Investigating the microstructure of high-calcium fly ash-based alkali-activated material for aqueous Zn sorption

Sukanta K Mondal; Adam Welz; Ali Rownaghi; Bu Wang; Hongyan Ma; Fateme Rezaei; Aditya Kumar; Monday U Okoronkwo

doi:10.1016/j.envres.2020.110484

Investigating the microstructure of high-calcium fly ash-based alkali-activated material for aqueous Zn sorption

Environ Res. 2021 Jul:198:110484. doi: 10.1016/j.envres.2020.110484. Epub 2020 Nov 17.

Authors

Sukanta K Mondal¹, Adam Welz¹, Ali Rownaghi², Bu Wang³, Hongyan Ma⁴, Fateme Rezaei², Aditya Kumar⁵, Monday U Okoronkwo⁶

Affiliations

¹ Sustainable Materials Laboratory (SusMatLab), Missouri University of Science and Technology, Rolla, MO, 65409, United States; Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, United States.
² Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, United States.
³ Department of Civil & Environment Engineering, University of Wisconsin-Madison, Madison, WI, 53706, United States.
⁴ Department of Civil, Architectural & Environmental Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, United States.
⁵ Department of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, United States.
⁶ Sustainable Materials Laboratory (SusMatLab), Missouri University of Science and Technology, Rolla, MO, 65409, United States; Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, United States. Electronic address: okoronkwom@mst.edu.

PMID: 33212134
DOI: 10.1016/j.envres.2020.110484

Abstract

The performance of adsorbents prepared by alkali activation of high calcium fly ash was investigated for removing aqueous Zn. Two formulations involving the use of NaOH and Na₂SiO₃ activating solutions were used to prepare the adsorbents that feature different microstructural characteristics. The Zn sorption data indicates a sorption process that is controlled by both chemisorption and intra-particle diffusion. The Na₂SiO₃-activated material displayed higher sorption rates compared to the NaOH-activated material. The sorption kinetics show strong dependence on the microstructures of the adsorbents, wherein the Na₂SiO₃-activated material featuring higher contents of amorphous phases (96 %_mass) in the hydrated phase assemblage, with attendant improved porosity and surface area, performed better than the NaOH-activated material (86 %_mass amorphous phases) which showed higher degree of crystallinity and coarse morphology. The Na₂SiO₃-activated material exhibited 100% Zn removal efficiency within the first 5 min in all studied initial adsorbate concentrations(corresponding to sorption capacity of up to 200 mg/g), while the NaOH-activated analogue tends to lag, reaching 99.99% Zn removal efficiency after about 240 min in most cases. The two formulations were also examined with thermodynamic modeling and the results agree with experimental data in indicating that the use of alkali-silicate activating solution is most suitable for converting high calcium fly ash into efficient adsorbent for removing aqueous heavy metals.

Keywords: Adsorption; Alkali-activated materials; Heavy metals; Thermodynamic modeling; Zinc.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Adsorption
Alkalies
Calcium
Coal Ash
Metals, Heavy*
Water Pollutants, Chemical*
Zinc

Substances

Alkalies
Coal Ash
Metals, Heavy
Water Pollutants, Chemical
Zinc
Calcium