Effects of cobalt, nickel, and manganese doping on the structure and dissolution properties of goethite and hematite

Trace metal dopant in goethite and hematite are common in soils, groundwater and sediments, and have strong influence on the structure and physicochemical properties of goethite and hematite. In this work, a series of Co, Ni and Mn-doped goethites and hematites were synthesized, fully characterized by powder X-ray diffraction (XRD), and the zeta potential of samples have been measured to study their structure. The dissolution kinetics of pure and trace metal doped goethites and hematites in proton-promoted, ligandpromoted, reductive ligand-promoted solutions were also investigated. Characterization results demonstrated that trace metal dopants affect crystal unit cell parameters, increase cell volume, and decreased the relative proportion of the main crystal facet. Additionally, zeta potential measurement indicated that trace metal dopants lower the zero point of charge of oxide. The dissolution experiments showed that trace metal dopant affect metal release extent and rate coefficient of goethite and hematite. Additionally, the dissolution experiments also indicated that the presence of ligand would promote metal release from goethite and hematite. A synergistic effect of reductant and ligand on the rate and extent of goethite and hematite dissolution was possible from the observation but still need more work to identify. The results of this research facilitate better understanding of the Co, Ni and Mn substitution on the structure and properties of goethite and hematite, and their dissolution process in different aquatic systems.