Precious Metals Refining: Alumina Catalyst Methodology
Precious Metals Refining: Alumina Catalyst Methodology
Traditionally, the precious metals refining of alumina catalysts begins with the process of recovery of the platinum group metals (PGMs) and rhenium by dissolving the spent catalysts in strong caustics or acids. This hydrometallurgical recovery process is commonly referred to in the industry as ‘digesting’.
Except for aluminosilicates (or zeolites), digestion is an effective precious metal recovery method from spent process catalysts in most cases. Certain events and circumstances encountered over the life of the alumina catalyst, however, can create many problems when trying to digest:
· Overheating during operation can harden substrates (gamma alumina converting to theta or alpha alumina), rendering them insoluble to even powerful solvents.
· Excessive fines or carbon content can prevent the exposure of the catalyst surface area to the solvents.
· Base metals present in the feed, or additives introduced to extend catalyst life, can create chemical imbalances, and interfere with the desired chemical reaction thereby restricting the precious metals recovery.
Individually, each of these factors can block the precious metals recycling process, but in combination these effects can be great. In some cases, as much as 20 or 30% of the rhenium contained can remain insoluble.
Should the insoluble materials still hold precious metals, the hydrometallurgical refiners must send them out to a copper smelter to recover the PGM…but the rhenium is lost.
Alternatively, a precious metals refiner that begins using a pyro-metallurgical technology (for example, Sabin’s Pyro-Re™ process) will ultimately recover virtually all rhenium from spent alumina catalyst lots. This maximizes the return value to the catalyst owner, as payment is made based on the total precious metals content.
Wise customers will watch the precious metals refining contract language very carefully: terms regarding the values being returned should be based on total precious metals contained and not on acid-soluble precious metals content. Settlement on acid-soluble values is almost always the equivalent of losing some of your precious metals’ assets.
If you have any questions or would like to chat more - please reach out to Brad Cook at bcook@sabinmetal.com
