Performance and Mechanism of Modified Mesoporous Tobermorite for U(VI)Adsorption in Water
Tobermorite(TOB)was prepared from waste fly ash and calcium carbide slag by hydrothermal method,and modified tobermorite(STOB)was produced by thermal acti-vation and acidification,and the experimental results showed that,after the modification,the crystal structure of calcium-oxygen octahedron of TOB was damaged,and more micro-porous and mesoporous pores were formed,so the specific surface area and pore volume of STOB increased significantly.At pH 5,temperature 303 K,reaction time 60 min,the ad-sorption rate of U(VI)by STOB was 91.72%,which was 22.27%higher than that of TOB.The most significant effect of interfering ions on the adsorption of U(VI)by STOB was attributed to the lack of specific functional groups associated with uranium in STOB,which led to other heavy metal ions competing with U(VI)for the adsorption sites of the material.In addition,pH also has some effects on the experiments,and the higher the acidity,the worse the adsorption performance of STOB.The adsorption isotherms of STOB on U(VI)coincide with the Dubinin-Radushkevich and Langmuir isothermal models,and the adsorption behavior of STOB on U(VI)is consistent with the quasi-second-order kinetic model,indicating that the adsorption mainly occurs on the surface and is a mono-layer dominated chemical reaction.The thermodynamic parameters revealed that the ad-sorption of U(VI)was a heat-absorbing spontaneous process,and its adsorption amount and removal rate increased with the increase of adsorption temperature.The removal effi-ciency of U(VI)was maintained above 64.65%after five cycles of use.
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