Removal of Pb(II) by lignin-sodium alginate composite in a fixed-bed column

A kind of adsorbent (Hydrogel-I) derived from sodium alginate and modified alkaline lignin (MAL) has been proved to possess a good adsorption performance for Pb(II)-loaded wastewater based on batch experiments. However, practical removal of Pb(II)-loaded-wastewater is a continuous and dynamic process. Herein, Hydrogel-I was further evaluated by packing it into a fixed-bed column. The breakthrough curves were established under different inflow rates (0.159-0.318 L/min), inflow directions (down-inflow mode and top-inflow mode), initial concentrations (5-20 mg/L) of Pb(II), and bed depths (20-60 cm). The results indicated that the slower inflow rate (0.159 L/min), down-inflow mode, lower initial concentration (5 mg/L), and higher bed depth (60 cm) prolonged breakthrough times (t_b) and saturation times (t_s). Compared to the top-inflow mode, the down-inflow mode guaranteed enough contact between Hydrogel-I and Pb(II). The values of adsorption capacity at t_b, t_s, and the removal efficiency under the down-inflow mode were higher than that under top-inflow mode by 2.33, 0.78, and 0.07 times, respectively. Hydrogel-I beads exhibited better adsorption performance than other adsorbents by comparing the rate constant (k_AB) and the adsorption capacity (N₀). The k_AB and N₀ of Hydrogel-I beads were calculated to be 0.0034 L/(mg·min^-1) and 678 mg/L. Hydrogel-I beads showed good regeneration ability in a three-adsorption-desorption cycle. Meanwhile, FT-IR analysis showed that the groups of -NH/-NH₂, C=S, and C-S were proved to be the adsorption sites. This study could prove valuable insight into the practical application of Hydrogel-I for dynamic removal of Pb(II) in an inflow-through column.