Adsorption of the aurocyanide, Au(CN)2- complex on granular activated carbons derived from macadamia nut shells – A preliminary study

In this study, waste macadamia nut shells were investigated for potential use as a hard organic precursor for the production of a granular activated carbon material. The processing of the macadamia shells commenced with the carbonised of the shells under a nitrogen atmosphere. This was followed by the physical activation of the shells under a carbon dioxide atmosphere, which was carried out at different temperatures to investigate the effect of the activation temperature on pore formation. The pore structure and gold loading capacity of the synthesised activated carbons were investigated. The porous nature and surface structure of the macadamia shell based activated carbon were examined by Scanning Electron Microscopy (SEM) at various stages of manufacture. In addition, gold loading studies were carried out in conjunction with elemental mapping of the activated carbon surface to determine the gold adsorption sites. The studies have revealed that the macadamia shell based carbons, activated at higher temperatures have a gold loading capacity that is comparable to the commercially available coconut based activated carbons.

Graphical abstract(Left) SEM image of CO2 activated macadamia-based carbon at 10 μm, indicating inner micropores within the wall structures of the carbon. (Right) Residual gold in solution and gold loaded on carbon material.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Carbonised waste macadamia nutshells under N2 at 800 °C were activated under CO2 at 800–1100 °C. ► The surface area and micropore area/volume increase with increasing activation temperature. ► Macadamia GAC (at 1000 °C) have an Au loading capacity comparable to coconut based carbons. ► The empirical carbon activity rate constant of Au(I) complex in the macadamia GAC was 23.4 h−1.