Hydroxyapatite and magnetic hydroxyapatite biochar from pine nut husks for anionic azo dye adsorption: Performance and reusability assessment

초록

This study examines the effects of hydroxyapatite (HAP) and magnetic HAP-modified pine nut husk biochar (PB) on the adsorption and removal of anionic synthetic dyes [i.e., Eriochrome Black T (EBT) and Congo Red (CR)]. HAP and magnetic HAP modification significantly improved the pore structure. The removal efficiency of EBT and CR on PB, PBH, and PBH-Fe was as follows: (i) Qmax of EBT: PB = 1.24 mg/g, PBH = 46.06 mg/g, PBH-Fe = 40.77 mg/g, and (ii) Qmax of CR: PB = 1.18 mg/g, PBH = 62.96 mg/g, PBH-Fe = 57.89 mg/g. These results demonstrate that HAP modification substantially enhances the adsorption capacities of EBT and CR. This is because the removal of EBT and CR by PB was primarily governed by hydrogen bonding interactions, whereas adsorption by PBH and PBH-Fe was attributed to electrostatic interactions and ion exchange involving phosphate and calcium components of HAP. In addition, PBH-Fe exhibited a recovery rate exceeding 90 % due to its magnetic properties after the adsorption of EBT and CR. Overall, magnetic HAP modification presents a practical and efficient approach to enhance both the removal and reusability of PB for anionic synthetic dye removal.

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