Guess the Yellow Impurity

[Simoski]

Howsit

 

I've been recrystallizing KNO3 from a fertilizer grade for a while and the supernate always has a yellow tinge upon cooling, it gets worse if I decant the supernate and drive off more water by boiling.

 

Any guesses as to what it is?

 

Edited May 3, 2018 by Simoski

[vinny1892]

My guess sulfur whats the name of the fertilizer you are using?

[Mumbles]

The real impurity in potassium nitrate is usually sodium nitrate and sodium chloride. Any yellow coloration is a sign of lower quality potassium nitate, and generally from dirt or clay, or sometimes iron contamination from corroded equipment.

[NeighborJ]

Do a simple taste test. Could provide some more insight and it won't hurt you.

[Simoski]

Taste NeighnorJ hmmm... it tastes nasty.... I was hoping to taste iron or something... but just salty nasty.

 

Vinny, maybe sulfur but I think I'd see it in the starting product, the name is "Omnia K" made by Kemapco. Here the webpage: http://kemapco.com/en/content/potassium-nitrate

 

Iron was what I was thinking Mumbles, how can I precipitate it out? What oxidation state are yellow iron ions in?

Edited May 4, 2018 by Simoski

[Mumbles]

Anything exposed to the air is probably going to be iron (III) in solution. Adding hydroxide might precipitate it, but you'll probably end up contaminating your product even more in the long run. I'd just keep crystallizing and toss the final supernatant.

[Simoski]

I have some KOH handy so I'll try that and report back...

 

thank you Grandmaster

 

: )

[Simoski]

Before and after adding KOH.

 

 

I think the after image is slightly green, indicating iron hydroxide in solution, I will wait a few hours to see if it settles at the bottom

Edited May 4, 2018 by Simoski