Oxidation by aeration or use of chemicals like chlorine, chlorine di-oxide or potassium permanganate followed by filtration alone or by settling and filtration can bring about the precipitation of iron and its removal. Use of zeolites as well as catalytic oxidation also serve the purpose.
Green sand is one of the oldest but proven oxidation technologies. Potassium permanganate, itself an oxidizer, is used to regenerate the greensand.
Manganese dioxide is a naturally mined ore with the ability to remove iron, manganese and hydrogen sulfide. The hydrogen sulfide capability exceeds that of either greensand or synthetic greensand and requires no chemical to regenerate.