Is it economically worthwhile to recover non-precious metals such as nickel from spent catalyst?Mar-2021
Mao Chen, TMS3 BV, firstname.lastname@example.org
When considering this question, it is difficult to limit the response to a purely economic decision and disregard other factors which are gathering momentum as lead news items. Whilst environmental considerations and protection may, on occasion, lead to an increase in the process lifecycle cost overall, the reputational value and positive business profile benefits as well as the moral obligation, whilst impossible to quantify in financial terms, should not be underestimated.
Increasingly severe natural disasters caused by global warming and environmental management factors have meant that the consideration and implementation of energy conservation initiatives, carbon reduction processes, and environmental protection have become critical.
Global refinery spent catalyst production has increased due to the processing of heavy crude oil which deactivates catalysts faster and shows higher metal and carbon deposition. Such spent catalysts are classified by EPA as refining waste or hazardous waste, which are subject to stringent environmental regulations regarding their disposal. Spent catalyst, provided it contains only Al, Si, and Fe, can be disposed of without any special precautions or can be used in construction materials.
The recovery of valuable metals from the spent catalysts is an attractive option for their recycling and utilisation. Accordingly, recycling methodologies and eco-friendly cost-effective recovery processes have been investigated in order to minimise spent catalyst waste which also reduces the environmental impact.
One of the methods for this recovery, hydrometallurgy, has been displacing inefficient pyrometallurgy in many countries. Hydrometallurgy, also called the leaching process, is a method of using leaching agents to extract metals from spent catalysts. Soda roasting leaching, basic leaching, and acidic leaching are all common hydrometallurgy processes.
Some experimental results showed that after roasting spent Al2O3 based catalyst at 750°C for 30 minutes at an Na2O:Al2O3 mole ratio of 1.2, the leaching recoveries of vanadium and molybdenum from the spent catalyst were both over 95%.
A basic leaching process involves adding ammonium salts based solutions to previously ground spent catalyst, with a recovery rate of vanadium <96% and molybdenum <95%.
Acidic leaching of previously de-oiled, dried, ground, and decoked spent catalyst can recover almost all metals (Mo, V, and Co) simultaneously, with leaching yields of about 95%. In some acid leaching studies, the recovery rate of 97% was achieved by using organic acids such as oxalic acid and ethylenediaminetetraacetic acid (EDTA), whereas inorganic acids tend to have lower efficiencies, for instance with sulphuric acid, the recovery rate for vanadium and molybdenum was around 92%.
Hydrometallurgical processes are also used for nickel recovery from spent catalyst. Sulphuric acid leaching of powdered spent catalyst, followed by separation of iron as well as silica and other impurities, has achieved extraction of 98% nickel.
The recovered metals including Mo, V, Ni, Co, and Ni have enabled industrial applications for use as alternative raw materials for catalyst preparation and steel manufacture.
Therefore, the spent catalysts recovery process is a vital and viable option for waste recycling and reutilisation as it not only reduces reliance on natural resources with associated economic benefits but also reduces hazardous waste disposal loads.
TMS3 supports this process by facilitating compliant, efficient, and economic waste metal transfer transactions which contribute to streamlining the management burden and overall process lifecycle cost.
Carl van der Grift, Catalyst Intelligence, email@example.com
It depends on the Ni content, the nickel market price, and the presence of other contaminants such as water, (hydro)carbon, sulphur, or other impurities which affect metal recovery and metal refining costs. In general, one can say that catalysts with more than 10 wt% Ni can be recovered economically. On the other hand, even when the nickel cannot be recovered economically, it may be wise to recover even the lower nickel content at a cost to avoid liabilities with the storage of spent catalysts. Several spent catalyst/metal reclaimers operate pyrometallurgical processes which will recover (part of) the nickel and convert the alumina support into a non-hazardous, non-leachable slag. Such conversion by an authorised waste company avoids future liabilities.
Christian Bellino, Eurecat, firstname.lastname@example.org
The economics of recovery of base metals from spent catalysts is dependent on many factors. Each metal and catalyst may have unique characteristics, costs, and prices which influence the economics of recovery. Geographic and regulatory considerations can have a significant impact. Finally, there are the environmental aspects of a circular and sustainable economy to consider as a responsible corporate citizen.
Unlike precious metal catalysts, in which the metals are usually recovered to their pure metallic state, base metals can be recovered in several different ways. Figure 1 shows the typical circular recovery options for base metal catalysts. Disposal options are not shown and should, in general, be minimised.
