Tooeleite: Direct immobilization of trivalent arsenic-Mechanisms, stability, and prospects for environmental...

Arsenic contamination represents a global environmental challenge, with trivalent arsenic (As(III)) posing significantly higher risks than pentavalent arsenic (As(V)). Compared to conventional arsenic removal approaches, mineral immobilization technology demonstrates superior efficiency, cost-effectiveness, and environmental compatibility by sequestering arsenic within stable crystalline structures. However, since arsenic in most arsenic-containing minerals exists in the pentavalent form, the arsenic mineral immobilization method requires pre-oxidation of As(III) to As(V), which compromises efficiency and increases operational costs. Tooeleite (Fe₆(AsO₃)₄(SO₄)(OH)₄·4H₂O), as the sole naturally occurring mineral capable of directly immobilizing As(III) without the pre-oxidation, with potential applications for arsenic removal from wastewater. However, there is a lack of comprehensive reviews that systematically evaluate the influencing factors and mechanisms of tooeleite mineralization in arsenic removal. This work systematically reviews the geochemical origin, crystal structure, thermodynamic stability, and environmental persistence of tooeleite. And the critical regulatory factors governing both biotic and abiotic synthesis pathways, including pH conditions, Fe/As/S ratios and microbial interactions, are elucidated. Evaluating the arsenic removal efficiency, limitations, and mineralization pathways of chemical versus biological synthesis approaches, Finally, future research potentials are proposed to advance the engineering applications of tooeleite, thereby providing theoretical foundations and technical references for targeted arsenic pollution remediation.