Unraveling the Adsorption and Stabilization Mechanism of Pb 2+ in Phosphoric Acid‐Based Geopolymers: A Combined Experimental and Molecular Dynamics Study

ABSTRACT Phosphoric acid‐based geopolymer (PAG) is an acidic cementitious material and owns an obvious solidification/stabilization (S/S) effect on Pb 2+ in acidic environment. However, the adsorption and stabilization mechanism of PAG on Pb 2+ are not clear. In this study, high‐purity aluminum silicate powder was employed as material, aluminum dihydrogen phosphate (ADP), and phosphoric acid (PA) were employed as activators to prepare PAG adsorbent, which was used to adsorb Pb 2+ in aqueous solution. The microscopic mechanism was analyzed by X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A molecular dynamics model was established to simulate the interaction mechanism of PAG with Pb 2+ . The findings indicated that the equilibrium adsorption capacity ( Q e ) of geopolymer for Pb 2+ enhanced with the rising Al/Si molar ratio, but reduced with an increasing P/Si molar ratio. Q e in acetic acid environment was higher than that in deionized water and sulfuric‐nitric acid environment. In the deionized water, sulfuric‐nitric acid, and acetic acid environments, the maximum adsorption capacity ( Q m ) for Pb 2+ was 2892.04, 845.12, and 985.57 mg/g, respectively. The adsorption mechanism of PAG for Pb 2+ chiefly included ion exchange and monolayer surface adsorption. The SiOP chain in PAG could preferentially react with Pb 2+ to generate SiOPb chain; SiOP chain had better S/S effect than SiOSi, SiOAl, SiOAlOP, and AlOP chains.