Effect of EDTA on Preparation Process of γ-FeOOH

The presence of EDTA in early reaction period can induce nucleation of γ-FeOOH from FeSO₄ and NaOH. If the concentration of EDTA in initial solution surprises a certain critical value, C^*, the pure γ-FeOOH can be obtained. The C^* increases with increasing alkaline ratio or temperature. During the process of nuclration of γ-FeOOH, Fe （Ⅱ）/Fe （Ⅲ）=2. Two carboxylic acid groups held at a certain distance in EDTA is the key radial to induce the nudeation of γ-FeOOH particles. PPA can also induce the nudeation of γ-FeOOH particles due to its soft chain.