Studies On The Interaction Between Uranium With Cement Clinker Mineralsand Hydration Products

Cement solidification is a commonly used method for immobilization of low-level radioactive wastes. Uranium is an important part of the low-level radioactive wastes and long-term radioactive contributors. The research on the interaction between uranium and Portland cement clinker minerals provides the data and theoretical research results for the cement solidifying uranium wastes.Four kinds of silicate cement clinker minerals were prepared by the traditional solid phase sintering method. The content of f-CaO in clinker was determined by "ethylene glycol method". The mineral composition of clinker was characterized by XRD analysis. The results show that four kinds of clinker characteristic diffraction peaks are well matched to its standard diffraction peaks. With the increase of the firing number, the f-CaO content decreases gradually.The effect of different concentrations of uranium simulated waste water on four kinds of clinker minerals hydration was studied by modern test methods such as TAM air,XRD, FTIR, and SEM-EDS. The results show that uranium can promote the hydration of mineral C3 S and C2 S, and inhibit the hydration of mineral C3 A and C4 AF. In addition, the increase of uranium concentration makes the above effects become more obvious. By comparing scanning of hydration products, it was found that the existence of uranium significantly changed the morphology of clinker hydration products.The removal of uranium properties of the hydrated products of the clinker at different temperatures and in different initial concentrations of waste water were studied using the static adsorption method. The results show that the higher the temperature, the shorter the removal equilibrium time of the uranium and the higher the removal rate. The effect of C2 S hydration products to remove uranium is better than that of C3 S hydration products under the same experimental conditions. When the initial concentration of the waste increases by 5 times, 10 times, and 15 times, the maximum removal rate decreases to some extent. This suggests that the hydration products of clinker minerals for the removing the uranium in the uranium simulated waste liquid process exists an optimal initial concentration.Three kinds of calcium silicon ratio pure C-S-H gel and adding uranium C-S-H gel were prepared by the hydrothermal synthesis method. The effect of heavy metal influence C-S-H gel structure in its formation progress was discussed using XRD and IR. Pure C-S-H gel removal effect of uranium in simulated wastewater was studied using static adsorption method. The results show that uranium makes the ordered gel becomes poor, reducing the crystallinity. Three kinds of calcium silicon ratio C-S-H(C/S=0.8, 1.3, 1.8) can quickly remove the uranium. The final removal rates of uranium for the three kinds of calcium silicate C-S-H gel are almost the same(97~98%), indicating that the C/S ratio has no obvious effect on the removal efficiency.