Carboxylated lignin-based adsorbents for the efficient separation of Mg from aqueous solutions containing Li.

This study focuses on the preparation of bio-based adsorbents composed of carboxylated lignin (LC) and potassium polyacrylate (PAS) to remove Mg from aqueous solutions in the presence of Li. The successful incorporation of carboxylate groups into lignin was achieved, which was corroborated by FT-IR. Acid-base titration allowed the quantification of 11.7 ± 0.016 mmol of -COO groups per gram of LC. Radical polymerization was used to obtain the bio-based adsorbents. The structural composition was corroborated by FT-IR and their porous morphology was evaluated by SEM and BET isotherms. The incorporation of LC improved the adsorption capacity of the material for Mg, increasing it by 60 %. The adsorption process was more accurately described by the PFO and Redlich Peterson kinetic models. The effective adsorption and the ion-exchange adsorption mechanism of Mg on the adsorbents were confirmed by XPS, FT-IR, and SEM/EDS analyses. Furthermore, the adsorbent systems were shown to be able to adsorb Mg in the presence of Li, reducing the concentration ratio from 8:1 to 6:1. However, Mg ions showed higher affinity for PAS-20 %-LC adsorbents (α = 3.78) as compared to PAS adsorbents (α = 0.50), confirming that the incorporation of LC into the adsorbent enhances Mg adsorption. A preferential affinity toward divalent ions was observed in multicomponent solutions after the adsorption process. The Mg adsorption capacity on PAS-20 %-LC remained almost constant even with increasing ionic strength of the system.