Characterization and Surface Study of Volcanic Ashes from Popocatépetl

Puebla City, Mexico, experienced several volcanic ash storms that polluted the city and its surroundings. The spectroscopic characterization of the volcanic ashes is reported in more detail herein using IR, ESR, SEM, and powder diffraction X-ray. We report for the first time the use of volcanic ashes from Popocatépetl, a natural material, functioning as an adsorbent for removal of the cationic dye methylene blue from aqueous media. Batch adsorption experiments were conducted under varying initial dye concentrations and contact times to describe the adsorption behavior of the ashes, was obtained a SSA = 0.7245 m²/g. The equilibrium data were fitted to the Langmuir and Freundlich isotherm models. The Langmuir model exhibited a strong correlation (<i>R</i> ² = 0.99351) that suggested monolayer adsorption on a homogeneous surface with a maximum adsorption capacity of <i>q</i> _max 3.46 mg/g. These findings support the notion that volcanic ash can act as a natural alternative adsorbent. The value of a pseudo-first-order kinetic constant <i>k</i> = 8.02 × 10^-3 min^-1 (<i>R</i> ² = 0.99489) was obtained by batch equilibrium adsorption experiments when 40 mg/L of MB was used. This value, along with <i>q</i> _max, is similar to activated carbon products from seeds. Remarkably though, adsorption by volcanic ashes did not require any additional treatment, unlike current carbon-based products.