海洋沉积物吸附Pb(Ⅱ)的特性研究

Study on the adsorption of Pb (Ⅱ) on marine sediment

以黄海海洋沉积物作为研究对象,研究了Pb在沉积物上的吸附行为,探讨了pH值、时间、温度和沉积物上不同成分对吸附作用的影响,并讨论了其吸附热力学性质和吸附机理,同时还进行了解吸研究。结果表明,pH值显著影响沉积物对Pb^(2+)的吸附,pH=6.0时吸附效果最好。其动力学行为符合Lagergren准二级动力学模型。Pb(II)的吸附量随着温度的升高而升高,Langmuir和Freundlich模型均能很好拟合等温吸附试验数据。热力学分析表明,该吸附过程是自发的吸热过程。沉积物中存在的碳酸盐、氯氧化物对沉积物吸附Pb的贡献最大。沉积物中的有机质与pb^(2+)结合更加牢固,使其不容易解吸。

The present paper takes it as its research goal to investigate the adsorptive behaviors of Pb^2＋ to the Yellow Sea marine bottom sediments. Experiments we have done were oriented for the exploration of different effects of pH, contact time and temperature on the sediments. We have also made discussions on the functions of the componential parts of the sediment in the adsorption process. As is known, the Pb（II） removal is pH-dependent, which is expected to reach its maximum at pH 6.0, whereas the adsorption process is expected to last 3 hours to reach its consequential pseudo-second-order kinetics and equilibrium. The rate constant tends to increase with the increase of temperature rising indicates its endothermic adsorption nature. Then we have analyzed the equilibrium data by using the Langmuir and Freundlich isotherm models, which is dependent on the temperature changes. Our analysis results indicate that the equilibrium adsorption capacity of Pb（II） can be deduced from the Langmuir equation, which are 227.79 mg/g, 174.52 mg/g and 118.48 mg/g respectively at 30 ℃ for the original sample, sample treated with H2O2, and HCl, respectively. As is shown from our thermodynamic studies, the positive value of ΔH stands for an endothermic process whereas the negative value of ΔG implies the spontaneous nature of the adsorption process. Moreover, the positive value of ΔS indicates the increased randomness at the solid-solution interface during the adsorption process. Last of all, it is necessary to mention that the carbonate and hydroxide in the sediment make more contributions than the organic matters. However, organic matters in the sediments fixed the Pb（II） ion more firmly than the former. Thus, it can be seen that the Yellow Sea marine sediments tend to have great impact on the transportation, transmutation and fate of Pb（II） in the seawater.