Recovering silver from solar panels using flotation

Solar panels are one of the defining technologies of the energy transition. But as the first generations of large-scale photovoltaic installations reach the end of their useful lives, a new challenge is emerging: what do we do with millions of tonnes of spent panels?

Australia is particularly exposed to this question. Around one in three Australian households has rooftop solar, and the country is expected to generate around one million tonnes of solar panel waste by 2035. Although panels contain large quantities of glass and aluminium, they also contain smaller quantities of higher-value materials, including copper, silicon and silver.

Silver is used because it combines exceptionally high electrical conductivity allowing tiny quantities of a very valuable metal to be distributed across a huge number of microscopic conductive pathways.

Silver represents only a tiny fraction of the mass of a photovoltaic module. The Queensland Government's recent solar-panel recovery pilot, for example, estimated silver at just 0.003% of panel mass. Yet across millions of panels, even these small quantities add up. The Silver Institute reported photovoltaic demand of 193.5 million ounces of silver in 2023, highlighting just how substantial the solar industry's consumption of the metal has become.

However the silver is finely distributed, embedded within the metallisation of the cell and bonded into the surrounding material. Recovering it selectively is therefore a separation problem and that is precisely where mineral processing enters the picture. Recent research from the University of Newcastle's Centre for Critical Minerals and Urban Mining, together with the ARC Centre of Excellence, published in the July issue of Minerals Engineering, has demonstrated that froth flotation could provide a new route for recovering silver from end-of-life photovoltaic cells.

Traditional research into silver recovery from end-of-life photovoltaic modules has focused heavily on hydrometallurgical approaches, particularly acid leaching. Leaching can be effective, but treating the entire feed chemically creates its own challenges. Large quantities of reagent may be required, and much of that reagent is effectively being used to process material that contains little or no silver.

The University of Newcastle work applies froth flotation as an upstream selective recovery step for metallic silver from end-of-life photovoltaic cells. In laboratory-scale experiments, delaminated cells from waste solar panels were processed using conventional flotation reagents and the results were striking. In a rougher flotation test using tap water, the researchers achieved approximately 98% silver recovery, with a 32-fold upgrade. The flotation response was also rapid, with around 80% recovery achieved within the first minute and around 90% after approximately three minutes. Perhaps most importantly from a flowsheet perspective, flotation reduced the material requiring subsequent leaching to just 2.8% of the original feed.

The researchers' cleaner-stage experiment illustrates the potential. A rougher-cleaner configuration increased the upgrade to approximately 63, at around 87% silver recovery, producing a concentrate containing approximately 47 wt% Ag.

Of course, these are only batch laboratory results rather than evidence of a commercial-scale flowsheet. In a recent preprint they have reported impressive continuous steady state results processing the silicon wafer sourced from almost half a tonne of solar panels, bordering on 100% silver recovery with 83-fold upgrade to around 50 wt% Ag.

There is still more work to be done around feed preparation, liberation, circuit configuration, reagent optimisation, scale-up and economics. But the conceptual leap is significant. This is exactly the sort of development that demonstrates why the scope of flotation continues to expand.

MEI's Flotation '27 will bring together researchers and practitioners to discuss everything from fundamental reagent chemistry and bubble-particle interactions to flotation kinetics, hydrodynamics, scale-up, circuit design, modelling, control and environmental considerations. The solar-panel work touches on almost all of these themes.

These are not simply questions about recovering silver. They are questions about how the mineral-processing toolbox can be adapted to the emerging world of secondary resources.

The ARC Centre of Excellence is a significant University of Newcastle credential. The fact that Newcastle was awarded $35m to lead a national centre, alongside universities such as Queensland, Melbourne, Monash, New South Wales and Curtin, is strong evidence that the research group is regarded as a leading Australian centre in this area and the Newcastle group has always had a strong involvement with MEI's flotation conferences. Their involvement in the solar-recycling research is an interesting illustration of how expertise developed around conventional mineral processing problems can be transferred to entirely new resources.

The energy transition is creating a paradox. Technologies designed to reduce environmental impact require enormous quantities of materials. Those materials have to be mined, processed, manufactured and eventually recovered. The challenge is therefore not simply to build more solar panels, batteries, wind turbines and electric vehicles. It is to develop systems capable of recovering the materials contained within them when they reach the end of their useful lives. That is where mineral processing has a vitally important role.

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August summary: the solar eclipse and a remarkable Cornish museum

August opened up with two more heatwaves, leading to drought conditions over most of England, including Cornwall. 

