| With the development of modern industry,the discharge of wastewater containing heavy metal ions and dyes causes severe pollution to the environment.Adsorption method is one of the effective methods to remove heavy metal ions and dyes in wastewater.In this paper different types of porous silicas,including the ones with large specific surface areas,the one coated on silica sand and the one which was modified further were used as adsorbents and packed in fixed beds to adsorb hexavalent chromium ions,zinc ions and methylene blue dye in aqueous solutions.Mesoporous and microporous silicas were prepared respectively under pH values by using partially dissolved silica from sand as silica source,cetyltrimethylammonium bromide?CTAB?as the surfactant.In the same way,SiO2-surfactant composite coating layer was formed on the surface of the undissolved sand particles,leading to porous silica coated silica sand?referred to loaded silica?after drying and calcination.The loaded Si O2 was further modified with 3-aminopropyltriethoxysilane?KH550?to obtain a modified porous silica?abbrivated as modified silica?.The influences of pH,initial concentration,flowing rate and the amounts of the adsorbents on the dynamic adsorptions of the heavy metal ions and the dye have been studied.The dynamic adsorption of hexavalent chromium ions and zinc ions by porous silica was fitted with the nonlinear Thomas model.The process of to dynamic adsorption of methylene blue was fitted with Thomas and Yoon-Nelson model,which shows that Thomas model was better fitted.The optimum conditions for the dynamic adsorption of hexavalent chromium and zinc ions were determined by experiments.Under the optimized conditions,when the mesoporous SiO2,microporous SiO2,modified SiO2,loaded SiO2 and the original silica sand were used as adsorbents,respectively,the removal efficiency toward Cr6+were 58.02%,99.06%,99.9%,16.17%,3.37%,respectively;the saturation time was 255 min,285min,185 min,65min,15 min,respectively.The adsorption efficiency of the adsorbents toward Zn2+were 92.3%,94.48%,98.49%,91.83% and 72.44% at 5 min,respectively;the saturation time were 250 min,270 min,240 min,125 min,65 min,respectively.It can be seen that the adsorption effectof the microporous SiO2 toward both Cr6+and Zn2+was better than that of mesoporous SiO2.The adsorption effect of the modified Si O2,loaded SiO2,the original sand decreased in order.The dynamic adsorption of methylene blue in aqueous solution by different porous silicas was studied.When the adsorbents were mesoporous silicas,microporous silicas,loaded SiO2,the original sand,the breakthrough time of dynamic adsorption were 215 min,375 min,255 min,7 min,respectively;the exhaustion time were 600 min,840 min,600 min,45 min,respectively.The results indicated that the adsorption methylene blue by microporous silica was better than that of mesoporous silica,and the adsorption effect of coated SiO2 was better than original silica sand. |
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