Sciencemadness Discussion Board

Green iron cyanide complex

Gammatron - 19-11-2023 at 20:34

Hello everyone, haven't posted in a while but I got a weird one, or at least to me.

As usual I am working on another uranium extraction. The ore was leached with H2SO4 + H2O2. I neutralized the solution with NaOH to precipitate the uranium and most other metals. Further increase of pH precipitates a thick blue/green sludge which I assume is Fe(OH)2 as it turns brown upon addition of H2O2. I would've thought everything would be completely oxidized from the leach but maybe the U4+ reduced all the iron? Anyways, dissolving the brown precipitate in HCl and addition of potassium ferricyanide (I don't have ferrocyanide) creates this intense green solution, I had to use a flashlight for it to show up in the pic. Adding a reducer turns it blue which I assume is Prussian blue. H2O2 + KI will turn it green again but neither one will do it on its own and reducing again returns the blue color. A quick google search didn't give any results for green iron cyanide compounds so I wonder if anyone here might know??

Here is a pic of the green solution and the blue after reducing it.

Stokes - 20-11-2023 at 07:23

It sounds like ferric ferricyanide, also known as Prussian green or Berlin green. Berlin green is insoluble in water, but forms dispersions easily, so if it is Berlin green, it should eventually settle to the bottom of the container.

Gammatron - 20-11-2023 at 10:08

I actually wondered if that was a real thing and if it's what I made. There doesn't seem to be much info on it other than paint pigments, It did settle to the bottom.

Stokes - 20-11-2023 at 11:11

I just did a quick search for "Berlin green" on google scholar, and it looks like most of the information is about using it for battery materials and electrochemical sensors. I've also encountered it myself when I was trying to make ferri/ferrocyanides by the old protein pyrolysis processes.

[Edited on 20-11-2023 by Stokes]

Gammatron - 20-11-2023 at 11:19

Oh yeah I saw those studies too but I didn't look into any of them. Thanks for the info. This confirms that I was able to precipitate the uranium and vanadium without getting much iron contamination which only complicates things