A parched Falmouth

The beaches have been packed, no more so than on the 12th of the month. August 7th-16th was  Falmouth Week, which  grew out of a sailing regatta whose roots go back to 1837. Today it's a Cornish mixture of sailing, harbour activity, live music, family events, parades and spectacular displays, bringing the town alive.

The 12th was particularly special as the Wednesday is usually dominated by an evening display by the RAF's Red Arrows, but this year there was another, more low-key evening air display and by an extraordinary coincidence the air display coincided with a 95% partial solar eclipse, the most significant solar eclipse visible from Cornwall since the total eclipse of 1999.

The aerial performances took place in the evening, from around 6pm, with the eclipsing Sun creating the backdrop as an eerie twilight descended.

Falmouth's Gyllyngvase beach at 6pm

95% totality just after 7pm

Although this was a rare occurrence I have to admit to being slightly underwhelmed. Maybe I still have in my mind exactly 27 years previously when Falmouth was on the line of totality. Although the weather was awful and the eclipsed sun was not visible I will always remember the slightly frightening sight of the black shadow racing across Falmouth Bay towards us and pitching us into total darkness as it passed.

August 11th 1999: 11am and a few minutes later

On the day after the eclipse many homes were destroyed and wildfires raged in parts of Britain as one of the highest temperatures of the year was recorded.

This summer is the hottest on record in the UK and much of Europe is on fire. The overwhelming consensus of the global scientific community is that human activity is the primary driver of current climate change (see posting of 24 August), so is 2026 the coolest year we will experience? It is an uncomfortable question, but perhaps one worth asking. The World Meteorological Organisation estimates an 86% chance that at least one year between 2026 and 2030 will be warmer than the current record year, 2024. It also puts the chance of at least one year temporarily exceeding 1.5°C above the pre-industrial average during that period at 91%. These are probabilities, not predictions that every year will be hotter than the last, since natural variations such as El Niño and La Niña will continue to cause fluctuations. But the underlying trend is clear: the baseline on which those fluctuations occur is getting warmer.

There is also a darker reminder of what a warming world can mean beyond heatwaves and wildfires. Last week, catastrophic flash floods struck Nepal after a section of glacier collapsed in the Himalayas, sending an avalanche of ice, rock and water downstream. Hundreds of people have died and thousands remain missing, with homes, roads, bridges and other infrastructure destroyed. Scientists caution that it is too early to attribute this particular event directly to climate change, but the disaster occurred in a region experiencing rapid warming and accelerating glacier loss. As glaciers retreat and high-mountain environments become increasingly unstable, the risks of landslides, avalanches and sudden floods are growing.

The Nepal disaster is a reminder that climate change is not simply a story of temperatures rising year after year. It is about a changing climate system, in which familiar patterns and natural hazards can become more dangerous. Heatwaves, wildfires, extreme rainfall, floods and the destabilisation of glaciers may look like separate events, but they are all part of a world in which the environmental baseline is shifting.

On a lighter note, last Wednesday Barbara and I celebrated our 59th wedding anniversary by visiting a remarkable museum in St. Ive (not to be confused with St. Ives), near Liskeard, 55 miles from Falmouth. The Story of Emily steps into the life and legacy of Emily Hobhouse, the famous humanitarian who was born in St. Ive, and lived from 1860 to 1926. She became internationally known for speaking out against the treatment of Boer women and children during the Second Boer War.

The British Army used a "scorched earth" policy, destroying farms and moving Boer civilians into concentration camps. Emily travelled to South Africa in 1900 to see the situation for herself. In January 1901 she visited the Bloemfontein camp, where around 2,000 women and children were being held. She was horrified by what she found. Women and children were living in terrible conditions, with inadequate food, sanitation and shelter. She documented what she saw and brought the situation to the attention of the British public and politicians. Branded an hysterical woman and traitor by many, she refused to be silenced, saving thousands of Boer women and children, leading social reforms, and single-handedly challenging an empire at war.

I remember visiting Bloemfontein in 1982. It was the capital of the old Orange Free State, one of the two Boer republics that fought Britain. The concentration camp there became one of the most important symbols of the suffering of Boer civilians and the memory was still very much alive, with some turning away as I asked for directions in English. 

