皇竹草生物炭的结构特征及对重金属吸附作用机制
Adsorption of heavy metals by biochar derived from Pennisetum sinese Roxb
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摘要: 本研究以皇竹草秸秆为生物质原料,在不同温度(400—700 ℃)下利用限氧热解法烧制一系列秸秆生物炭.利用扫描电镜(SEM)、X射线衍射(XRD)和拉曼光谱对所得生物炭样品进行分析,结果表明,500 ℃可使皇竹草秸秆生物炭充分热解,所得的生物炭晶体构成主要由半晶体结构涡轮层碳和一些矿物晶体组成,表面含有芳香类化合物、不饱和的醚类物质、无定形碳和C—C、C—O、C—OH等官能团.吸附实验表明,不同热解温度的皇竹草秸秆生物炭对混合重金属(Cr(Ⅵ)、Cu2+、Cd2+)的吸附效果差异显著.在EDTA共存的条件下,皇竹草秸秆生物炭对Cr(Ⅵ)的吸附量远高于Cu2+、Cd2+,其中500 ℃下热解得到的生物炭对Cr(Ⅵ)的吸附量达1.525 mg·g-1,而对Cu2+和Cd2+的吸附量约在0.05—0.15 mg·g-1.pH影响实验表明,在酸性条件(pH 1—4)下有利于Cr(Ⅵ)的吸附,其吸附量最高可达1.836 mg·g-1,在碱性条件(pH 9—13)下有利用于Cu2+的去除,其吸附量最高可达0.836 mg·g-1.Cu2+和Cd2+在生物炭的吸附作用主要发生在C—C/C—H、C—O/C—OH等官能团上,重金属与生物炭中C—O官能团中的氧原子可能存在配位作用.Abstract: A series of biochars were prepared from Pennisetum sinese Roxb straw by limited oxygen pyrolysis at different temperatures (400—700 ℃). The biochar samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscomy. The results show that biochars produced at 500 ℃ were completely pyrolysed. The crystal formation of biochars was composed mainly of turbostratic carbon with semi-crystal structure and some mineral crystals. The biochar surface contains aromatic compounds, unsaturated ethers, amorphous carbons and functional groups such as C—C, C—O, C—OH. Adsorption experiments indicate that straw biochars prepared at different temperatures exhibited significantly different adsorption capacities for heavy metals (Cr(Ⅵ), Cu2+, Cd2+). In the presence of EDTA, the adsorption capacity of Cr(Ⅵ) by the biochars was much higher than those of Cu(Ⅱ) and Cd(Ⅱ). The highest adsorption capacity of Cr(Ⅵ) was achieved at 1.9 mg·g-1, and the adsorption capacity of Cu(Ⅱ) or Cd(Ⅱ) was about 0—0.2 mg·g-1. Acid environment (pH 1—4) is beneficial for the adsorption of Cr(Ⅵ), and alkaline environment (pH 9—13) for Cu(Ⅱ). Adsorption of Cu(Ⅱ) and Cd(Ⅱ) onto biochar mainly occurred at sites with functional groups such as C—C/C—H and C—O/C—OH. There might be a coordination interaction between heavy metal ions and the oxygen atoms of the C—O functional groups of biochars.
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Key words:
- Pennisetum sinese Roxb /
- straw biochar /
- heavy metals /
- adsorption.
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