Maximising precious metals returns from spent process catalysts
What you think you know, what you don’t know, and what you should know
Bradford M Cook
Sabin Metal Corp
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Most hydrocarbon, petrochemical, and chemical processors operate precious metals asset recovery departments in one form or another. These are typically managed as independent profit centres which, because of global economic uncertainties, have assumed more important roles in the past few years. Selecting the right organisation to recover and refine precious metals from spent process catalysts can make a significant difference in return values, thus enhancing corporate profitability. While this technology is thought of as a science and an art, there are many misconceptions about how precious metals refiners work with their customers; how they extract precious metals from spent process catalyst lots; how they provide return values to their customers; and, many more considerations. Some organisations perceive their precious metals refiners as merely “job shops,” moving from one to another at random between change-outs without much sense of “customer-vendor” loyalty. This may not be the best approach when working with a refiner as you’ll see later. To put it bluntly, there are precious metals catalyst users who don’t know fact from fiction about this industry; there are really no “official” or sanctioned standards for reference. Our intention here is to provide some insight into the workings of the industry, hopefully to provide you, as a catalyst owner with solid technical, practical, and productive knowledge to help enhance your profitability and peace-of-mind when selecting and working with a precious metals refiner.
Precious metals in process catalysts
Typically, precious metals employed in hydrocarbon and petrochem processes include platinum (Pt), palladium (Pd), ruthenium (Ru), and rhodium (Rh); these are usually referred to as PGMs. Rhenium (Re), while not considered a PGM, is often present in precious metal-bearing catalysts and is also a valuable metal. When it’s time to recover these metals, the first thing that you should know is that all precious metals refiners are not the same; in fact, there are significant differences among them. Some of these differences can result in added costs (trans-shipping, settlement delays, metals leasing fees, etc.), less rhenium values returned, and even liability for environmental violations. The differences in refining organisations mainly have to do with how they recover and refine PGMs, rhenium, or other precious metals from spent process catalysts. Essentially, there are two different refining technologies used for this purpose: pyrometallurgical and hydrometallurgical. This is important because there is a clear distinction between these technologies that will affect the outcome with regard to capturing the highest possible amounts of remaining precious metals in a spent catalyst lot—including rhenium (now valued at about $3000/kilo).
Sampling and assaying - the start of the recovery process
Fundamentally, the recovery/refining process begins with complex, sophisticated sampling and analysis techniques to determine what metals-and their quantities-are present in a spent catalyst lot (which might weigh 500,000 pounds and contain millions of dollars worth of precious metals). Simply put, sampling is a series of processes used to create a homogeneous mass from spent catalyst lots which are randomly “sampled” in order to determine the type-and the percentage-of precious metals remaining in the entire lot.
Assaying the samples ultimately enables the precious metals refiner and the catalyst owner to agree on the value of the recoverable precious metals contained in the spent catalyst lot. Once this is done, the actual refining begins: the process that extracts the precious metals by one of the two previously mentioned techniques. Much information has been disseminated on these subjects over the years, and is available from the web, previously published articles, and other sources; therefore, we’ll consider sampling and assaying outside the scope of this article. That said, it would be prudent to seek out this information in the public domain, as well as discuss it with precious metals refining organisations.
Added value from rhenium recovery
Because Re is both valuable and present in many spent process catalysts, you should be aware that while all precious metals refiners are capable of recovering most of the rhenium content from spent process catalysts on soluble alumina carriers, until recently none has been able to recover virtually all of the rhenium content. The main reason for this is the inability to separate the remaining rhenium with a practical process for recovery and subsequent refining. That’s because most precious metals refiners recover rhenium by dissolving their carriers (typically gamma aluminum oxide) with strong caustic or acidic chemicals (the hydrometallurgical or “digesting” process). While this process is capable of recovering the soluble PGMs and rhenium content in spent catalysts, an unknown portion of the desirable “pay metals,” sometimes as much as 20%, may remain behind due to the insolubility of their substrates or carriers. That insolubility occurs because the substrate may change phase as a result of overheating during years of operation, preventing their dissolution, even with strong solvents (Figure 1). Therefore, a refiner that uses pyrometallurgical technology (for example, the Pyro-Re® process) can recover virtually all of the Re content from spent catalyst lots (semi-regenerative and cyclic fixed bed), particularly from catalysts on substrates that cannot be dissolved with caustic chemicals. This process also offers significant advantages for maximising return value of all remaining precious metals in the lot (Figure 2).
Not all precious metals refiners are the same
You know the phrases, “Cheapness is false economy,” and “You get what you pay for.” It’s no different in this industry. There’s more than one type of precious metals refiner, and to serve your organisation well you must know the differences. There are full service refiners (those organisations that provide complete in-house recovery and refining capabilities-including logistics to eliminate trans-shipping charges and delays for settlement returns); there are “samplers/processors” (those organisations which partially process your materials, perhaps upgrading them somewhat and combining smaller lots into larger lots); and, there are brokers (companies or individuals who simply buy and sell refining services and use off-site, third-party refiners). A decision on which refiner to work with should be obvious when you consider the bottom line transaction. For example, if a refiner promises 99.99% return of remaining precious metals value to you, it’s prudent to question exactly how that can be done. In other words, ask the refiner, “99.99% of what?”
Do your homework thoroughly
Also, if you consider quotes of a few pennies per pound difference for recovery and refining services when significant amounts of money are involved, you may want to look deeper into the refiner’s business practices and capabilities. While refiners understandably want to cut costs whenever possible (just like any other business), this strategy has little to do with real money involved-the actual return value of precious metals in your spent catalysts. On the contrary, it simply proves that cheapness is false economy since there may be tens of thousands of dollars in precious metals value that the catalyst owner may never receive. Again, do your homework and look into a “full-service” refiner beginning with storage and shipping arrangements and continuing through in-house sampling and assaying, with an open line for the catalyst owner or its representative to be present at any stage of the process.
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