Recovery of Precious Metals in Spent Process Catalysts

Catalysts, which are used to enhance and expedite chemical reactions, are a necessary part of pharmaceutical processing. That process not only involves using the catalyst in the synthesis of an active ingredient or intermediate but further involves recovery of the catalyst. When the catalyst includes Platinum Group Metals (PGMs), such as platinum, palladium, ruthenium, and rhodium, efficient recovery is particularly important in controlling costs in a manufacturing. Effective selection of a precious-metal refiner in the catalyst recovery process is a factor in achieving those cost savings.

Precious metals in pharmaceutical processing

Precious-metal catalysts are typically supported on carriers. Carbon supports are the most common carrier media for precious metal-bearing catalysts in the pharmaceutical processing industry. Heterogeneous palladium on carbon, platinum on carbon, palladium on alumina, and palladium on calcium carbonate are examples of catalysts and their supports that facilitate hydrogenation of intermediates. These catalysts do not last forever and, when spent, the PGMs from the catalysts need to be recovered. A precious-metal refiner can be used for this function.

Precious-metal recovery and refining

The precious-metals recovery and refining process involves complex procedures and policies that include materials documentation, contamination removal, sampling, assaying, recovery, refining, processing turnaround time, and environmental considerations. A refiner's effectiveness in executing these functions can determine the amount of PGMs recovered from spent catalysts, the turnaround time, and the value returned to a pharmaceutical manufacturer. The monetary value of PGMs varies with their price fluctuations on a given commodities market. To understand the criteria in selecting a precious-metal refiner (see sidebar), it is important to understand the equipment, sampling techniques, and environmental considerations in precious-metal catalyst recovery.

Selection criteria for a precious-metal refiner.

Equipment. Most refiners use a wide variety of equipment to process spent catalysts. This equipment includes rotary and crucible furnaces, kilns, roasters, thermal processors, pulverizers, granulators, screens, blenders, auto samplers, reactors, dissolvers, precipitators, electrolytic cells, and filter presses. In selecting a precious-metals refiner for a partner relationship, a pharmaceutical manufacturer should be aware of some of the key steps within the refiner's process and how the various equipment and tools are applied to spent catalyst lots. Sampling and assaying are two of the more important procedures that help to ensure optimum return of PGMs from spent catalysts.

Sampling techniques. Precious-metal refiners generally use three different sampling techniques: dry sampling, melt sampling, and solution sampling. The choice of method depends on the type of material to be processed and its precious-metal content. Because most catalysts for pharmaceutical processing are based on carbon, dry sampling is often applied to these materials. Dry sampling is the most complex of the three sampling approaches and is used when materials cannot be dissolved in a solution or are not suitable for melt sampling because of their structure. Because it is difficult to achieve true homogeneity by means of dry sampling, refiners using this technique should have expertise and sound judgmental skills. And for maximum sampling accuracy, spent catalysts must be properly prepared prior to dry sampling.

Dry sampling. For pharmaceutical catalysts, dry sampling begins with a thermal oxidation step to remove built-up organic contaminants, carbon, and moisture from the catalyst materials. Removing contaminants helps increase sampling accuracy significantly. A low-temperature burn in a tray furnace removes moisture, followed by a higher-temperature burn to remove carbon without volatizing the precious metals. Once these contaminants have been removed, dry sampling involves grinding the spent catalyst into smaller and smaller particles that are passed through a series of screens. Properly following this process of particle size reduction and successive screening can provide a typical representative sample accuracy of ± 2%. (see Figure 1).

Figure 1

Melt sampling and solution sampling. Similarly, melt sampling (see Figure 2) and solution sampling (see Figure 3) involve the reduction of spent catalysts and their PGMs into slurries and liquid solutions, respectively, from which the amount of precious-metals content can be accurately determined.

Figure 2

The choice of sampling approach is often critical to the amount of precious metal recovered from a spent catalyst. Clear communication between the refiner and the pharmaceutical manufacturer and, in some cases, a third-party expert hired by the pharmaceutical manufacturer to monitor the process (known as an "umpire") is necessary to ensure that no questions arise regarding the choice of sampling method and/or the final results of the sampling process.

