Polyfill and iron binding during AA treatment

[Brian Malone]

Hi - a question for the chemists on the TF Pool forum: Does polyfill fiber have a chemical binding action to sequestered iron? I see many posts saying to use polyfill to filter out iron but there is no explanation on the mechanism of action. Iron in water is in solution, and this is not a standard mechanical separation/filtration operation - this requires some type of ionic action, right??? I see some posts that say the polyfill turns dark with use but that doesn't convince me iron is being filtered out - the dark color could be any particulate/contaminant in the water that is being mechanically filtered - the polyfill would be performing a water clarifying function. Thanks!

 

[Texas Splash]

Polyfill is all about mechanical filtration. Sometimes it works while other times not so much. Its effectiveness depends on the state of the iron at the time. To my knowledge that's where the water chemistry comes into play as it can influence the degree of precipitation of the iron, but not the polyfill itself. I'll tag @Donldson to see if there is more to clarify.

 

[JoyfulNoise]

Fe(2+) is highly soluble in water but it is not stable and will oxidize quickly to Fe(3+). Fe(3+) is not soluble in water and quickly forms iron oxide/hydroxide compounds, aka, rust, which is what imparts the yellow (low concentration) to brown (higher concentration) color to water. The precipitates formed by Fe(3+) are extremely tiny, only a few microns in size at most. Polyfill has very high surface area and finer filtration properties than standard pool sand. That combination makes it good at capturing fine iron precipitates. So yes, it’s a mechanical filtration process.

 

[Brian Malone]

Polyfill is all about mechanical filtration. Sometimes it works while other times not so much. Its effectiveness depends on the state of the iron at the time. To my knowledge that's where the water chemistry comes into play as it can influence the degree of precipitation of the iron, but not the polyfill itself. I'll tag @Donldson to see if there is more to clarify.

Yes, precipitation of iron would make sense for mechanical capture of iron in the polyfill fiber - and precipitation would require creation of the right condition(s), i.e. supersaturation, or addition of a precipitation promotor. Putting polyfill in the skimmer or in a bag/container connected to the water input/return does not seem to me to change the solution concentration of iron in the water or add anything, and the water flow rate is high and constant. I am really curious on what is the chemistry function that would make this work! Thanks!

 

[Brian Malone]

Hi  JoyfulNoise - I was typing while you were explaining! So, the polyfill is filtering the very small iron precipitation particles! That makes sense and eliminates 'magic' !! ️

With a mechanism of action described, I will spend money on polyfill fiber and give this iron removal method a try. Thanks!!!