Efficient adsorption and mechanistic analysis of phosphorus in acid leaching solution of incinerated sewage sludge ash by zirconium-modified reed biochar

Resource recovery of phosphorus (P) from incinerated sewage sludge ash (ISSA) was achieved by wet chemical leaching and selective adsorption of biochar material. Sulfuric acid was used to extract P from ISSA to obtain a Prich solution with a leaching rate of 96.56 %. Zirconium-modified reed biochar (Zr-RB) was prepared by impregnation method, which could efficiently and selectively recover P from acid leaching solution with high adsorption efficiency of more than 99 %. Three adsorption kinetic models and four adsorption isotherm models were fitted to the batch adsorption experimental data, and it was found that the quasi-second kinetic model and the Freundlich model as well as the Redlich-Peterson model could better describe the adsorption of P by Zr-RB. It showed that the adsorption of P by Zr-RB was an easily occurring adsorption process dominated by multilayer adsorption and nonuniform adsorption, supplemented by monolayer and uniform adsorption. Calculations of surface adsorption energy, molecular electrostatic potential and spin-polarized molecular orbitals based on material characterization and density functional theory (DFT) were carried out to explore the interaction mechanism of Zr-RB adsorption on P involving surface precipitation, pore filling and ligand exchange. In addition, Ca5(PO4)3(OH) product with a P bioavailability rate of 80.17 % was generated from the recovered P. In conclusion, the effective recovery of P from ISSA and the use of Zr-RB as an efficient P adsorbent have broad application prospects.