Production and characterization of cost-effective magnetic pine bark biochar and its application to remove tetracycline from water

Low-cost adsorbent, pine bark biochar (PBB) from the forest residue, was produced and applied to remove tetracycline (TC) from aqueous solution via adsorption pathway. The PBB, hence obtained, was modified using aqueous ferric and ferrous ion solutions to obtain magnetic pine bark biochar (M-PBB). Batch adsorption experiments were conducted to examine the adsorption of TC by PBB and M-PBB in the variation of pH, contact time, dosage, and temperature. The adsorbents were characterized by SEM/EDX, TGA, and pHpzc. The adsorption mechanism was evaluated by fitting Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherms model. Also, the experimental data were analyzed by kinetics models (pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich) and thermodynamics. The maximum adsorption capacity (qm) of M-PBB was 15.3 mg/g from the experiment at pH 6. A high correlation coefficient (R2 ≈ 0.9) of Freundlich isotherm postulated multi-layer adsorption of TC on M-PBB at pH 6. The kinetic studies showed that the pseudo-first-order was more suitable for representing the adsorption of TC molecules on the surface. The thermodynamic analysis was showed that the adsorption process is favorable, spontaneous, and endothermic at studied temperatures. M-PBB demonstrated a potential for removal of TC from water as a low-cost and convenient adsorbent.