Synthesis and development of Fe₃O₄/SiO₂/CaCO₃ nanocomposite adsorbents for ammonia adsorption in the shrimp pond waste

We developed a Fe₃O₄/SiO₂/CaCO₃ magnetic nanocomposite adsorbent, with SiO₂ synthesized from sea sand and CaCO₃ derived from coral skeletons. The Fe₃O₄/SiO₂/CaCO₃ nanocomposite was characterized and employed as an adsorbent to reduce ammonia levels in shrimp pond wastewater where ammonia concentrations ranged from 11.9 to 38.8 mg/L. We further explored the effects of various parameters on the removal efficiency, adsorption capacity, thermodynamics, isoterm, and kinetics of the adsorption process. Specifically, we examined the influence of pH (3–8), adsorbent mass (0.025–0.25 g), temperature (27–60 ℃), and contact time (10–120 min). Ammonia concentrations in the filtrate were measured using the Nessler method. The synthesis of CaCO₃ from coral skeleton, SiO₂ from sand, and Fe₃O₄/SiO₂/CaCO₃ adsorbent was successfully achieved, as confirmed by XRF, FTIR, and XRD characterizations. The adsorption process adhered to the second-order kinetics model, exhibited spontaneous behavior with a negative ΔG value, and followed the Langmuir isotherm model (R² = 0.9267). The results indicated an optimal adsorbent mass of 0.025 g, achieving 89.3% adsorption at 60 minutes of contact time, a temperature of 27 ℃, and an optimal pH of 5. When applied to shrimp pond wastewater, the Fe₃O₄/SiO₂/CaCO₃ adsorbent demonstrated an adsorption efficiency ranging from 52.1% to 86.8% and an adsorption capacity between 6.2 and 30.9 mg/g.