玉米秸秆和玉米芯生物炭对水溶液中无机氮的吸附性能

为探明玉米秸秆和玉米芯生物炭对水溶液中无机氮的吸附性能,研究了其对NH₄⁺-N、NO₃^--N和NO₂^--N的吸附动力学过程;并用等温吸附模型对NH₄⁺-N和NO₃^--N的吸附过程进行拟合,探讨制得生物炭对无机氮的吸附机理.结果表明,400℃和600℃制得玉米秸秆和玉米芯生物炭均呈碱性,表现为400℃ < 600℃;同种原材料,与400℃制得生物炭相比,600℃制得生物炭碱性含氧官能团数量较多,而酸性含氧官能团数量较少.400℃制得生物炭对NH₄⁺-N的吸附能力较强(玉米秸秆和玉米芯生物炭的平衡吸附量分别为4.22和4.09mg/g);而600℃制得生物炭对NO₃^--N和NO₂^--N的吸附能力较强(玉米秸秆和玉米芯生物炭对NO₃^--N的平衡吸附量分别为0.73和0.63mg/g;对NO₂^--N的平衡吸附量分别为0.55和0.35mg/g).与NO₃^--N和NO₂^--N相比,玉米秸秆和玉米芯生物炭对NH₄⁺-N的吸附能力更强,4种生物炭对NH₄⁺-N的平衡吸附量是NO₃^--N/NO₂^--N的4.29~20.2倍.等温吸附模型拟合研究表明,玉米秸秆和玉米芯生物炭对水溶液中NH₄⁺-N和NO₃^--N的吸附过程均可用Freundlich模型描述,其在生物炭表面的吸附是多分子层吸附.

The adsorption characters of inorganic nitrogen in aqueous solution by maize straw- and corn cob-derived biochars

In order to explore the adsorption characters of inorganic nitrogen in aqueous solution by maize straw- and corn cob-derived biochars, the adsorption kinetics of NH₄⁺-N, NO₃^--N and NO₂^--N were studied. The adsorption processes of NH₄⁺-N and NO₃^--N were fitted by Langmuir and Freundlich isothermal adsorption models, and the adsorption mechanisms were also elucidated. The results showed that the maize straw- and corn cob-derived biochars produced at 400℃ and 600℃ were both alkaline (400℃ < 600℃). As for the same raw material, the biochar produced at 600℃ showed relatively higher alkaline oxygen-containing functional group content and lower acidic oxygen-containing functional group content compared with the biochar produced at 400℃. The biochars produced at 400℃ had a stronger adsorption capacity to NH₄⁺-N (the equilibrium adsorption amounts of maize straw- and corn cob-derived biochars were 4.22 and 4.09mg/g, respectively). However, the biochars produced at 600℃ had a stronger adsorption capacity to NO₃^--N and NO₂^--N (for NO₃^--N: the equilibrium adsorption amounts of maize straw- and corn cob-derived biochars were 0.73 and 0.63mg/g, respectively; for NO₂^--N: 0.55and 0.35mg/g, respectively). Compared to NO₃^--N and NO₂^--N, all the four kinds of biochar showed stronger adsorption capacity to NH₄⁺-N, and the equilibrium adsorption amounts of NH₄⁺-N were 4.29~20.2 times more than NO₃^--N/NO₂^--N. The isothermal adsorption model study showed that the adsorption of NH₄⁺-N and NO₃^--N in aqueous solution by maize straw- and corn cob-derived biochars could be described by Freundlich model, and the multi-layer adsorption was the major adsorption mechanism.