Uranium acting really weird. Maybe something is complexing with it?

I recently received a radioactive rock from a friend. I wanted to determine if it was U or Th, so I scratched off a few of the black specks, then dissolved them in around 0.5ml of aqua regia. The solution went yellow as expected, and was observed to be fluorescent, again, as expected. It was dissolving slowly, so it was heated to it's boiling point with a hot air gun and stirred by repeatedly sucking it into and out of a pipette. By the end of this the solution was a brilliant lemon-peel-yellow color. After it had cooled I added ammonia. After all the acid was neutralized, some pumpkin-orange material precipitated. I continued adding ammonia, but then it all re-dissolved and the solution became colorless. My first thought is that maybe ammonium diuranate is soluble alkaline solutions, as the pH was 11, so I added a bit of HCl to bring the pH back down to neutral. While the solution became yellow again, no precipitate was observed. My next thought was maybe there was now too much water. It was then boiled to dryness. A light yellow mass, obviously mostly ammonium chloride with a little bit of uranyl chloride and nitrate was observed.

So umm, what happened? My only guess is that maybe the uranium containing rock had something else in it that complexed with the uranium to keep it in solution, but I have absolutely no proof for that, or any idea as to what it could even be that did that.

I'm pretty perplexed as to what could have happened. I've worked with uranium before, and it's never behaved like this. The fact that the solution went colorless is also kind of odd. Uranium tends to produce very vivid colors in solution.



Attached is a photo of the solution right after I put the rock in, but before the solution was boiled.



A picture of the rock the uranium came from. The black spots are much more visible to the eye than they are through the camera. It registers about 120cpm on my awful geiger counter, around 12-15 times background. It should be noted that my geiger counter can only pick up gamma and high energy beta, so most of the radiation isn't getting detected. Still, it is without a doubt radioactive.

Edit - I should note that the boiled down mass will likely just go in my uranium waste bin, as it's not worth saving and purifying 50mg or so of uranium compounds. I'm just curious as to what happened.

[Edited on 18-3-2021 by itsallgoodjames]

[Edited on 18-3-2021 by itsallgoodjames]

Quote: Originally posted by unionised

Could there be carbonate in your ammonia solution?

Quote: Originally posted by njl

Any carbonate would've been destroyed by the aqua regia though, right?