Synthesis of mesoporous molecular sieve using sewage sludge ash and surface modification applications of heavy metal adsorption

• Main Authors: Tzu-kuang Huang, 黃子光
• Other Authors: Kuen-sheng Wang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/16005023985996754553

碩士 === 國立中央大學 === 環境工程研究所 === 99 === This study investigated the feasibility of synthesizing mesoporous molecular sieve (i.e., referred to as MCM-41), using sewage sludge ash (SSA) as the starting SiO2 sources. Furthermore, the MCM-41 as synthesized was modified, and its performance was evaluated. Firstly, to prepare the precursor solution for MCM-41 synthesis, the target SiO2 component was extracted from SSA by heating the ash with NaOH (i.e., alkaline fusion). This reaction resulted in the formation of Quartz, Al2O3, Fe2O3, and ash residue. And then, after the ash residue was removed, deionized water was added to the filtered solution at a proper L/S ratio to prepare the precursor solution. As the Al2O3 concentration in the precursor solution may affect the synthesis of MCM-41, the L/S ratio was so determined that resulted in both the highest SiO2 concentration and the lowest Al2O3 concentration (i.e., the highest Si/Al ratio) in a resultant precursor solution. The results indicate that a NaOH/SSA (by weight) of 1.25 and heating a temperature at 400 oC were found to be optimal conditions for alkaline fusion; and a L/S=7 for deionized water and the filtered solid would generated a precursor solution with a highest Si/Al ratio (i.e., 51 in this study). Secondly, the MCM-41 was synthesized by hydrothermal method at 100 oC, using the precursor solution, ammonium hydroxide, and C16TAB (Cetyltrimethylammonium bromide, as surfactant). After the synthesis process, the resultant products were filtered and calcined at 550 oC to remove the surfactant and the MCM-41was formed. However, due the presence of Al2O3 derived form sewage sludge ash, the MCM-41 as synthesized contained alumiuoxide (referred to as Al-MCM-41). The composition of Al-MCM-41 as synthesized using SSA as starting SiO2 source was found close to that using sodium metasilicate as starting SiO2 source, the former containing 98.2 %(by weight) of SiO2, and the latter 94.7% SiO2, 3.2% Al2O3, 1.6% Na2O, and trace percent of other oxides. The Al-MCM-41 synthesized from SSA in this study had a surface of 932 cm2/g and a pore volume of 0.93 cm3/g, as compared to 1047 cm2/g and 1.05 cm3/g, respectively, of control sample synthesized from Na2SiO3. 27Al MAS NMR analysis of Al-MCM-41 synthesized from the precursor solution revealed that the extracted Al species from SSA was tetrahedrally incorporated in the framework effectively. On the other hand, the ash residual filtered from the extraction process was also successfully synthesized into zeolite (Cancrinite) by alkali hydrothermal reaction, showing a beneficial recycling of the SSA. Finally, in this study, the surface of MCM-41 as synthesized was further modified with 3-aminopropyltriethoxysilane (APTES) to bonding ammoniums-functional groups to the surface, forming ammonium-functionalized mesoporous materials (AFMM). The resulted showed that the coverage of functional group on MCM-41 surface were increased with increasing surface area of MCM-41 and longer reaction time of refluxing. A FM7-12H sample (i.e., sample generated at L/S=7 and fluxing time=12 hours) had the largest number of functional groups (N content=2.55 mmole/g), as compared to that of the control sample (N content=2.56 mmole/g). The efficiency to remove heavy metal ions in aqueous solution by the modified MCM-41 were evaluated. It was proved that the adsorption behavior of AFMM on heavy metals ions was best fitted by the Langmuir model. It was noted that the maximum adsorption capacities of FM7-12H sample for Pb(II), Cu(II), Cd(II) were 204.08 mg/g, 80 mg/g, and 80 mg/g, as compared to 200 mg/g, 84.04 mg/g, and 78.74 mg/g, of control sample (FMS-24H), respectively. It is demonstrated that the AFMM synthesized using SSA as SiO2 source was equal-effective in metal adsorption as that prepared using pure SiO2 source (Na2SiO3), suggesting that the preparation of AFMM using SSA as SiO2 source is feasible, effective, and environmental beneficial.