天然有机质对土霉素在西北灰钙土上吸附行为的影响

抗生素被广泛应用于日常生活中，大量含有抗生素的废弃物通过多种途径进入土壤给人类健康和土壤环境带来了严重危害，因此，探索抗生素类有机污染物在土壤中的吸附机理对土壤污染防治具有重要意义.以西北灰钙土为研究对象、以OTC（oxytetracycline，土霉素）为目标污染物，采用批量法分析灰钙土在添加有机质前、后对OTC的吸附动力学、热力学特征及其影响因素.结果表明:OTC的动力学吸附过程分快吸附阶段（0~2 h）和慢吸附阶段（2~10 h），10 h之后吸附基本达到平衡，吸附过程拟合均符合准二级动力学模型.对不同温度下OTC在灰钙土上的吸附过程进行拟合显示，Langmuir和Freundlich热力学模型拟合的R2分别在0.930~0.985和0.967~0.973之间；对于不同初始ρ（OTC）在添加有机质灰钙土上的等温吸附过程，Langmuir和Freundlich热力学模型拟合的R2分别在0.952~0.988和0.936~0.971之间，表明这两种模型均可较好地解释此吸附过程；热力学参数ΔGθ（吉布斯自由能变）小于0，ΔHθ（焓变）和ΔSθ（熵变）均大于0，表明吸附为自发进行的混乱程度增大的吸热反应.添加外源性有机质HA（humic acid，胡敏酸）和FA（fulvic acid，富里酸）能增加OTC的吸附量，且自制有机质的促进作用大于市售有机质，HA的促进作用大于FA.随着初始ρ（OTC）的增大，吸附量呈增加趋势；Ca2+和Na+的加入均使OTC的吸附量减小，且离子浓度越高、价态越高，抑制效果越明显；不同pH对OTC吸附的影响均较小.研究显示，不同来源、种类的有机质均可促进OTC吸附，但不会改变吸附平衡时间；HA的疏水性较FA强，对OTC的吸附量较高；溶液pH对OTC吸附影响不显著，但不同价态、浓度的金属阳离子对OTC的吸附有较大影响. 

Effect of Natural Organic Matter on Adsorption Behavior of Oxytetracycline onto Sierozem Soils in Northwest China

Antibiotics are widely used in daily life. At the same time, a large number of wastes containing antibiotics enter the soil through some ways, which brings serious harm to human health and soil environment. It is of great significance to explore the adsorption mechanism of antibiotic organic pollutants in the soil to prevent and control the soil pollution. In the present study, oxytetracycline (OTC) was selected as the target pollutant to investigate the effect of organic matter on sierozem soils based on the batch experiments. The research mainly included adsorption kinetics, thermodynamics and some influencing factors. The results indicated that the adsorption kinetic process could be divided into a fast (0-2 h) and slow (2-10 h) adsorption stages and reached equilibrium in 10 h. The adsorption kinetics could be better described by the pseudo-second-order model. For the adsorption thermodynamic process of OTC on sierozem soils at different temperatures, the fitting R2 values of the Langmuir and Freundlich thermodynamic models were between (0.930-0.985) and (0.967-0.973), respectively. For the isothermal adsorption process of OTC with different initial concentrations on sierozem soils with organic matter, the fitting R2 values of the Langmuir and Freundlich thermodynamic models were between (0.952-0.988) and (0.936-0.971), respectively, showing that both models explained the two adsorption processes well. The thermodynamic parameter analysis of OTC adsorption onto sierozem soils showed that the Gibbs free energy (ΔGθ) was less than zero, while entropy (ΔHθ) and enthalpy (ΔSθ) were more than zero, indicating the adsorption of OTC onto sierozem soils was a spontaneous endothermic adsorption, which increased the degree of disorder during the process, and it was a physical adsorption. The addition of exogenous organic matter increased the adsorption capacity of OTC, and the promotion effect of self-made was greater than that of the commercial product. Meanwhile, the effect of HA was also greater than FA. The adsorption capacity of OTC onto sierozem soils showed a rapidly increasing trend when the initial concentration of OTC increased. The addition of Ca2+ and Na+ reduced the adsorption of OTC, and the higher the concentration and the valence state, the more obvious the inhibition effect. The effect of pH on the adsorption of OTC was small. The results showed that organic matter from different sources and types could promote the adsorption of OTC, but did not change the adsorption equilibrium time. HA had stronger hydrophobicity than FA, and had higher adsorption capacity for OTC. The pH value of solution had no significant effect on the adsorption of OTC, but metal cations with different valence and concentration had greater effect on the adsorption of OTC.