Revealing Insights into the Mechanism of Hg0 Removal over MnO2 Hollow Sphere Adsorbents: Effect of Calcination Temperatures

Abstract

In this study, MnO2 hollow spherical adsorbents were synthesized using the template approach, and the impacts of calcination temperatures on their physicochemical parameters and Hg0 removal ability were investigated. The adsorbent calcined at 300 °C (labeled as Mn300) demonstrated the highest performance; at 200 °C, the Hg0 removal efficiency reached over 90%. The presence of surface acid sites promoted the physisorption of Hg0 and compensated for the relatively weak oxidative ability, which made much of the Hg0 susceptible to capture on the adsorbent surface and consequently explained Mn300’s superior Hg0 capture capacity. The Mars–Maessen mechanism helped to understand the Hg0 capture pathways over Mn300, with Mn4+ and chemisorbed oxygen serving as the active species to oxidize Hg0 to HgO. Finally, Mn300 demonstrated reasonable recyclability and a rather weak gas-component adaptability, indicating that additional modification is required to improve the practical use of the adsorbent.