Progressive Nickel Incorporation into Fungal and Abiotic Manganese Oxides with Aging

Abstract

Manganese oxides influence Ni partitioning in natural and metal-polluted systems through adsorption and incorporation. Understanding Ni behavior within environmental contexts requires knowledge of its binding to environmentally relevant minerals such as birnessite during and after precipitation. Here, we compare Ni binding at initial (48-h) and aged (14-day) time frames onto fungal (via Stagonospora sp. SRC1lsM3a) and abiotic birnessite, as fungi are important Mn oxidizers in contaminated sites, with two timing-of-addition scenarios: reacting preformed birnessite and coprecipitation. X-ray absorption spectra were collected to track the mineral structures and Ni binding modes. Aging abiotic and fungal birnessites reacted with Ni increase the hexagonal sheet symmetry and average Mn oxidation state (AMOS), while coprecipitation yields similar initial (and stable) structures. Aging also shifts Ni from biomass- and edge-bound sites in fungal and abiotic systems, respectively, to binding the above vacancies and incorporating into the mineral structure. Incorporated Ni is positively correlated with AMOS and Mn(IV) content, with both fungal- and abiotic-aged samples achieving 2.3 mol % (mol Ni:mol Mn) incorporation, albeit with different timing-of-addition scenarios. These results suggest an equilibrium structure for Ni-substituted phyllomanganates, with birnessite and fungal biomass acting as Ni sinks and sources in environmental systems.

Our research highlights how nickel interacts with manganese oxide minerals, revealing progressive nickel incorporation into manganese oxide minerals over time, with distinct Ni binding behaviors between fungal versus abiotic manganese oxides.