Transforming Oily Sludge and Food Waste via Co-pyrolysis into High-Performance Hybrid Activated Carbon for Selective Pb(II) Adsorption.

Abstract

Effective resource utilization is key to sustainable solid waste management. Co-pyrolysis as a method provides the advantage of resource utilization in the form of char and enhanced removal of a variety of pollutants through adsorption. In this study, an innovative hybrid activated carbon (HAC), obtained via co-pyrolysis of oily sludge cake (OSC) and food waste (FW) to effectively test its adsorption capacity for Pb(II) ions. The Biochar was activated with ammonium hydroxide (NH4OH). Two Kinetic models (pseudo-first-order,

pseudo-second-order) and isotherm models (Langmuir, Freundlich, Temkin, Dubinin- Radushkevich) were employed to analyze the adsorption process. The pseudo-second- order kinetic model and Langmuir isotherm best represented the Pb(II) adsorption

behavior. The Langmuir isotherm indicated a maximum Pb(II) adsorption capacity of 362.98 mg g-1

. When experimented for the effect of competing cations (Ca2+, Mg2+, Na+, K+) on Pb(II) removal, the presence of Mg2+ resulted in the maximum reduction of Pb(II) (removal efficiency, 7.52%). The synthesized HAC possessed a high surface area of 786.21 m2 g -1 . Fourier Transform Infrared (FTIR) and X-ray diffraction (XRD) analyses revealed the formation of new mineral precipitates (hydrocerussite, Pb3(CO3)2(OH)2) and cerussite (PbCO3) during Pb(II) adsorption, indicating that mineral precipitation and ion exchange are the dominant mechanisms. Notably, the prepared HAC demonstrated promising capabilities for simultaneously removing multiple heavy metals including Pb(II), Cd(II), Zn(II), and Ni(II). Furthermore, the HAC exhibited excellent reusability, maintaining high Pb(II) removal capacity even after four regeneration cycles (90.5% removal). This indicates HAC’s potential for practical water and wastewater treatment applications.