Sorption of the trace metals Ni(II), Zn(II), Co(II), Cd(II) and Mn(II) in anoxic aqueous suspensions of green rust, a mixed valent Fe(II)-Fe(III) layered double hydroxide (LDH), was studied with macroscopic batch kinetic experiments complemented with synchrotron X-ray absorption spectroscopic (XAS) analyses. The amount of metal uptake by green rust (GR) was higher for Ni(II), Zn(II) and Co(II) than for Cd(II) and Mn(II). In addition, Ni(II), Zn(II) and Co(II) sorption reached equilibrium with GR slowly whereas rapid equilibration was observed for Cd(II) and Mn(II) sorption. XAS results showed that trace metal sorption predominantly involved exchange with structural Fe(II). For Cd(II) and Mn(II), exchange likely occurred with Fe(II) exposed at GR particle edges in what is essentially an adsorption reaction. The sorption of the other metals was dominated by incorporation reactions into the GR lattice and/or into secondary Me(II)-Fe(III)-LDH phases that are isostructural to GR. Incorporation likely is the result of dynamic recrystallization of the GR sorbent mediated by aqueous Fe(II) and/or may involve partial dissolution and reprecipitation of the GR sorbent driven by solubility differences between the GR and secondary Me(II)-Fe(III)-LDH phases. The results of this work improve our knowledge of the fate and retention of trace metals in reducing environments containing green rust.

Dynamics and mechanisms of trace metal sorption onto green rust

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.