Heavy metal removal from water using lignosulfonate-graft-poly(4-vinylpirydine) with grafts obtained by SI-ATRP

Sodium lignosulfonate (LSNa) was obtained from a pine tree biomass using a gas-phase acid pretreatment process (GPAPP). The resulting lignosulfonate was subsequently modified via esterification of the hydroxyl groups at its surface with α-bromoisobutyryl bromide (BIBB) under mild conditions (room temperature, THF solvent). The BIBB-functionalized lignosulfonate was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) spectroscopy, and employed as a macroinitiator for surface-initiated atom-transfer radical polymerization (SI-ATRP) of 4-vinylpyridine (4VP). Successful grafting of poly(4-vinylpyridine) (p4VP) onto lignosulfonate was confirmed by FTIR, TGA, XPS, GPC and NMR analyses. The ability of the resulting lignosulfonate- graft -poly(4-vinylpyridine) (LS- g -p4VP) for the removal of lead (Pb) and iron (Fe) ions from aqueous solutions was evaluated. Adsorption experiments were conducted at room temperature (25 °C), with the solution pH maintained between 5.5 and 6.0, a contact time of up to 180 min, and initial metal concentrations of 100 ppm and 50 ppm. Under optimal conditions, the LS- g -p4VP adsorbent achieved removal efficiencies of 78% for lead and 40% for iron within the first 30 min. In contrast, the unmodified LSNa exhibited significantly lower removal percentages of only 5% for lead and 16% for iron under the same conditions. These results demonstrate that LS- g -p4VP combines the advantages of a low-cost, renewable, and biodegradable biomass resource with significantly enhanced adsorption performance, exhibiting much faster and higher removal efficiencies for Pb and Fe ions than unmodified lignosulfonate and is competitive with many synthetic adsorbents.