Zinc Presence during Mineral Formation Affects the Sorptive Reactivity of Manganese Oxide

Abstract

The sorptive reactivity of layered manganese (Mn) oxides is controlled by their layer and interlayer structure, which can be affected by processes such as metal coprecipitation. This study investigated the effects of Zn coprecipitation on the sorptive reactivity of δ-MnO 2 , a common layered Mn oxide mineral. Selected cation (i.e., Cd) and anion (i.e., phosphate and arsenate) species were used to probe the changes in δ-MnO 2 sorptive reactivity. Cd uptake by δ-MnO 2 was suppressed by Zn coprecipitation but total metal uptake (Cd and Zn) was enhanced, indicating more available vacancy sites (e.g., smaller particle size and higher vacancy site density) in Zn-coprecipitated δ-MnO 2. Phosphate and arsenate sorption on δ-MnO 2 was significantly enhanced by Zn-coprecipitation, and the enhancement was more effective compared to Zn sorption on pure δ-MnO 2. X-ray diffraction and X-ray adsorption spectroscopy analysis did not detect the formation of surface precipitations and/or ternary complexes. The enhanced anion sorption on Zn-coprecipitated δ-MnO 2 was likely due to the compensation of negative surface charge by sorbed Zn, as well as the structural modifications introduced by Zn coprecipitation. Results from this study can provide a better understanding on the interactions between metal-coprecipitated Mn oxides and other species in natural environments.

Photocatalytic Oxidation of Dissolved Mn2+ by TiO2 and the Formation of Tunnel Structured Manganese Oxides

“…They play important roles in numerous elemental cycles and affect the electron flow in nature. − They have high reduction potential ( E MnO 2 /Mn 2+ ∼ 500 mV at pH 7) and high specific surface area (around 10–200 m 2 /g), , and are among the most reactive minerals and the most significant solid oxidants in nature. Thus, understanding the redox reactions of Mn in terristrial, freshwater, and high-salinity aqueous systems (e.g., seawater) has been considered a key for understanding the geochemical electron cycles in the history of Earth and Mars. − With their high redox reactivity and adsorption capacity, Mn oxides are also widely used in energy and environmental engineering systems for energy storage, water treatment, and contaminant removal. − For example, recent studies demonstrated the application of Mn oxides for harvesting energy from wastewater and salinity gradient , as well as for the degradation of antimicrobial agents, organic contaminants, and heavy metals. − …”