Recovery of gold from electronic waste and soils using alpha-cyclodextrin derived from selected non-edible plants

Abstract

Gold recovery has been a central issue in a wide range of studies as a consequence of its high demand. The existing processes of recovering gold from different matrices are cyanide leaching and mercury amalgamation. These processes have detrimental effects to human health and the environment if poorly handled. In this study, the metal-coordination ability of alpha-cyclodextrin (α-CD) was employed to complex gold and thus isolate and extract it from different matrices of acid-digests of electronic waste and soil. The crude α-CD used was extracted from cassava and yam starch of the non-edible plant species using Escherichia coli cyclodextrin glucanotransferase (CGTase), with yields ≥ 62%. The reaction was monitored progressively by UV-Vis and checked with IR for the presence of α-CD. The crude α-CD extract was refluxed with gold containing-electronic waste and soil predigested in a mixture of NaBr/HNO3 for 4-7 days. Recoveries of 22.9% and 70.8% gold were achieved from electronic waste and soil, respectively using 0.1M α-CD. This approach is cheap, effective, and environmentally benign.