Chemical, mineralogical and technological properties of the kaolins of Tresnuraghes mining district (Western Sardinia, Italy) for an application in the ceramic industry

Kaolinitic materials, which crop out in the Tresnuraghes mining district (Western Sardinia, Italy), are hosted in three main deposits, located at Patalza, Salamura and Su Fongarazzu. They were investigated in order to assess their potential in the ceramic industry. The parent rock-types of this raw material are the Oligocene-Miocene rhyolitic-rhyodacitic ignimbrites. Chemical and mineralogical analyses were performed on representative samples of each deposit, by XRD and XRF techniques. The chemical analyses generally show high silica and low alumina contents in all samples, typical of weakly kaolinized materials. The mineralogical association mainly consists of kaolinite and cristobalite; quartz and smectite are minor components. Alunite may be present as main mineral in the Kaolinitic materials crop out in the Tresnuraghes mining district ?Western Sardinia, Italy. Three main kaolinitic deposits, located in the Patalza, Salamura and Su Fongarazzu areas, respectively, were investigated in order to assess their potential in the ceramic industry. The parent rock-types of this raw material are the Oligocene-Miocene rhyoliticrhyodacitic ignimbrites. Chemical and mineralogical analyses were performed on representative samples of each deposit, by XRD and XRF methodologies. The chemical analyses generally show high silica and low alumina contents in all samples, typical of weakly kaolinized materials. The main mineralogical association consists of kaolinite and cristobalite with quartz and smectite as the minor components. Alunite may be present as a main mineral in the Salamura and Su Fongarazzu deposits, making these clay materials unsuitable for ceramic applications. The Patalza deposit exhibits low iron and sulphur contents, but low plasticity and excessive refractoriness. The Patalza materials can be used as unconventional raw materials to replace both kaolin and silica in white-firing bodies. Results show that the introduction of the Patalza AkaolinsB was well tolerated in bodies for tableware, wall and floor tiles, without significant changes in porosity, bulk density, pore size distribution and coefficient of thermal expansion. The main drawback of using the Patalza material is the slight increase of firing shrinkage, while the main advantage is a systematic increase in mechanical resistance.