Precipitating phosphate out of KCl?

[JimWelsh]

I recently read an article about dosing potassium chloride to raise potassium levels, and in an online discussion about the article, it was mentioned that bulk KCl can contain phosphate as a contaminant, so the proponent of this dosing method suggests dripping the KCl solution through GFO to remove the phosphate. Considering the poor solubility of calcium phosphates and magnesium phosphates, would mixing CaCl2 and/or MgCl2 into the KCl solution be a viable alternative way to remove phosphate via precipitation?

 

[Habib(Salifert)]

You could use some MAGIC

Mg(OH)2....

http://www.aslo.net/lo/toc/vol_37/issue_1/0105.pdf


It is also relatively easy to decant or filter out the phosphate rich precipitate.

 

[JimWelsh]

Admit it: You've been waiting for an opportunity to use that link, haven't you, Habib?

 

[JimWelsh]

So, then, if I understand correctly, one could add, say, 25 mM of MgCl2 to a KCl solution, and then use an excess of KOH instead of NaOH to precipitate Mg(OH)2, which will take the vast majority of the P with it via coprecipitation. Then, after centrifugation/filtration/decanting, the supernatant can be neutralized with HCl, if desired, leaving a quite pure KCl solution. Did I get that right?

Also, even though they keep referring to phosphorus-32 in the paper, I should assume that my KCl will only contain the stable isotope of P, and that this method applies equally well to both the stable and the radioactive isotopes, correct?

 

[Randy Holmes-Farley Verified Community Expert]

Perhaps just use Milk of Magnesia (magnesium hydroxide).

Add excess, let it settle, and use the clear liquid.

That's essentially what I did here with calcium hydroxide to remove copper (which is nice because you can see it):

http://www.advancedaquarist.com/2003/5/chemistry

from it:

Figure 1. Copper sulfate solution before (left) and immediately after the addition of calcium hydroxide (right).

Figure 2. Copper sulfate solution before (left) and several hours after the addition of calcium hydroxide (right).

 

[Habib(Salifert)]

Admit it: You've been waiting for an opportunity to use that link, haven't you, Habib?

Jim, to be perfectly honest, I have to admit that!