A question often asked in the recovery of precious metals from processing scrap catalysts is about “metal accounting”. In other words, how does one reconcile the known content of platinum (Pt), palladium (Pd) and rhodium (Rh) in a scrap catalytic converter with the quantity of metal actually recovered? And by extension, how does this relate to cash value?
The key takeaway is that during the process of precious-metal recovery:
Around 15% of the physical metal in-situ* is ‘lost’.
Around 20% of the in-situ cash value of the metal is lost.
To account for this, we consider the combined effect of physical losses, costs and fees in the processes of PGM recovery by smelting and refining, as well as other less-quantifiable factors that come into play pre-processing. Although simplifications and approximations have been used for this purpose, these are supported by our research and experience processing scrap catalysts.
A lot of dismantlers, scrappers and other cat dealers have very good knowledge of the amount of Platinum Group Metals (PGMs) in individual catalytic converters, whether by hard-won experience or by the increasingly reliable (?) catalogues commercially available. As far as is known (and I stand corrected), most of the available catalogues are based on the catalytic converter manufacturers’ specifications, i.e. as new. Departure from these PGM content specifications is however likely for a number of reasons:
Physical disintegration during the functional lifetime of the catalytic converter before it is scrapped. Dependent on age and vehicle usage factors.
After scrapping, during dismantling, storage & transportation, improper handling has been observed to physically break the monolith, resulting in some loss
Decanning, monolith** crushing and sampling have been observed to result in loss of monolith material if not done carefully.
These pre-processing losses are likely to be highly variable and are difficult to estimate. The only way to determine the precise PGM content is by elemental analysis of the (crushed and homogenised) monolith material immediately prior to processing. Some processing facilities offer an in-house or 3rd party laboratory analytical service, although handheld XRF (X-ray fluorescence) spectrometers such as those of Thermo-Scientific and Olympus provide accuracy and precision to near laboratory standard (and will be the subject of a later post).
Included here are losses that are unavoidable due to the technical processes of metal recovery, as well as those deductions which are frequently levied by smelters and refineries as part of their processing fees.
There are several metallurgical methods to recover the precious metals from scrap catalysts, including hydrometallurgical, pyrometallurgical and other novel techniques such as deep eutectic solvents or ionic liquids, amongst others. An overview of these methods will be given in future posts, though for the current purpose we will consider the typical process pathway for economically processing large quantities of PGM-bearing material, broadly:
Smelting: Pyrometallurgical treatment, typically in a plasma-arc or other very high temperature furnace, of crushed monolith to produce a PGM-enriched alloy. Non-recoverable PGMs mostly report to the slag, with recoveries typically in the region of 97% for Pt and Pd, and as low as 85% for Rh. In addition to these physical process losses, the cost of smelting (the ‘treatment cost’) ranges up to around $3.50 / kg of monolith matrix treated, or up to 5%*** of the gross in-situ value of contained metal.
Refining: Multi-stage hydrometallurgical (chemical) and pyrometallurgical recovery and separation of the PGMs to produce high purity bullion (99.95% or better for London Good Delivery). Here we consider the common approach of ‘paid metal’ to cover the charges, which may be in the region of 90% for platinum and palladium, and around 75% for rhodium. The refinery thus extracts its profit by withholding a percentage of the metal recovered. For our purpose this is considered a loss metal for the scrap cat dealer.
Taking all of these processing losses into account, metal losses of around 15% and cash value losses of around 20% can be expected from the gross in-situ precious-metal content of a catalytic converter.
These losses are compounded by current metal prices at or near historical lows, supply chain positioning and various other factors.
Follow our posts as we continue to discuss all aspects of the market as relevant to scrap catalyst dealers, and how to maximises the value of your autocat stock when processing scrap catalysts.
*In-situ: relating to the gross metal content in an unprocessed catalytic converter.
** ‘monolith’ is analogous to the frequently used terms ‘honeycomb’ or ‘matrix’, the synthetic extruded cordierite (Mg-bearing aluminosilicate) host of the thin layer of PGM catalyst.
***estimate variable, proportional to metal price and grade.