Interaction of ammonium with birnessite: Evidence of a chemical and structural transformation in alkaline aqueous medium

TL;DR

This study reveals that ammonium interacts with Na-birnessite in alkaline solution through both ion exchange and chemical transformation, leading to structural and chemical changes in the mineral.

Contribution

It provides new evidence of chemical and structural transformations of birnessite upon ammonium interaction in alkaline media, combining surface and bulk analyses.

Findings

Birnessite acts as a cationic exchanger for NH4+

Chemical reactions occur, altering birnessite's structure and composition

Surface analysis shows distinct ammonium environments

Abstract

The ammonium cation interaction with Na-birnessite in aqueous alkaline medium was studied. Solution and solid analysis give evidence that birnessite is not only acting as a cationic exchanger toward NH4+. The surface analysis performed by XPS showed that N1s spectra are characterized by the existence of two different environments: one assignable to an interlayer NH4+ and the second to a chemisorbed N-species. Structural and chemical transformations were observed on birnessite with nitrogen mass balance deficit. The monitoring of NH4 +, Na+, Mn2+, NO3- and NO2- and solid changes (average oxidation state of Mn, cation exchange capacity, solid nitrogen content and symmetry evolution identified by XRD and FTIR) indicate unambiguously that NH4+ reacts chemically with the birnessite.