How to choose a refiner for your precious metals catalyst
Kevin M. Beirne, Sabin Metal Corp., USA
Most hydrocarbon and petrochemical processors operate precious metals recovery or asset recovery departments in one form or another. These are typically managed as independent profit centers, 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 profitability.
There are more than a few unfortunate stories about an organization’s selection of, and relationship with, its precious metals refiner. A relationship with a refiner may have significant legal implications if the refiner violates environmental regulations when processing spent catalyst.
PGMs and Other Precious Metals
Precious metal-bearing catalysts are widely used for facilitating or accelerating hydrocarbon/ petrochemical processes (where they “rearrange” hydrocarbons into specific molecules); for hydrocracking lowquality feedstock into higher-quality, more commercially useful products; and for controlling/abating harmful or unlawful volatile organic compounds and NOx emissions.
Catalysts help reduce energy use in a wide range of other petrochemical/chemical manufacturing processes. For all these applications, the catalysts typically contain platinum, palladium, rhodium or ruthenium; these metals are commonly referred to as platinum group metals (PGMs). Hydrocarbon processing catalysts may contain two or more PGMs, and they may also include rhenium (another valuable precious metal) in addition to gold, silver or other metals. A variety of carriers, or supports, for these metals are also used, depending upon application; these typically include soluble or insoluble alumina, silica/alumina or zeolites (FIG. 1).
Over the past few decades, worldwide demand for PGMs has increased significantly, mainly as a result of emerging economies. However, the volatility of global financial markets and geopolitical instability has also served to escalate costs for many precious metals. Precious metals costs represent only a small portion of the total processing/production dollar with regard to raw materials, equipment, personnel, transportation, etc. Nonetheless, they can still be significant when their market value is factored in, along with leasing costs for replacement metals, delays in transit and processing time for recovery and refining, and legal implications if the precious metals refiner commits an environmental infraction.
With the dynamics of costs, profits and possible legal problems, it is clearly in an operator’s best interest to work with a precious metals refining organization that does the following:
1. Provides the highest possible returns for PGMs from spent catalysts
2. Provides rapid processing turnaround time
3. Complies with applicable environmental standards concerning process effluent disposal or atmospheric discharges at its refining facilities.
Choosing the wrong refiner can prove to be an expensive and troublesome mistake.
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 that process spent catalyst with PGMs. These include the policies and procedures associated with the refiner’s sampling, assaying, processing and logistics arrangements. Each of these areas are briefly covered as a way of examining how to select and work with the right refiner to meet a plant’s specific requirements.
Precious Metals Sampling
To accurately determine the amount of precious metals present in materials for recovery, refiners typically use three different sampling techniques. These techniques are dry sampling, melt sampling and solution sampling. Each of these techniques offers discrete advantages; determining the most appropriate sampling method depends on the type of material being processed, as well as its estimated precious metals content.
In-House Moisture And Contaminants Removal
To provide an accurate determination of remaining precious metals in spent catalyst lots, representative samples of these catalysts must be obtained under accurate and repeatable conditions. Over time, process catalysts become contaminated by sulfur, carbon, volatile organics, moisture and other unwanted elements. As a result, when the catalyst is removed from the process, it is usually moist and sticky, and it will not flow freely through automatic sampling equipment. Contaminants in the catalysts must first be removed to ensure accurate sampling and analysis of the remaining precious metals. This process is accomplished with an indirectly fired rotary kiln (FIG. 2), which not only greatly enhances sampling accuracy to ensure maximum recovery value of remaining precious metals, but also significantly reduces overall refining costs when handled directly at the refiner’s facility. This is a key issue with regard to the total cost of recovery and refining, and, by inference, to the overall profitability of a precious metals refining and recovery program. The typical rotary kiln will remove up to 25% of the materials’ sulfur content and up to 40% of the carbon content, usually at a rate of 300 lbs/hr to 1,000 lbs/hr.
Figure 2. Contaminants in the catalysts are removed with an indirectly fired rotary kiln, enhancing sampling accuracy and reducing overall refining costs.
