This study focuses on synthesizing and optimizing a fl y ash-based geopolymer modifi ed with activated carbon to effi ciently

remove manganese from contaminated solutions within a permeable reactive barrier. Using the RSM–BBD strategy, the

synthesis process was optimized, resulting in infl uential parameters set at 40% activated carbon with fl y ash as a precursor,

12 M NaOH concentration, 2.5 Na 2 SiO 3 /NaOH ratio, 55 °C curing temperature, 14 h curing time, 30% solid content, and

37 kHz sonication. Characterization via FESEM revealed the sorbent’s high porosity, crystalline nature, and heterogeneous

surface with a wide size distribution. The potential of the synthesized geopolymer sorbent to eliminate Mn 2+ from synthetic

wastewater was further assessed using the RSM-CCD approach. Results showed complete removal of Mn 2+ ions at a solution

pH of approximately 2.3, adsorbent dosage of 0.2 g, pollutant solution volume of 20 ml, pollutant concentration of 500 ppm,

stirring rate of around 300 rpm, and contact time of approximately 60 min. Additionally, sorption kinetics, isotherms, thermodynamics,

and possible adsorption mechanisms were scrutinized. Kinetic data revealed that the phenomenological internal

mass transfer (IMT) model provided the best fi t, with internal diff usion as the rate-controlling mechanism. Isotherm analysis

confi rmed multilayered and homogeneous interactions between the adsorbent and adsorbate, with a physical adsorption type.

Thermodynamic results indicated feasible, spontaneous, and endothermic sorption.