八宝景天热解动力学特征及其对六价铬的吸附

Kinetic of Hylotelephium erythrostictum pyrolysis and Cr(Ⅵ) adsorption by the derived biochar

植物修复是治理重金属复合污染土壤的一种高效可行的修复方法,八宝景天近年来被应用于植物修复,修复土壤的同时又能美化环境.但修复后的八宝景天含有污染物,需要对其进行有效处理防止二次污染.将八宝景天进行热解制备生物炭,并用于污染物吸附是一种可行的方法.本文考察八宝景天的热解动力学及其生物炭对Cr(Ⅵ)的吸附.由于活化能的波动较大,动力学补偿效应线性关系较差,所以单步反应不能描述其热解速率.热解动力学的复杂性采用基于等转化率的离散分布活化能模型考察,结果显示,模型可以很好地与实验数据拟合;热解液化作用阶段活化能为274 kJ·mol^-1;转化率0.75后热解行为主要为生物炭的二次裂解,占28.8%的权重.生物炭去除Cr(Ⅵ)包括吸附和还原过程,其中吸附速率符合伪二级反应动力学模型.Cr(Ⅵ)去除率随热解温度的升高而降低,400℃下热解的生物炭去除率最高,其等温吸附均符合Langmuir和Freundlich模型,最大吸附量为220.8 mg·g^-1.

Phytoremediation is an efficient and feasible remediation method for the treatment of soil contaminated by heavy metals.Taking the hylotelephium erythrostictum(HE)as a typical example,it has been widely used in phytoremediation in recent years,which can repair the soil and beautify the environment simultaneously.However,the HE used for soil remediation still contains pollutants,which needs to be effectively treated to prevent secondary pollution.Therefore,it is a feasible method to prepare biochar by pyrolysis of HE and use it for pollutant adsorption.In this paper,the pyrolysis kinetics of HE and its derived biochar adsorption performance on Cr(Ⅵ)were investigated in detail.The results showed that the single step reaction could not describe its pyrolysis rate due to the large fluctuation of activation energy and the poor linear relationship of kinetic compensation effect.Afterwards,the complexity of pyrolysis kinetics was investigated by using the discrete distributed activation energy model based on equal conversion rate.The results demonstrated that this model can fit well with the experimental data,and the activation energy of pyrolysis liquefaction stage was 274 kJ·mol^-1.Besides,the pyrolysis behavior after 0.75 conversion rate was mainly the secondary pyrolysis of biochar,accounting for 28.8%of the weight.The removal of Cr(Ⅵ)by biochar prepared by pyrolysis of HE included adsorption and reduction processes,in which the adsorption rate accorded with the pseudo-second-order reaction kinetic model.This resultant biochar on the removal rate of Cr(Ⅵ)along with the rise of pyrolysis temperature was reduced,and the corresponding value reached the highest at 400℃.Finally,its isothermal adsorption conformed to both Langmuir and Freundlich models,with a maximum adsorption capacity of 220.8 mg·g^-1.