Bloemfontein has the Anglo-Boer War Museum and the National Women's Memorial (left), which commemorates the women and children who died in the camps. The museum specifically tells the story of the concentration camps and the suffering of civilians, and although speaking English can cause some resentment in this predominantly Afrikaans city, ironically Emily became enormously respected among Afrikaners because she had stood up for Boer women and children and the Bloemfontein War Museum presents her positively, describing how her visit exposed the conditions in the camps and helped bring about improvements. 

She was invited to unveil the Women's Memorial in 1913, but she was too ill to attend. The wife of President Steyn unveiled it on her behalf, reading her prepared speech at the ceremony. 

Emily died in 1926. Her funeral in London was remarkably small and received little attention. A few months later, however, South Africa gave her a very different farewell.

Her ashes were sent to South Africa, where Isabella "Tibbie" Steyn, the widow of former Orange Free State president Martinus Steyn and a close friend of Hobhouse, helped organise a state funeral in Bloemfontein, the first state funeral for a woman in South Africa. It took place on 27 October 1926 at the National Women's Monument attended by more than 20,000 people. Shops and businesses closed and flags were flown at half-mast and Emily's ashes were placed at the monument.

I'm sure that South African visitors to Cornwall, and anyone interested in South African history, would find the Story of Emily of great interest. The museum is deliberately divided into two very different experiences:

• The Victorian Rectory shows Emily's childhood and early life in rural Cornwall, with restored rooms and gardens recreating the world in which she grew up.
• The War Rooms provide a modern, dark, immersive exhibition about her experiences in South Africa and the concentration camps. It uses original objects, photography, film, animation, sound and virtual reality to put visitors into the historical setting.

The contrast is intentional: the peaceful Cornish home represents Emily's early life, while the stark War Rooms represent the traumatic world she encountered later. One particularly striking feature is that the War Rooms are kept around 26°C, helping recreate the heat of South Africa. The exhibition takes visitors through different environments and uses sound, mirrors and visual effects to convey the scale and human impact of the camps.

Inside the rectory, Emily's Cornish family home

Visiting a "virtual" Boer farmhouse stoep

A devastated farmhouse during Kitchener's scorched earth policy

As well as being overshadowed by the ongoing wars in Iran and Ukraine, August will also be remembered for the loss of two iconic singer-songwriters, Bonnie Tyler and Dolly Parton, whose distinctive voices, unforgettable songs and remarkable careers left an enduring mark on popular music. Their deaths brought an end to two extraordinary chapters in music history on both sides of the Atlantic.

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Is replacing copper with aluminium the most effective way to deal with the looming global copper shortages?

A series of recent studies by reputable organisations have all forecast significant global shortages of copper starting in the mid 2030s.

In a keynote lecture at Critical Minerals '26, Martin Lynch, of the University of Queensland, will argue that substitution is the likely remedy.

Martin will highlight three main points:

• Substitutes (including PEX piping, fibre optic cables, and aluminium tubes) supplied 40% of the global demand for copper over the past 50 years, during which there were two periods of shortage.
• Of the copper consumed globally in 2023, about 70% could have been replaced by substitutes (including aluminium wiring, cables and tubes) without significant negative impacts.
• The main barrier to using substitutes is copper’s reputation for quality, and the reluctance of manufacturers and consumers to trust substitute products (including in building wire, aircon HX and renewables cabling) even though they are proven to work just as well as copper.

According to the author, history has shown that the barriers to substitution tend to crumble quite quickly when shortages appear.

Martin Lynch is the son of the late Prof. Alban Lynch, the first Director of Australia's JKMRC. He graduated in 1982 as a BE (Chem) from the University of Queensland (UQ) and worked in a series of mining companies including Rio Tinto and Iluka Resources.  During that time he wrote Mining in World History, a book which traces the history of global mining from 1500 to the 1970s (posting of 13th July 2026).  

He changed career path in 2009, becoming the owner and manager of a renewables energy business.  This was sold in 2024, following which he began a PhD at UQ focusing on the use of substitutes for copper with the aim of managing forecast global copper shortages.

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Is CO₂ Still the Most Maligned Gas in History? — Eight Years On

In the middle of August homes were destroyed as wildfires brought devastation to parts of Britain. The apocalyptic vision of the world on fire, with wildfires raging across Europe and the UK, prompted me to look again at a post I wrote eight years ago, Is CO₂ the Most Maligned Gas in History?. I wrote it in December 2018 when I was sceptical of the evidence attributing most recent climate change to human activity. Eight years later, I think some of the questions I raised remain worth asking, but the scientific answers have become considerably clearer.

