From pottery clay to moon bricks: How mining waste could solve two global crises

By  Fran Molloy 5 November 2025 7 min read

When CSIRO scientist Clint McNally needs to run experiments on mining excavation waste, instead of trekking to a remote mine site, he drives to his local pottery store.

“Some of my experiments rely on a highly repeatable form of the clay found in a lot of excavation waste, so I’ll buy bags of kaolinite from the local pottery store,” Clint says.

“I want the same base material that potters are after: good quality, pure clay with no sand or other bits of material.”

It turns out the same clay potters use to create delicate porcelain, is also the basis for geopolymers – a rock-solid concrete formula poised to solve one of the mining industry’s most wicked problems.

Mine tailings are a monumental challenge in Australia. Tailings, stored in dams all over the country, comprise all the rock, clay, water and other materials remaining after separating ore from everything miners dig up, often forming a wet slurry making up around 80 per cent of the volume extracted.

CSIRO’s Recovering Tailings group within the Sustainable Mining Technologies program are pioneering a solution that transforms this liability of massive amounts of waste, into valuable construction material.

They’re converting mine tailings into geopolymer concrete, a cement alternative that could simultaneously address mining’s waste crisis, and construction’s carbon problem.

The scale of the Tail-ings – a monumental challenge

The University of Queensland’s Sustainable Minerals Institute estimates 13 billion tonnes of mine tailings is generated globally each year. Australia’s Department of Climate Change, Energy, the Environment and Water found the sector produced 620 megatons (Mt) of mining waste in 2020-21.

Waste volumes have increased by more than 20 per cent from the 502Mt recorded during 2018-19 – and about 96 per cent of the waste material is stored in tailings dams.

Geoscience Australia’s Atlas of Australian Re-mining Potential, launched in 2023, identifies more than 1050 sites containing historical and operational tailings. And nationally, about 620 million tonnes of mining waste is generated each year, stored across 250 active tailings dams.

When these dams fail, the consequences are devastating. A 2022 study exploring the impacts of mine reservoir failures globally found that, between 1965 and 2020, large tailings facilities worldwide failed at a rate of 1.2 to 1.8 per cent, with each major failure killing an average of 64 to 98 people.

Environmental costs often run into hundreds of millions of dollars per disaster, and can be deadly – 270 people were killed in the 2019 Brumadinho iron ore tailings dam collapse in Brazil, for example.

The chemistry of turning waste to value

Geopolymers are binding agents that replace cement in concrete. Instead of using limestone heated to 1400 degrees, geopolymers use aluminosilicates – clays rich in aluminium and silicon compounds. The key ingredient is often kaolinite, the same porcelain clay Clint buys at the pottery shop. 

“Geopolymers can be substituted for the cement used in most concrete,” Clint explains.

“By using an aluminosilicate instead of limestone, we can get a significant amount of our clays from mining waste.”

And geopolymers can be tailored to different purposes – high-strength blocks for roads, or stable forms for safe disposal, for example, depending on how the ingredients are mixed.

“It’s a bit like making a cake,” Clint says.

“Change the ratio of eggs, sugar and flour to get the type of cake you want.”

The environmental advantages are substantial. Geopolymers cut CO₂ emissions by 80 to 90 per cent compared with Portland cement, which contributes about 8 per cent of global carbon emissions. A 2025 study found geopolymer concrete greenhouse gas emissions are 12 to 50 per cent lower than conventional concrete.

However, there’s a cost barrier. The same research found geopolymer concrete costs about twice as much as Portland cement, mainly due to alkaline activator production. CSIRO’s approach – using waste tailings rather than purchased materials – could solve this economic hurdle while addressing the waste crisis.

From sludge to solid blocks

The transformation begins with understanding what traditional tailings management gets wrong.

“Mine sites normally handle tailings using a fines circuit, where waste goes to a large dewatering pond,” Clint explains.

“After the solids drop out, the underflow of about 30 per cent solids gets pumped to a tailings dam.”

This 30 per cent solids slurry typically creates the catastrophic risk; it remains liquid enough to fail under stress, washing away everything downstream.

CSIRO’s process uses solid bowl centrifuges and pressure filters to remove much of the water, creating what Clint calls ‘breathing room’ to add chemical reagents to trigger the transformation.

