A novel strategy for preparing porous Fe/Ca-loaded biochar transformed from municipal sludge towards phosphate removal

The removal of phosphate from wastewater has gained much attention, and the cost-effective adsorbent with great performance is still a urgent need. In this study, a Fe/Ca-loaded biochar composite adsorbent (gBC600-4B) was obtained by simply mixing iron oxide, calcium oxide, and municipal sludge followed by co-pyrolysis. A high specific surface area (SSA) of the gBC600-4B was detected to be 160.79 m2/g with a porous structure, which was mainly attributed to the washing after pyrolysis. The phosphate removal efficiency of gBC600-4B was determined to be 97.97 % with a phosphate adsorption max capacity of 2.414 mg/g. Combining the pseudo-secondorder kinetic model, Sips isothermal adsorption model, and thermodynamic analysis, it was determined that the phosphate adsorption process is endothermic, spontaneous, and involves monolayer chemisorption. The main adsorption mechanisms included electrostatic attraction, hydrogen bonding, chemical precipitation, and monodentate and bidentate coordination between phosphate and FeOOH, leading to an effective phosphate adsorption. The gBC600-4B exhibited an outstanding regeneration capability and stability, which maintained a removal efficiency of 74.39 % and desorption rate of 86.73 % even at fifth adsorption cycles. Nearly 90 % of phosphate could be removed by the gBC600-4B with the presence of the co-existence ions, demonstrating its strong anti-interference capability. A novel and cost-effective strategy for adsorbent preparation through waste biomass in this study, revealing the key role of the porous structure and the adsorption capacity of biochar with metal oxides.