A significant contributor to the cost, energy consumption and carbon footprint of silver production is in the refining steps to remove, recover and recycle zinc from Parkes Crust silver-zinc intermetallic compounds.
A fundamental redesign of the silver process to improve dezincing kinetics — the rate-limiting step in silver refining — was recently reported in the Journal of Sustainable Metallurgy. The new Britannia Silver Process (BSP) introduces a redesigned vacuum dezincing unit and removes a liquation stage that requires the crust to be melted and mixed with lead.
“The use of natural-gas heating in the BSP dezincing process compared to electric-induction operation used in current processes delivers significant energy-efficiency improvements. Liquation in the current process is very energy-intensive, and its replacement also delivers significant energy-efficiency gains,” explains Steven King, a principal metallurgist with the Glencore Group (Baar, Switzerland; www.glencore.com), who conducted the work along with Alberto Striolo, professor of chemical engineering at University College London (UCL; www.ucl.ac.uk) and University of Oklahoma (Norman; www.ou.edu), at Glencore’s Britannia Refined Metals (BRM) facility in the U.K. The work carried out at BRM was conducted with a significant emphasis on process safety with no accidents, despite the experimental nature of the project, notes King.
A new silver-refining technology is cutting the carbon footprint of silver production
In pilot operation, the new process has demonstrated dezincing kinetics 44% higher than the original process, as well as a higher purity and recovery efficiency of zinc. “The pilot plant used to develop the process and validate performance metrics was a¼-scale rendition of a full-scale plant. Development of a demonstration-scale plant is now in progress. I would consider the dezincing geometry we have developed to be new and fully original,” says King. The pilot-scale operation also revealed a nearly 40% reduction in energy usage and 31% reduction in Scope 1 carbon emissions, while producing a silver product of comparable quality to traditional refining processes.
Another benefit of the BSP is the promise of recycling and reducing waste, such as slag. “Current processes dispose of this waste stream. The BSP presents the opportunity to recycle the flux and direct the zinc oxide/lead oxide residue to the zinc-recovery processes,” adds King.