Adsorption of chalcophile, siderophile, and lithophile elements from aqueous solutions using syngenetically modified biochar

Abstract

This study evaluates the adsorption capacity of syngenetically modified lignin-derived biochar for chalcophile (zinc, Zn), siderophile (copper, Cu) and lithophile (manganese, Mn) ions in single- and multicomponent solutions. Lignin, biochar feedstock, was chosen for the research. Lignin was pyrolyzed at 450°C for 2 h. The experiments studied how adsorption depends on adsorbent dose (0.10–0.30 g), pH (2–10), contact time (5–180 min), temperature (25°C–45°C), and initial concentrations of elements in solution (25–150 mg/L). The impact of contact time was also investigated using breakthrough curves. The adsorption of multicomponent, potentially toxic elements by lignin-derived biochar was lower than the adsorption for single-component, potentially toxic elements. In all cases, Cu(II) had the highest adsorption efficiency and capacity. The adsorption processes of Cu(II) were also the most spontaneous and thermodynamically favored. The ΔG° values of these processes were almost always negative and much lower than those during the adsorption of the other elements studied. The adsorption process in single-component and multicomponent Zn(II) and Cu(II) solutions and in the multicomponent Mn(II) solution was endothermic and physical in nature. The adsorption of elements in the single-component Cu(II) solution and the single-component Zn(II) solution by lignin-derived biochar was more in line with the pseudo-second order equation model (R2=0.8697 and R2=0.5359, respectively). The experimental data was modelled by various isotherm models. The results revealed that adsorption isotherm in the case of single-component Zn(II) was more in conformity with the Langmuir isotherm (R2=0.79), suggesting the dominant adsorption of lignin biochar was via monolayer adsorption. Meanwhile, the adsorption isotherm in the case of single-component Mn(II) was well fitted to the Freundlich adsorption model (R2=0.79), indicating adsorption was multilayer in nature.