花生壳基和木屑基生物炭对离子型染料和Pb(Ⅱ)的吸附性能研究

摘要

采用花生壳和木屑为原材料分别在300、600℃ 限氧条件下热裂解制备4种生物炭,研究了其对阳离子型染料亚甲基蓝(MB)、阴离子型染料刚果红(CR)和重金属Pb(Ⅱ)的吸附等温线和吸附动力学效应以及生物炭上Pb(Ⅱ)的解吸再生效应.结果表明,相比Freundlich方程,生物炭对MB和Pb(Ⅱ)的吸附等温线更符合Langmuir方程.其中,生物炭对MB的吸附受到表面含氧官能团和平均孔径影响,对Pb(Ⅱ)的吸附机制以离子交换或共沉淀为主.相比Langmuir方程,生物炭对CR的吸附等温线更符合Freundlich方程,吸附机制主要以疏水作用为主.300℃ 热裂解花生壳制备的生物炭对MB吸附效果最好,最大吸附量达28.0 mg/g;600℃ 热裂解制备的生物炭对CR吸附效果最好;300、600℃ 热裂解花生壳制备的生物炭对Pb(Ⅱ)吸附效果均较好,最大吸附量分别为63.7、73.2 mg/g.生物炭对MB、CR和Pb(Ⅱ)的吸附基本在24 h内达到平衡,相比准一级动力学模型,吸附过程均更符合准二级动力学模型.0.1 mol/L盐酸能有效解吸4种生物炭吸附的Pb(Ⅱ).生物炭的吸附效果和吸附机制与生物炭制备时的热裂解温度和原材料种类关系密切.%Biochars were derived from peanut shell and saw dust through the pyrolysis under limited-oxygen condition at 300 ℃ and 600 ℃ ,respectively .Adsorption isotherm and kinetics of cationic dye methylene blue (MB) , anionic dye Congo red (CR) and heavy metal Pb( Ⅱ ) onto biochars ,as well as desorption of Pb ( Ⅱ ) from biochars were investigated .Results showed that isothermal adsorption curves of MB and Pb( Ⅱ ) onto biochars were better con-sistent with Langmuir model while CR better obeyed Freundlich model .The adsorption capacity of MB onto biochars was affected by the number of surface functional groups and the average pore diameter of biochars .The adsorption mechanism of Pb( Ⅱ ) onto biochars was ionic interaction or coprecipitation .The adsorption mechanism of CR was hy-drophobic reaction .The biochar derived from peanut shell under 300 ℃ was the optimum adsorbent on MB and its maximum adsorption capacity was 28 .0 mg/g .The biochar derived under 600 ℃ had the optimum adsorption effects on CR .Biochars derived from peanut shell under 300 ℃ and 600 ℃ were the optimum adsorbent on Pb( Ⅱ ) and their adsorption capacity were 63 .7 ,73 .2 mg/g ,respectively .Adsorption of MB ,CR and Pb( Ⅱ ) onto biochar reached equilibrium in 24 h basically and the process better obeyed the pseudo-second-order kinetic model compared with pseudo-first-order kinetic model .The adsorbed Pb( Ⅱ ) could be desorbed when treated with 0 .1 mol/L HCl .The ad-sorption capacity of MB ,CR and Pb( Ⅱ ) onto biochars were closely related to the pyrolysis temperature and types of raw materials .