Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite

• DOI: 10.1021/acs.est.2c04971
• Publication Date: 2022-10-11T19:33:12Z
• Authors: Alireza Namayandeh; Olaf J. Borkiewicz; Nefeli M. Bompoti; Maria Chrysochoou; F. Marc Michel
• Keywords: Oxyanion; Ferrihydrite

The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, the presence other ions in system such as nitrate (NO3–), sulfate (SO42–), arsenate (AsO43–). Although mechanism Fh oxyanion complexation have been separately studied, effect surface complex type strength on remains only partly understood. We developed a kinetic model that describes effects goethite (Gt) hematite (Hm). Two sets oxyanion-adsorbed samples were prepared, nonbuffered buffered, aged 70 ± 1.5 °C, then characterized using synchrotron X-ray scattering methods wet chemical analysis. Kinetic modeling showed significant decrease for complexes dominated strong inner-sphere (SO42– AsO43–) versus weak outer-sphere (NO3–) bonding control. results also influenced with increasing bonding, smaller fraction Gt forms compared Hm. These findings are important understanding predicting role controlling transport fate metal metalloid oxyanions natural applied systems.