Biochar-supported magnesium oxide as high-efficient lead adsorbent with economical use of magnesium precursor

With unique porous structure inherited from lignocellulose, biochar was an appropriate carrier for small-size MgO materials, which could simplify the synthetic process and better solve agglomeration and separation problems during adsorption. Biochar-supported MgO was prepared with impregnation method. Under different synthesis conditions, the obtained MgO presented diverse properties, and moderate pyrolysis condition was conducive to the improvement of Mg conversion rate. The Pb(II) capacity was highly correlated with Mg content, rather than the specific surface area. Reducing the pyrolysis temperature or increasing the usage of supporter could improve adsorption efficiency when using Mg content-normalized capacity as the criterion. The better release ability of Mg, contribute by the higher extent of hydration and better spread of MgO, were the critical factors. The maximal Mg content-normalized capacity could reach 0.932 mmol·mmol-Mg⁻¹ with the mass ratio of biochar/MgCl₂·6H₂O = 4:1 at the pyrolysis temperature of 600 °C. Considering the ultimate utilization efficiency of Mg in precursor, the optimum Mg consumption-normalized capacity was 0.744 mmol·mmol-Mg⁻¹ with the mass ratio of biochar/MgCl₂·6H₂O = 1:1 at 600 °C.