L-Lysine-Modified Lignin for Polishing Alkaline Road-Marking Wash Water: High Uptake of Cationic Dyes with Acid-Enabled Regeneration

Road-marking operations generate alkaline wash water with intense color and soluble cationic additives. A new biomass adsorption material (LML) was developed to address dye pollution in road-marking wash water effectively. Enzymatically hydrolyzed lignin was used as the raw material for the first time. L-lysine was modified to the structure of the lignin benzene ring using a simple one-step synthesis method, which endowed lignin with a large number of active carboxyl and amino functional groups to improve its adsorption capacity. The adsorption performance of LML for methylene blue in water was also investigated. The experimental results show that the LML has a high dye removal rate under alkaline conditions. The fitted adsorption model shows that the saturated adsorption capacity of LML for methylene blue (MB) is $129.4$$\mathrm{m}$$\mathrm{g}$/$\mathrm{g}$ and malachite green (MG) is $244.9$$\mathrm{m}$$\mathrm{g}$/$\mathrm{g}$, which is in line with the Langmuir isotherm adsorption model. The adsorption process is endothermic, which means that the adsorption capacity increases with increasing temperature. Kinetic studies showed that the adsorption process reached equilibrium within 120$\min$ following a pseudo-second-order kinetic model. The cycle experiment shows that the removal efficiency of the adsorbent for dyes can still reach 90 after five cycles, indicating a good practical application value for the polishing of road-marking wash water.