Adsorption of Sb(III) and Sb(V) over gibbsite surfaces and regulatory effects of doping

Antimony (Sb) represents a priority contaminant over global scale and is associated preferentially with aluminum and iron (hydr)oxides. Herein, DFT calculations are conducted to unravel the mechanisms and critical specifics for Sb(III) and Sb(V) adsorption by gibbsite, the largest fraction of minerals in economical-grade bauxite horizons. Then, doping is extensively utilized to explore efficient gibbsite-based scavengers. Over pristine surfaces, Sb(III) predominates as outer-sphere complexes while Sb(V) as bidentate binuclear complexes, and Sb(V) exhibits stronger adsorption. Chemisorption is indispensable for anion production from Sb(OH)₃ and Sb(OH)₆^-. Doping pronouncedly regulates Sb adsorption, and Ca²⁺ doping and Mn⁴⁺, Fe⁴⁺, Fe³⁺ doping Mn⁴⁺ are highly efficient respectively for Sb(III) and Sb(V) adsorption. Particularly, inner-sphere Sb(III) complex becomes the most preferred upon Ca²⁺ doping that greatly promotes Sb(III) immobilization, and Fe²⁺ doping may trigger auto reduction of Sb(V). Sb(V) adsorption affinities decline due to pH elevation, and those with stronger adsorption are more affected. The larger ionic radius favors Sb(III) adsorption while the smaller ionic radius difference between dopants and Al³⁺ favors Sb(V) adsorption. Orbital interactions also contribute significantly to Sb adsorption, especially for transition metals that participate more actively during electron transfers. Instead of orbital interactions, Sb(V) exhibits stronger adsorption than Sb(III) due to promoted interactions with surface and water, while alteration of surface charge properties weakens Sb(V) adsorption at higher pH. Results provide insights for understanding of transport, fate and bioavailability for Sb(III) and Sb(V) at minerals surfaces, and feed back the development of efficient Sb scavengers.