Valorization of industrial silica waste for the synthesis of iron oxide-coated calcium silicate hydrate composite for the removal of nitrate from aqueous solutions

Nitrate pollution, primarily driven by industrial activity, is a key contributor to global water contamination, resulting in serious consequences for environmental and public health. To overcome this, a hydrothermal reaction method was implemented to produce a composite of iron oxide and calcium silicate hydrate from alum waste. The products were characterized utilizing SEM, BET, XRD, TGA, and FT-IR analyses, while UV-Visible spectroscopy was used to measure the concentration of NO 3 - . The obtained result demonstrates successful surface binding of NO 3 - onto the MCSC surface, attributed to its extensive active sites and porous structure. The finding from response surface methodology ensured an optimum 98.7% of nitrate ions were removed from wastewater at (94 minutes, 2 pH, 55 mg/L conc., and 3.5 g/L dose) utilizing 25% weight of Fe 3 O 4 -loaded to calcium silicate hydrate. The pseudo-second-order model (RMSE = 0.49, SSE= 1.7 and R 2 = 0.999) and the Langmuir model (R 2 = 0.993, RMSE = 0.179 and SSE = 0.16) provided the best fits to the experimental data. The adsorption process is spontaneous and endothermic from thermodynamic investigation. The maximum adsorption capacity of 27.93 mg/g was acquired, and after five adsorption-desorption cycles, 70.42% removal efficiency was realized. In general, the findings of this research showed that the Fe 3 O 4 -coated calcium silicate hydrate was a highly fascinating, and recyclable adsorbent for the effective elimination of nitrate ions across aqueous solutions and wastewater.