Non-stoichiometric dissolution of sepiolite

Sepiolite is one of the few Mg-phyllosilicates thought to precipitate at Earth’s near-surface conditions, and in hydrothermal systems. Understanding the dissolution mechanisms of sepiolite can elucidate Mg-silicate dissolution processes in general and can provide a better estimation of the availability of divalent cations for CO2 sequestration. Batch experiments containing sepiolite were conducted over a pH range of 3.6-10.4, and the changes in Si/Mg ratio in solution were measured over time. The reaction products were analyzed with scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Under all conditions sepiolite dissolution proved to be non-stoichiometric, where Mg was preferentially released under acidic and neutral conditions, while Si was preferentially released in alkaline solutions. Under acidic and neutral conditions, sepiolite could thus release ample divalent cations for CO2 sequestration.