Comparative petrophysical and geochemical characteristics of thermal and volcanic ash from southeastern India

This paper examines the difference in the geophysical and chemical characteristic of the volcanic ash and thermal fly ash to evaluate environmental pollution. Natural volcanic ash (VA) samples from Sagirelu, Cuddapah dist., Andhra Pradesh and thermal fly ash (FA) samples from the Thermal Power Station, Ennore, Chennai, were collected, analysed and compared. The particle sizes of the ash samples were determined using the laser particle size analyzer and the different surface morphological characters were studied using SEM analyses. The chemical components such as pH, major oxides, trace metals and mineral compositions were determined using pH metre, XRF and XRD methods. pH value of the volcanic ash varies from 8.5 to 8.9 indicating its alkalinity (8.5 to 9) in volcanic ash, while the thermal ash is neutral to mildly alkaline with pH varying from 6 to 7.5. Both the ash samples have higher concentration value in SiO₂ (VA - 69.25%, FA - 46%) in major oxides and Cl (VA - 0.8%, FA - 0.1%) in trace elements. Quartz is the dominant mineral in both the types of ash, however, the volcanic ash has amorphous silica, while the fly ash contains crystalline quartz.