Structural Characterizations of MCM-41 Synthesized from Coal Gasification Slag: Effect of Metal Impurities

Gasification slag has been viewed as a secondary resource for preparing various high-value-added materials with enormous potential. Residual silicon in gasification slag can be used to prepare mesoporous silica materials, such as MCM-41. However, it is challenging to avoid doping impurities from gasification slag, including metal impurities, such as Fe, Mg, and Ca, in the synthesis of MCM-41. This study used the supernatant of leached gasification slag to synthesize MCM-41 with a controllable Si/Al atomic ratio, and MCM-41 synthesized from chemical agents was used as a control group. In addition, XRD characterized two kinds of mesoporous molecular sieves: SEM-EDS, N₂ adsorption/desorption isotherm, ²⁷Al, and ²⁹Si solid-state NMR spectroscopy. It has been found that the crystallinity of the MCM-41 crystal structure decreased due to the doping of metal impurities. No octahedral aluminum was observed in MCM-41 synthesized by gasification slag, which may be related to the change of charge pairing cations (partial substitution of Na⁺ by Ca²⁺) in the aluminosilicate framework of MCM-41. On the other hand, the specific surface area, pore size, and pore volume of MCM-41 synthesized from gasification slag were affected by metal impurities. This can be attributable to partial mesopores blocked by metal oxide nanoparticles. This study provides a new understanding of the structural change of molecular sieve MCM-41 due to the metal impurities of gasification slag. These results also provided insight into the efficient recycling of gasification slag and the production of high-value-added materials from solid waste.