Surface and Elemental Properties of Mount St. Helens Volcanic Ash

Sized fractions of Mount St. Helens volcanic ash were examined by SEM, EDXA, and ESCA. Particle size distributions, density, and specific surface area were determined. The size distribution was bimodal. Both EDXA and AAS demonstrated the presence of Si, Al, Fe, Na, K, Ca, and Mg. The EDXA demonstrated that Si and Al were present in all particles, except one, which was over 99% Si. Particle-to-particle variation in composition was large. X-ray diffraction demonstrated the presence of labradorite (plagioclase), albite, orthoclase, and anorthite, with a high background from amorphous material. ESCA demonstrated the presence of Na as a surface contaminant. No surface sulfur was detected, nor hydrocarbons at levels exceeding those normally found on air-exposed surfaces. The variation of specific surface area with particle size showed that the surface of the ash has a fractal dimension of 2.23 ± 0.03. Specific surface areas ranged from 1 m2 g−1 to 10 m2 g−1. From our study we estimated that the total surface ar...