solution before going to the "regular" stockpot? a 'dirty' piece of gold contaminated with PGM's would refine itself eventually, leaving only PGM powders left?
The cemented gold in the regular stockpot would then be almost free of PGM's?
Or am i mistaken and does this not apply to the most noble metals in the reactivity series?
The last bit of undissolved gold will also have a bit of the same PGM's left, but much less compared to what the whole bath would have contained?
Maybe someone has experienced this while using gold to consume the last bit of free nitric from the pregnant solution.
Consuming all the nitric by adding enough gold would prevent redissolving of these powders back into solution if nitric is still present.
I would like to hear your thoughts on this.
Martijn.
The button almost dissolved and the powder laying in the middle after giving it a swirl.
I will filter the powder before all the gold is dissolved and redissolve that in AR to test with stannous, should give a clear answer, if Pt or Pd is present.
Martijn.