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黄河兰州段沉积物对水体中萘的吸附行为及影响
蒋煜峰
兰州交通大学环境与市政工程学院
摘要:
为研究典型有机污染物在黄河兰州段沉积物的吸附规律及影响因素,以黄河兰州段的沉积物为供试样品,选择萘(Naphthalene)为代表性有机污染物,采用批量实验法研究了污染物萘在黄河沉积物上的吸附动力学、吸附热力学、初始浓度、pH、离子强度、粒径等影响因素以及解吸动力学。结果表明:黄河沉积物对萘的吸附动力学更符合准二级动力学模型,且吸附过程主要分为快吸附(0~4 h)和慢吸附(4~8 h)两个阶段,在8 h左右达到平衡;Freundlich模型能较好地拟合热力学吸附特征。在25~45℃的温度范围内,E(吸附平均自由能)为0.288~0.316 kJ/mol(<8 kJ/mol),吸附过程中,ΔGθ(吉布斯自由能)小于0,ΔSθ(熵变)与ΔHθ(焓变)均大于0,说明萘在黄河沉积物上的吸附是一个自发的混乱度增大的吸热过程,且以物理吸附为主。影响因素分析结果显示,随着沉积物粒径的增大,萘在其上的吸附量逐渐减小;增大吸附体系中的离子强度,萘在沉积物上的吸附过程受到抑制;当萘初始浓度增大时,吸附量增加;酸性条件抑制吸附过程,碱性环境促进吸附过程;黄河沉积物对萘的解吸量远小于吸附量,存在解吸滞后现象。研究显示,萘在黄河沉积物中的吸附速率受内部扩散、表面吸附和液膜扩散的共同影响,并且吸附过程同时受到沉积物粒径和溶液的pH和离子强度的影响。
关键词:  黄河沉积物    吸附动力学  吸附热力学  影响因素
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基金项目:天然有机质及生物碳对寒旱区石油污染黄土中典型有机污染物环境行为影响的研究
Adsorption Behavior and Affecting of Naphthalene on Sediment of Yellow River in Lanzhou Section
JIANG Yu-feng
School of Environmental Municipal Engineering,Lanzhou Jiaotong University
Abstract:
In order to study the adsorption behavior of polycyclic aromatic hydrocarbons (PAHs) on sediment of the Yellow River in Lanzhou section, naphthalene was selected as the target pollutants to understand the adsorption kinetics and thermodynamics of Naphthalene (Nap) onto sediment collected from the Yellow River in Lanzhou section based on the batch experiments. Meanwhile, the influence of initial concentration, particle size, pH value, ionic strength and other factors on the adsorption process of Nap in the sediment of the Yellow River in Lanzhou section was also investigated. The results indicated that the adsorption kinetics of Nap onto sediment could be better described by Pseudo-second-order-model, the adsorption process was mainly divided into two stages: fast adsorption (0~4 h) and slow adsorption (4~8 h), which reached equilibrium at about 8 h, indicating that the adsorption process is controlled by various effects. The adsorptions thermodynamic of Nap onto sediment were fitted well with the Freundlich model. At a temperature of 25℃ to 45℃, E (average adsorption free energy) of 0.288~0.316 kJ/mol, E < 8 kJ/mol, The Gibbs free energy (ΔGθ) is less than zero, Enthalpy (ΔHθ) and Entropy (ΔSθ) were more than zero in the adsorption process, which tend to prove that the adsorption of Nap on sediment is a spontaneous and Chaos increased of endothermic process and is dominated by physical adsorption. The analysis results of the influencing factors are shown: the smaller the particle size, the greater the adsorption capacity of the Nap; with the ionic strength increases, the adsorption amount of Nap was decreased; when the initial concentration increased, the adsorption capacity also increased; strong acid conditions inhibit the adsorption process, alkaline environment promote the adsorption process. The desorption amount of Nap from the Yellow River sediment in Lanzhou section is much less than that of adsorption, meaning a phenomenon of desorption hysteresis.The results show that the adsorption rate of naphthalene in sediments of the Yellow River in Lanzhou section is affected by both internal diffusion, surface adsorption and liquid film diffusion, and the adsorption process is affected by both the particle size of the sediment and the pH and ionic strength of the solution.
Key words:  Sediment  Naphthalene  Adsorption kinetics  Adsorption Thermodynamics  Affecting factors