Re-valorization of Electronic Waste - Moss as a Biosorber for Gold Recovery?

Abstract

Electronic waste contains high amounts of gold and is therefore an important secondary source of this raw material. While conventional metal recovery processes are associated with environmental and health risks along with high energy demand, bio-based methods represent a sustainable alternative of growing importance. In our previous work, we discovered that the moss Physcomitrella patens not only selectively binds Rare Earth Elements (REEs) but can also bind gold with even higher efficiency. This prompted us to conduct a comparative study on the biosorption of gold by P. patens and two further moss species (Physcomitrium eurystomum and Physcomitrium sphaericum). Sorption capacities from model gold solutions reached 1.2 ± 0.4 mmol g-1, 1.1 ± 0.6 mmol g-1 and 0.8 ± 0.1 mmol g-1, respectively, and were up to 3.7-folds higher than these obtained for selected REEs. As expected, the efficiency of gold removal was affected by the pH of the metal solution. Furthermore, reduction of gold ions seems to play an important role in the gold recovery by mosses. Thus, although further studies on the mechanisms of gold recovery by moss species are needed, the work presented here provides important insights into the use of moss for the re-valorisation of e-waste as a secondary source of gold.