Life After End of Life

The limited lifespans of wind turbines and solar panels mean many of the vital materials involved in their manufacture are often lost to landfill. Amanda Jasi talked to the innovative companies striving to ensure renewables ARE renewable

SOLAR PV waste is forecast to reach 212m t by 2050 according to global projections by The International Renewable Energy Agency, working to a 1.5°C scenario. That waste includes silicon, silver, and copper, as solar panels reach the end of their life (around 25 to 30 years).

Meanwhile, Adamas Intelligence predicts that the global undersupply of the NdFeB alloy and powder used in their manufacture of wind turbines – with a lifespan of around 20 to 25 years – will amount to 60,000 t/y by 2030, rising to 246,000 t/y by 2040.

The ability to recover these valuable materials through the recycling process has been limited, but that looks set to change.

“Let’s go after the materials that have been neglected up to this point,” said Zebulon Hart, whose company, Verdant Beneficiated Resources, is targeting recovery from solar panel modules. “If we’re serious about an energy transition, that’s going to be a requisite.”

Pulverise and demagnetise, remagnetise, repeat

The use of a permanent magnet machine eliminates the need for gearboxes in offshore wind turbines, with a large turbine containing more than five tonnes of magnet material. But despite playing a fundamental role in energy generation, less than 5% of rare earth elements (REEs) are recovered from end-of-life products.

This is because products containing magnets made using REEs, including electronics and electric vehicles, are usually processed via bulk recycling. In these processes, components that can’t be manually separated are shredded together. As rare earth magnets are extremely brittle, shredding causes them to break apart into highly magnetic powders that stick to any nearby ferrous scrap. As a result, the magnet materials in that scrap are “melted down and lost”, explained Allan Walton, a professor of critical and magnetic materials at the University of Birmingham in the UK.

The university’s spinout, HyProMag, is advancing technology to recycle rare earth magnets using patented technology. Hydrogen Processing of Metal Scrap (HPMS) “liberates magnets from components,” said Walton. Specifically, HPMS solves the challenge of extracting and demagnetising neodymium iron boron (Nd₂Fe₁₄B) magnets, one of two primary rare earth magnet compositions.

Nick Mann, general manager of operations at HyProMag, jumped in to explain HPMS, which the company is currently using for recovery from end-of-life electronics. He said it relies on a hydrogen reaction with the magnet. When exposed to hydrogen at room temperature and pressure, the magnet reacts to form NdFeB hydrides, triggering volume expansion. “That volume expansion basically rips the magnet structure apart,” Mann said. “Simultaneously, the magnets become demagnetised.”

The reaction can be achieved without separating the magnet from magnet-containing components, so long as the hydrogen can reach the magnet. In HPMS, components are loaded inside a porous drum inside a hydrogen vessel. The drum tumbles during hydrogen exposure and as it is pulverised and demagnetised, the hydrided NdFeB powder exits via the pores for collection at the bottom of the vessel.

Following its process, the HyProMag team can remove contamination – such as nickel flakes or little bits of plastic – using simple techniques such as sieving. This can reduce the presence of particles from, for example, 5% down to about 400 ppm, sufficient to allow reuse in a new magnet.

Mann said: “As long as we can get the contamination down to sensible levels, which nine out of ten times we do, then that means we can short loop that powder back into a sintered magnet…If we’ve got carbon contamination, it makes the most difference in where you have to put it back into the loop. Carbon can replace the boron in the alloy, so if you have significant carbon then it goes back to chemical processing.

“[But] our preferred option for most scrap is to pass it through the shortest loop process,” said Walton.

Mkango Resources, which owns 90% of HyProMag through its subsidiary Maginito, is building a pilot line to complement HyProMag’s process. The process will chemically strip out rare earths from recovered material to pass back through magnet production, beginning at the mineral decomposition stage (See Figure 1).
Meanwhile, HyProMag has already proven the commercial viability of their recovery process using a pilot plant sited at the University of Birmingham. The pilot can intake loads of up to 2 t, and output 50 kg of powdered magnet material. The company is now working to scale up to a semi-continuous demonstration plant that can process 6 t loads and output 300–400 kg of magnet material per batch.

The demonstration plant will be at Tyseley Energy Park in Birmingham, backed by £4.3m from Innovate UK’s Driving the Electric Revolution (DER) fund. Will Dawes, director of HyProMag and CEO of Mkango, said that the first production runs will be carried out this year, with commercialisation planned for 2024. He added that as HyProMag’s technology continues to develop in the UK, Mkango is supporting further scaleup and rollout. Towards these goals, a HyProMag subsidiary has been set up in Germany, and a North American joint venture is targeting US capacity. “We’re also very interested in other jurisdictions, such as Canada and Japan, because this isn’t geographically limited,” said Dawes.

