Robert T. Jacobsen, Sabin Metal Corp., USA, argues that a thorough
understanding of sampling processes is the key to determining
the precious metals content of spent catalyst materials

A comprehensive article on recovering and refining precious metals from spent reaction catalysts appeared in the July 2003 issue of Hydrocarbon Engineering.1 This article discussed methods and equipment used by precious metals refiners for maximising returns of remaining precious metals in spent catalysts from hydrocarbon reaction processes. Most hydrocarbon/petrochemical processors employ fixed or moving bed catalytic reaction processes to facilitate hydrogenation of intermediates, and also to control and/or abate harmful or unlawful exhaust emissions for end of pipe applications.
Precious metals used in most catalytic reaction processes are referred to as platinum group metals (PGMs) and typically include platinum, palladium and rhodium. The previous article described in detail many of the key activities performed at a precious metals refining facility.
Specifically, issues such as sampling; assaying; processing turnaround time; documentation; and environmental concerns were covered. While each of these functions is important to the precious metals recovery and refining process, sampling procedures for spent catalyst materials are perhaps the most critical element with regard to maximising yields on remaining precious metals catalysts.
As a sequel to the July article, this article will provide more detail concerning specific sampling techniques and their influence on value received for spent precious metal catalysts. As a user of precious metal catalysts, it is in the reader’s best interest to have a clear understanding of how sampling processes help to determine precious metals content of spent catalyst materials, and ultimately the value that is returned to their owners.
Fundamentally, sampling spent catalysts containing precious metals can be compared to sampling any homogenous mass. The problem is that even new catalysts on substrates (carriers), such as soluble and insoluble alumina, silica alumina, zeolite, or carbon supports, are not homogenous masses. Indeed, after years of exposure to the extremely harsh catalytic reaction environment, spent catalysts are even further away from being considered homogenous, wherein ‘lies the rub’. If one imagines what occurs during the hydrogenation process, one can more easily understand that spent catalysts accumulate many different contaminants of various densities, among them sulfur, carbon, solvents and water.
In order to assure maximum (or as close as possible) accuracy in determining the quantity (and quality) of remaining PGMs in spent catalyst materials, the spent catalysts must first be ‘reduced’. This process basically involves working with large quantities of spent catalysts (many t) and ultimately ‘reducing’ them to smaller quantities (to as little as a few g), as well as eliminating all possible non essential contaminants. The goal is then to arrive at as precise a representative sample of the overall material lot as possible, in a material lot that is as homogenous as possible, so as to make as accurate a determination as possible of the actual value of recoverable precious metals in the lot. Clearly, this is easier said than done, as there are many processes, evaluations, equipment and systems involved in the sampling process. There are also vastly different sampling methods depending upon the circumstances. Then there is the matter of experience and expertise, as some sampling procedures, and their ultimate outcome, are solely affected by judgment. In any case, all of these steps must be accomplished to arrive at an accurate, final determination of value.