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THERMAL BEHAVIOR OF NATURAL AND CATION-EXCHANGED CLINOPTILOLITE FROM SARDINIA (ITALY)

¹ Dipartimento di Studi Geologici ed Ambientali, Via Port’Arsa 11, 82100, Benevento, Italy
² Laboratorio Materiali del Dipartimento di Meccanica, Strutture, Ambiente e Territorio dell’Università di Cassino, Via Di Biasio 43, 03043 Cassino (FR), Italy
³ Istituto di Scienze Geologico-Mineralogiche dell’Università di Sassari, Corso Angioj 10, 07100 Sassari, Italy
⁴ Dipartimento di Scienze della Terra dell’Università Federico II, Via Mezzocannone 8, 80134 Naples, Italy

^* E-mail address of corresponding author: langella{at}unisannio.it

The thermal behavior of two clinoptilolites from an epiclastic and a pyroclastic deposit of central-northern Sardinia and of their exchanged forms (Li, Na, K, Cs, Mg, Ca, Sr and ammonium) were investigated by differential thermal analysis and thermogravimetry up to 1000°C. Their thermal stability was studied by evaluating the residual crystallinity (expressed as rehydration capacity) after 2 h thermal treatments at 450, 600 and 900°C. The water loss at 1000°C was linearly related to the radius (r) and the charge (z) of the exchangeable cations by the equations r²/z or r³/z, which are proportional to the inverse of the charge density over the surface or to the charge density over the volume of the cations.

The cation composition plays a crucial role in determining the thermal behavior of clinoptilolite. The presence of cations such as Cs or K, which have low surface or volume charge densities, was found to increase the thermal resistance. In particular, the crystallinity of Cs- and K-exchanged forms of both clinoptilolites was not affected by thermal treatment at 450°C and was only slightly reduced by thermal treatment at 600°C.

Predicting the thermal behavior of natural and cation-exchanged forms of these clinoptilolites can provide useful information for possible applications in catalysis, in the case of high thermal stability, or for thermal transformation into ceramics or lightweight aggregates.

Key Words: Clinoptilolite • Ionic Potential • Rehydration Capacity • Thermal Stability • Sardinia • Italy