Mesoporous Silica Nanoparticles for the Adsorptive Removal of Cu(II), Mn(II), and U(VI) from Acid Mine Drainage

The adsorption of Cu(II), Mn(II), and U(VI) ions by mesoporous silica nanoparticles (NPs) was investigated by batch experiments to assess the potential using NPs to remediate acid mine drainage (AMD) contaminated water. Adsorption reactions were found to be rapid, attaining equilibrium within 5 min for Cu and less than a minute for Mn and U. Calculated adsorption rates based on the pseudo-second order model (R (2) = 0.99) showed that Mn adsorption was > 3 times faster than Cu and 7 times faster than U. Adsorption increased with pH and temperature, and a dagger GA degrees and a dagger HA degrees values indicate that the process was spontaneous and endothermic. Isotherm data were best described by the Freundlich and Temkin models (R (2) = 0.99), with chemisorption responsible for the removal of Cu and Mn, and adsorption and precipitation for U removal. Importantly, Fe3+, Mn, and SO4 (2-) ions increased adsorption from 52, 56, and 49 % to 77, 66, and 76 % for Cu, Mn, and U, respectively. Cu removal was, however, inhibited in 1:2 Cu:Mn solutions. NPs were then applied to actual AMD-contaminated ground and surface water. As in simulated AMD, adsorption was higher for Mn than Cu and removal efficiencies of up to 60 % for Mn and 34 % for Cu were attained. These NPs therefore offer an alternative for Mn removal that precludes pH adjustment and the copious amounts of lime required for that. Importantly, they can be used for cost-effective treatment of AMD-contaminated water.