Figure 3

Handling practices. A pharmaceutical manufacturer can check on certain best practices to ensure that a precious-metals refiner is handling its spent catalyst material properly. The material should be properly stored at the refiner, weighed on certified, inspected scales, and assigned a tracking or control number. The measured weight should be in agreement with the value determined by the pharmaceutical manufacturer prior to shipping the material to the refiner. The material should be supported by proper documentation by the refiner, including confirmation of the materials' description, piece counts (if applicable), and weights. Any differences between the refiner's information and that of the pharmaceutical manufacturer should be documented.

Assays. Once samples are obtained, the refiner and the pharmaceutical manufacturer typically assay the samples for their precious-metals content independently. Ideally, the percentage values of PGMs found in the samples by the two assays agree fairly closely. If not, the two values can be averaged to obtain a final agreed-upon figure for valuation of the PGMs in the spent catalyst.

Specialized instruments designed for materials analysis are used to perform assays on the sampled materials. These instruments include machines capable of performing X-ray fluorescence measurements for identifying contaminants still contained within the samples, atomic absorption and inductively coupled plasma emission spectroscopes and tools for performing classic volumetric, gravimetric, and fire assay techniques.

The type of materials to be assayed will determine the analysis approaches and equipment used in the assay. The techniques described above have been approved by the American Bureau of Standards and by the New York Metal Exchange/Commodities Exchange. In combination, these methods provide an accurate means of determining the amount of precious-metals content in spent pharmaceutical catalysts.

Advanced laboratories typically perform assays in triplicate to ensure the accuracy of PGM measurements. In a true partnership, a precious-metals refiner will invite a pharmaceutical manufacturer to not only be present while materials are being sampled, but also to conduct their own independent analysis.

Environmental compliance

The working relationship between a pharmaceutical manufacturer and precious-metals refiner involves many legal and environmental responsibilities. Even though the spent catalyst materials will be handled by the refiner, and the PGMs will be recovered at the refiner's site, the pharmaceutical manufacturer is as much responsible for ensuring that all applicable environmental codes and standards for waste material disposal and atmospheric emissions are adhered to by the refiner. It is also possible to check that a refiner has an approved status with all applicable agencies at local, state, and federal levels. A reputable refiner will gladly share the appropriate documentation on its facility's legal and environmental adherence, including permits under the Clean Air and Water Acts.

The Comprehensive Environmental Response, Compensation, and Liability Act, commonly known as the Superfund Act, addresses the direct responsibility of a precious-metals refiner and its customers in the United States. The law requires that both the company that is the source of the materials for precious-metals recovery and the precious-metals refiner share in the responsibility as well as future liability for the proper treatment and/or disposal of any materials.

To ensure that a refiner offers an environmentally friendly operation, equipment used for contamination removal, such as thermal oxidation systems, should be properly equipped with properly scaled afterburners to ensure complete combustion of organic contaminates. A refiner should also use and properly maintain neutralizing equipment when liquid effluent is involved. The refiner's water-treatment process should minimize all causes of pollution. Any atmospheric discharge must be managed with pollution-control systems that result in little or no pollutants being emitted before, during, and after the precious-metals refining process. Any gases generated by the process should be passed through a scrubber system for environmental control.

Looking forward

The high value of Platinum Group Metals (PGMs) in spent catalysts requires manufacturers to work with a precious-metal refiner to recover as much of those PGMs as possible. Choosing a refiner is the same as choosing a partner. The manufacturer and the precious-metal refiner both stand to gain but also both hold responsibility for the processing steps required to recover the PGMs. Careful choice of the right refiner that meets specific selection criteria is therefore crucial.

Kevin Beirne is vice-president of sales and marketing at Sabin Metal Corporation, 300 Pantigo Place, Suite 102, East Hampton, NY 11937, tel. 732.244.1451, fax 732.244.2231, kbeirne@sabinmetal.com.