生物碳和土壤性质对乙草胺吸附行为的影响

生物碳施加到土壤中可能会影响污染物的环境归趋,而吸附作用是其关键控制因素,为此,本研究考察了400、500和600℃下制备的玉米秸秆生物碳(分别记作CS400、CS500和CS600)和土壤性质对乙草胺吸附行为的影响。结果表明,生物碳和土壤对乙草胺的吸附等温线符合Freundlich模型(R2≥0.99)。随着生物碳热解温度的升高(从CS400到CS600),生物碳吸附乙草胺的非线性指数n值减小且logKOC值增大,说明吸附非线性程度和吸附能力增强,这是因为生物碳炭化程度增强(H/C原子比减小),疏水性增强(O/C原子比减小)和比表面积增大而有利于对乙草胺的吸附,吸附机制以表面吸附为主(比如疏水作用、π-π EDA作用和孔填充作用)。然而,土壤吸附乙草胺的n值(0.95)接近1.0,说明该吸附作用几乎是线性吸附,以分配作用机制为主。3种生物碳对乙草胺的吸附能力都高于土壤,特别是CS600对乙草胺的吸附能力(logKOC)比土壤及文献报道的土壤和沉积物高一个数量及以上,说明生物碳可能会有效保留土壤中的乙草胺而降低其迁移性。

Effect of biochar and soil properties on sorption behavior of acetochlor

Application of biochars into soil may influence the fate of contaminants. Sorption process is the key factor which influences the ultimate fate of the contaminants. Therefore, this study investigated the effect of properties of corn straw biochars prepared at 400, 500 and 600℃ (being referred to as CS400, CS500 and CS600) and soil collected from Tianjin on sorption behavior of acetochlor. Freundlich model describes sorption isotherms of acetochlor to biochars and soil well (R2 ≥ 0.99). With increasing pyrolytic temperature of biochars (from CS400 to CS600), nonlinearity index n values decrease and logKOC values increase, indicating the enhancement of nonlinearity of sorption isotherms and sorption abilities of biochars. This result indicates that the increase of carbonization degree (decrease of H/C), the increase of hydrophobicity (decrease of O/C) and increase of surface areas facilitate for the sorption of acetochlor by biochars. Surface adsorption was the dominant mechanism for sorption of acetochlor by biochars (e.g., hydrophobic binding, π-π EDA interaction and pore-filling). However, the n value for the sorption of acetochlor to soil (0.95) approximated to 1.0, indicating that the sorption isotherm was nearly linear and partition was the dominant mechanism. Sorption abilities of acetochlor to the three biochars are higher than that to soil, especially for CS600 which exhibits more than one order of magnitude higher sorption ability than soil and the soils and sediments reported by other literatures. This result indicates that biochars may retain acetochlor in soils effectively, which may reduce the mobility of acetochlor in soil.