Surface and thermal properties of fine black and white volcanic ash

Abstract

In this study, the surface and thermal properties of fine black and white volcanic ash from Harrat Khaybar, located in the western region of Saudi Arabia have been investigated. The fine volcanic ash samples were characterized using the following methods: X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), thermogravimetric and differential scanning calorimetry analysis (TG-DSC), specific surface area and pore size analyzer (BET). On the basis of the characterization, it was concluded that the volcanic ash exhibits differences in mineralogical, elemental compositions, morphology, surface, density, porosity, and thermal behavior. The two samples of volcanic ash are in an amorphous phase. Additionally, the samples contain SiO2, Al2O3, CaO, and Fe2O3 as major elements, and K2O, MgO, MnO, Na2O, P2O5, TiO2, and SO3 as minor elements. Based on the content of the silica, through XRF measurement, the black ash (SiO2 ∼ 47.02%wt.) was classified as a scoria and the white ash (SiO2 ∼ 71.62%wt.) as a pumice. Furthermore, measurements obtained from the thermal differential analysis (DTA)/thermogravimetric analysis (TGA) showed that both the fine volcanic ashes have a good thermal stability with a high melting temperature. These results indicate that fine volcanic ash is a highly available, natural, and low-cost material that has promising applications in many industrial and economic fields, such as geopolymers, polishing compounds, paint filers, fertilizers, concrete production, and the treatment of water.