河流沉积物对镉和铊的竞争吸附-解吸特性

On the mechanism of the competitive adsorption and desorption of cadmium and thallium by the river sediments

探讨了不同粒径的表层沉积物对镉(Cd^(2+))和铊(Tl^+)的单一、竞争吸附-解吸特性,并通过对吸附前后沉积物颗粒进行红外光谱和X-光电子能谱分析,探讨了其吸附机理。结果表明,重金属吸附量均随溶液初始质量浓度增加而增大,且随沉积物粒径增大而减小;吸附率随初始质量浓度增加而减小。沉积物对Cd^(2+)的吸附量高于Tl^+,且Cd^(2+)和Tl^+的吸附等温线均符合Langmuir和Freundlich吸附模型。重金属解吸量随吸附量增加而呈指数增加趋势。当重金属Cd^(2+)和Tl^+共存时,各吸附量均有不同程度的下降,而解吸率略高于单一环境。红外光谱分析表明,沉积物中羟基与羧基均参与了Cd^(2+)和Tl^+的吸附;X-射线光电子能谱分析表明,沉积物吸附Cd^(2+)和Tl^+后,金属价态不发生改变。

This paper takes it as its target to investigate the adsorptive mechanism of cadmium （ Cd2 ＋ ） and thallium （Tl ＋ ） by the sediments in Hejiang River. For this purpose, we have taken the surface sediments of Hejiang River, Guangxi, as a case study sample, when the comaminant accident by heavy metal Cd2＋ and Tl＋ residuals. In doing so, we have done an investigation with the single and competitive adsorption - desorption simulation of Cd2 ＋ and Tl＋ by the surface sediments with different particle sizes in hoping to find the adsorption mechanisms through Fourier transform infrared spectroscopy （ FT - IR） and X-ray photoelectron spectroscopy （XPS） analysis. The experimental results of our work show that the adsorption amount of Cd2＋ and Tl＋ by the sediments tends to increase gradually with the increase of the initial concentrations with the adsorption ratios done in a reversed trend. On the other hand, with the decrease of the particle size of the sediments, the adsorption capacity of the heavy metals tends to show a gradual increase tendency. What is more, the adsorption amount of Cd2＋ tends to increase further than those of Tl＋ , and the adsorption isotherms of Cd2＋ and Tl＋ prove to be in the conformity to Langmuir and Freundlich equations. Moreover, the desorption amount proves to increase exponentially with the accumulation of the heavy metals in the sediments. What is more, we have also made clear that, in the competitive system, the competitive influence of Cd2＋ and Tl ＋ on the surface of the sediments tends to occur in an order of the adsorption capacity identical with that in the single system. On the other hand, the adsorption quantities both of Cd2＋ and Tl＋ tend to be declining to some ex- tent, whereas the desorption ratio in the competitive environment tends to be higher than that in the single system. Thus, it can be concluded from FT - IR investigation that there may clearly exist various functional groups in the environment, such as hydroxyl and carboxyl in the binding of Cd2＋ and Tl＋. Furthermore, XPS results have shown that Cd2＋ and Tl ＋ may remain unchanged with their valence state in the adsorption process. The above results of our investigation can thus be regarded as a contribution to the better understanding of the adsorption mechanism in Tl＋ and Cd2＋ pollution events in the said river.