The Adsorption Of Thorium Polymers To Nanopowder Form Of Germanium Saponite

In view of the mobility of actinide colloids from nuclear waste repository to natural environment when infiltration of local water occurs,a new nanopowder form of germanium saponite was synthesized and its removal of thorium and uranium in aqueous solution was studied.On the one hand,TEM,XRD,SAXS,N₂ adsorption-desorption isotherms and FT-IR were used to analyze the structure of germanium saponite,and the effects of particle size and morphology on the adsorption of thorium polymers and polynuclear uranium complexes.On the other hand,hydrolysis process of Th（IV）in nearly neutral condition（p H=5.5）was studied via SAXS.The paper mainly contains the following three parts:（1）SAXS and TEM showed that germanium saponite contained plates approximately 100nm long and 80 nm wide and also showed the presence of randomly stacked platelets and particles;Si-saponite is a spherical particle formed by agglomeration of nano-plate structure（≤20 nm）with microporous structure and pore size of 0.8 nm.（2）Polynuclear thorium colloids and thorium dioxide crystallites,formed by the condensation of hydrolyzed Th⁴⁺solutions（3 m M;initial p H 5.5）aged for up to 18 months,were studied using small-angle X-ray scattering.Scattering profiles were fitted using a unified Guinier/power-law model（Beaucage model）to extract the radii of gyration and Porod exponents.Analysis of the scattering profiles from a dispersion aged for 5 months indicated that both polymer coils and more compacted structures（radius of gyration Rg～10nm）were present,which translated in the Kratky plots as a plateau and a peak maximum,respectively.After 18 months,the SAXS data were consistent with the presence of agglomerates of Th O₂ particles suspended in aqueous solution（p H 3.2;[Th]=1.45 m M）.The measured radius of gyration（Rg）of the agglomerates was 5.8 nm,whereas the radius of the Th O₂ particles was 2.5 nm.（3）The distribution coefficient（K_d mL/g）values for thorium（20μg/mL）at p H 4 were:Ge-saponite（10~5）≈Si-saponite（10~5）>raw saponite（10~4）≈raw saponite（washed）（10~4）.The Kd values for uranium（20μg/mL）at p H 5.5 were:Ge-saponite（10~3）≈raw saponite（washed）（10~3）≈Si-saponite（10~3）≈raw saponite（10~3）.The difference in uranyl adsorption performance observed between the two nanoparticle forms of saponite was attributed to a larger pore width for Ge-saponite（3.5 nm）compared with Si-saponite（0.8 nm）.It is speculated that the adsorption mechanism of germanium-saponite on thorium polymers is surface complexation or precipitation and on uranium is ion exchange.Germanium saponite,a new nanomaterial preapared in this paper,has excellent adsorption performance on thorium and uranium colloid,providing a new nano material with high efficiency for the solidification of nuclear waste.