Selective Recovery of Superalloy Metals Using Ionic Liquid Solvents



The demand for high-performance metals, so-called Superalloys, is increasing by approximately 10-15% per annum. Their excellent mechanical strength and corrosion resistance at high temperatures give them a range of applications in the aviation (e.g. turbine blades) and oil and gas sectors.
Superalloys are difficult and expensive to recycle once scrapped. Key metals Rhenium, Tantalum, Cobalt and Tungsten represent over 25% by weight of the alloy. Of these high value metals, the latter three are considered by the EU as "Critical Raw Materials", with Rhenium being close to "Critical". Even Nickel, which composes 60% of the Superalloys, is a key strategic metal since substitution in many cases is impractical, with numerous applications in technologies to tackle climate change, for instance for its corrosion resistance and mechanical properties.
Current practices for recycling these key elements from turbine blades involves either Pyrometallurgical processing in large smelting plants, or Hydrometallurgical methods in strong acid mixtures. The former expends large amounts of energy, and while the latter is preferred on a local or national scale because of its lower environmental impact and capital investment required, but still suffers from certain disadvantages (e.g. environmental effects from acids, precipitates, sludge's to landfill).
To date there are no UK operations of either kind in the UK, and the vast majority of scrap Superalloy materials are transported to Germany, Holland or USA for hydrometallurgical recycling.
It is proposed to use specific types of novel ionic liquid to selectively extract and recover the valuable metals at a recycling efficiency at least equivalent to those using current techniques. The process has been proven to extract metals from surface finishing filter cake and battery waste, and the technology will be used here to treat turbine blade waste, which represents a market of approximately 3000-4000 tonnes per annum globally. Scrap from manufacturing will add substantially to this. Aviation turbine blades contain approximately 25% wt of metals classified by the EU as "Critical" or near-to critical (Co, Ta, W, Re), and 60% Nickel, which as well as Co, Ta, and Re, is classed by The House of Commons Science and Technology Committee’s Strategically Important Metals report (2011) as of "Strategic Importance". Approximately 30% of the global demand for turbine blades is supplied from secondary sources, with the UK providing none of the current recycling activities.
The proposed technology uses traditional hydrometallurgical equipment, and the process operates at close to ambient temperature using low cost, non-toxic ionic liquids that are 100% recyclable.
Significant energy savings and reductions in CO2 emissions in comparison to current hydrometallurgical methods are anticipated, and the process will contribute towards resource efficiency and sustainable recycling because of its extremely low secondary waste production. Furthermore, since the UK is a major consumer of these Superalloys, the technology will provide UK industry with oppoprtunites to take maximum value from the waste stream and close the loop on these valuable resources.

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