玉米秸秆对Cr(Ⅵ)的生物吸附及热力学特征研究

Biosorption of Cr(Ⅵ) by corn stalk biomass:thermodynamics and mechanism

以玉米秸秆粉为吸附剂,通过批实验讨论了玉米秸秆粉对Cr(Ⅵ)的去除率、体系初始pH值、吸附剂用量和温度等对水溶液中Cr(Ⅵ)吸附的影响,并讨论了Cr的化学形态变化和吸附过程的热力学特征.结果表明,向50mL浓度为50mg.L-1的Cr(Ⅵ)溶液中加入0.5g玉米秸秆粉,于25℃、200r.min-1、pH1.0的条件下恒温震荡3h,玉米秸秆粉对溶液中Cr(Ⅵ)的去除率达97.77%,吸附过程伴随着氧化还原反应的发生.随着体系温度的升高,玉米秸秆粉对Cr(Ⅵ)的吸附量增加.用Langmuir、Freundlich和Dubinin-Radushkevick模型对吸附等温线进行拟合,发现Langmuir模型能更好地反映吸附过程特征,在298K时最大吸附量为14.46mg.g-1.对吸附热力学参数ΔG0、ΔH0和ΔS0的计算表明,吸附过程是吸热的自发过程.最后结合FTIR和SEM谱图,对吸附机理进行了探讨.研究发现,玉米秸秆粉对Cr(Ⅵ)同时存在吸附和还原能力,玉米秸秆粉是具有吸附污水中铬能力和潜在利用价值的生物质吸附剂.

Corn stalk powder was used as a biosorbent for Cr（Ⅵ） aqueous solution to investigate its Cr（Ⅵ） removal capacity. The effect of experimental parameters, such as pH, sorbent dosage and temperature were examined and the optimal experimental conditions were determined. The results showed that reduction of Cr（Ⅵ） to Cr（Ⅵ） occurred during the adsorption process and 97.77% of Cr（Ⅵ） was removed by adding 0.5 g corn stalk powder into 50 mL solution which contained 50 mg·L^-1 Cr（Ⅵ） under pH 1.0, 30℃, 200 r·min^-1 and 3 h contact time. The adsorption capacity increased with temperature. Langmuir, Freundlich and Dubinin-Radushkevick isotherms were used to fit the adsorption equilibrium data and the adsorption process followed the Langmuir isotherm adsorption model. The adsorption capacity of the biosorbent was 14.46 mg·g^-1, which is higher or comparable to the adsorption capacity of various adsorbents reported in the literature. Thermodynamic parameters of the adsorption process, such as ΔG^0、ΔH^0 and ΔS^0, were calculated and the results indicated that the overall adsorption process was endothrmic and spontaneous. Finally, the removal mechanism is discussed by deduction from the experimental results, FTIR, and SEM images. The adsorption of Cr（Ⅵ） coexists with the redox process, and the corn stalk powder is a potential biosorbent which could be used in treatment of chromium contaminated wastewater.