Mechanism and Quantitative Contribution Analysis of Pb(II) and Cd(II) Adsorption by Lignite Modified with Phanerochaete chrysosporium

To address the imbalance in aquatic ecosystems caused by lead and cadmium wastewater, this study proposes a novel approach using Phanerochaete chrysosporium-modified low-calorific lignite to prepare a lignite-based adsorbent (LBA) for efficient removal of Pb(II) and Cd(II) from wastewater. Through batch adsorption experiments, combined with kinetic, isotherm, and thermodynamic modeling, as well as multi-scale microscopic characterization techniques (BET, SEM-EDS, XRD, XPS, FTIR, and 2D-COS), the adsorption characteristics and mechanisms of LBA toward Pb(II) and Cd(II) were systematically investigated, and the quantitative contributions of each mechanism were analyzed. The results show that the optimal dosages of LBA for treating Pb(II) and Cd(II) wastewater are 0.4 g·L−1 and 1.3 g·L−1, respectively. Under initial pH conditions of 4~6 and initial concentrations of 10 mg·L−1 (Pb(II)) and 3 mg·L−1 (Cd(II)), both heavy metal removal efficiency and equilibrium adsorption capacity reached their peak values. The adsorption processes fit well with the pseudo-second-order kinetic model and the Langmuir monolayer adsorption isotherm model, achieving maximum saturated adsorption capacities of 51.20 mg·g−1 (Pb(II)) and 57.34 mg·g−1 (Cd(II)). The adsorption of heavy metals on LBA is synergistically driven by four mechanisms—ion exchange, mineral precipitation, complexation with oxygen-containing functional groups, and π-electron coordination—among which complexation with oxygen-containing functional groups dominates (32.6%), followed by mineral precipitation (27.1%), π-electron coordination (23.4%), and ion exchange (16.9%). After three adsorption–desorption cycles, LBA still maintained over 70% removal efficiency for both Pb(II) and Cd(II), demonstrating excellent regeneration stability. In real automotive paint wastewater, removal rates for Pb(II), Cd(II), Cu(II), Zn(II), Fe(II), and Mn(II) all exceeded 83%, indicating strong practical applicability. Overall, the lignite-based adsorbent developed in this study exhibits outstanding adsorption performance and high potential for recyclability, offering a promising new technological pathway and theoretical foundation for treating lead- and cadmium-contaminated wastewater.