Selective Gold Precipitation by a Tertiary Diamide Driven by Thermodynamic Control

Area of Science:

• Materials Science
• Inorganic Chemistry
• Computational Chemistry

Background:

• Selective precipitation of precious metals from e-waste is crucial for resource recovery.
• Diamide ligands have shown promise in precipitating gold from acidic solutions.

Purpose of the Study:

• To determine the selectivity order of a diamide ligand (L) for precipitating various metals.
• To investigate the thermodynamic stability and driving forces behind the precipitation process.

Main Methods:

• Direct competition experiments were conducted to establish selectivity.
• Thermal analysis was used to assess the thermodynamic stability of precipitates.
• Computational modeling, including ion exchange calculations, was employed to understand the precipitation mechanism.
• Hirshfeld, noncovalent interaction (NCI), and quantum theory of atoms in molecules (QTAIM) analyses were performed on crystal structures.

Main Results:

• The ligand L exhibits selective precipitation of gold, followed by gallium and iron, under specific conditions.
• Gold, gallium, and iron precipitates are thermodynamically stable at room temperature, unlike tin precipitates.
• Computational modeling confirmed the thermodynamic driving force and matched experimental selectivity.
• Intermolecular interactions, particularly halogen···halogen contacts and C-H···metal interactions, are key to gold precipitate stability.

Conclusions:

• The diamide ligand L demonstrates high selectivity for gold precipitation, with potential for recovering gallium and iron.
• Thermodynamic stability and specific intermolecular interactions dictate the observed selectivity order.
• This study provides fundamental insights into metal-ligand interactions for selective metal recovery applications.