“This binds individual, very fine clay particles into a solid block, which can still absorb water, but in a solid structure rather than as individual particles that turn into a slurry.”

The results are impressive. Test blocks achieve compressive strengths of 20 to 50 megapascals – equivalent to general purpose or high-strength concrete. Unlike conventional concrete, which degrades at 300 degrees, geopolymer blocks maintain stability to 800 degrees.

“A lump of clay dried in an oven at 60 degrees would be solid – but if you stood on it, you could crush it,” Clint says.

“But the chemical transformation means the lumps of geopolymer clay can be baked at a far lower temperature and still get equivalent strengths to concrete.”

World-leading characterisation

CSIRO’s edge lies in its ability to precisely characterise tailings from any mine site and formulate the right geopolymer recipe.

The Recovering Tailings team operates six labs across Australia, using X-ray diffraction to identify crystalline phases and measure clay content, and X-ray fluorescence to determine elemental composition, with the expert support of CSIRO’s world-leading Characterisation group.

“Our labs can identify whether a tailings sample has the right aluminosilicates present, and in what proportion, which then indicates the ratios of reagents needed to get the required result,” Clint says.

The team has partnered with CSIRO’s Sensing and Sorting group to develop real-time analysis technology for tailings streams, a crucial service for industrial-scale mine operations where the natural composition of waste material varies across the site.

Clint’s background as an agricultural scientist provides an unexpected advantage. Soil physics and chemistry overlap significantly with clay mineralogy and flotation processes.

“I understand the many different types of clay we deal with. Now, instead of growing plants in them, I’m exploring how to use them as a feed material to make a concrete product.”

Space – the final frontier?

Geopolymers have been around for years, and numerous sites demonstrate their commercial viability. The most impressive involved 25,000 cubic metres in heavy-duty aircraft runway material installed at West Wellcamp Airport in Toowoomba, Queensland in 2014.

Queensland company Wagners supplied a total of 40,000 cubic metres of its Earth Friendly Concrete geopolymer for the project. Along with runways, geopolymer concrete was used for an entry bridge, kerbs, road barriers, precast culverts, tilt panels, footings and sewer tanks.

Construction was 30 per cent faster than conventional concrete methods, and saved thousands of tonnes of CO₂ emissions, and sample testing found the material strength was far greater than requirements.

Other examples include precast geopolymer beams used in major buildings, tunnel segments in Australia, Malaysia and Germany, and water tanks which show promising crack-healing properties.

Clint has even created geopolymer blocks from lunar regolith, opening possibilities for space construction.

“Lunar regolith is an aluminosilicate, so it works well.”

The disruptive potential of geopolymer from waste

The potential for geopolymer concrete as a key component of a circular economy transformation can even extend beyond mine sites to the construction industry, where clay-rich subsoils excavated during earthworks – currently dumped as ‘clean fill’ – could be used for local production of geopolymers.

“By switching waste – whether from mining or construction - from a problem, into something that can earn revenue, there’s potential for a big, disruptive change to the way we do things,” Clint says.

“Anywhere you can use concrete, it can potentially be replaced with a geopolymer concrete.”

Clint says his team progressed from kilogram-scale experiments to 50-kilogram batches and is working toward commercial production.

But scaling up faces several hurdles – starting with the difficulty in getting consistency across different sources of mine tailings. Clint says that developing a process on large sites to sample tailings at the source, rather than after they are stored, is a likely solution.

Another challenge is the cost and difficulty of transporting heavy raw materials from remote mine sites to higher population areas where they are in demand for construction.

Building the future from waste

As Australia ramps up critical minerals mining to support the global energy transition, tailings volumes will grow. At the same time, there is an international push for better regulations around tailings management.

The timing is right for a technology transition tranforming mine tailings from catastrophic liability to valuable construction material – where every tonne of waste becomes a building block for roads, bridges, tunnels and buildings.

Even cities on the moon might end up being built from geopolymer concrete.

“We have to either work out something to do with mining waste, or work out some better way to store it,” Clint says.

“Geopolymers are a way to do both; our process is able, not just to make tailings strong enough so it holds together more safely, but to also make it into something with value.”