Aqueous Fe(II) (Fe(II)(aq))-catalyzed recrystallization of iron (hydr)oxides is the important chemical reaction of iron cycle in anaerobic environments, which poses significant effects on the environmental behavior of heavy metals in soils and sediments. Ferrihydrite is the initial iron mineral phase during the ferrous mineralization and has relatively unstable crystal structure. The structure transformation behavior of ferrihydrite is active and also poses important effects on environmental behavior of soil heavy metals. However, the Fe(II)(aq)-catalyzed phase transformation of ferrihydrite has been rarely reported, especially with the coexisting metal ions. In the present study, the effects of coexisting heavy metal of Pb(II) on the Fe(II)(aq)-catalyzed phase transformation of ferrihydrite coupling the environmental behavior of Pb(II) were systematically studied. The results show that ferrihydrite underwent efficient phase transformation rates when catalyzed by Fe(II)(aq) whenever with or without the effect of Pb(II). Compared with the reaction system that without Pb(II), the adsorption of Fe(II) on the surface of ferrihydrite was inhibited due to the competition of Pb(II) when with the coexistence of Pb(II), which further decreased the rates of Fe atom exchange between Fe(II)(aq) and structural Fe(III) of ferrihydrite. With the inhibited Fe atom exchange reaction, the phase transformation rates were relatively decreased and transformation products were changed during the Fe(II)(aq)-catalyzed phase transformation of ferrihydrite. Goethite and magnetite were found to be the final transformed products of iron (hydr)oxides when without Pb(II), while lepidocrocite was determined to be the main transformed product with little goethite and magnetite as the other transformed products when with Pb(II). During the Fe(II)(aq)-catalyzed phase transformation of ferrihydrite with the coexistence of Pb(II), some Pb were stabilized through being incorporated into the structure of ferrihydrite transformed products with the possible mechanisms of occlusion by the crystal lattice and structural incorporation, so as to decrease the activity of the polluted heavy metal of Pb. The obtained results in the present study are expected to provide further insights for understanding the iron cycle coupling with the environmental behavior of heavy metals in soils and sediments.

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