Silk sericin and chitosan biosorbents derived from waste biomass displayed good capacity and excellent selectivity for gold adsorption.
They are low cost but highly efficient and have good potential for recovery of precious metals from industrial process and effluent waters.
Chemical and spectroscopic analyses showed that both adsorbents are rich in alkyl, carboxyl, carbonyl and amine groups that played an active role in the metal adsorption.
The carbonyl and amine groups of silk sericin participated in gold adsorption, whereas gold was adsorbed on chitosan mainly by the amine groups.
Both biosorbents displayed large adsorption capacity for gold despite having very low surface area (ca.3m2 g−1).
Chitosan has higher capacity (>3.3mmolg−1) and greater affinity (Kd = 34,000) for gold adsorption compared to silk sericin, which adsorbed less gold (ca. 1mmolg−1) and has a Kd of 450.
However, separation studies using 2, 5 and 6-component gold solutions consistently showed that silk sericin has better selectivity (SelAu > 2.4) at comparable capacity as chitosan.
It is possible to recover gold at 99.5% purity by silk sericin and 90% if the solution
contained palladium and although chitosan can reach 99% purity, it is more sensitive to the other components of the solution.
The silk sericin used in this work is a raw biomass and did not undergo any additional processing.
It is believed that techniques including freeze-drying and compositing with polymers could be
used to increase the surface area and porosity of silk sericin, and thus increase their accessibility and capacity for metal adsorptions