Abstract: The initial nucleation and phase transformatin process of the Fe(OH)3 gel in five different mineralization systems with different dextran concentrations(from 0～2.0%(w) and the same [Fe3＋]=0.012 mol•L-1) have been investigated. The mineralizational phases in the initial stage were characterized by FTIR, XRD and ICP-AES spectrometry. The results showed that the concentration of Fe3＋ ions in supernatant increased suddenly in the third day during aging and then its secondary reduction stage occurred. There were the same chages of pH as [Fe3＋] in these process. The initial phases formed in the systems with dextran were mainly β-FeOOH, not α-FeOOH which growing rapidly in the system without dextran. The dextran molecules were adsorbed on the surfaces of iron oxide particles by complexing with Fe3＋. The adsorbed dextran molecules would facilitate the phase transformation from β-FeOOH into α-Fe2O3 by a dissolution-recrystallization mechanism. The secondary reduction stage of [Fe3＋] corresponded to the process of the phase transformation from β-FeOOH into α-Fe2O3. With the increasement of the concentrations of dextran (up to 2.0%(w)) in solution, the dissolution of β-FeOOH and the formation of α-Fe2O3 in these mineralization systems were accelerated. It was clear that dextran molecules could control the nuclei type and its phase transformation of the Fe(OH)3 gel.

Key words: Biomineralization, Dextran, Ferric hydroxide gel, Transformation, Dissolution-recrystallization