Additive manufacturing of sodalite monolith for continuous heavy metal removal from water sources

Herein, we present a simple strategy for preparing monolithic sodalite adsorbents via sequential additive manufacturing and post-treatments. In detail, the method includes (i) 3D printing of cylindrical monoliths using clay as the base material; (ii) thermal activation of the 3D-printed clay monoliths by calcination (to produce reactive alumina and silica species and enable mechanical stabilization); (iii) conversion of the activated clay monoliths to hierarchical porous sodalite monoliths via hydrothermal alkaline treatment. Parametric studies on the effect of calcination temperature, alkaline concentration and hydrothermal treatment time on the property of the resulting materials (such as phase composition and morphology) at different stages of preparation was conducted. Under the optimal conditions (i.e., calcination temperature of 850 °C, NaOH concentration of 3.3 mol⋅L⁻¹, reaction temperature of 150 °C, and reaction time of 6 h), a high-quality pure sodalite monolith was obtained, which possesses a relatively high BET surface area (58 m²⋅g⁻¹) and hierarchically micro-meso-macroporous structure. In the proposed application of continuous removal of heavy metals (chromium ion as the model) from wastewater, the developed 3D-printed sodalite monolith showed excellent Cr³⁺ removal performance and fast kinetics (∼98% removal efficiency within 25 cycles), which outperformed the packed bed using sodalite pellets (made by extrusion).