HyProMag’s efforts to prepare for managing future wind waste also include an Innovate UK-backed project, Re-RE WIND, intended to establish the UK’s first circular supply chain for rare earth magnets used in wind turbines.

Borrowing ideas

Based at the University of New South Wales (UNSW) Sydney in Australia, the Shen Lab, relying on process modelling and optimisation (ProMO) of reacting flows, is also developing solar panel recycling technology. The ProMO group is led by Yansong Shen, professor of chemical engineering at UNSW Sydney. Shen stepped into the solar panel recycling space when he realised his background in metallurgy could serve technology development.

He said: “In the metallurgy discipline, we hope to extract metal from silicon-based natural ore...for solar panel recycling, we hope to extract metal from the man-made silicon material.”

His team includes expertise in mineral processing, pyrometallurgy, and hydrometallurgy. It is developing a start to finish process for material recovery. Towards this goal, the group has performed numerous experiments and currently has more than ten patents in the pipeline.

According to Shen, crushing and particle separation is one key bottleneck. “We have one patent filed within this step and, within the step, we also have two more in the pipeline,” he said.

Shen explained thermal delamination, another bottleneck, saying: “We use a very traditional pyrometallurgy mindset, pyrolysis, because when we heat it up to around 500 to 550°C the EVA will be vaporised…[The process] has been customised and optimised for PV recycling by borrowing ideas from their coke-making experience.”

The researchers can then shred the solar cells before crushing and separation.

The patented aspect of the process is the use of steel balls for more effective material separation. To achieve this, at benchtop scale, researchers load the steel balls into the top of a vibrating and tiered sieving container, along with the shredded PV cell debris. Different sieve sizes hold back different debris, and fine residue collects at the very bottom. The group can then recover valuable material such as silver via leaching. Shen said silver recovery is the ProMO group’s current focus.

Guided by numerical experiments to screen out designs, the group has developed a suitable thermal delamination furnace and tested several reactors for chemical leaching. Shen said the group is now ready to develop a pilot and is already in discussions with industry partners to plan further scaleup.

The single most important component

Nripan Mathews at Nanyang Technological University (NTU) Singapore is working on solar panel recycling as part of a joint lab with the French Alternative Energies and Atomic Energy Commission (CEA), Singapore-CEA Alliance for Research in Circular Economy (SCARCE). An associate professor at NTU’s School of Materials Science and Engineering, his previous work revolves around processing electronic materials into newer types of devices, including perovskite solar cells. He now leads a team working to do the reverse.

His group set several constraints for their process, including that it would not use burning or any thermally driven oxidative processes. The main driver for this was to avoid oxidising the silicon and complicating the recovery of what he referred to as “the single most important component of the panel” in terms of the embedded energy. Because it is so difficult to recover, he said that it most often gets “trashed”.

An additional consideration was that many polymeric back sheets used in panels contain fluorinated compounds and burning these releases carcinogens and other problematic gases.

The team also set out to develop green chemistry process, and to pursue recoveries that “make sense” commercially, to encourage companies to close the loop. Adhering to their green chemistry goal, Mathews’ team enables access to the solar cell layer by first cracking the glass surface of the panel and soaking it in ethyl acetate for 30 minutes to an hour. The researchers then remove the glass to access solar cells beneath. The back sheet can then be removed by applying heat and peeling it away, or “attacking” the aluminium at the bottom of the solar cells until the aluminium is removed. Further chemical treatment can then be performed to recover silicon. Alternatively, after the glass is removed, the cells can then be crushed and sieved, and the researchers can recover material from the “smaller dimension material”, Mathews said. They can then leach out the metals to leave behind the silicon.

Mathews’ group is further exploring using the recovered silicon in batteries, and he noted that electric vehicle manufacturers are using it to improve battery performance. His team is demonstrating the potential use for the recovered silicon by using it to fabricate anodes for coin cells, such as those found in watches.

The team mix the silicon with carbon in a ball-milling process. They then add a binder to create a slurry which they use to “print” battery anodes. “We found out as long as we can get most of the aluminium out, even if there is a bit of silver left behind in the silicon, that doesn’t affect our battery performance too much,” he said.

For now, they have already signed agreements with local companies to scale up silicon recovery from lab scale. But their direct next step in the lab is to be able to process 1 kg/h of panel waste.

But even as his group works to manage waste from existing technologies, Mathews encouraged solar panel manufacturers to consider how they can change designs. “Recycling should be embedded at the design…you have to think of the kind of material you would use, and the kind of assemblies you would use such that you could make it easier to recycle,” he said. “But that’s also a bigger challenge.”