Development of Dithiobiuret-Based Ligands for Coordination and Selective Extraction of Precious Metals

Gold. Silver. Palladium. Platinum. These elements are part of a group known as the precious metals, named for their highly coveted status and desired for both their lustrous appearance and their growing industrial applications. The combination of desirability and scarcity make the precious metals especially valuable, which directs research toward improved methods for obtaining and recovering them. Most modern methods of precious metal procurement begin with leaching or dissolving the metals in aqueous media from which the metal can be isolated and recovered. Solvent extraction is commonly employed for this purpose; however, it is often limited by a lack of selectivity or by the necessary use of environmentally damaging organic solvents. Therefore, it is the goal of this research to develop novel extractants that are both selective for precious metals and usable in more economically and ecologically desirable solvents. This thesis presents the synthesis and characterization of novel sulfur-based ligands known as dithiobiurets. These compounds are analogous to thiourea dimers and have previously shown indications of coordination to precious metals. A variety of dithiobiurets have been synthesized, with significant differences in properties manifesting from small changes in structure; this includes differences in colour, solubility, and physical state. These ligands are capable of coordination with precious metals, exhibiting unique binding modes for gold and palladium. For gold, a reductive elimination produces an ion-pair product, while palladium forms more traditional coordination complexes. Under solvent extraction conditions, dithiobiurets show selective extraction capacities in excess of 95% for both gold and palladium. For those ligands with hydrophobic substituents, this behaviour persists even when dichloromethane is substituted with toluene or hexanes as the organic phase. Moreover, some of the dithiobiuret ligands are able to extract precious metals without the need for any organic solvents; however, this comes at the expense of extraction rate. Ultimately, the disparity in ligand behaviour can be traced back to the differences in physical and chemical properties brought about by structural alterations to the dithiobiuret foundation.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Saskatchewan

Year dc:date.issued

2024

Author dc:creator

• Dessert, Braeden

Advisor dc:contributor.advisor

• Foley, Stephen

Committee members dc:contributor.committeemember

• Palmer, David
• Price, Eric
• Scott, Robert
• Wang, Hui
• Ritch, Jamie

• Dithiobiuret
• Gold
• Palladium
• Coordination Chemistry
• Solvent Extraction

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10388/16175

OAI identifier oai:identifier

oai:harvest.usask.ca:10388/16175