IRON REMOVAL - GREEN FLOC

[ozfish]

When raising the pH of ground water with high fe2+ concentration of 47ppm, using NaOH or Lime, a green floc is produced - if the water is aerated first, the floc is brown?

Both situations result in iron removal but I am curoius as to what is actually happening?

Regards

 

[kenvlach]

Aeration oxidizes the Fe⁺²(green) to Fe⁺³(rust-color). The Fe⁺³ has lower solubility, so you can get more complete removal as Fe(OH)₃.

 

[ozfish]

Thanks for the response.
What would produce a better result - aerate the water before raising the pH with NaOH or
- should I add the NaOH and then aerate.

 

[kenvlach]

In principle, it is better aerate first.
If instead you add NaOH first, more of it will be wasted by reacting with CO₂.