Removal of arsenate from contaminated waters by novel zirconium and zirconium-iron modified biochar.

A novel biochar metal oxide composite was synthesized for effective removal of arsenate (As(V)) from aqueous solution. The materials synthesized for As(V) removal was based on a biosolid-derived biochar (BSBC) impregnated with zirconium (Zr) and zirconium-iron (Zr-Fe). The synthesized materials were comprehensively characterized with a range of techniques including Brunauer-Emmett-Teller (BET-N2) surface area, zeta potential, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results confirmed that loading of Zr and Zr-Fe onto the biochar surface was successful. The influence of pH, biochar density, ionic strength, As(V) dose rate, major anions and cations on As(V) removal was also investigated. Under all pH and reaction conditions the Zr-Fe composite biochar removed the greatest As(V) from solution of the materials tested. The maximum sorption capacity reached 15.2 mg/g for pristine BSBC (pH 4.0), while modified Zr-BSBC and Zr-FeBSBC composites achieved 33.1 and 62.5 mg/g (pH 6), respectively. The thermodynamic parameters (Gibbs free energy, enthalpy, and entropy) suggested that the adsorption process is spontaneous and endothermic. The ZrBSBC and Zr-FeBSBC showed excellent reusability and stability over four cycles. Unmodified biochar resulted in partial reduction of As(V) under oxic conditions, whilst modified biochars did not influence the oxidation state of As. All results demonstrated that the Zr and Zr-Fe BSBC composites could perform as promising adsorbents for efficient arsenate removal from natural waters.