海洋环境体系中放射性核素吸附-解吸迟滞机制研究

Mechanism of Adsorption-desorption Hysteresis of Radionuclide in Marine Environment

  • 摘要: 通过宏观吸附-解吸等温实验,系统研究了放射性核素110Agm在海洋环境中表层沉积物上的吸附动力学过程及不同沉积物浓度和核素初始浓度条件下吸附-解吸迟滞机制(吸附不可逆性)。研究结果表明:Freundlich等温吸附模型可很好地描述110Agm在海水沉积物上的吸附解吸过程;110Agm吸附速率开始很快(0~24 h),呈指数型增加,而后逐渐趋于平缓,体系达到吸附平衡;改变沉积物浓度会产生明显的固体浓度效应,即110Agm吸附等温线随沉积物浓度的升高而显著下降。体系解吸迟滞性可用解吸迟滞系数(TII)和解吸滞后角量化表征,在沉积物浓度0.1~3.0 g/L范围内,解吸迟滞系数和解吸滞后角先增大后减小,不可逆程度与110Agm在颗粒表面与吸附点位的结合方式及微小颗粒物相互作用团聚导致的吸附剂有效吸附表面和吸附点位减小有关;对于不同沉积物浓度吸附体系,随核素初始浓度的增加,解吸迟滞系数总体先降低后增加,体系解吸迟滞性呈先减小后增大的变化趋势,其主要受两方面因素控制:1)110Agm分子在颗粒物表面与吸附点位的结合方式;2) 在浓度梯度力作用下,110Agm分子扩散吸附导致颗粒物微孔乃至超微孔隙结构发生形变,孔隙通道形变有效锁定了内表面吸附的110Agm,无法解吸脱落从通道中扩散出来,从而使吸附体系表现出一定程度的解吸迟滞性。

     

    Abstract: The adsorption and desorption hysteresis of 110Agm on marine sediment interfaces under various particle concentrations, initial concentrations and adsorption kinetics were studied using traditional batch experiments. The results show that the adsorption and desorption process of 110Agm on marine sediments can be well described by the Freundlich isothermal model. The adsorption rate of 110Agm increases exponentially in 0.24 h, with a high adsorption rate immediately, and then gradually tends to be gentle. There is particle concentration effect phenomenon. Because with the increase of particle concentration, the isotherms tend to decrease. Desorption hysteresis is described by hysteresis angle (θ) and thermodynamic index (TII). With the particle concentrations increasing from 0.1 g/L to 3.0 g/L, the values of TII and θ first increase and then decrease. The adsorption expresses less reversible because as the adsorption of 110Agm to adsorption-sites of different combinations and particles could integrate after collision, this would decrease the specific adsorption surface area and sites. With the initial 110Agm concentration increasing, the value of TII first decreases and then increases, and the desorption hysteresis of 110Agm first decreases and then increases. There are two main reasons. Firstly, these phenomena are possibly caused by different microscopic structures of 110Agm on the marine sediment. Secondly, it is due to the diffusion restriction of narrow pore throat induced by the imbedded 110Agm molecules during high –concentration gradient force.Thus the adsorption system shows a certain degree of desorption hysteresis.

     

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