Most contaminants associated with spent precious metal-bearing catalysts typically exhibit high loss on ignition (LOI), in addition to other contaminants previously mentioned. The removal of moisture and other contaminants is critical to the downstream sampling process. The reason for this is that the materials must be free flowing (with low LOI) initially to arrive at a final evaluation sample that is accurate to ±2%. Here, pre-burning can make a key difference; if the high moisture content and other contaminants are not removed, a suitably accurate sample cannot be obtained by the refiner, thus eliminating the possibility of providing a fair and true return value to the catalyst owner.
Figure 3. The highest-accuracy results for loss on ignition are determined when analysis is conducted as closely as possible to the sampling procedure.
Contaminants in spent catalysts also may be removed by a multiple hearth furnace or fluidized-bed furnace. Whatever the case, this first step (i.e., pre-burning) is critical to the sampling process. Just as important—at least from a financial perspective— is where and how the contaminants are removed. This is because many catalyst users must first ship large lots of spent catalysts (35,000 lbs to 500,000 lbs is a typical range) to an independent facility, where strip-burning removes their hydrocarbon content, and coke burning removes carbon. Another furnace may be required for the drying of fine particulates and other materials to eliminate moisture content. Offsite pre-burning involves additional turnaround time of up to several weeks, along with additional costs for transportation and for leasing replacement metals during the time the PGMs are unavailable to the catalyst user. Offsite pre-burning also adds costs for catalyst owners’ representatives, who must account for their clients’ materials. A refiner’s facility should be equipped with high-volume pre-burning capabilities, since high sampling accuracy requires that contaminants be removed from the mix first.
The effects of high LOI after pre-burning in an oxygen environment can account for significant weight reduction in the processed spent catalyst materials, so accurate measurements are important before and after any pre-burning steps. Also, samples must be hermetically sealed following pre-burning to mitigate weight gain from moisture absorption. Accurate LOI data is vital for minimizing measurement errors due to weight changes while a sample is in transit. In general, the highest-accuracy results for LOI are determined when analysis is conducted as closely as possible to the sampling procedure (FIG. 3). Consequently, it is prudent for the catalyst owner to select a refiner that handles in-house LOI determinations under the supervision of independent inspectors.
Time And Cost For Offsite Contaminants Removal
Added turnaround time and additional costs are the two main considerations associated with offsite strip and coke burning of spent catalyst materials. Unless these capabilities are available at the refiner’s facility, catalyst users must pay substantial transportation charges for shipping to an independent, offsite facility. It is not uncommon for the material to remain there for up to a month for processing before it is again shipped to the refiner for sampling, analyzing, recovery and refining.
During this time, the PGMs are unavailable to the catalyst user, and new metal must be acquired at current market prices and interest rates. As an example, with today’s interest calculations on platinum for a typical petroleum/hydrocarbon process at around 3.5%/yr, the interest cost per troy ounce per week is about $1.10 at the present platinum value of approximately $1,625 /troy ounce. There is another, equally important advantage of having a refiner handle the pre-burning procedure in-house: The control, or “accountability,” that the refiner has over individual catalyst lots eliminates the possibility that materials could be mixed in with unrelated materials from another organization. If that happens, an accurate calculation of actual catalyst value cannot be made.
After the pre-burning process, the spent catalyst lot is ready for sampling. Dry sampling 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. Precious metal- bearing catalysts applied in hydrocarbon and petrochemical processes are usually sampled with this technique (FIG. 4). Since it is difficult to achieve homogeneity, dry sampling is more complex and potentially less precise than melt or solution sampling. The principle of sampling involves reducing large quantities of precious metal-bearing materials (as much as many tons) into small quantities (as little as a few grams), which yields amounts that are suitable for accurate analysis.
Figure 4. Precious metal-bearing catalysts employed in hydrocarbon and petrochemical processes are usually dry sampled.
In the sampling process, a precious metals refiner typically will assign a tracking number to incoming spent catalyst materials from a customer (FIG. 5). Prior to sampling, the catalysts are tested for viscosity and for any elements or impurities that might pose workplace hazards to the refiner, to determine the most appropriate sampling approach.
