Upcycling waste asphalt into calcium-enriched carbonaceous adsorbent for ultrafast Cd(II) immobilization

The valorization of construction solid wastes into functional materials presents a dual opportunity for environmental remediation and sustainable infrastructure development. Herein, we successfully repurposed asphalt-based solid waste into calcium-enriched carbonaceous adsorbent through sequential pyrolysis (C Asp ) and ball-milling (C Asp, bm ) techniques for 4 h at a constant rotational speed of 550 rpm. It was noteworthy that both the C Asp and C Asp, bm demonstrated an ultrafast adsorption efficiency for Cd(II), achieving equilibrium within 5 min. The maximum adsorption capacity (207.54 mg/g) was obtained through pyrolysis at 900 ℃ followed by ball-milling (C Asp, bm -900). The adsorption process closely followed the pseudo-second-order kinetic model and Freundlich isotherm, characterized by an ultrafast adsorption phase succeeded by a slower equilibrium stage. The adsorption process was spontaneous and involved multilayer adsorption, primarily governed by chemisorption mechanisms. The analysis of ions species and characterizations revealed that both pyrolysis and ball-milling processes enhanced the removal efficiency of Cd(II) by altering the surface composition and functional groups, specific surface area, and surface defects of C Asp and C Asp, bm . The primary mechanisms for Cd(II) adsorption on C Asp, bm -900 included ion exchange with Ca(II), precipitation in conjunction with CO 3 2- , and electrostatic attraction. Unfortunately, the presence of Cu(II) and Pb(II) significantly inhibited the removal of Cd(II), attributed to their markedly higher electronegativity. This study proposes a promising strategy for fabricating cost-effective and high-efficiency adsorbents through the upcycling of waste asphalt into functional materials, thereby enabling the effective removal of heavy metals from wastewater.