How insoluble is rhodium in nitric acid ?

Help Support Gold Refining Forum:

Geo

Well-known member
Joined
Mar 1, 2011
Messages
6,965
Location
Decatur,Ala.
I observed this behavior only with alloys or mix of PGMs. When we once treated PtPdRh solution with zinc to obtain workable cement - this cement when treated with 65% nitric will dissolve not only Pd but also awful lot of Pt. After 3-4 days at 100+°C it become to dissolve Rh too.
PdPt alloy with few % of Pt is also easily dissolved in nitric. This I know from processing old MLCCs. Final button of metals is easily digestible in hot nitric. Most commonly, silver is used as collector metal, so the dissolution is a lot quicker and yields are better. With silver, it goes to the solution pretty much by itself.
Did you roast the cemented powder before leaching in nitric acid?
 

orvi

Well-known member
Joined
Apr 13, 2021
Messages
663
Location
EU
Did you roast the cemented powder before leaching in nitric acid?
I never roasted the powders, so I cannot say. Only thing that comes to my mind is that you will sinter some of the sponge and (big MAYBE) create a less reactive material. Just seems logical to me, but it is just a guess.
 

Geo

Well-known member
Joined
Mar 1, 2011
Messages
6,965
Location
Decatur,Ala.
Roasting cemented metal to red heat does two important things that I can think of. It tempers the metal and removes residual acids. It does make most metals more resistant to oxidation. It may help with Pt dissolving in just nitric acid.
 
Top