[Phosphorus Enrichment Efficiency of CaO₂@FA Composites and the Effect of Its Recovered Material on Soil Improvement]

To explore the resource utilization of phosphorus (P) in wastewater and industrial waste fly ash, we used an efficient composite material (CaO₂@FA) for phosphorus removal by loading nano-CaO₂ on the surface of fly ash as well as in the pores using the surface precipitation method. The results showed that the material had a larger specific surface area and porosity after loading CaO₂ on the fly ash surface. The specific surface area increased to 4.641 m²·g^-1, and the total pore volume was up to 0.025 cm³·g^-1. The adsorption process of CaO₂@FA on P could be described using the Langmuir isothermal adsorption model, and its maximum adsorption capacity was 185.776 mg·g^-1(20℃). The adsorption mechanism was attributed to chemical precipitation, mainly the formation of calcium hydroxyphosphate. The enrichment efficiency of CaO₂@FA composites on P was significantly higher than that of fly ash, and the efficiency was increasing with the increase in the dosage added. HCO^3- and CO₃^2- in the coexisting ions had a negative effect on P adsorption by the composites. The enrichment rate of P in domestic wastewater was up to 93% when the dosage of CaO₂@FA composites was 2.0 g·L^-1. The content of biological P in the recovered precipitates reached 1.658 mg·g^-1. The soil improvement test showed that the biological P content in soil increased by 102.9% when the recovered precipitates were added into the soil. This indicated that the operating cost of recovering 100 mg of P by this composite was as low as 0.76 yuan.