Recovering and refining precious metals
November 1, 2015
Some factors to consider when choosing a route for recovering precious metals from catalyst
BRADFORD COOK and ROBERT JACOBSEN Sabin Metal Corp
Precious metals are perhaps among the most recycled commodities on Earth, mainly because their value usually makes it worthwhile to spend time and effort to recover them. The process of recovering and refining precious metals has been around for a long time, but even today it remains somewhat of a ‘hidden’ industry. This article aims to clear up some of the most common myths surrounding what is considered both a science and an art for recovering maximum value from spent precious metal-bearing catalysts.
When spent precious metal-bearing materials are reclaimed, there are really only two essentials to consider: accurate sampling and precise analysis of the entire catalyst lot. That is because there are still organisations (or even individuals) who will offer to pay you for the remaining precious metals in your spent process catalysts based upon some unknown (mythical?) and unproved premise instead of actual precious metal content and an accurate assay during the recovery and refining process. A catalyst owner must be aware of this kind of transaction; do your homework, and check your quotes and contracts carefully.
Another area that feeds this myth concerns the recovery and refining process itself: the methods and procedures that ultimately extract the remaining precious metals from spent catalyst lots.
Two methods for PGM recovery
Precious metals refiners typically use one of two methods to recover and refine platinum group metals (PGMs) from spent catalysts. PGMs include platinum (Pt), palladium (Pd), ruthenium (Ru), and rhodium (Rh). Rhenium (Re), which is not considered a PGM, is also present in many spent catalysts and is a valuable precious metal too. These refining methods are pyrometallurgical and hydrometallurgical technologies. There is a clear distinction between these technologies that affects the outcome with regard to capturing the highest possible amount of remaining precious metals in the spent catalyst lot, including Re, now worth about $3000/kg.
Sampling is a series of processes used by precious metals refiners to create a homogeneous mass from spent catalyst lots
After a batch of spent precious metal-bearing catalysts is homogenised and a representative sample drawn, a series of laboratory instrument analysis procedures is conducted, commonly known as assaying. Sampling is a series of processes used by precious metals refiners to create a homogeneous mass from spent catalyst lots which are randomly sampled in order to determine the type and percentage of precious metals remaining in the entire lot. However, in cases where the lot size is large (as it usually is in the petroleum and petrochemical industries), sampling is accomplished from a moving stream (auto sampling).
Assaying 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. Once this is done, the actual refining – the processes that extract the precious metals by one of the two previously mentioned techniques – can begin.
Pyrometallurgical vs hydrometallurgical processing
What happens when spent catalysts contain a significant quantity of Re? Re is usually present in about a third of PGM-bearing hydrocarbon processing catalysts; for example, in combination with Pt for reforming naphthas into other desirable products. While all precious metals refiners are capable of recovering most of the Re content from spent process catalysts on soluble alumina carriers, until recently none has been able to recover virtually all of the Re content. There are many reasons for this, but the main reason concerns the inability to separate the remaining Re with a practical process for its recovery and subsequent refining. This is because refiners recover Re 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 Re 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. Insolubility occurs because the substrate may change phase as a result of overheating during years of operation, preventing dissolution, even with strong solvents.
A refiner who uses pyrometallurgical technology (for example, Sabin’s Pyro-Re® process) can recover virtually all the Re content from spent catalyst lots (semiregenerative and cyclic fixed bed), particularly from catalysts on substrates that cannot be dissolved with caustic chemicals. The Pyro-Re® process also offers advantages with regard to maximising the return value of all precious metals in the catalyst lot, including PGMs.
Cheaper is not better
Cheapness usually proves to be false economy. Take, for example, a precious metals refiner’s recovery/ refining reclamation contract that is five cents lower per kilo than the next lowest quote. The myth here lies in the fact that many refiners are middle men who simply broker materials out to third party vendors. In the precious metals refining industry, there are essentially three categories of refining organisations: full service refiners (those organisations that provide full in-house recovery and refining capabilities, including transport logistics to eliminate transshipping charges and delays for settlement returns); samplers/processors (those organisations which partially process materials, perhaps upgrading them somewhat and combining smaller lots into larger lots); and brokers (companies or individuals who simply buy and sell refining services and use off-site, third party refiners). We have seen some of these organisations promise returns as high as 99.99% of remaining precious metals. The question arising here is: 99.99% of what? We have seen this happen many times over the years, where major refineries award recovery/refining contracts on the basis of a few pennies per pound difference in processing fees. In fact, there are organisations that require the lowest bidder to get the business, no matter what the cost. While they are understandably trying to cut costs, this strategy has little to do with the real money involved; the actual returned value of precious metals in the spent catalysts.
This is another good reason why catalyst owners should consider working with a refiner who provides full in-house processing capabilities, 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 of stage of the process. Middle men simply add margin but no value. Many times, large lots of spent catalysts are sent to two or three different processing facilities, obviously adding costs and delays along the way.
‘Quality’ precious metals recovery and refining requires skilled people, sophisticated equipment and many years’ experience
When this happens, settlements are delayed, and the catalyst owner may have to finance replacement metals for new catalyst to ensure a seamless process flow.
‘Quality’ precious metals recovery and refining requires skilled people, sophisticated equipment and many years’ experience to complete the full cycle and arrive at accurate (and agreed upon) samples that are used to determine actual precious metals content in a spent catalyst lot.
Precious metals in spent catalysts
Documentation is supplied regarding the type and quantity of precious metals incorporated into process catalysts when they are purchased. You may even have had some of this material sampled and tested. However, there are many circumstances that can affect the ‘bottom line’ with regard to acquiring the highest possible amounts of remaining precious metals. Here are a few to consider.