The most common way to recover base metal catalysts is via regeneration and optionally rejuvenation. Limitations on recovery in this manner are usually physical. To reuse catalysts following regeneration/rejuvenation, their particle length and strength should be high enough that there is no risk of pressure drop developing in reuse. Short particles can be removed using special sieving techniques; however, the economics of recovery will suffer if the yield of usable material is too low. The activity of recovered catalyst is often close to fresh when proper techniques are applied. If performance is a concern, recovered catalysts may be applied in lower severity units. In some cases, the recovered catalysts may even be used in a completely different service than originally applied.
When catalysts become too short or weak for reuse, the next best use is reshaping the catalyst into new particles. There are many different options and applications for reshaping. One of the most common uses for reshaped catalysts is in guard reactors or beds. Activity requirements are generally low for this service and they are often sacrificial to trap feed contaminants.
Catalysts which have been poisoned by contaminant metals during operation are generally not recovered by regeneration/rejuvenation or reshaping and are best sent for metals recovery. Depending on the type of metal, concentration, metals pricing, and contaminant level, the cost of recovery can be partially offset by the value of the recovered products. In a few cases (specific metals, high metal pricing, and/or very high concentration), spent catalyst may even have positive residual value. Since many of the base metals used in catalysis are also used in various metal alloys, they are typically recovered as alloys or salts for use in steel production. In general, recovery of spent catalyst metals to a form suitable for reuse in fresh catalyst is not cost effective.
Eurecat actively participates in all the base metal catalyst recovery options discussed here. They can advise on the most economical approach to metals recovery for each catalyst and application, and facilitate processing according to the recommendations.
Rahul Bhaduri, Advanced Refining Technologies LLC (ART), email@example.com
Spent catalyst economics are dependent on market conditions (metal prices), business value, and volume through the recycler’s gate, operating expenses, and an optimised processing stream. Currently (Feb 2021), spent catalysts containing precious metals have significant value to the recycler because of inflated precious metal (Pt, Pd, Au, Ag) market prices. Conversely, spent catalyst comprising base metals (Mo, Ni, V, W, Co) has witnessed a considerable depression in metal values over the past decade, resulting in reduced payback, if at all, by the recycler to their refinery customer. As is the norm with most metal recyclers that do not yield high value products (rhodium, iridium, osmium, and so on), the ability to process high volumes at low opex with superior recovery is key to surviving an extended bear market.
Susan Simpson, Johnson Matthey, Susan.Simpson@matthey.com
With the vision of a circular economy for our products and a world that is cleaner for future generations, minimising disposal and designing out waste is essential. And in many instances, it makes economic sense as well.
Spent catalyst contributes significantly to the solid waste generated by our industry. Recovery of non-precious metals minimises disposal costs. Three main drivers determine whether recovery is economical: metal value, transportation costs, and processing costs.
Metal value is determined by the market commodity price. Currently, copper, nickel, and zinc products will typically generate a positive net value when recovered. Iron products generally result in a cost. Molybdenum could go either way, being very dependent on the current pricing.
Transportation costs are dependent on distance from site to the processing facility and the amount of material to be moved. If a site is remote, transportation costs can flip the economics of metal recovery. Also, if the spent catalyst has a lower metals content, the transportation costs can be a dominant economic factor.
Processing costs remain relatively stable. However, if heavy metals such as mercury, arsenic, or cadmium are present on the spent catalyst, recovery may not be feasible.
Other factors to consider include the reduction in disposal cost and TRI (toxics release inventory) recordings and shrinking resources of metals globally.
At Johnson Matthey, designing out waste with innovative catalyst solutions is core to supporting this vision. Our patented Core Shell catalyst technology places active catalyst material where it is needed most and leads to intensification of the catalytic reactions within a flow sheet. For example, Johnson Matthey’s KATALCO 57-6Q series of steam methane reforming catalysts has reduced the active nickel metal by over half while still maintaining the performance customers count on. In addition, coated components offered by Johnson Matthey can intensify a reaction while reducing the overall weight of material used by over half in steam methane reforming applications. Both solutions approach the recycling issue by reducing the waste materials generated.
The effects of the three main drivers determine if it is economical to recover non-precious metals from spent catalysts. In addition, next generation catalysts are being designed to minimise waste materials generated. Both support our industry’s commitment to environmental sustainability.