水稻秸秆生物碳对重金属Pb2+的吸附作用及影响因素

以农业废弃物水稻秸秆为原料,采用限氧裂解法制备了不同温度(350、500和700℃)下的秸秆生物碳(RC350、RC500和RC700),研究了生物碳对Pb2+的吸附性能、作用机制及影响因素,为准确预测生物碳还田固碳对土壤中重金属迁移行为的影响提供理论参考.结果表明,生物碳对Pb2+的吸附行为符合准一级动力学方程,Pb2+在RC350、RC500、RC700上的吸附速率分别为0.167h-1、0.154h-1、0.388h-1;其等温吸附曲线符合Langmuir方程,最大吸附量分别为65.3、85.7和76.3mg·g-1,是原秸秆生物质RC100的5～6倍、活性炭AC的2～3倍.生物碳单位面积上的有效吸附点位比AC高约10倍.经酸化去除表面矿物成分后,RC350和RC700对Pb2+的吸附能力急剧下降,其最大吸附量、吸附亲和力与AC相近;红外光谱分析表明,去灰分后生物碳上有机碳官能团并无明显减少,而无机矿物(如SiO2)含量显著降低.生物碳中的有机碳组分和无机矿物组分对其吸附Pb2+均有重要贡献,其中无机矿物组分的吸附量及亲和力均大于有机碳组分.

Adsorption of Pb2+ by rice straw derived-biochar and its influential factors

Three types of biochar (RC350, RC500 and RC700) were prepared by pyrolyzing rice straw at different temperatures (350, 500 and 700 ℃) under a limited oxygen condition. Adsorption and its influential factors of Pb2+ to the biochar in aqueous solution were investigated. Sorption kinetics of Pb2+ onto biochar followed pseudo first order kinetic model, and the sorption rates were 0.167 h-1, 0.154 h-1 and 0.388 h-1 for RC350, RC500 and RC700, respectively. Adsorption isotherm fit well with Langmuir equation, and the individual maximum sorption capacity (Qm) of RC350, RC500 and RC700 were 65.3, 85.7 and 76.3 mg·g-1. The Qm values were about 5~6 times higher than that of raw rice straw (RC100), and 2~3 times higher over that of commercial activated carbon (AC). The adsorptive sites per unit of biochar surface area were 10-time higher than that of AC. After de-ashed by acid treatment, both adsorption capacity and affinity of RC350 and RC700 decreased sharply and approached the adsorption of AC. The infrared spectroscopy analysis indicated that organic carbon components of biochar were preserved, but mineral components (such as SiO2) were removed. Therefore, both organic carbon and mineral components contributed to the adsorption of Pb2+ by biochar, and mineral components exhibited higher sorption capacity and affinity than the organic carbon residues. These observations provided useful information in precisely predicting the adsorption behavior of heavy metal in soil amended with biochar for carbon sequestration.