Cation-Dependent Gold Recovery with α-Cyclodextrin Facilitated by Second-Sphere Coordination

Area of Science:

• Materials Science
• Green Chemistry
• Coordination Chemistry

Background:

• Gold recovery is crucial for resource sustainability.
• Existing methods may involve harsh chemicals or low efficiency.
• Cyclodextrins offer potential for selective guest encapsulation and precipitation.

Purpose of the Study:

• To develop an eco-friendly and efficient gold recovery method.
• To investigate the role of alkali metal cations and cyclodextrins in gold complex precipitation.
• To elucidate the structural basis for selective gold co-precipitation.

Main Methods:

• Mixing alkali metal salts of [AuX4](-) anions with α-, β-, or γ-cyclodextrins (CDs) in aqueous solutions.
• Characterization of co-precipitates using single-crystal X-ray diffraction.
• Optimization of co-precipitation yield by adjusting temperature and molar ratios.

Main Results:

• Selective co-precipitation observed with α-CD and KAuBr4, RbAuBr4, or CsAuBr4.
• α-CD and KAuBr4 combination yielded the highest gold recovery efficiency.
• Structural analysis revealed 2:1 sandwich-type adducts driven by second-sphere coordination and hydrogen bonding, with a unique ion wire formation in the α-CD/KAuBr4 adduct.

Conclusions:

• Alkali metal cation-dependent second-sphere coordination with α-CD enables efficient and selective gold recovery.
• The study demonstrates a green and sustainable approach to recovering gold from aqueous solutions.
• Optimized conditions for the α-CD/KAuBr4 system provide a promising route for industrial application.