The post is still relevant as a historical account of the debate, and some of its points remain valid. CO₂ is essential to life, it is quite different from conventional air pollutants, and mining will be essential to any large-scale transition away from fossil fuels. But its central scientific position, that climate change was probably mainly natural and that the contribution from human activity was uncertain, is no longer supported by the evidence.

In the 2018 article I wrote: “An increase in 40% [of CO₂] seems a lot, but in absolute terms this is an increase in concentration from just under 0.03% to the present level of just over 0.04%. Can this small increase have such a profound effect?” 

The science can now provide a much better answer to that question.

We can also now be much more precise about where the additional CO₂ is coming from. Scientists can distinguish fossil-fuel carbon from naturally circulating carbon by examining the isotopic “fingerprint” of atmospheric CO₂. Fossil fuels contain virtually no radioactive carbon-14, because it has decayed away over the millions of years that they have been underground. They are also relatively depleted in carbon-13. By measuring these isotopes in atmospheric CO₂, scientists can identify the contribution from fossil fuels and distinguish it from carbon being exchanged naturally between the atmosphere, oceans and living organisms.

This provides an important independent line of evidence. We are not simply assuming that the additional CO₂ is coming from burning coal, oil and gas because fossil-fuel use has increased at the same time as atmospheric CO₂. The chemical and isotopic fingerprints show that the extra carbon has the characteristics expected of ancient plant material,  precisely what we would expect from fossil fuels. The National Oceanic and Atmospheric Administration notes that these measurements can be used to determine what proportion of CO₂ in an atmospheric sample is derived from fossil fuels.

The important thing is not simply the percentage of the atmosphere occupied by CO₂, but the physical properties of the molecule and its effect on the Earth's radiative balance. CO₂ absorbs infrared radiation at specific wavelengths. Increasing its concentration makes it more difficult for the Earth to radiate energy back into space. The climate system then warms until outgoing radiation once again balances incoming energy. CO₂ does not have to make up a large proportion of the atmosphere to have a significant climatic effect.

Furthermore, we are no longer relying simply on correlations between CO₂ concentrations and temperature. The radiative effect of increasing greenhouse gases can be observed directly. NASA explains that its climate instruments measure how greenhouse gases affect the movement of infrared radiation through the atmosphere, and a 2024 NASA and Jet Propulsion Laboratory study directly measured how increasing atmospheric CO₂ reduces the Earth's ability to emit infrared radiation into space.

Looking back at my 2018 post, I would therefore no longer argue that the human contribution to recent warming is fundamentally uncertain. The evidence is now much stronger that the current rise in atmospheric CO₂ is overwhelmingly the result of human activity, principally the burning of fossil fuels, and that this increase is the dominant cause of the warming observed since the pre-industrial period.

But that does not make CO₂ a “villain” in the conventional sense. It remains an essential gas for life, occurs naturally, and has played an important role in regulating Earth's climate throughout geological history. Nor does recognising the importance of CO₂ mean that all environmental problems can be reduced to carbon dioxide. Conventional air pollutants such as particulate matter, sulphur dioxide and nitrogen oxides remain important threats to human health.

What has perhaps become even more relevant since I wrote the original article is the other side of the argument. If we accept the need to reduce greenhouse-gas emissions, then mining, a major emitter of CO₂, is not the enemy of the green revolution,  it is one of its essential foundations. Wind turbines, solar panels, electricity networks, batteries and electric vehicles all require large quantities of metals and minerals. The energy transition will therefore require more mining, not less (see posting of 10 April 2023).

The scale of the challenge is illustrated by the graphic below. In 2023, the world was still consuming enormous quantities of coal, oil and natural gas, with China and the United States among the largest consumers. Replacing an energy system of this scale is clearly going to be a very substantial undertaking.

Source: elements.visualcapitalist.com

This brings us back to the paradox at the heart of this article. If we accept the need to reduce greenhouse-gas emissions, mining is not the enemy of the green revolution, it is one of its essential foundations. The challenge is not simply to “stop mining”, but to produce the minerals needed for decarbonisation while reducing the environmental footprint and carbon intensity of their extraction and processing.

In that sense, my 2018 article is worth revisiting not because its scepticism about human-caused climate change has been vindicated, but because its underlying question has become even more important: how do we reconcile our environmental ambitions with the enormous material requirements of a modern, low-carbon society?