First, consider the variability (contents) of precious metals loading when the catalyst was manufactured; we know that each catalyst bead is slightly different, so it stands to reason that each drum of catalyst is also slightly different. Anyone who manufactures a product composed of at least one extremely valuable ingredient is going to try very hard to keep the level of that ingredient at the bare minimum. In other words, it is not impossible that a drum filled with precious metal-bearing catalyst contains slightly less precious metals content than was contracted for. On the other hand, sometimes half the drums contain less than the average, and half contain more than the average. An average is an average.
The second key issue is the amount of water the catalyst contains prior to a processing campaign which typically lasts for a number of years. The average water content may be listed on the certificate when the catalyst was purchased, but there is no way for the catalyst owner to accurately determine the average water content after the catalyst’s life cycle. The difference here can be significant with regard to total precious metals recovered.
Adding to the myth of actual precious metal-bearing catalyst composition are the other elements that accrue during processing such as coke, carbon, sulphur, and perhaps additives that may have been used to extend their life cycles. All these elements have an effect with regard to final recovery at the precious metals refiner.
However, when the spent catalyst lot is processed by hydrometallurgical techniques, these factors become more critical since they can interfere with the ‘digesting’ method and its ability to capture all of the lot’s remaining precious metals and its Re content as well. This should be clearly understood by the catalyst owner with regard to which technique – pyrometallurgical or hydrometallurgical – is used for recovery and refining. Also, when conventional pyrometallurgical processes are used, everything in an electric arc furnace melts but the Re may be lost by vaporisation of its oxide. Sabin’s Pyro-Re® process eliminates this loss.
Are you getting your original precious metals back?
Precious metals refiners of any significant size receive thousands of customers’ spent catalyst lots every year. It is obviously not cost-effective to refine each lot separately; that is, after the sampling stages are completed and remaining values are agreed upon with the catalyst owner. Instead, think of the entire recovery/refining process as you would think about how a bank works. You deposit your money, but when you withdraw it you do not get the same cash back. Obviously, it is irrelevant that you get the same cash back because that is not what matters. What matters is that your money was counted properly when you made the deposit, and that is why proper sampling and analysis is critical to help assure maximum returns of remaining precious metals.
Accurate sampling for maximising returns
In order to determine commercial value, the materials must first be treated or processed to allow them to be homogenised. Once the materials are rendered homogeneous, samples are drawn that represent the actual precious metals content of the entire bulk materials lot. There are a number of ways of doing this: melting, dissolving into solution, and blending are a few examples. Suffice to say that the method chosen to achieve this uniform state must be fit for purpose. The goal is to eliminate anything that can get in the way of obtaining that representative sample, because without that even the best analytical lab in the world will be of no use.
Once a precious metals refiner and the catalyst owner have agreed on a value, or ‘settled the lot’ as it is known in the industry, the money can change hands. Usually this money is in the form of high-purity metals returned to a pool account with a catalyst manufacturer so the customer can order another parcel of fresh catalyst, but other options are typically available for the final commercial transactions including replacement metals and/or payment.
In other words, the catalyst owner does not receive the same metal back, only its equivalent in new metal or cash. In the end, mathematical calculations determine the values, and the cost-effectiveness is achieved by the precious metals refiner by refining large batches of like materials in a single run.
Finding and working with the right refiner can make a significant difference in returns, thus enhancing overall corporate profitability
Enhancing corporate profitability Most hydrocarbon and petrochemical 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. Finding and working with the right refiner can make a significant difference in returns, thus enhancing overall corporate profitability. There are more than a few unfortunate stories about organisations’ selection of, and relationship with, its precious metals refiner. There may be serious legal implications if the refiner violates environmental regulations when processing spent catalysts.
Enhancing corporate profitability
Most hydrocarbon and petrochemical 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. Finding and working with the right refiner can make a significant difference in returns, thus enhancing overall corporate profitability.
There are more than a few unfortunate stories about organisations’ selection of, and relationship with, its precious metals refiner. There may be serious legal implications if the refiner violates environmental regulations when processing spent catalysts.
With the dynamics of cost, profits and possible legal issues, it is clearly in your best interest to work with a precious metals refining organisation that does the following:
- Provides the highest possible returns
- Provides rapid processing turnaround time
- Complies with applicable environmental standards concerning process effluent disposal or atmospheric discharges at its facilities.
There are many criteria to consider when selecting a precious metals refiner. Mainly the rules come down to specific areas that can be controlled and that apply to virtually all refiners who process spent catalysts containing PGMs, Re or other precious metals. These include the policies and procedures associated with the refiners’ sampling, assaying, processing and logistics arrangements. Each of these areas is briefly covered as a way of examining how to select and work with the right refiner to meet the catalyst owners’ specific requirements.
The key to selecting and working with a precious metals refining organisation hinges upon due diligence on the owner’s part with regard to determining all of its policies and procedures, including point-to-point transport logistics which will also reduce costs and speed processing and thus return materials’ values quickly. Key emphasis must be placed on the refiner’s environmental policies and procedures.
Pyro-Re® is a registered trademark of Sabin Metal Corporation.
Bradford M Cook is Vice President Sales and Marketing with Sabin Metal Corporation, with an extensive background in the precious metals industry.
Robert T Jacobsen is a Vice President of Sabin Metal Corp, with a background in the precious metals industry, starting in the mid-1960s. He holds a BA in chemistry from the University of Rochester, a master’s degree in education from Columbia University, and a PhD in chemistry