Recovering Precious Metals From Catalysts – The Basics
September 1, 2013
Catalyst Recovery Part 1
Robert T. Jacobsen, Sabin Metal Corp.
When selecting a precious metals refiner, it’s important to first understand the basics of sampling, assaying and environmental issues, as well as the concept of leasing metal.
MANY CHEMICAL AND PETROCHEMICAL processes use precious-metal-bearing catalysts for facilitating and/or speeding chemical reactions. Precious-metal-bearing catalysts are also used for end-of-pipe pollution abatement applications, mainly to eliminate atmospheric emissions of volatile organic com- pounds (VOCs) and other harmful pollutants.
Most catalysts used for these applications are composed of platinum group metals (PGMs), including platinum, palladium, ruthenium and rhodium. In some applications, these metals are used in combination, and could also include gold. Various carriers, or supports, for these metals are employed depending on the application, including soluble or insoluble alumina, silica/alumina, zeolites or metal alloys. Homogeneous catalysts in aqueous solution are also common.
Regardless of how catalysts are used, or whether they take the form of monolithic structures, pellets, beads, extrudates or solution, most companies in the chemical process industries depend on precious metals refiners to recover the valuable metals from their spent catalysts. In addition to precious-metal-bearing catalysts, other sources of recoverable precious metals include process byproducts such as filter cakes, papers, cloths, polishing filters, floor sweepings, and protective clothing.
Many businesses facing profit squeezing overlook the potential to maximize returns for the remaining precious metals in spent process and pollution abatement catalysts. This is unfortunate, since working with the right refining organization can be a pleasant and rewarding experience, as well as profitable. Perhaps more important, though, is the fact that working with the wrong refiner can have serious — and costly — consequences. For example, many catalyst users may not be aware of the legal requirements concerning environmental discharges by the refiners they select, and violations are taken seriously by regulatory agencies at all levels.
This article is part of a three-part series that provides information to help you select and work effectively with a precious metals refiner. It describes some important activities performed in precious-metals recovery and refining, and discusses sampling, assaying, processing turnaround time, environmental concerns, and metals leasing and financing.
To accurately determine the amount of precious metals present in materials for recovery, three different sampling techniques are typically used — melt sampling, solution sampling and dry sampling. Each technique offers specific advantages, and determining the most appropriate sampling method depends on the type of material being processed as well as its estimated precious metals content.
The fundamental principle of sampling involves reducing large quantities of precious-metal-bearing material (as much as many tons) into small representative samples (which may consist of as little as a few grams). Sampling begins by converting precious-metal-bearing scrap into as homogeneous a state as possible so that the concentration of precious metals and other constituents is evenly distributed. Results of sampling the homogeneous mass thus represent an accurate ratio of the precious metals content in the overall matrix.
Melt sampling (Figure 1) employs a collector metal, such as copper, that is melted along with the precious-metal-bearing material. The resulting molten metal is poured into ingots, which are sampled at the beginning, middle and end of the pour. Subsequent processing steps yield an extremely high degree of accuracy, with tolerances as close as ±0.1% relative between samples. Metal mesh pollution-abatement catalysts may be sampled in this fashion.
Solution sampling (Figure 2) is used for precious-metal-bearing solutions, such as homogeneous catalysts, and is cost-effective as well as extremely accurate in determining precious metals content. This technique also involves achieving a homogeneous dispersion of precious metals and other constituents to the molecular level with precision comparable to melt sampling. Multiple samples are taken from different parts of the solution for further analysis.
Dry sampling (Figure 3) is used whenever materials cannot be dissolved in solution or are inappropriate to melt, either because of their structure or because of the cost associated with melting vs. the possible return. Because it is difficult to achieve homogeneity, dry sampling is more complex and potentially less precise than melt or solution sampling and therefore requires more judgmental skills than the other sampling methods. Materials for dry sampling are homogenized, generally by grinding large pieces into smaller and ever-finer particles. The material is allowed to free-fall into a full-stream, cross-cut, timed automatic sampler. Representative samples are taken periodically and sampling accuracy is typically ±2% relative. Most industrial precious-metal-bearing catalysts fall into this class because of the support material and are designated as heterogeneous catalysts. They are usually sampled with this technique.
Although inorganic supported catalysts could conceivably be sampled by melting the entire lot, this is not a practical approach. Ceramic-based catalysts require a high melting temperature that normal fossil fuels or induction furnace melting cannot achieve, and electric arc furnaces must generally be used. Maintaining lot integrity while concentrating the precious metal in a collector metal, pouring off the slag layer, and finally pouring the precious metal bullion layer is, in most cases, unrealistic, since many electric arc furnaces cannot be completely emptied. Therefore, most of these catalysts are dry sampled after they have been prepared to be free flowing and relatively void of volatile components.