As the name suggests, the sampling process reduces a large batch of spent catalysts into smaller amounts suitable for accurate analysis. The goal of any materials sampling method is to maintain the relative amounts of component materials in the mix while reducing the amount of the material to a practical level. This permits accurate determination of the remaining precious metals content in the catalysts.
Dry sampling involves the use of mesh screens, vibratory feeders and rotary samplers. A typical process begins by extracting two portions equal to 10% of an initial materials lot. Then, 10% samples of these portions are taken, resulting in two 1% samples of the initial lot. One of the 1% samples is used for an LOI test. This test burns moisture and other contaminants to further reduce sample volume, while the other 1% sample is further subdivided to create smaller, laboratory-sized samples for the determination of the precious metals content. Samples are then extracted for analysis from different fractions and/or different stages of the resulting sub-lot.
To put it simply, the sampling procedure begins by converting PGM-bearing spent catalysts into a homogenous mass so that molecules of precious metals and other constituents are evenly distributed. Results of sampling the homogeneous mass thus represent an accurate ratio of the precious metals content in the overall matrix.
During the dry sampling process, materials are allowed to free-fall in a stream into a cross-cut, timed automatic sampler. Representative samples are also taken periodically. Since precious metal-bearing catalysts are made in many sizes and configurations (i.e., pellets, beads, monolithic structures and extrudates), determining the best sampling technique is crucial to recovering the most value from spent catalyst.
Accurate sampling of hydrocarbon/petrochemical catalysts involves tight process control to ensure that each sample has the representative composition of the initial material lot. For example, materials must be weighed at every step of the sampling process to minimize the effects of atmospheric conditions (e.g., absorption of moisture) on any measurements performed on the samples.
Accurate and repeatable assaying procedures, on the other hand, require sophisticated instrumentation for measuring precious metals content of materials being reclaimed. A well-equipped analytical laboratory utilizes advanced X-ray fluorescence equipment (FIG. 6), atomic absorption and inductively coupled plasma emission spectroscopy. It also incorporates classic 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 catalyst materials, thus ensuring the highest possible returns. Generally, specific assaying techniques are determined by the types of materials being processed.
Figure 5. In the sampling process, a precious metals refiner typically will assign a tracking number to incoming spent catalyst materials from a customer.
Processing Turnaround Time And The Bottom Line
The speed at which spent catalysts are processed and their precious metals recovered (i.e., reclamation turnaround time) must also be considered, since this can impact both costs and profits. Faster turnaround reduces interest charges accrued for leasing replacement precious metals obtained to minimize or eliminate plant process/production downtime.
Faster processing turnaround time also reduces the need for purchasing precious metals on a volatile spot market for use in the timely manufacture of catalysts, allowing uninterrupted processing or production. Additionally, the refiner’s in-house capabilities for pre-burning spent catalysts avoids the necessity for trans-shipment of large lots of spent catalysts, which can introduce an entire new set of problems, as previously stated.
There are a number of nuances and fine details associated with the fundamentals of selecting a precious metals refiner. Essentially, however, selection criteria must cover—in as much detail as possible—the refiner’s sampling, assaying, processing and shipping procedures, including turnaround times and environmental compliance issues. All of this information should be made available to the plant operator.
Environmental concerns and legal implications
The legal implications associated with processing procedures at a precious metals refiner must also be evaluated. In addition to choosing the wrong refiner with regard to maximum PGM recovery and fastest possible turnaround, choosing the wrong refiner with regard to possible unlawful effluent or atmospheric discharges could become even more costly. The reason for this is simple: If a refiner violates an environmental law, not only is the refiner subject to legal action (most likely by more than one authority), but the catalyst owner will also be cited and held responsible, in most instances.
