Probing the efficiency of magnetically modified biomass-derived biochar for effective phosphate removal

Characterization of the driving forces for effective and economical phosphate (PO₄^3-) removal from wastewater by using magnetically modified biochar was performed in this study. The biochar produced from slow pyrolysis of local agricultural biomass (wood and rice husks) were magnetically modified by co-precipitation of Fe(II) and Fe(III) ions in their presence. The surface characteristics before and after modification and their efficacy for PO₄^3- sorption, and desorption were compared. Results show that, even though magnetic biochar surface modification slightly decreased their surface area, PO₄^3- adsorption to the modified biochars was almost double (25-28 mg g^-1) than that to the raw biochar (12-15 mg g^-1). The adsorption isotherm of raw biochars was better simulated via the Langmuir model, while that of modified biochars was better fitted to the Freundlich model. Moreover, the integrated analysis by XRD, EDX, and FTIR show that PO₄^3- sorption to modified biochars could be attributed to the simultaneously-occurring electrostatic attraction, surface precipitation, and ligand exchange. While the electrostatic attraction was dominant in the presence of unmodified biochars. The regenerated modified biochars retained substantial PO₄^3- adsorption capacity up to several regeneration cycles. Their high reusability potential leads to the effective and economical phosphate recovery and thus modified biochars could offer a viable strategy for PO₄^3- removal.