Molecular-Level Insights into Adsorption Characteristics of Arsenite, Selenium and Cadmium on {201} Tio2

Acid mine drainage (AMD) polluted from multiple coexisting heavy metals is a significant concern, and the AMD treatment remains a challenge due to the lack of fundamental knowledge of the interfacial chemistry and efficient adsorbents. Herein, the antagonistic and synergistic effect of multiple metals at the mineral interface was observed by investigating As(III), Se(IV) and Cd adsorption on {201} TiO2 using X-ray absorption spectroscopy and density functional theory calculations. The Langmuir adsorption capacity of As(III) and Se(IV) on {201} TiO2 was 0.32 mmol/g and 0.25 mmol/g, respectively. Competitive adsorption results demonstrated that both Se(IV) and As(III) formed bidentate binuclear inner-sphere complexes at the bridge-Ti4C of {201} TiO2. The hybrid orbital energy for Se(IV) adsorption (-2.42 eV) was lower than that for As(III) adsorption (-2.26 eV), which controlled the distinct adsorption characteristics of Se(IV) and As(III). Co-adsorption results indicated that Cd(II) formed ternary complexes with Se(IV)/As(III) on {201} TiO2, enhancing the Freundlich adsorption of Se(IV) to 0.69 mmol/g and As(III) to 0.43 mmol/g. The introduction of Cd altered the orbital hybridization interaction, which was the driving force underlining the As(III)/Se(IV) surface chemistry. Gaining insights into the surface chemistry of these antagonistic and synergistic reactions can deepen our understanding of the transport and removal of trace elements in AMD.