The Removal Of Uranium And Cobalt From Wastewater Through Adsorption By Mesoporous Calcium Silicate Material

Aiming at the removal of radionuclides in radioactive wastewater, the adsorption properties of Co(II) and U(VI) on mesoporous calcium silicate material derived from fly ash were studied through static experiments.The results show that the main chemical composition of mesoporous calcium silicate material is CaO and SiO2, and it contains little amount of Al2O3, Fe2O3, TiO2. Hydrated Calcium Silicate(C-S-H(I)(x Ca O?y Si O2?z H2O),Ca4.5Si6O15(OH)3?2H2O) was its main phase. With high BET specific surface area(732.8m2/g) and hole volume(1.619 cm3/g), the mesoporous calcium silicate is belonged to typical mesoporous material for adsorption. The data of 29 Si nuclear magnetic resonance, infrared spectroscopy, and Raman spectroscopy indicate that mesoporous calcium silicate material has short chain structure and contains a lot of hydration water and a certain amount of silanol(Si-OH). In addition, its lower zero potential point(pHPZC=1.5) and good pH buffer capacity render the material to be capable of playing a role in a wide pH range.The adsorption of Co(II) on mesoporous calcium silicate material can reach equilibrium in 150 min. With the increase of temperature, the material’s adsorption capacity for Co(II) increases from 35.07 mg/g to 90.05 mg/g. Through model fitting and thermodynamic calculation, the adsorption of C O(II) on mesoporous calcium silicate material fits Langmuir single molecule layer chemical adsorption well, the adsorption process is endothermic reaction, and the mainly adsorption mechanism for Co(II) is ion exchange. The removal efficiency of Co(II) on mesoporous calcium silicate material increases from 1% to 81%~99% along with the increasing adsorbent dosage. When the p H increases, the structural damage of the material decreases, thus the removal rate of Co(II) increases, and finally reached the equilibrium. With the increase of electrolyte concentration, the removal efficiency of Co(II) by calcium silicate mesoporous material reduces.It is found that the equilibrium can be reached in 180 min for the adsorption of U(VI) on mesoporous calcium silicate material. Under the condition of p H = 2 and adsorbent dosage=0.75 g/L, the adsorption capacity of mesoporous calcium silicate material rises from 67.25 mg/g to 95.86 mg/g with the increase of temperature. Through model fitting and thermodynamic calculation, the adsorption of U(VI) on mesoporous calcium silicate material fits Langmuir single molecule layer chemical adsorption well, adsorption process is endothermic reaction and the adsorption mainly relied on the complexation effect between U(VI) and the adsorbent. When the adsorbent dosage is 2 g/L or 5 g/L, the removal rate improves significantly by precipitation and complexation effect. Under the condition of p H=11(0.7 g/L Na2CO3 solution), the adsorption capacity of U(VI) on mesoporous calcium silicate material decreased to 48 mg/g. In addition, the ionic strength has little effect on the adsorption of U(VI) on mesoporous calcium silicate material.To test the absorption properties of mesoporous calcium silicate material, it was used to treatthe germanium ore wastewater containing uranium, and nuclear power plant overhaul wastewater, at laboratory scale. T he removal efficiency is higher than 98%. In addition, the mesoporous calcium silicate material also exhibits certain removal ability of other heavy metal ions. Speaking from the perspective of practical application, the mesoporous calcium silicate material not only has high compatibility with cement which is good to the radionuclide stabilization, but also can replace part of cement to achieve the reduction of the radioactive solidification blocks. Because of the above mentioned environmental and economic benefits, the mesoporous calcium silicate material evidently has potential application in removal of radioactive transition nuclide wastewater.