The Effect of Aeration on Mn(II) Sorbed to Clay Minerals and Its Impact on Cd Retention

Manganese is a redox-sensitive element in soils and sediments that plays an important role the retention of trace elements. Under anoxic conditions, clay minerals were shown to increase Cd by favoring precipitation Mn(II) phases. In this study, we investigated influence aeration on anoxically formed Mn solid phases its impact presence two with low Fe contents, natural kaolinite (KGa-1b) synthetic montmorillonite (Syn-1). Ca-saturated KGa-1b Syn-1 pre-equilibrated Mn2+ Cd2+ under conditions for 1 or 30 days subsequently exposed air days. The analysis synchrotron X-ray absorption spectroscopy (XAS) revealed extended pre-equilibration (30 days) partially prevented oxidation sorbed (MnSiO3 Mn(II)Al-LDH). Extended exposure ambient short favored formation feitknechtite (β-MnOOH) birnessite (δ-MnO2). Aeration resulted decrease pH net release into solution, indicating re-sorption Mn(III/IV)-phases was insufficient compensate due dissolution Mn(II)-containing pH. Our results demonstrate significance (trans)formation Mn-containing their metal environments undergoing fluctuating redox conditions.