动植物来源生物炭对水体中Cd^(2+)的吸附特性

Cd^(2+) Adsorption Characteristics of Animal-Waste-and-Plant-Derived Biochars in Water

以动植物来源(鸡粪便和小麦秸秆)的生物质为原料,在350和650℃条件下慢速热解制备生物炭并表征其理化性质,采用批量吸附试验研究不同吸附时间、溶液pH值和Cd^(2+)浓度条件下生物炭对Cd^(2+)的吸附特性。结果表明,随着热解温度升高,生物炭的pH值和灰分含量升高,芳香性和疏水性增强,极性减弱。相同热解温度条件下,动物来源的鸡粪炭pH值和灰分含量比植物来源的小麦秸秆炭高,芳香结构更完备。生物炭对Cd^(2+)的吸附动力学过程均符合准二级动力学模型(R2>0.99),吸附在12 h时达到平衡,吸附过程均由外部液膜扩散、表面吸附和颗粒内扩散共同控制,且后者是主要限速步骤。随着溶液pH值的升高(2.0~6.0),生物炭对Cd^(2+)的吸附量均逐渐增加。Langmuir模型能很好地描述植物来源的小麦秸秆炭对Cd^(2+)的吸附行为(R2为0.970 3~0.981 5),Freundlich模型更适用于动物来源的鸡粪炭(R2为0.971 7~0.976 9),动物来源的鸡粪炭对Cd^(2+)的吸附效果优于植物来源的小麦秸秆炭。阳离子-π作用和沉淀作用是650℃生物炭吸附Cd^(2+)的主要机制。

Four types of biochars were prepared out of chicken droppings or wheat straw through pyrolysis at 350 or 650℃separately and analyzed for physic-chemical properties.Batch sorption tests were conducted to explore Cd 2+adsorption characteristics of the biochars relative to duration of the adsorption,pH of the solution,and Cd 2+concentration in the solution.Results show that the higher the temperature of pyrolysis,the higher the pH,ash content,aromaticity and hydrophobicity and the lower the polarity of the biochar.Under the same temperature in pyrolysis,the chicken manure derived biochar was higher in pH and ash contents than the plant-derived one,and more complete in aromatic structure.The Cd 2+sorption kinetics of the biochars well fitted the pseudo second order kinetic model(R 2>0.99),and the adsorption reached equilibrium in 12 h.And the sorption processes were controlled jointly by external liquid film diffusion,surface adsorption and intraparticle diffusion,and the latter was found to be the main rate-controlling step.With pH in the solution rising from 2.0 to 6.0,Cd 2+adsorption rate of the biochars gradually increased,and peaked at pH 6.0.The Langmuir model can be used to describe Cd 2+adsorption isotherm of the plant-derived biochars(R 2,0.970 3~0.981 5),whereas the Freundlich model was better at describing the chicken-manue-derived biochars(R 2,0.971 7~0.976 9).The chicken manure-derived biochars are superior to the plant-derived biochars in Cd 2+adsorption.Cation-πaction and precipitation were the two main mechanisms for biochars pyrolyzed at 650℃adsorbing Cd 2+.