Here we study the effect of humic acid (HA) co-precipitation on ferrihydrite (Fh) structure, reduction and secondary mineral formation by a dissimilatory Fe(III) reducing bacterium. Despite similar crystal structure, resembling Fh, the presence of co-precipitated HA resulted in lower surface areas due to increased aggregation. X-ray microscopy analysis of the co-precipitates indicated that the HA was homogenously distributed within the Fh particles. In terms of reactivity, co-precipitated HA resulted in slower Fh bioreduction rates at low C/Fe ratios (i.e., C/Fe = 1), while high C/Fe ratios (i.e., C/Fe = 2) enhanced the extent of bioreduction compared to pure Fh. The co-precipitated HA also altered the secondary Fe mineralization pathway by inhibiting goethite formation, reducing the amount of magnetite formation, and increasing the formation of a green rust-like phase. This study indicates that co-precipitated NOM likely plays an important role in Fe cycling and anaerobic Fe respiration within soils and sediments.

Dissimilatory reduction and transformation of ferrihydrite-natural organic matter co-precipitates

245th National Meeting (2013)

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