A new strategy for enhanced phosphate removal from waters using ferric oxide impregnated biochar

Abstract

To overcome application limitation of the available biochar-based metallic oxide composites for the removal of anionic pollutants like phosphate, a new strategy was proposed that metallic oxide was anchored in the positively charged biochar, acquired by introducing high-density quaternary ammonium groups. The resultant nanocomposite adsorbent Fe@N-BC exhibited high adsorption speed, capacity and preference to phosphate. In the existence of competing anion Cl- at higher levels, Fe@N-BC possessed 3–5 times greater working adsorption capacity of phosphate than a commercial phosphate adsorbent D201 and the mixture of ferric oxide and N-BC with the same proportion as the composite. Fixed-bed adsorption runs of Fe@N-BC could treat ∼ 194 bed volumes (BV) of a synthetic phosphate-polluted wastewater before breakthrough achieving (<0.1 mg P/L in effluent), about 7.46 times greater than that of D-201. The saturated Fe@N-BC could be thoroughly regenerated with 10 % NaOH solution for repeated use with negligible loss of adsorption capacity and ferric. The specific inner-sphere complexation between phosphate and the immobilized ferric oxide was proven to the dominant pathway for preferable adsorption of phosphate onto Fe@N-BC. The obviously enhanced removal of phosphate by Fe@N-BC was ascribed to the introduced quaternary ammonium groups in N-BC, which triggered the dispersion of the impregnated ferric oxide nanoparticles (with sizes of 8.8 ± 1.0 nm) and Donnan member effect. Besides, Fe@N-BC was preliminarily proven to have no biotoxicity. This study can shed new light on how to expand the application of the traditional biochar-based composites to the decontamination of anionic pollutants.