Most of the iron in the diet is in the ferric (Fe3+) form. It is actively absorbed in:
Stomach
Duodenum
Large intestine
Ileum
Gastric secretions dissolve the dietary iron and permit it to form soluble complexes with ascorbic acid and other substances that aid its reduction to the Fe2+ form. Almost all iron absorption occurs in the duodenum. Transpo of Fe2+ into the enterocytes occurs divalent metal transpoer 1 (DMT1). Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 26. Digestion, Absorption, & Nutritional Principles. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.