Valorization of fly ash and GGBS derived green concrete composite for simultaneous removal of nitrate and phosphate from aqueous systems

• Green concrete composite (GCC) from FA and GGBS for nutrient removal • Optimal NO 3 − (92.21%) and PO 4 3− (74.55%) removal at pH 6.7, 3 g/L and 60 min • NO 3 − removal was driven by electrostatic attraction and ion exchange • PO 4 3− adsorption involved electrostatic forces, ligand exchange and Ca 2+ precipitation • Multi-pollutant system revealed synergistic adsorption effects . Nutrient pollution caused by elevated nitrate (NO 3 − ) and phosphate (PO 4 3− ) concentrations is a major driver of eutrophication, while growing volumes of fly ash and ground granulated blast furnace slag (GGBS) from industrial activities presents pressing solid waste challenge. This study introduces dual-functional M40 grade of green concrete composite (GCC) that functions both as structural material and as adsorbent for water treatment. GCC was fabricated by alkali-activating fly ash and GGBS, producing porous, amorphous aluminosilicate framework with tailored surface chemistry, hydroxyl and silicate groups, minor crystalline phases, thermal stability, and high point of zero charge (pH pzc ). Batch adsorption experiments examined effect of contact time (0-360 min), GCC dosage (0.5-10 g/L), initial concentration (1-100 mg/L), and solution pH (3-11). Maximum adsorption capacities of 14.08 mg/g for NO 3 − and 4.13 mg/g for PO 4 3− were achieved under optimal conditions (pH 6.7, 3 g/L and 60 min). Adsorption followed pseudo-second-order kinetic model and Langmuir isotherm, indicating chemisorption. Mechanistic analysis revealed NO 3 − removal occurred via electrostatic attraction and ion exchange, whereas PO 4 3− uptake involved electrostatic interactions, ligand exchange, and Ca 2+ induced precipitation. In multi-pollutant systems, synergistic adsorption enhanced removal to 22.37 mg/g (NO 3 − ) and 12.90 mg/g (PO 4 3− ). GCC exhibited potential for regeneration and reusability over three cycles, with desorption efficiencies gradually decreasing for both pollutants across successive cycles. These findings highlight GCC as novel, low-cost, regenerable, and environmentally sustainable alternative to conventional adsorbents, presenting an integrated approach to water purification and industrial waste valorization. .