Effects of calcium ions on surface characteristics and adsorptive properties of hydrous manganese dioxide

The effects of calcium ions (Ca2+) on the surface characteristics and adsorptive properties of hydrous manganese dioxide (δMnO2), taking arsenic and humic acid as model pollutants, were systematically investigated. The FTIR spectra and SEM/EDX analyses indicate coordination between Ca2+ and the surface hydroxyls (Mn–OH) of δMnO2, which leads to an increase of the surface ζ potential. Ca2+ can facilitate δMnO2 aggregation, as indicated by the particle size distribution (PSD) and on-line flocculating index (FI). The variation of δMnO2 surface characteristics that is induced by Ca2+ enhances the adsorption of humic acid (HA) and arsenic onto δMnO2. The adsorption of HA is enhanced more significantly by Ca2+ than that of arsenic, which is positively related to the coordination strength between Ca2+ and individual pollutants. The SEM/EDX analysis shows the formation of Ca–HA complexes, which have a higher affinity for δMnO2 than HA. The bridging effect of Ca2+ plays a major role in enhancing HA adsorption onto δMnO2. Due to different interactions between Ca2+ and pollutants, the adsorption mechanism is pollutant-dependent in the presence of Ca2+.

Ca2+ impacted the stability and the dynamic aggregation of δMnO2. Ca2+ at different concentrations changed the particle size distribution and significantly increased the particle diameter of δMnO2.Figure optionsDownload as PowerPoint slide