First-principles investigations of arsenate doping into the ettringite lattice

Abstract

Hazardous wastes are commonly immobilized using cementitious materials. Ettringite (Ca6Al2(OH)12(SO4)3∙26H2O) is one of the main components of hydrated cement and is known to stabilize anionic species. Thus, it is a promising material for the stabilization of arsenate (As(V)) in cementitious waste streams. However, the effects of As(V) incorporation into the ettringite structure on the structural properties of As and ettringite remain unclear. Herein, As(V) doping into the structure of ettringite was investigated based on the first-principles calculations using density functional theory (DFT), and the results suggested that the mechanism involving the substitution of AsO43− by SO42− was energetically favorable and that As doping increased the total bond order of ettringite, leading to a more stable structure. The elastic properties and anisotropy of ettringite and As-doped ettringite were also investigated using DFT calculations. The results showed that the mechanical properties of the As-doped ettringite structure were stable according to Born's criterion. Moreover, As doping increased the elastic constants and elastic modulus of ettringite but reduced its elastic anisotropy. These results provide valuable insights into the long-term stabilization of As species and their migration in cementitious wastes.