This study is of great practical significance to carry out research on the sorption mechanism of uranium on microorganism-clay mineral composites, which helps to reflect the environmental behaviors of uranium accurately. 

It is well known that uranium (U) is a kind of radionuclide with chemical toxicity. Once U enters the soil system, it will inevitably undergo physical, chemical and biological effects, which is extremely important to the geochemical behaviors of U.  

This research proved that under different pH conditions, the sorption mechanism of U(VI) on kaolinite and illite is mainly attributed to ion exchange, outer-sphere complexes (OSCs), and inner-sphere complexes (ISCs).  

Aspergillus niger could obviously change the charge density, sorption sites and other physical and chemical properties of illite and kaolinite to a certain extent, thereby promoting the sorption of U(VI).  

At the same time, the sorption mechanism of U(VI) on the surface of the clay- Aspergillus niger composites could be only attributed to the ISCs. It showed that the sorption process of U(VI) on the bio-composites is significantly different from clay minerals.  

The study also showed that U(VI) mainly complexed with the phosphate group, amide group and carboxyl group derived from the biomass of Aspergillus niger in the bio-composites, which further weakened the effect of ion exchange and complexation with Si-OH and Al-OH on illite and kaolinite.  

Besides, X-ray photoelectron spectroscopy (XPS) found that U(VI) was partly reduced to non-crystalline U(IV) by Aspergillus niger in the bio-composites.  

The findings further clarified the geochemical process of U(VI) in a complicated environmental system, and provided an important theoretical basis for accurately assessing and predicting the environmental behavior of uranium. 

The above research has been published in Chemosphere in an article entitled New insights into the sorption of U(VI) on kaolinite and illite in the presence of Aspergillus niger.  

The sorption process and mechanism of U(VI) on kaolinite- and illite-A. niger composites surface. (A)-(D): SEM images of kaolinite- and illite-A. niger composites after U(VI) sorption. (E): The contents of U(VI) at the different areas of clay, A. niger, and clay-A. niger composites (Green and Blue points are the hyphae surface and clay, respectively. Red square is the area of clay-A. niger composites). (F)-(H): The relationship of element U with S, P and N elements. (I): The sorption mechanism of U(VI) on clay-A. niger. (Image by FAN Qiaohui) 

Contact: 

FAN Qiaohui 

E-mail: fanqh@lzb.ac.cn