Selective Extraction of Gold by Niacin

Gold recovery using a sustainable and inexpensive method has tremendous environmental and economic implications. We developed a highly cost-effective and sustainable method of gold extraction in which aqueous Au3+ is precipitated selectively as it is complex with the biomolecule niacin, having an overall formula, [AuCl4]−[2Niacin + H]+, abbreviated as I. This selective precipitation occurs from mixtures of Au3+ with Ni2+, Cu2+, and Zn2+ along with commonly occurring alkali (Na+/K+) and alkaline earth (Mg2+/Ca2+) metal ions. From single-crystal studies, it was confirmed that electrostatic attraction and supramolecular interactions are the reasons for such co-precipitation, which was also confirmed by spectroscopy. Using the method, about 96.5% of gold was extracted in 2 min from electronic waste composed of Au, Cu, and Ni. This method was also employed to extract gold from nanomaterial waste generated in laboratories. Niacin, being inexpensive and renewable, costing ∼US$ 6000 per ton in the local market, the method may be used for cost-effective, selective and sustainable extraction of gold from diverse raw materials.