农林废弃物制备生物炭及其吸附性能研究

Study on Biochar Production from Agricultural and Forestry Wastes and Its Adsorption Properties

以农林废弃物花生壳和松木屑为原材料,在400℃和700℃下热解制备得到4种生物炭,分别记作PH400、PH700、PW400和PW700。选取多环芳烃的典型代表物萘作为污染物,考察4种生物炭对水中萘的吸附能力、动力学特征及相关机理。结果表明,热解温度和原材料对生物炭吸附萘的能力均存在影响。高温下制备的生物炭具有更大的比表面积、芳香性、疏水性以及更发达的孔隙结构;与花生壳生物炭相比,松木屑生物炭具有更大的比表面积和微孔体积。4种生物炭对萘的吸附量为:PW700(146 mg/g)>PH700(78.7 mg/g)>PH400(29.6 mg/g)>PW400(24.4 mg/g)。经动力学模型、颗粒内扩散模型和吸附等温线数据拟合,发现4种生物炭对萘的吸附更符合准二级动力学模型和Freundlich模型,而对颗粒内扩散的拟合呈现不同,花生壳生物炭的吸附过程分为3个阶段,松木屑生物炭则两阶段达到平衡,这说明萘的吸附不是单纯的单分子层吸附,还与生物炭提供的吸附位点有关,且内扩散不是唯一的限速步骤。

Agricultural and forestry waste peanut hull and pine sawdust were used as raw materials to prepare four types of biochar by pyrolysis at 400℃and 700℃,which were recorded as PH400,PH700,PW400 and PW700,respectively.Naphthalene,a typical representative of PAHs,was selected to investigate the adsorption capacity,kinetic characteristics and related mechanisms of four kinds of biochar on naphthalene in water.The results showed that the pyrolysis temperature and raw materials both had an impact on the ability of biochar to adsorb naphthalene.The biochar prepared at high temperature had larger specific surface area,aromatics,hydrophobicity and more developed pore structure.Compared with peanut hull biochar,pine sawdust biochar had a larger specific surface area and micropore volume.The adsorption capacities of the four biochar on naphthalene were as follows,PW700(146 mg/g)>PH700(78.7 mg/g)>PH400(29.6 mg/g)>PW400(24.4 mg/g)。By fitting the kinetic models,intra-particle diffusion model and adsorption isotherm data,it was found that the adsorption of naphthene by four biochar was more consistent with the quasi-second-order kinetic model and Freundlich model,but the fitting of intra-particle diffusion was different.The adsorption process of peanut hull biochar was divided into three stages,while pine sawdust biochar reached equilibrium in two stages.It was indicated that the adsorption of naphthalene was not a simple monolayer adsorption,but also related to the adsorption sites provided by biochar,and internal diffusion was not the only rate-limiting step.