High mechanical resistance - porous ceramics by cold sintering of volcanic ash from Mount Etna

The disposal of the volcanic ashes from explosive eruptions, like those of Mount Etna (Sicily, Italy), poses significant health, environmental, and economic concerns. Herein, we show that the volcanic ashes can be transformed into porous ceramics by the cold sintering process (CSP) at temperatures lower than 200°C. The consolidation is aided by a liquid medium that can be either water or a caustic KOH solution and by the application of a few hundred megapascals. The obtained porous materials possess a residual porosity between 22% and 39%, depending on the sintering conditions (pressure, temperature, KOH concentration). The CSP ash exhibits a fairly low thermal conductivity between 0.6 and 1.1 W/m K, which matches the benchmark of common ceramic bricks fired at high temperatures, but with substantially improved mechanical resistance ranging from 13 to 70 MPa (well above traditional bricks). In summary, CSP offers a new avenue to recycle inorganic waste materials and transform them into industrial products with potential application in the building industry. • Volcanic ash can be a raw material for porous ceramics production via cold sintering. • The volcanic ash can be consolidated between 25 and 200°C. • Caustic solution and high pressure facilitate densification. • The mechanical/thermal properties are equal to or superior to those of fired bricks.