(2019) Environment International_Mechanistic insights into red mud, blast furnace slag, or metakaolin-assisted stabilization/solidification of arsenic-contaminated sediment

Wang L., Chen L., Tsang D.C.W., Zhou Y., Rinklebe J., Song H., Kwon E.E., Baek K., Ok Y.S.

(Elsevier Ltd) Environment International ISSN: 1604120 Vol.133 Issue. Article No.105247 DOI: 10.1016/j.envint.2019.105247

Elevated level of arsenic (As) in marine sediment via deposition and accumulation presents long-term ecological risks. This study proposed a sustainable stabilization/solidification (S/S) of As-contaminated sediment via novel valorization of red mud waste, blast furnace slag and calcined clay mineral, which were selected to mitigate the increased leaching of As under alkaline environment of S/S treatment. Quantitative X-ray diffraction and thermogravimetric analyses illustrated that stable Ca-As complexes (e.g., Ca₅(AsO₄)₃OH) could be formed at the expense of Ca(OH)₂ consumption, which inevitably hindered the hydration process and S/S efficiency. The 29Si nuclear magnetic resonance analysis revealed that incorporation of metakaolin for As immobilization resulted in a low degree of hydration and polymerization, whereas addition of red mud promoted Fe-As complexation and demonstrated excellent compatibility with As. Transmission electron microscopy and elemental mapping further confirmed the precipitation of crystalline Ca-As and amorphous Fe-As compounds. Therefore, red mud-incorporated S/S binder achieved the highest efficiency of As immobilization (99.9%), which proved to be applicable for both in-situ and ex-situ S/S of As-contaminated sediment. These results advance our mechanistic understanding for the design of green and sustainable remediation approach for effective As immobilization. © 2019 The Authors

The authors appreciate the financial support from the Hong Kong Research Grants Council (PolyU 15223517 and E-PolyU503/17 ) for this study. The authors also gratefully acknowledge the support of the University Research Facility on Chemical and Environmental Analysis (URFCE) of PolyU.