This is the paradox we should be discussing now. The route to a lower-carbon world runs, at least for the foreseeable future, through a mining industry that itself has to become substantially lower carbon.

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August Cornish Mining Sundowner, and Cornwall's next Industrial Chapter?

A cool evening, a rare occurrence this long hot summer. It was a pleasant 17C last night in Falmouth for the Cornish Mining Sundowner at the Chain Locker, with a modest attendance of around a dozen.

The Chain Locker sits by Falmouth's inner harbour, the more sheltered, upstream section around the town quays, while the wider Falmouth Harbour extends out towards Carrick Roads (the Fal estuary) and the sea, so there was something rather appropriate about discussing Cornwall’s industrial future from the Chain Locker last night.

The Inner Harbour and the Chain Locker

Look across Falmouth Harbour and you see centuries of working history, ships, quays, docks and warehouses. But the harbour may also have a role in Cornwall’s next industrial chapter.

A proposed £150 million redevelopment of Falmouth Docks aims to modernise the ageing infrastructure, increase cargo capacity and support the emerging floating offshore wind industry in the Celtic Sea. Importantly for Cornwall’s renewed interest in critical minerals, the plans could also create new import and export facilities supporting Cornish lithium and battery manufacturing.

Cornwall once exported copper and tin through its ports to markets around the world. Could Falmouth once again become part of a supply chain built around Cornwall’s natural resources, this time alongside renewable energy and modern marine engineering?

There is, however, another side to the story. The redevelopment has attracted opposition from oyster fishermen and environmental campaigners, particularly over proposed dredging and its potential impact on the Fal estuary and its habitats. So the question isn't simply whether Cornwall can bring industry back, it is what sort of industry we want, and how we balance economic opportunity with the environment and communities that make Cornwall special.

Join us at the Chain Locker for the next sundowner, which will be on Thursday September 17th, from 5.30pm.

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Eriez is the latest sponsor of Flotation '27

We are pleased to welcome Eriez as the latest sponsor of next year’s Flotation ’27. In fact, we are delighted to welcome them back, as Eriez has sponsored every MEI flotation conference since Flotation ’19, held just before the pandemic.

The Eriez booth at Flotation '19, the company's first year as a sponsor

The Eriez Flotation Division (EFD) delivers advanced flotation solutions designed to boost recovery while reducing operating costs. With more than 1,000 flotation systems designed, supplied and commissioned worldwide, Eriez offers a range of technologies aimed at achieving step-change improvements in mineral processing.

The strategic theme behind EFD is essentially more mineral recovery with less energy, water, equipment and grinding, using its broad range of flotation technologies. These include HydroFloat for coarse-particle recovery, CavTube Column Flotation, StackCell mechanical flotation and advanced sparging systems.

President and CEO Jaisen Kohmuench and Mining and Minerals Head Todd Burchett discussed step-change technologies at the SME Annual Meeting in Salt Lake City in February, highlighting integrated flowsheets incorporating HydroFloat Coarse Particle Flotation and StackCell systems.

Through technologies such as the HydroFloat separator, Eriez continues to advance coarse-particle recovery, with the potential to significantly reduce grinding energy, conserve water and enable safer tailings management. This work is often carried out in partnership with other equipment providers, including Comminution '27 sponsor Weir Minerals. In 2022 Weir Minerals announced a cooperative agreement with Eriez to design and develop coarse-particle flotation systems, allowing the two companies to better integrate Eriez flotation equipment with Weir Minerals’ expertise in slurry classification and conveying.

The commissioning of a HydroFloat installation at BHP’s Carrapateena copper mine in Australia is one of the more significant recent commercial references for Eriez’s HydroFloat technology.

Eriez is also addressing both ends of the particle-size challenge in mineral flotation: HydroFloat for coarse particles and CavTube for ultrafine particles. The current growth story for CavTube appears to be strongly linked to fine-particle and slimes recovery, as well as applications in phosphate and potash, with potential for other challenging ultrafine applications.

EFD is also participating in the University of Queensland’s Collaborative Consortium for Coarse Particle Processing Research, alongside major mining companies including BHP, Rio Tinto, Vale and Codelco. The second five-year phase of the programme, running from 2025 to 2030, is investigating coarse-particle and fluidised-bed flotation as potential routes to reducing grinding energy and improving mineral-processing efficiency.

There is clearly much happening within EFD, and with Flotation ’27 still 15 months away, we can look forward to hearing much more from Eriez next year, both in the conference room and at the Eriez exhibition booth.

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