碳化温度对稻壳生物炭的影响及其对Cr(Ⅵ)的吸附性能

Properties of Rice Husk Biochar Produced Under Different Carbonization Temperature and Its Sorption Capability to Cr(Ⅵ)

以稻壳为原料,在不同的温度(300,500和700℃)下采用限氧碳化法制备了生物炭,并利用扫描电镜(SEM)和红外光谱(FTIR)表征了生物炭的结构和性质,同时考察了pH值对生物炭吸附的影响,初步探讨了吸附机理。结果表明,制备的生物炭官能团种类和总量相近,均含有烷基、芳香基及一些含氧官能团,随着碳化温度的升高芳香族化合物增加,芳香化程度增强。试验条件下稻壳生物炭(RH700)对Cr(Ⅵ)的饱和吸附量达到16.68 mg/g,降低pH值有利于对Cr(Ⅵ)的吸附。稻壳生物炭等温吸附曲线更符合Langmuir模型,对吸附过程中焓(△H)、熵(△S)和吉布斯自由能(△G)的计算表明,稻壳生物炭对Cr(Ⅵ)的吸附是自发的吸热反应,其吸附行为更符合伪二级动力学模型,拟合的qe值与实测值相差小于0.38 mg/g。颗粒内扩散表明膜扩散和颗粒内扩散共同控制着吸附过程。

Biochar from rice husk was also obtained and prepared under different pyrolysis temperatures of 300 ℃,500 ℃,and 700 ℃ in an oxygen-limited condition. The structure and properties of the rice husk biochar were characterized by SEM and FTIR,the effects of pH value on the adsorption behaviors were investigated and the adsorption mechanisms were initially discussed. Results showed that the total quantity of surface oxygen-containing functional groups in biochar under different temperatures was similar,all containing alkyl group,aromatic group and some oxygen containing functional groups and aromatic compounds increased with the increase of carbonization temperature.The maximum adsorption capacity of the RH700 biochar could reach 16. 68 mg/g under experimental conditions and the reduction of pH value was conducive to Cr（VI） adsorption. The adsorption isotherms corresponded well with the Langmuir equation. ΔH,ΔS,ΔG indicated that the two adsorptions were a spontaneous endothermic reaction and the pseudo-second order kinetic desorption model provided a better pseudo-first order kinetic data fitting,wherein the desorption capacity difference is smaller than 0. 38 mg/g between the desorption capacity calculated by the model and actual measurement. The intraparticle diffusion was influenced and controlled mainly by the film and internal diffusions.