Enhanced phosphate adsorption on Ca-Mg-loaded biochar derived from tobacco stems.

Tobacco stems were used as precursors to prepare biochars (YGs) and develop Ca-Mg-loaded biochars (CMYGs) to enhance phosphate adsorption from aqueous solutions. Some influencing factors, such as pH, adsorption time, temperature, and structure characterization, were investigated. Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns showed several new peaks, indicating that Mg(OH) and MgO have been present on the surface of the CMYGs. The adsorption could reach equilibrium in 100 min reaction. The equilibrium data were well described by the Langmuir and Freundlich model. After five recycles, the phosphate removal capacity of CMYGs biochar retained over 50%. Moreover, the XRD and FTIR analyses showed that the phosphate sorption mechanisms involved surface electrostatic attraction, inner-sphere complexation and precipitation reactions. Overall, the soaking method could be used to effectively load Mg onto the surface of YGs. The CMYGs synthesized at 750 °C is a promising adsorbent for phosphate removal with a high adsorption capacity for phosphate-polluted wastewater.