Carbon-supported catalysts present a special case for sampling. Carbon catalysts cannot be melted, because carbon doesn’t melt and its high loss-on-ignition characteristics
(typically 80–90%) essentially prevent obtaining an accurate sample as received. (This will be covered in detail in Part 3 of this series.) Instead, the carbon must be burned off and the remaining residue dry sampled or possibly melt sampled.
Because precious-metal-bearing catalysts are made in many sizes and configurations (pellets, beads, monolithic structures, and extrudates, for example), determining the best sampling technique is crucial to recovering the most value from a spent catalyst.
Typically, precious metals used in catalytic processes — especially platinum and palladium — are not purchased on an outright basis by their users. Instead, they are “leased” by their users and held in a “pool account” at one of a number of physical locations, where the metal is commingled with other owners’ or lessees’ metal. Owners or lessees of these metals draw from this material on an as-needed basis or are provided with credit from a pool account on which to draw. From this pool, users can request delivery of metals for incorporation into catalysts.
Leasing platinum group metals (PGMs) for catalyst production is a financial transaction where the user has no desire to purchase the metal, but rather “borrows” it, the same as borrowing money from a bank. Lease rates vary widely depending upon supply and demand. In fact, the rate fluctuation is substantially greater than the interest rate on money, which is generally fairly constant and much more predictable. Most businesses can usually borrow money from lending institutions at one or two points above prime. However, metal leasing rates during the past five years have been as low as 1% per annum and as high as 200%! That incredible difference is caused purely by supply and demand.
Another common practice in the precious metals industry might be referred to as “metal banking.” Owners of metals will “lend” them to institutions or other businesses, which pay interest charges to the owners just as a bank would pay interest on dollar deposits. These institutions, in turn, lease out these metals to users as a method of generating profits.Banking is not very common with regard to PGMs employed by catalyst users, but is more closely associated with metals speculation or accumulation for future consumption. For example, a speculator or consumer may purchase metal today, but not require it physically for 6–12 months in the future. In order to defray some of the financing costs, they may “lend” this metal back to the market.
Most users make the lease vs. buy decision based on their perception of prevailing lease rates and trends over extended time periods. Many catalyst users prefer not to “own” precious metals, since they don’t want the costs to appear on their balance sheet as inventory or as a fixed asset; consequently, they are willing to incur the added expense of leasing. They also may be averse to assuming the risk associated with metal price variability. Typically, people who lease precious metals are not consuming them, but instead using them to produce their products or having others fabricate them into catalysts. Since much of the precious metal in catalysts is recoverable, users get their metal back after the recovery and refining process.
Because of these operating practices, it is in the best interest of precious-metal-catalyst users to obtain the highest possible recovery for their precious metals, and then to work with a refiner that offers the fastest possible processing turnaround time in order to minimize lease charges.
Accurate and repeatable assaying procedures depend on both classical and instrumental techniques for measuring the precious metals content of the materials being reclaimed.
A well-equipped analytical laboratory utilizes X-ray fluorescence equipment, atomic absorption (AA) and inductively coupled plasma (ICP) emission spectroscopy, and also incorporates classical volumetric, gravimetric and fire assay techniques. When all methods are used together, they provide the most thorough and precise approach for determining precious metals content in spent catalysts, thus assuring the highest possible returns.
In general, the specific techniques used for assaying are determined by the types of materials being processed. For example, alumina-substrate catalysts can’t easily be dissolved and instead must be subjected to fire assay methods that flux out the non-metallic materials, leaving the precious metals behind. The matrix (the material other than the precious metals) always affects the assay method used. As in all analytical chemistry procedures, the matrix of the sample, as well as the particular mix of analytes, will determine such things as the collector metal used in fire assay, or which wavelength (or
combination of wavelengths) is used in ICP analysis.
One major difference between the typical analytical laboratory and the laboratory experienced in precious metal work inolves the region of accuracy and precision needed for satisfactory results. Many laboratories routinely perform very-high-accuracy, high-precision analyses when the level of the analyte is also quite high (10% or higher). Many other laboratories, especially environmental labs, are capable of analyzing extremely low analyte levels of ppb and lower, but at relatively low precision (e.g., ±20% relative).
Precious metal labs are usually not concerned with the extremely low analyte levels, because the resulting value of the metal usually does not justify reclamation. For example, 100 ppb of platinum in a lot as large as 10 tons is worth only about $30. Precious metal labs similarly seldom need to produce results with extremely high precision, since the system is often limited by the precision of the sampling protocol. Rather, the precious metal laboratory must be capable of producing highly accurate results at moderately high precision (±1% relative) at analyte levels on the order of 0.1%. These assays will be applied to lot sizes of several tons and will result in payments of hundreds of dollars per troy ounce contained. For example, the platinum in a 10-ton lot of material containing 0.1% Pt would be worth about $250,000.
The speed at which catalysts are processed and their precious metal recovered (known as the reclamation turn-around time) is the third key factor in maximizing returns. Faster reclamation turnaround minimizes the interest charges a user accrues for leasing replacement precious metals to eliminate process downtime.
