Printed Circuit Boards Leaching Followed by Synthesis of Gold Nanoparticle Clusters Using Plant Extracts

This work investigates the potential of 70% ethanolic leaf extracts of Rubus idaeus L., Cistus ladanifer L. and Erica andevalensis in the metal separation from synthetic unimetallic solutions of different metals and a leachate obtained from the leaching of PCBs. Results from the experiments with unimetallic solutions revealed R. idaeus and E. andevalensis extracts induced separation of more than 95% of the initial Au( III), while C. ladanifer separated similar to 78% of this metal. Thereafter, application of three plant extracts to real Au bearing leachate obtained from PCBs leaching, revealed about 96, 95 and 90% Au recovery with R. idaeus, C. ladanifer and E. andevalensis extracts, respectively with 15-60% co-removal of Pb and less than 15% of other metals. The reduction of Au(III) ions into Au(0) nanoparticles by R. idaeus extract was confirmed by molecular UV-Visible, and FT-IR analysis showed the involvement of plant secondary metabolites in Au bio-reduction and bio-stabilization. Particles obtained from the application of R. idaeus extract to the leachate were initially analyzed with XRD and results confirmed the presence of Au(0) with contamination of PbSO4, which was completely removed by washing with 1 M HCl. Thereafter, results from STEM-EDS analysis showed the presence of Au particles conjugated with organic material and other metals. Consequently, particles were subjected to another washing step with acetone. Afterwards, STEM-EDS showed pure Au microparticle clusters (similar to 0.8 mu m) with flower-shaped or apparently cubic morphologies, and HRSTEM showed the tiny nanoparticles (similar to 20 nm), which form the clusters. [GRAPHICS] .

Automated summary

This study investigates the potential of plant extracts from Rubus idaeus L., Cistus ladanifer L., and Erica andevalensis in metal separation. The results show that the extracts from R. idaeus and E. andevalensis have a separation rate of more than 95% for Au(III), while C. ladanifer has a separation rate of 78%. When applied to real Au-bearing leachate obtained from PCB leaching, the R. idaeus extract has the highest gold recovery rate of 96%.