Hey everyone,

I recently picked up some Potassium Nitrate from a source I don't fully trust, and it’s heavily loaded with that classic blue "fertilizer" dye. I’m trying to purify it via recrystallization, but I’m running into some issues and could use some advice.

The Process So Far:

Dissolution: I used 800ml of distilled water to dissolve 240g of the product at 100°C.

Filtration: I ran the hot solution through standard filter paper while boiling to catch any insolubles.

Cooling: It’s currently crashing out at room temp, and I plan to move it to the fridge (2°C) once it hits ambient.

The Problem:

The dye doesn't seem to be staying in the mother liquor. Even after the initial hot filter, the solution is still a deep blue, and the crystals starting to form look like they're trapping the pigment rather than rejecting it.

Also, the solubility seems off—800ml for 240g at boiling feels like a lot of water for KNO3.

Questions:

Is this specific dye likely an organic complex that survives simple recrystallization?

Should I try adding activated charcoal to the boiling solution before the next filter?

Would a solvent wash (like ice-cold ethanol) on the final crystals help, or is the dye likely "baked into" the crystal lattice?

Any tips from people who have cleaned up dirty fertilizer before would be much appreciated!

I did the flame test  light purple color was visible 

Struggling to strip blue dye from "untrusted" Potassium Nitrate—recrystallization failing?