I am working on one inquiry in which Fe fines (Inlet:500 ppm, Outlet Reqd: 5 ppm) is present. This is Cold Rolling Mill Effluent.

At which pH this Iron will precipitate.

In which form Fe is present in effluent that I dont know i.e. whether Fe+3 or Fe+2.

I have gone through many literature and came to know that Fe+3 precipitate at 4 pH and Fe+2 at 8-9 pH.

Kindly guide me which pH should I consider for precipitation.

Also, I am wondering is there a possibility of settling of any substance at 4 pH? Is there any relevenace of pH and Settling i.e. substance settle at alkaline pH only???

I agree with Sobisch generally, but you need to consider the fluids used for cold rolling which could include oil emulsions. You may need to separate the oil from the water phase (a lot of the iron particles may be suspended in the oil phase) as well as in the water phase. UF filtration may remove both oil and iron from the water phase. I suspect that you need to do a little lab work to accomplish you goal.

grrun