Magnetic spent bleaching earth carbon (Mag-SBE@C) for efficient adsorption of tetracycline hydrochloride: Response surface methodology for optimization and mechanism of action.

The utilization of spent bleaching earth (SBE)-based materials for adsorption of pollutants from water and wastewater has received growing attention. In this work, a comparative study of magnetic spent bleaching earth carbon (Mag-SBE@C) and spent bleaching earth carbon (SBE@C) was performed to remove tetracycline hydrochloride (TCH) from aqueous solutions. Mag-SBE@C exhibits the larger adsorption capacity (0.238 mmol/g) obtained by the Langmuir model than the original SBE@C (0.150 mmol/g). The adsorption process fits well with the pseudo second-order model and is found to be exothermic (ΔH < 0) and spontaneous (ΔG < 0). The optimal adsorption conditions (Mag-SBE@C dose 2.217 g/L, initial TCH concentration 0.113 mmol/L, initial solution pH 6.533) predicted by the response surface methodology (RSM) are consistent with the actual verification results. The inhibition extents of coexisting cations are ranked in a decline: Al > Cu > Fe > Mg > K > Na. Various characterization results indicate that the adsorption mechanism of TCH by Mag-SBE@C likely includes the π-π interactions, hydrogen bonding, electrostatic interactions, π-cations interactions, FeN covalent bonding, and changes in physical and chemical properties. Mag-SBE@C is easily solid-liquid separated using magnetic field, and can be potentially reused for 13 times before completely losing its activity, exhibiting great potential to antibiotics elimination.