Enhanced Cr(VI) removal from acidic solutions using biochar modified by FeO@SiO-NH particles.

FeO@SiO-NH magnetic particles with core-shell structure were attached on carboxylated biochar derived from phoenix tree leaves to synthesize a novel magnetic biochar for removing Cr(VI) ions from acidic solutions. FSEM, FTEM, XRD characterizations of the synthesized magnetic biochar revealed that the FeO@SiO-NH magnetic particles distributed uniformly on the surface or macrospores of carboxylated biochar by strong chemical bonding. The Cr(VI) ions adsorption capacity of magnetic biochar was 27.2mg·g, surpassing original carboxylated biochar (18.2mg·g). VSM and XPS characterizations demonstrated that the attached FeO@SiO-NH magnetic particles not only endowed biochar with perfect magnetic property (23emu·g) but also provided complexing sites for binding Cr(III) cations reduced from Cr(VI) anions. The Cr(VI) ions removal by magnetic biochar contained three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The adsorption recycling test showed that magnetic biochar kept 85% of its initial Cr(VI) adsorption capacity at the sixth cycle, and the Fe leakage under pH1.0 was smaller than 0.25mg·L. The results indicated that this novel magnetic biochar was applicable for the practical treatment of Cr(VI)-containing wastewater.