Ion-exchange resins
Ion-exchange resins are high surface area active materials on an inert base that allow for the exchange of similarly charged ions. Because lignin and lignosulfonates have metal-complexing capabilities, research has been done to increase their use for ion exchange.
To produce sulfonated lignin with an ion-exchange capacity similar to that of commercial ion-exchange resins, phenolation of hydrolysis lignin, followed by resinification and sulfonation, was performed.The ion-exchange capacity was 3.2 meq g−1 for the lignin produced by this method, whereas commercial phenol-type and sulfonated lignin resins had a charge density in the range of 2–3 meq g−1.
The capacity of styrene-type cation-exchange resins produced under the same conditions varied from 4 to 5 meq g−1, which implied that sulfonated lignin had inferior properties to those of styrene-type ion-exchange resins.Another study investigated the condensation polymerization of lignosulfonates with glucose, which resulted in an ion-exchange capacity of 4.1 mmol g−1 and a specific surface area of 13–20 m2 g−1; the product could be used effectively to remove Cr3+, Cu2+, Ni2+, Pb2+, and Cd2+.The cation-exchange capacity of the lignosulfonates may be applied to sensor applications, despite pH sensitivity.