Development of high-silica fly ash-based adsorbents for efficient dye removal from wastewater: a comparative study of MSAM and SDS/FA

Solid waste fly ash is challenged by accumulation, storage, low comprehensive utilization, insufficient high-value use technologies, and environmental and ecological risks. Owing to its high silicon content and superior adsorption capability, two novel adsorbents-mesoporous silicon aluminum material (MSAM) and sodium dodecyl sulfate modified fly ash (SDS/FA)-were prepared using ultrasonic-assisted, alkali fusion-hydrothermal, and surface modification methods. Their ability to enhance the adsorption of dyes (MB, MV) on high-silica fly ash through various modification strategies was explored. The effects of the alkali-to-ash ratio, ultrasonic time, hydrothermal time, and hydrothermal temperature on MSAM adsorption were evaluated, and the optimal preparation conditions were determined using Box-Behnken response surface methodology. Likewise, the impact of particle size, SDS dosage, ultrasonic time, and oscillation time on the SDS/FA system was analyzed, and optimal conditions were established. XRD, SEM, FTIR, and BET were used for characterization. Dynamic column experiments assessed the performance of SDS/FA in removing MB and MV from dye wastewater. Results showed that: (1) MSM and SDS/FA optimal preparation conditions were determined, with MSAM (alkali-to-ash ratio 1.2 : 1, ultrasonic 20 min, hydrothermal 8 h, 100 °C) achieving 94.70% and 80.05% removal for MB and MV, respectively; SDS/FA (0.25-0.38 mm, 3 g SDS, 20 min ultrasound, 8 h oscillation) achieved 85.33% and 95.38%. Characterization revealed significantly enhanced surface area and active sites. (2) Dynamic experiments demonstrated that SDS/FA columns increased MB and MV removal by 34.41% and 37.92% compared to high-silica fly ash, with stable effluent pH over time. The static adsorption of MSAM supports its application in dye wastewater treatment, and the structure-property relationship provides a new pathway for the high-value use of fly ash.