Effect of Mn(II) and Phytic Acid on Cr(VI) in the Ferrihydrite-Cr(VI) Co-precipitates: Implication for the Migration Behavior of Cr(VI)

Understanding the influences of ferrihydrite conversion and co-existing substances on the migration of Cr(VI) in the co-precipitates of ferrihydrite and Cr(VI) (Fh–Cr) is helpful in predicting the migration path of Cr(VI). This work studied the influence of phytic acid on the immobilization of Cr(VI) in ferrihydrite and the migration of Cr(VI) in the presence of phytic acid and Mn(II). The results revealed that phytic acid hindered the retention of Cr(VI) in ferrihydrite and the conversion of ferrihydrite to goethite and hematite. Phytic acid inhibited the formation of hematite by inhibiting ferrihydrite particle aggregation, and the combination of phytic acid and iron ions prevented the formation of goethite. Although phytic acid significantly retarded the conversion of Fh–Cr, it did not hinder the migration of Cr(VI). Besides, the presence of Mn(II) eliminated the negative effect of phytic acid on the immobilization of Cr(VI) in ferrihydrite. The results of this study were helpful in understanding the interaction among ferrihydrite, phytic acid, Mn(II), and the migration path of Cr(VI) during the conversion.