How To Select A Precious Metals Refiner
To ensure that a relationship with a precious metals refiner will be mutually profitable and based on trust and fair treatment, operators must address several key questions. This checklist may help:
• Select a refiner that uses state-of-the-art techniques and equipment
• Select a refiner that has a long and successful history and a good reputation within the industry
• Discuss the refiner’s performance and policies that it maintains with its customers
• Request appropriate reference material, including environmental regulation documentation
• Request the final destination for effluent leaving the processing plant
• Determine whether the refiner has the financial resources to arrive at a settlement in a timely manner
• Select a refiner that has full in-house capabilities, without the use of outside subcontractors that might affect returns in values and timeliness
• Ask the refiner for detailed weight and analysis reports on shipments
• Ask the refiner if sample materials are assayed in triplicate
• Ask the refiner if it is allowable to be present during materials sampling, and whether an independent analysis can be conducted, if desired.
Avoiding Problems In Refiner Selection
When selecting a refiner, one must not only be aware of how the plant’s materials will be processed, but also of how materials from the refiner’s other customers are processed. It is the operator’s responsibility to determine how any solid, liquid or gaseous byproduct is handled at the processing facility.
Ideally, no hazardous waste should be shipped from a precious metals processing facility. While this may no longer be possible because of increasingly stringent environmental regulations, some refiners will ship hazardous waste materials under approved procedures and conditions; an operator should be aware of this difference.
In addition, minimal pollutants should be emitted before, during or after refining. Exhaust air quality should be managed with state-of-the-art pollution control systems (FIG. 7). The refiner’s process water treatment procedures should minimize all causes of pollution. While each of these functions is fundamental, there are many hidden pitfalls surrounding them with regard to environmental compliance.
Request Full Documentation From Your Catalyst Refiner
Requesting detailed documentation on environmental law compliance may also help determine that the selected refiner will not violate any applicable law or regulation. To responsibly recover and refine precious metals, a refiner must use well controlled processes that comply with applicable environmental agencies, such as the US Environmental Protection Agency (EPA). In the US, legislation such as the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), or the Superfund and the Superfund Amendments and Reauthorization Act (SARA), establish guidelines for reporting and managing chemical and toxic emissions. The Super-fund Act makes it clear that a user of precious metal-bearing catalyst materials and its precious metals refiner are responsible for the materials and the processing of those materials in recovering PGMs. Many European countries have even more stringent environmental regulations.
Similarly, the Resources Conservation and Recovery Act (RCRA) encompasses the generation, storage, transportation, treatment and disposal of solid and hazardous wastes. The Clean Air Act (CAA) and the Clean Water Act (CWA) are mandated by the US EPA to set environmental standards for air and water, respectively. There also exists another, more recent series of laws under the overall umbrella of the USA PATRIOT Act that could have significant negative impact on precious metals users and refiners. The PATRIOT Act, in short, mandates that virtually all transactions involving precious metals must be fully traceable. The scope of this law is so broad that it makes sense to review it thoroughly before engaging any precious metals refiner.
One way to determine if a refiner can comply with all of these criteria is to check its use of appropriate pollution-abatement technology such as afterburners, bag houses, wet scrubbers, and liquid effluent neutralizing equipment. Also, the refiner’s approval status with all applicable agencies at the local, state and federal levels should be evaluated.
Most precious metals refiners will provide copies of required documentation, which could include permits under the CAA and CWA mandates, and proof that the refiner qualifies as a bona fide precious metals refiner, as specified in Subpart F of the RCRA regulations and the preamble to the Boilers and Industrial Furnace rule and its amendments.
The information here is designed to provide a general approach to seeking and working with a precious metals refiner for PGM-bearing spent catalyst materials. While each of the areas discussed is important on its own merits, the issue of a refiner’s compliance with regard to environmental regulations might be the most critical.
All else being equal (getting maximum returns on precious metals values as quickly as possible), environmental violations at a refinery have the potential to create problems for an operating company. These steps, and the refiner’s overall policies with regard to applicable pollution codes and standards compliance, should provide operators with the knowledge and confidence to select the right precious metals refiner for a specific application. In any case, the relationship with that refiner must be viewed as a partnership, and it must be based on mutual trust and fair treatment.