Zeolites synthesis from Tajogaite eruption ash (La Palma, Canary Islands) and its performance for CO2 capture

The 2021 Tajogaite eruption (La Palma, Canary Islands) produced large volumes of volcanic ash that represent an underutilized aluminosilicate resource. Representative ash samples are rich in SiO₂ and Al₂O₃ and show a low Si/Al ratio (~2.5), making them promising precursors for low-silica zeolites with high cation density and strong affinity for polar molecules such as CO₂—properties of interest for direct air capture (DAC).

Here we investigate a conversion route from Tajogaite ash to zeolitic adsorbents and assess their suitability for CO₂ capture. The synthesis follows an alkaline fusion–hydrothermal approach: ash is fused with NaOH at >400 °C for varying times, the fusion product is dissolved to form an aluminosilicate gel, and hydrothermal crystallization is carried out at different temperatures over a range of crystallization times to steer phase selectivity.

X-ray diffraction is used to track zeolite crystallization and phase evolution (e.g., FAU-type zeolite X at shorter times versus sodalite-type phases at longer times), while BET surface area/porosity, thermogravimetric analysis, and CO₂ adsorption isotherms are used to quantify accessible microporosity, thermal/regeneration stability, and CO₂ uptake/affinity in DAC-relevant conditions.

To efficiently optimize performance and resource intensity (e.g., alkali usage, fusion/crystallization conditions), we implement a structured Design of Experiments (DoE) workflow: an initial screening stage using fractional factorial designs to identify the most influential synthesis factors, followed by response surface methodology to locate optimal operating windows for maximizing low-pressure CO₂ adsorption while maintaining robust regenerability.

Overall, this work links volcanic ash valorization with carbon management, advancing locally sourced sorbents for DAC within a circular-economy framework relevant to energy, resources, and environmental sustainability.