Mg-modified analcime crystal structure-orientation constructed from non-activated fly ash for As(V) high-efficiency...

In response to the technical challenges associated with the high-temperature activation of fly ash and the reliance on costly metal modifications to synthesize fly ash-based zeolites for As(V) removal, this study introduces a novel crystal structure-oriented synthesis approach. Given the mullite skeleton in fly ash is highly compatible with the Al-O-Si bond angles in the β-cage structure of analcime. Instead, a β-cage structure characteristic of analcime forms via structural reorganization of mullite, involving bond angle adjustments and silicon supplementation. This study thus reports, for the first time, the one-step hydrothermal synthesis of analcime from non-activated fly ash. Furthermore, inexpensive Mg²⁺ ions were introduced to create Mg-modified analcime (Mg-analcime), a novel synthesis approach. The incorporation of Mg²⁺ stabilizes the hexagonal ring skeleton through electrostatic interactions and enhances the pore architecture, significantly increasing the specific surface area of Mg-analcime. As(V) removal by Mg-analcime primarily occurs via hydroxyl substitution between Mg-OH and As(V), forming Mg-O-As complexes, achieving a maximum adsorption capacity of 154.8 mg/g. Even in the presence of competing ions, Mg-analcime maintains 90% selectivity for As(V) and retains its adsorption capacity after five cycles. This study demonstrates the feasibility of synthesizing Mg-analcime from non-activated fly ash using the crystal structure-oriented strategy, achieving efficient As(V) adsorption capacity, and laying the groundwork for the large-scale production of cost-effective, efficient solid waste-based adsorbents.