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摘要
In order to clarify the contributions of different nitrogen species of nitrogen-rich biochars in their adsorption for heavy metals, three nitrogen-rich biochars with different nitrogen configurations (Pr-NBC with pyrrolic nitrogen, Pd-NBC with pyridinic nitrogen and Gp-NBC with graphitic nitrogen) were prepared by pyrolysing corn straw with urea. Results of adsorption kinetics and adsorption isotherms showed that the adsorption of Pb(II) and Cr(VI) by nitrogen-rich biochars were dominated by chemical adsorption. The adsorption capacity for Pb(II) was directly proportional to the ionic strength of the solution, which indicated that the adsorption may be dominated by the formation of inner complexes. Cr(VI) can be removed by nitrogen-rich biochars through adsorption and reduction. The adsorption capacity for heavy metals was greatly affected by pH, revealed that electrostatic attraction may be the main driving force. Characterization of materials before and after adsorption showed that nitrogen-rich biochars mainly removed Pb(II) through electrostatic attraction, cation exchange, precipitation and cation-π bond interaction, while Cr(VI) was adsorbed by electrostatic attraction and partially reduced to Cr(III). The roles of different nitrogen species on the adsorption were quite different. Specifically, graphitic nitrogen mainly promoted adsorption by forming cation-π bond with Pb(II). Pyrrolic nitrogen and pyridinic nitrogen reduced Cr(VI) into Cr(III) to achieve attenuation. To assess the interaction between nitrogen-rich biochars and heavy metals in the environment accurately, the influences of nitrogen configurations should be fully considered. ? 2021, Science Press. All right reserved.
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