Supramolecular Gold Stripping from Activated Carbon Using α-Cyclodextrin.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Mining Engineering

Background:

• The gold mining industry relies on efficient methods for gold extraction.
• Cyanide-based processes are common but pose environmental concerns.
• Molecular recognition offers a potential avenue for selective metal ion binding.

Purpose of the Study:

• To investigate the molecular recognition of the gold cyanide anion (Au(CN)2−) by alpha-cyclodextrin (α-CD).
• To explore the application of this recognition for gold stripping from activated carbon.
• To assess the selectivity and efficiency of the process for potential industrial use.

Main Methods:

• X-ray single-crystal structure analysis of supramolecular complexes.
• 1H NMR and isothermal titration calorimetry for binding studies in solution.
• Density Functional Theory (DFT) calculations to model interactions.
• Experimental gold stripping from activated carbon.

Main Results:

• α-Cyclodextrin effectively binds linear metal-coordination complexes like Au(CN)2− and Ag(CN)2−.
• A 1:1 binding stoichiometry and a binding constant of ~10^4 M−1 were determined for Au(CN)2−/α-CD in water.
• The binding is enthalpy-driven, with hydrophobic effects and specific interactions contributing.
• Selective stripping of Au(CN)2− from activated carbon was achieved at room temperature.

Conclusions:

• α-Cyclodextrin exhibits strong molecular recognition for Au(CN)2−.
• This supramolecular interaction provides a selective and efficient method for gold stripping.
• The process holds potential for environmentally friendly and cost-effective gold mining applications.