The costs for PGMs have been fluctuating wildly over the past few years, at one point reaching as high as $1,100/oz for palladium and up to $900/oz for platinum. While prices have decreased since those highs, there still is good reason to seek out a precious metals refiner who will return maximum value to you.
Typically, it could take as long as three months to have a new catalyst fabricated, and just as long to have the spent catalyst reclaimed — a period of six months during which new metals may have to be financed. Consider a simple (and realistic) example involving a 40,000-lb shipment of 0.6% platinum catalyst with platinum at $650/oz, at a lease rate of 12%. Leasing the metal contained in this material would cost in excess of $5,000/wk. Therefore, if one refiner has a 6-wk turnaround and another a 12-wk turnaround, the additional six weeks would cost more than $30,000 in lease charges.
The variations in lease rates are governed by worldwide production for primary (mine production) sources and the immediate, local availability of the physical metal. For the catalyst user, PGM lease rates usually represent a significant cost, since “new” precious metals are often financed while spent catalysts are being recovered and refined. By providing faster spent catalyst-reclamation turnaround times, substantial cost savings may be realized, in many cases translating into thousands or hundreds of thousands of dollars each year. These are serious numbers, so there is a clear trend in industry toward establishing independent asset-recovery programs (or departments) functioning as profit centers for the recovery of precious metals within an organization.
When selecting a refiner, be aware of how the materials will be processed as well as those of the refiner’s other customers. Determine how any solid, liquid or gaseous byproduct is handled at the processing facility.
Ideally, there should be no hazardous waste materials shipped from a precious-metals processing facility, although some plants will ship them under approved procedures and conditions. Minimal pollutants should be emitted before, during and after refining. Exhaust air quality should be managed with state-of-the-art pollution control systems. The process water recovery procedure should minimize all sources of pollution. While each of these functions is fundamental, many potential pitfalls with regard to environmental compliance exist.
In the U.S., both the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Responsibility and Liability Act (CERCLA), or Superfund Act, address the direct responsibility of the generator (customer) and the operator (refiner). These laws mandate that both the company that is the source of the precious metals being recovered and the precious metals refiner share in the “cradle-to-grave” responsibility, as well as future liability, for the proper treatment and/or disposal of any waste materials. If the refiner commits any violation of environmental laws or regulations, the catalyst user could incur high legal costs and be subject to heavy fines.
Requesting detailed documentation on environmental compliance can help determine whether the refiner violates any applicable law or regulation. Check its use of appropriate pollution-abatement technology, such as afterburners, baghouses, wet scrubbers and liquid-effluent neutralizing equipment. Also, evaluate the refiner’s approval status with all applicable agencies at the local, state and federal levels. Most precious metals refiners willingly provide copies of environmental documentation.
Many interrelated variables associated with recovering precious metals from spent catalysts must be considered when evaluating a precious metals refiner. Consider the relationship with a precious metals refiner as a partnership — mutually profitable and based on trust and fair treatment. To achieve — and maintain this kind of relationship — consider the issues discussed here when evaluating and selecting a precious metals refiner.
- Select a refiner that uses state-of-the-art techniques and equipment.
- Choose a refiner that has a long and successful history and good reputation in the industry.
- Discuss the refiner’s performance and policies with its customers.
- Request appropriate reference material, including environmental documentation.
- Determine whether the refiner has the financial resources to pay you in a timely manner.
- Select a refiner that has full in-house capabilities. The use of outside subcontractors might affect your returns, in terms of values and timeliness.
- Ask the refiner about laboratory techniques and replications.
- Request detailed weight and analysis reports on your shipment.
- Ask if you are allowed to be present during sampling of your material and whether you can conduct your own independent analysis if desired.
ROBERT T. JACOBSEN is vice president of Sabin Metal Corp., (East Hampton, NY; Phone: (585) 538-2194; Fax: (585) 538-2593; E-mail:firstname.lastname@example.org).
He has an extensive background in the precious metals industry, starting in the mid-1960s when he served at Sprague Electric Co. in research, development, engineering and production of precious metals, ceramics and electronic components. He joined Sabin Metal in 1980 and has served in a variety of technical and management positions, including general manager and corporate technical director of the company’s Scottsville (Rochester), NY, refining facility. Over the years, he has been involved in development and production of pyrometallurgical and hydrometallurgical activities for recovering maximum values from recyclable precious metals. He taught chemistry at a number of American institutions, including Clarkson and Cornell Universities in New York, and North Adams state and Williams Colleges in Massachusetts. He is on the board of the International Precious Metals Institute (IPMI) and serves on that organization’s Environmental and RegulatoryAffairs Committee. He has served as chairman of the Precious Metals Committee of the American Society for Testing and Materials (ASTM). He is a member of AIChE, the American Chemical Society, Sigma Xi and the New York Academy of Sciences. He holds a BA in chemistry from the Univ. of Rochester, a Master’s degree in education from Columbia Univ., and a PhD in chemistry from Clarkson Univ.