Synthesis of novel magnesium ferrite (MgFe2O4)/biochar magnetic composites and its adsorption behavior for phosphate in aqueous solutions

- Magnesium ferrite/biochar magnetic composites (MFB-MCs) have been synthesized.
- MFB-MCs exhibited superior removal performance than either biochar or MgFe2O4 alone.
- The phosphate adsorption follows an inner-sphere coordination mechanism.
- Kinetic and isotherm results indicate the physisorption and endothermic in nature.
- MFB-MCs could be separated magnetically and regenerated effectively.

In this work, magnesium ferrite (MgFe2O4)/biochar magnetic composites (MFB-MCs) were prepared and utilized to remove phosphate from aqueous solutions. MFB-MCs were synthesized via co-precipitation of Fe and Mg ions onto a precursor, followed by pyrolysis. Characterization results confirmed that MgFe2O4 nanoparticles with a cubic spinel structure were successfully embedded in the biochar matrix, and this offered magnetic separability with superparamagnetic behavior and enabled higher phosphate adsorption performance than that of pristine biochar and sole MgFe2O4 nanoparticles. Batch experiments indicated that phosphate adsorption on the MFB-MCs is highly dependent on the pH, initial phosphate concentration, and temperature, while it was less affected by ionic strength. Analysis of activation and thermodynamic parameters as well as the isosteric heat of adsorption demonstrated that the phosphate adsorption is an endothermic and physisorption process. Lastly, highly efficient recyclability of the MFB-MCs suggested that they are a promising adsorbent for phosphate removal from wastewater.

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