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.