Selective recovery of gold by novel lignin-based adsorption gels

Three different kinds of adsorption gels, viz., cross-linked lignophenol, cross-linked lignocatechol, and crosslinked lignopyrogallol, were prepared by the chemical modification of wood lignin. The adsorption behaviors of these gels for Au(III) along with some other metals were studied and compared to that of activated carbon. All three gels were found to be more selective for Au(III) than activated carbon with comparable adsorption capacities. Of the lignin gels, cross-linked lignophenol exhibited the highest selectivity for Au(III) and was found to be almost inert toward other metals tested. All three novel lignin gels as well as activated carbon were found to be efficient in reducing Au(III) to elemental gold, as indicated by XRD analysis of the sorbents taken after adsorption. However, a significant difference between the novel sorbents and activated carbon was found, i.e., the latter exhibited no selectivity among the metal ions tested, whereas the novel gels have a high selectivity to only Au(III). In addition, gold aggregates were visually observed in the case of the lignin gels and not in the case of activated carbon. This result provides a new approach for effective gold recovery.