Optimization of preparation of modified fly ash ceramsite by response surface method and its removal mechanism of iron in acid mine wastewater

In order to solve the problem of iron ion pollution in acid mine drainage ( AMD ) and the high cost and poor adaptability of traditional treatment technology, this study takes ' waste to waste ' as the core, and uses fly ash from thermal power plants to prepare modified ceramsite adsorption materials. Through batch experiments, response surface optimization experiments based on central composite design and various characterization techniques, the iron removal performance and mechanism were systematically explored. The results showed that the specific surface area of the modified fly ash ceramsite increased from 1.68 m²/g to 21.13 m²/g, and the pore volume and pore size were significantly improved, which provided sufficient active sites for iron ion adsorption. The optimal single factor conditions determined by batch experiments were particle size of 2 mm, solid-liquid ratio of 100 g/L, and reaction time of 240 min. At this time, the iron removal rate reached 99.28%. The response surface optimization further revealed the interaction between key parameters. The optimal process conditions were determined as solid-liquid ratio 115 g/L and reaction time 235 min. The measured iron removal rates were 98.63%, 97.89% and 99.47%, respectively, which were highly consistent with the model predicted value ( 99.76% ). Through a series of characterization methods, it was confirmed that the iron removal mechanism of ceramsite was mainly oxidation precipitation, supplemented by the synergistic effect of electrostatic attraction, ion exchange and surface complexation. After the enrichment of Fe²⁺ by electrostatic interaction, the alkaline substances such as Ca²⁺ in ceramsite were ion exchanged and dissolved, forming a local high pH microenvironment on the surface of the particles, and then most of Fe²⁺ was oxidized to Fe³⁺, and finally goethite (α-FeOOH) precipitate was formed. This study provides theoretical support and practical reference for the high-value utilization of fly ash and the low-carbon and efficient treatment of AMD.