Phosphorus adsorption mechanism from water by magnesium/calcium salt impregnated biochar

In recent years, excess phosphorus (P) discharged into surface water has caused environmental pollution.Therefore, the removal and recovery of phosphate are urgent needs that need to be developed.Biochar derived from macadamia shell impregnated with Ca (or Mg) was prepared to evaluate the adsorption and recovery of P from water.Batch adsorption experiments were performed to determine the optimal conditions for the adsorption process (initial pH, adsorbent dosage) and the adsorption mechanism of P on the material based on adsorption isotherm equilibrium, adsorption kinetics and FTIR spectral structure analysis.The results showed that Bio 300Mg and Bio 300Ca both exhibited high P adsorption and recovery capacities, with P adsorption capacities reaching 36 and 39 mg g -1 , and recovery efficiencies reaching 87.6 and 97.0%, respectively, at 10 g L -1 of Bio 300Ca and Bio 300Mg, initial P concentration of 400 mg L -1 and an initial pH of 4. The Freudlich isotherm model and pseudo-secondorder kinetic model were used to explain the P adsorption mechanisms of the two materials.The main interaction mechanisms included: (1) electrostatic interactions, (2) hydrogen bonding, and (4) chemical co-precipitation and chemical precipitation.These results provide valuable insights for the development of efficient and environmentally friendly P-recovery biochar materials for reuse in agriculture.