CO-assisted 'Weathering' of Steel Slag-Derived Calcium Silicate Hydrate: A Generalized Strategy for Recycling Noble Metals and Constructing SiO-Based Nanocomposites.

The spent adsorbent loaded by toxic metals is a solid hazardous waste which could cause significant secondary pollution due to potential possible additional release of metal ions. Therefore, the main subject is direct reutilization of spent adsorbents which can further economically and realistically offer new features, like recycling metal adsorbed, or formation of functional SiO-based nanocomposites. The nanoporous structure and negative surface charges enable steel slag-derived amorphous calcium silicate hydrate (CSH) to retain effectively the incoming metal ions (e. g. Au, Ag, Pd, Fe, Co, Ni, Cu, Zn, Ce, Y, and Gd) by chemisorption. Sparked by natural carbonation 'weathering', which ultimately sequestrates atmospheric CO by alkaline silicate minerals to leach calcium from mineral matrix, the decalcification reactions of metal-bearing CSH results in successful recovery of noble metals (Ag, Au, Pd) upon NaOH etching the resultant SiO support. Further, SiO-based heterostructures, containing nanocrystalline metals (e. g. Au, Ag, Pd, Fe, Co, Ni, Cu, and Zn) or rare-earth oxides (e. g. CeO, YO, and GdO), are formed after reduction in H/Ar (5 vol% H) flow, which is also very important for the multipurpose immobilization of diverse hybrid materials on SiO surface (e. g. Cu-Ag@SiO, Cu-CeO@SiO, and Cu-Ag-CeO@SiO).