The adsorption properties of steel slag-based porous geopolymer for Cu2+ removal

Blocky geopolymer was employed as a cost-effective and efficient adsorbent for the removal of Cu2+, and 72 wt% of steel slag was used as the raw material. This study focuses on the adsorption process and mechanism of copper ions by steel slag-based porous geopolymer (SPG). A series of adsorption experiments show that the adsorption of Cu2+ depends on the oxygen-containing functional groups and silica-containing functional groups of SPG. And a large number of blue flocs containing CuSiO3, Cu2(OH)2CO3, and Cu(OH)2 are attached to the surface of the adsorbent. Furthermore, it is considered that electrostatic attraction, ion exchange and chemical precipitation are the main adsorption mechanism. Based on adsorption isotherm and kinetics analysis, the adsorption process of Cu2+ conforms to the Freundlich isotherm model and the pseudo-first-order kinetic model. Therefore, multi-layer chemical and physical adsorption coexists, and physical adsorption controls the adsorption rate and adsorption potential. This study provides a fundamental basis for the removal of Cu2+ from aqueous environments by porous geopolymers with a bulk structure.