Q: What is your product?
The Tetronics plasma metal recovery system recovers precious metals (PM) and platinum group metals (PGM) from a range of waste materials, including spent catalysts, electronics waste and mine tailings/wastes.
Q: How does it work?
The waste is blended with fluxes (e.g. CaO), to reduce the slag melting temperature and increase slag fluidity, plus a collector metal (usually iron or copper), to extract the PM/PGM. The blend is fed into a plasma furnace, where the high temperature generated by the plasma arc (typically 1400 to 1600°C) allows the materials to separate into different streams. The volatile and organic content of the waste is driven off into the furnace exhaust gas while the inorganic content is melted to form a bath of layered slag and metal. (More below)
The collector metal percolates through the slag and dissolves the PM/PGM as it sinks by density difference, forming a layer of liquid metal in the base of the furnace that contains practically all the valuable metals. The slag overflows from the side of the furnace while the collector metal layer, which is typically 5 to 10wt% PM/PGM, is removed periodically and then cast and crushed into a form suitable for downstream metal refining operations. The result is that the PM/ PGM are extracted and concentrated in the collector metal alloy, increasing its value per kilogram and making it far more amenable to further refining by hydro-metallurgical techniques than the starting waste.
Q: How is it different?
The high temperature and tight control of the process chemistry, the continuous rather than batch nature of the process and the conditions in the plasma furnace provide the best possible conditions for the separation of the PM/PGM from the slag, and thus for the recovery of the metals.
Q: Where would it be ideally used?
Typically, either in a waste processing context alongside waste collection or mining operations or at a specialist PM/PGM refiners where the metals can be separated and refined for re-use.
Q: What benefits does it offer?
Industry-leading recovery rates for the PM/PGM (typically >98%), combined with a small scale, physical footprint and ‘excellent’ environmental and emissions performance. The slag is classified by the Environment Agency as suitable for sale as a construction aggregate.
Q: Any savings?
These are very high value materials - spent catalytic converters, for example, are typically worth £50,000 per tonne. The greatest savings of the Tetronics’ plasma metal recovery system actually results from achieving very high PM/PGM recovery rates compared with competing technologies.
Q: Where has it been used?
There are two plants operating in the USA, one in the UK, two in South Korea and one in Taiwan, plus two under construction; one in Japan and a further one destined for China.
This depends on throughput and scope of supply (associated upstream and downstream equipment) but a typical plant processing 2,000 tonnes a year of waste will cost between £3m - £4m.
Q: What about maintenance?
The plasma torches have some consumable parts that need replacing after a week of continuous use, which can be done in under a minute without any special tools. Beyond this and general housekeeping, the plasma furnace typically requires relining two to three times a year, depending on usage.
Q: Life span?
They are designed for a 20-year life, but its first plant was installed 30 years ago and is still going strong.
Answers supplied by Tetronics