Surface complexation modeling of arsenic(III) and arsenic(V) adsorption onto nanoporous titania adsorbents (NTAs)

Abstract

Nanoporous titania adsorbents (NTAs) were synthesised and applied to remove As(III) and As(V). Optimal pH ranges for As(III) removal were between pH 4 and pH 7 for Ti (25)–SBA-15 and between pH 8 and pH 11 for MT. Maximum removal efficiencies for As(V) by Ti (25)–SBA-15 were observed to be near pH 4 and the maximum for MT was in the pH range between pH 4 and pH 7. The SCM for As(III,V) adsorption by NTAs demonstrated the role of mono- and bidentate surface complexes in arsenic adsorption. For As(III) sorption on Ti (25)–SBA-15, monodentate surface complexes were more important than bidentate ones over the entire pH range investigated, but bidentate complexes played a role near pH 8. When As(III) was being sorbed onto MT, the model predicted that monodentate complexes dominate arsenic removal, except below pH 6 when a higher initial concentration was used. For As(V) adsorption, monodentate surface complexes are apparently responsible for As(V) removal over the entire pH range at both initial As(V) concentrations. At higher solid concentrations of Ti (25)–SBA-15, the patterns of surface speciation that were observed for both As(III) and As(V) adsorption were the same as those observed at lower solid concentrations. This behavior was also true for As(III) adsorbed to MT. For As(V) adsorption onto MT, however, the contribution of bidentate surface complexes at low pH became more intense than observed for lower solid concentrations with the same initial As(V) concentration.