Process Engineering: Get the most from spent catalysts

The process of recovering from precious metals from spent catlysts is a necessary move.  Making sure that you recover fair market value demands accurate sampling.

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Throughout the sampling procedure, the refiner must adhere to applicable environmental codes and standards for effluent disposal and atmospheric emissions. Therefore, an ideal sampling system typically should be enclosed for dust control and evacuated under a low volume flow into a dedicated baghouse. The dust collected during this sampling process is also recovered and sampled separately. Its value — which can be substantial — is returned to the catalyst owners.

Other process issues
Accurate and repeatable assaying methods also play a major role in properly determining the values of remaining precious metals. Once the final samples are obtained, sophisticated instrumentation is used to measure their precise precious metals’ content. Among the equipment and methods employed in a well-equipped analytical laboratory is X-ray fluorescence to determine the approximate grade of recoverable precious metals. X-ray fluorescence helps fix the amount of copper to be added to the mix to obtain the desired bullion grade, and to provide information on the matrix or non-precious-metal constitution. Other assay procedures employ atomic absorption, inductively coupled plasma-emission spectroscopy and classic volumetric, gravimetric and fire assay techniques.

After sampling and analysis, the value of the precious metals in the entire spent catalyst lot, or “reject” as it is called after the pre-burning step, is determined and agreed upon between the refiner and its customer. Finally, the spent catalyst lot is loaded into an electric arc furnace (EAF) for refining. The EAF helps maximize precious metals recovery, essentially producing two end products: molten precious metals and slag, which contains trace amounts of precious metals and is also subsequently refined. The molten precious metals are made into ingots, which weigh about 500 lb each, and go to storage vaults.

The reclamation turnaround time also is a key factor in achieving the maximum return. Logically, a shorter turnaround minimizes interest charges a user accrues for leasing replacement precious metals (a common practice) or the necessity of purchasing PGMs on the volatile spot market.

Environmental concerns
You also must consider your legal exposure. Choosing a refiner that does not provide maximum recovery and fastest possible turnaround is costly, but choosing a refiner that follows marginal pollution-abatement procedures could become even more costly.

When selecting a refiner, find out how your materials and those of other customers will be processed. Determine how any solid, liquid or gaseous byproduct is handled and whether the plant uses state-of-the-art equipment, including afterburners, baghouses, wet scrubbers and liquid-effluent treatment equipment.

Ideally, no hazardous waste materials should be shipped from a precious-metals-processing facility. At a minimum, though, make sure the plant ships them properly and to approved treatment facilities.

Requesting detailed documentation on environmental compliance may also help you determine that the refiner does not violate any applicable law or regulation. In the United States, the Superfund Act (CERCLA) addresses the direct responsibility of customer and refiner. This law mandates that both the catalyst owner and refiner share in the “cradle-to-grave” responsibility, as well as future liability, for the proper treatment or disposal of any materials. Essentially, a refiner’s violation of environmental laws or regulations could result in heavy fines and legal costs for you.

Also, evaluate the refiner’s approval status with applicable agencies at local, state and federal levels. Most precious metals refiners are willing to provide copies of all required documentation. This could include permits under the Clean Air and Water Acts and proof that the company qualifies as a bona fide precious metals refiner as specified in the preamble to the Boiler and Industrial Furnace Rule and its amendments.

Full value
Obtaining maximum value from spent catalysts depends foremost on the thoroughness and accuracy of the materials’ sampling process, with assaying of the sample lots close behind. You must look carefully into these areas and work closely with the refiner whenever possible.
It’s also crucial that all environmental compliance regulations are adhered to fully. All else being equal, choose a refiner based on its pollution-abatement performance.

These steps should provide you with the knowledge and confidence to select or work with the proper refiner. Remember, too, that your relationship with the refiner should be viewed as a partnership and based upon mutual trust and fair treatment.

Richard J. DeSantis is vice president of corporate operations at Sabin Metal Corp., East Hampton, N.Y. He has extensive experience in the precious metals industry, and currently is president of the International Precious Metals Institute. E-mail him at rjdesantis@sabinmetal.com.

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