| Adsorption method is an effective method and frequently used in the purification of water contaminated by metal ions. The adsorbent is an important factor affecting the adsorption effect, whereas in the physical adsorption process, the specific surface area plays a key role in the adsorption. In this work, porous silica coatings were prepared on the surface of silica sand which is the raw materials of glass. The modified silica sand was then used to adsorb Cr3+, Cr6+ and Cd2+ ions in aqueous solutions. Finally, the silica sand with metal ions was applied in the preparation of color glasses. The results provide a new route to a combined solution of the removal and reutilization of metal ions in wastewater as well as the problem of secondary pollution of the used absorbents.Combining sol-gel method with template method, tetraethoxysilane(TEOS) as the silica source was hydrolyzed and condensed in NaOH solution, whose products were assembled with hexadecyl trimethyl ammonium bromide(CTAB) on the surface of silica sand. Modified silica sand with porous SiO2 coating was obtained after calcining the powder to remove the organic template. SEM, IR, TG, N2-adsorption were used to characterize the structure and properties of the modified silica sand. The effects of the composition, reaction temperature and time on the formation and properties of the coating have been investigated, leading to the optimized synthesis conditions. The result shows that the particle size of the sand increases after the modification. The edges of the sand turn round and the surface become rough after the formation of SiO2 layers. In the experimental region, the specific surface area of the silica increases first and then decreases with the amounts of CTAB, H2 O, TEOS, and NaOH concentration, and the synthesis temperature. The surface area of the sand only slightly increases with the reaction time increasing from 1 to 24 h. The optimized conditions were determined as: 0.36 gCTAB, 50mlH2 O, 1.5mlTEOS, NaOH concentration of 0.3M, 2g silica sand and reaction temperature 60 oC, reaction time 3h. The surface area of modified silica sand is about 41m2/g under this condition.In order to further increase the specific surface area of the silica sand, five-time coating process was performed under the optimized conditions. The resultant sand has a specific surface area of the sample 176m2/g, which is about 1796 times of the original silica sand. This modified silica sand was used to absorb Cr3+, Cr6+, Cd2+ ions in solutions. By changing the pH value, initial concentration of the ions, dosage of the modified silica sand, adsorption temperature and time, the adsorption efficiency was evaluated and the optimal adsorption conditions were obtained. Under the optimal conditions, the adsorption of Cr3+ by the modified silica reaches 70%, the adsorption capacity of sand is 0.35mg/g. These values are 26.91%, 0.37mg/g and 49.55%, 0.74mg/g in the cases of Cr6+ and Cd2+ ions, respectively.The silica sand with Cr3+ was used in glass preparation. The spectrum of the sample is same as the glass colorized with K2Cr2O7. Using the silica sand with Cr6+ to melt MnO2 containing purple glass, the adsorbed Cr6+ enhances the purple color of the glass. The silica sand with Cd2+ used in sulfur selenium glass leads to a small shift of cut-off adsorption edge to short wave. |
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