热解温度对黑碳阳离子交换量和铅镉吸附量的影响

Effects of Pyrolytic Temperature on Cation Exchange Capacity and Pb^(2+) and Cd^(2+) Sorption of Black Carbon

为探讨热解温度对秸杆燃烧物提取黑碳阳离子交换量和重金属吸附量的影响,在150～500℃范围24h热解小麦秸秆,提取黑碳,测定黑碳阳离子交换量(CEC)和黑碳吸附铅(Pb2+)和镉(Cd2+)量。结果表明,黑碳的CEC远低于矿物和腐植酸的,黑碳吸附Pb2+和Cd2+量也远低于矿物和腐植酸。Langmiur吸附方程能较好地描述黑碳对Pb2+和Cd2+的吸附.热解温度相同时,黑碳对Pb2+的最大吸附量显著大于对Cd2+的。热解温度由150上升到300℃时,黑碳CEC及黑碳吸附Pb2+和Cd2+量显著增大;热解温度由300上升到500℃时,黑碳CEC及黑碳吸附Pb2+和Cd2+量显著降低;黑碳CEC及黑碳吸附Pb2+和Cd2+量按如下热解温度顺序降低:300℃>400℃>500℃>250℃>150℃,这与热解中黑碳极性基团含量随热解温度的变化显著相关。

To study the effects of pyrolytic temperature on the cation exchange capacity （CEC） of the crop-residue-derived black carbon （BC） and the Pb^2＋ and Cd^2＋ sorption on BC, the BC was isolated from the charred wheat residues by pyrolyzing the wheat residues under the oxygen-limited conditions for 24 h at 150, 250, 300, 400 and 500 ℃（2 respectively. The CEC of BC was determined by the CH3COONa replacement, the Pb^2＋ and Cd^2＋ sorption on BC was tested by the batch equilibrium sorption. The CEC of BC was very small and much lower than those of minerals and humic materials, therefore the sorption amounts of Pb^2＋ and Cd^2＋ on BC were much lower than those of minerals and humic materials respectively. The Pb^2＋ and Cd^2＋ sorption on BC fitted with the Langmiur equation very well. The maximal sorption amount of Pb^2＋ on BC was much higher than that of Cd^2＋ at the same pyrolytic temperature. When the pyrolytic temperature increased from 150 ℃ to 300 ℃, the CEC of BC and the Pb^2＋ and Cd^2＋ sorption on BC increased significantly, while, which decreased significantly when the pyrolytic temperature increased from 300 to 500 ℃. Furthermore, the CEC of BC and the Pb^2＋ and Cd^2＋ sorption on BC changed with the pyrolytic temperature following the order. 300 ℃〉400 ℃〉500 ℃〉250 ℃〉150 ℃, which significantly correlated with the variation of the polar-group content on BC during the pyrolysis while changing the pyrolytic temperature.