Structural substitution for SO4 group in tooeleite crystal by As(V) and As(III) oxoanions and the environmental implications

Abstract

Two different SO4-free tooeleite were prepared for the first time through structural substitution for SO4 group by As(V) and As(III). As(III)-tooeleite and As(V)-tooeleite have similar crystalline structure to SO4-tooeleite but incorporate different anions in the interlayer space. The removal of As can reach 94% by forming SO4-free tooeleite crystals, and As leaching in TCLP tests can be much lower than that of SO4-tooeleite. Therefore, SO4-free tooeleite crystals are of great potential in As removal and immobilization. Moreover, our study indicates the different affinities of Fe(III) towards As(III), As(V) and SO4, which can explain that a) the coordination structure of As(III)-tooeleite is much closer to the ideal crystal structure but easily affected by As(V) and SO4 group; b) tooeleite mineral found in natural environments is commonly a SO4-containing mineral and associated with scorodite due to the abundance of As(V) and SO4 group.