Dephosphorization using ceramsites modified by coprecipitation with FeSo4 and KMnO4 and high-temperature combustion

Abstract

Water eutrophication can be controlled through phosphorus adsorption. Herein, ceramsites were used as carriers and FeSo4 and KMnO4 as modifiers to create superior adsorbents for phosphorus. After coprecipitation with the modifiers, various types of adsorbents were prepared by high-temperature combustion. The modification process increased the Langmuir specific surface areas of the ceramsites, which correlated well with the theoretical maximum saturation adsorption amount (R2= 0.9275). Phosphorus adsorption by the modified ceramsites was consistent with the Langmuir isothermal adsorption model. The FeSo4-, KMnO4-, and FeSo4+KMnO4—modified ceramsites exhibited maximum saturation adsorption capacities of 2.444, 1.538, and 2.751 mg/g, respectively, while that of the untreated ceramsites was 1.182 mg/g. The results show that dense nanoparticles of Fe2O3 and (Fe0.67Mn0.33)OOH formed on the FeSo4+KMnO4-modified ceramsites. The main phosphorus absorption mechanism was the replacement of hydroxyl groups by phosphate on the Fe-Mn oxide surfaces to form a monodentate and bidentate complex.The modified ceramsites had lower phosphorus desorption rates, which increased as the initial phosphorus concentration increased. The pseudo-second-order kinetic model was capable of accurately describing the phosphorus adsorption kinetics of the modified ceramsites. At higher reaction temperatures, the initial adsorption rates (IARs) of various types of ceramsites were increased. Additionally, the modified ceramsites had larger IARs than the untreated ceramsite under similar temperature conditions. An analysis of the adsorption thermodynamics showed that phosphorus adsorption via ceramsites was a spontaneous and endothermic process.