Designing water treatment systems with contaminant removal based on zero-valent iron (ZVI) requires an understanding of the formation of a series of iron oxyhydroxides produced during corrosion of the thermodynamically unstable ZVI core. X-ray diffractometry (XRD) and geochemical modelling were used to investigate the mechanisms of copper and zinc removal and the formation of iron oxyhydroxides in batch experiments at 4 and 25 degrees C, over a period of 349 days. Copper removal was predominantly associated with a mineral product, which was unstable in an aerobic environment. Zinc and some copper were sequestered into the iron oxyhydroxide structure and did not redissolve when the pH was reduced. X-ray diffractometry and geochemical modelling suggest that ZVI reacted to form magnetite and lepidocrocite, with lepidocrocite being the most stable mineral observed under the experimental conditions. However, XRD analysis did not allow the identification of poorly crystalline intermediate or substituted products which were most likely also present.Capsule AbstractDuring zero-valent iron treatment heavy metal contaminants are sequestered into iron oxyhydroxide structures formed during corrosion.