Preparation of plane trees' bark biochar/ZnAl-LDH and its adsorption performance for phosphate and recovery

Biochar is an excellent adsorbent for organic pollutants, but the removal effect for inorganic phosphorus is not satisfactory. In order to improve its phosphorus removal effect, ZnAl-LDH modified plane trees' bark biochar was presented in this paper. The plane trees' bark biochar was prepared by chemical-activation method by utilizing K₂CO₃ as the activation agent. And then, ZnAl-LDH modified biochar was prepared by in-situ co-precipitation method with ammonia as the precipitate agent. As the sample was as little as 10 mg, the adsorption ratio was about 93% for the 25 mL of 20 mg/L PO₄^3-. The saturated adsorption capacity for PO₄^3- was 103.1 mg/g, calculated by Langmuir equation, revealing the adsorption was mainly mono-molecular layer adsorption. The possible adsorption mechanism of phosphate mainly contained interlayer anion exchange, surface complexion and ligand exchange. Moreover, the absorbed sample were soaked in 5.5% Na₂CO₃ solution for phosphate desorption, nearly 60% of the absorbed phosphate could be recovered and may reuse in the future.