Enhanced adsorption of phosphate from pickling wastewater by Fe-N co-pyrolysis biochar: Performance, mechanism and reusability

A one-step method of preparation using a novel nitrogen (N)-doped Fe-rich biochar (N5-CB) resulted in a maximum adsorption capacity (314.52 mg/g) compared with Fe-rich biochar (CB, 104.044 mg/g). It can be used to adsorb phosphate (P) efficiently. Additionally, the adsorption kinetics, isotherms, and thermodynamics indicated that the adsorption of P onto N5-CB was mainly mediated via multilayer coverage, endothermic, spontaneous, and physical mechanisms. The main adsorption mechanisms include Fe-P precipitation, FeOP bonding, and electronic effect. Further, the highly active Fe-Nx sites and graphitic N induced by N doping were the dominant driving force underlying enhanced P adsorption. Active Fe-Nx sites resulted in a positively-charged carbon structure and P absorption via electrostatic effect. Based on the simple method of pyrolysis, N5-CB can be used in P removal from pickling wastewater with excellent adsorption capacity and remarkable recyclability.