Preparation of nitrogen doped magnesium oxide modified biochar and its sorption efficiency of lead ions in aqueous solution.

A N-doped couping MgO-modified biochar (MgO-N-BC) was synthesized from corncob-to-xylose residue by two-step slow pyrolysis method. The biochar exhibited a remarkable Pb(II) sorption capacity (maximum 1429 mg·g-1) in aqueous solution. The sorption of Pb(II) onto MgO-N-BC best fitted Freundlich model and pseudo-second-order equation. Further analysis demonstrated the final product of Pb were mainly hexagonal crystal hydrocerussite flakes. The combine of ion-exchange and precipitation process play key role in the sorption of Pb(II), while interactions between Pb(II) and functional groups work, too. The sorption capacity decreased by 63.5% with CO2 free, however over supply of CO2 effects little on the sorption capacity while that can shorten equilibrium time from near 360 min to about 30 min. Only few co-existing ions such as Ba2+ and Fe3+ can decrease the sorption partly, and NH4+ block the sorption obviously, while Mg2+ had an enhancement effect.