Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs
AbstractClinoptilolite is a natural zeolite used for the abatement of ammonium in the treatment of urban wastewater. By considering that mullite was obtained through thermal treatment of NH4-exchanged synthetic zeolites, this work aimed to evaluate if this phase can be obtained from NH4-clinoptilolite. A material containing about 90 wt % of clinoptilolite, prepared using a Sardinian zeolite-rich rock, was NH4-exchanged and subjected to treatments up to 1200 °C. After dehydration, de-ammoniation, and dehydroxylation processes, the clinoptilolite structure collapsed at 600 °C. An association of mullite, silica polymorphs, and glass, whitish in color, was obtained for treatments between 1000 and 1200 °C. The higher degree of crystallinity was reached after a 32 h heating at 1100 °C: mullite 22 wt %, cristobalite 59 wt %, tridymite 10 wt %, glass 9 wt %. It is possible to speed up the kinetics of the transformation by increasing the temperature to 1200 °C, obtaining the same amount of mullite in 2 h, but increasing the residual amorphous fraction (16 wt %). These results indicate that NH4-clinoptilolite could represent a raw material of potential interest in the ceramic field, in particular in the production of acid refractory, opening scenarios for a possible reuse of clinoptilolite-based exchangers employed in ammonium decontamination. View Full-Text
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Brundu, A.; Cerri, G.; Sale, E. Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs. Minerals 2017, 7, 11.
Brundu A, Cerri G, Sale E. Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs. Minerals. 2017; 7(1):11.Chicago/Turabian Style
Brundu, Antonio; Cerri, Guido; Sale, Eleonora. 2017. "Thermal Transformation of NH4-Clinoptilolite to Mullite and Silica Polymorphs." Minerals 7, no. 1: 11.
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