Wealth in waste? Using industrial leftovers to offset climate emissions

Helena I. Gomes, Mike Rogerson, and Will Mayes.

More than a billion tonnes of potentially toxic, bleach-like waste is produced and piled in landfills every year, with often devastating effects. And yet most people haven’t even heard of these “alkaline wastes”.

We want to change this. Our research has identified nearly two billion tonnes of alkaline residues that are produced in the world each year, most of which can contaminate groundwater and rivers if not proper managed. We should be doing much more about the problem – these wastes can even be put to good use.

Alkaline waste can be solid or sludgy. It mostly involves slags, ashes or muds formed as a byproduct of steel, aluminium or coal power plants, waste incineration or the construction industry. All these wastes are different, but what they have in common is that they rapidly create bleach-like solutions when they meet rainwater.

Steel slag, a byproduct of the steel industry and an example of an alkaline residue.

Often it’s simply stored in piles or sent to landfill. This isn’t safe. The waste can form toxic dust that blows into the atmosphere, while rain that lands on top can filter through, picking up toxic chemicals and producing caustic “leachates” that can flow out into rivers and groundwater.

Steer well clear

Alkaline leachates have a toxic effect on aquatic life (we wouldn’t want to swim through bleach, either). It raises the water pH and metal concentrations, and consumes oxygen.

Carbonate precipitates in a small stream smothers aquatic habitats.

Once this stuff has been produced it’s hard to stop. Steel mills can be a source of alkaline leachates even 30 years or more after closure. Water with pH higher than 12 (somewhere between soapy water and bleach) has now leaked from one chromite waste tip for more than 100 years.

It’s hard to determine the exact link between contamination and problems for plants and animals, but alkaline waste can clearly cause harm. Studies have found ash from coal plants has killed geese and made tree swallows smaller and less fertile.

Perhaps the most severe case of alkaline waste poisoning happened in 2010, when a dam failed at an aluminium refinery in Ajka, Hungary. This released a million cubic metres of “red mud”, a byproduct of aluminium production with a pH level of around 13 in this case – similar to oven cleaner. The red mud inundated 1,000 acres of agricultural and urban land and was transported more than 120km down the Marcal river to the Danube, “extinguishing” all life in the tributary. The flood drowned ten people and left many more with severe chemical burns.

Can we make it stop?

We can treat alkaline leachates through aeration or by adding acid to neutralise it but this is expensive. We need sustainable alternatives. One promising proposal involves constructing wetlands in and around polluted sites, where the marshy ground, the plants and the associated microorganisms restrict the contamination.

Many attempts have been made to find ways of reusing these wastes but none of them are practical enough to stop landfill disposal. Alkaline wastes have been used in road construction, concrete, cement and plasterboard, for example.

Adding these wastes to the soil can reduce acidity, so usage as phosphate fertiliser is also common, while labs are testing whether it can be used in wastewater treatment.

All right junk in all the right places?

It can even help the fight against climate change. Chemicals in the wastes such as calcium and magnesium react with carbon dioxide and remove it from the atmosphere, storing it as a stable mineral. This form of carbon sequestration essentially mimics natural weathering processes and could be a safe and permanent storage option since only acid or extreme temperatures of 900°C or more can release this CO₂. It could even help offset some of the emissions from the energy-intensive industries that create alkaline wastes in the first place.

In fact, if all materials that contain silica (cement, construction and demolition wastes, slag, ash and combustion products) were used for sequestration they could take 697-1,218 megatonnes of CO₂ out of the atmosphere each year.

Steel slags alone could capture 170 megatonnes per year, while the red mud stored worldwide could capture 572 megatonnes. If all the red mud produced in a year was carbonated, 3–4% of the aluminium industry’s global CO₂ emissions could be captured.

Red mud has already sequestered 100 megatonnes of CO₂ worldwide from the late 19th century to 2008 – without the industry even trying. Boosting this number could allow for some real downward pressure on its emissions.

Maybe it’s time to get clever

Recent studies have shown alkaline wastes also contain large quantities of metals we would like to recover for recycling. Some are critical in terms of supply, or essential to new green technologies. For example vanadium, used in offshore wind turbines, lithium and cobalt for vehicle fuel cells, and rare earth elements crucial for solar power systems.

The obvious solution: try to unify the needs of resource recovery and remediation, by developing treatment methods for alkaline leachates that recover critical elements soluble at high pH, suppress dust production, increase carbon sequestration and treat the pollution caused.

With thanks to our study co-authors Douglas Stewart, professor of geo-environmental engineering, and Ian Burke, associate professor of environmental geochemistry, both at the University of Leeds.

To learn more about the Alkaline Remediation project, visit the website: https://alkalineremediation.wordpress.com/ 
 

Helena I. Gomes, Postdoctoral researcher in Environmental Sciences, University of Hull; Mike Rogerson, Senior Lecturer in Earth System Science, University of Hull, and Will Mayes, Senior Lecturer in Environmental Science, University of Hull

 
This article was originally published on The Conversation. Read the original article.

Images from the ends of the Earth

By Lucy Clarke (@DrLucyClarke)

Thinking about Antarctica conjures up images of a remote ice covered wilderness; it’s the coldest, windiest and driest continent and the only one to not have permanent residents living on it. It is the last terrestrial frontier on Earth that we haven’t yet fully conquered. So when I got the chance to work at the British Antarctic Survey (BAS) in Cambridge it felt like the opportunity of a lifetime – I would get to work on this distant continent… Sadly my current project doesn’t involve fieldwork, but I do get access to a huge archive of aerial photographs so I can explore large areas of Antarctica remotely, plus I’m not giving up hope of heading ‘South’ just yet!

Lots of research and the recent Intergovernmental Panel on Climate Change (IPCC) report published last year have all highlighted the retreat of Antarctica’s ice sheets and glaciers, and are concerned with the impact of future melting on global sea levels. My research, in collaboration with colleagues at the University of Newcastle, will contribute to this debate by quantifying glacier change during the 20^th and 21^st Century.

Photograph of Ryder Bay (left) and the Sheldon Glacier (right) on the Antarctic Peninsula (Photographs courtesy of the BAS Photo Repository)

Antarctica can be divided into 3 areas: the West Antarctic ice sheet, the East Antarctic ice sheet and the Antarctic Peninsula… it is the latter that is the focus of my research. The Antarctic Peninsula is situated on the north-western tip of Antarctica and unlike the rest of the continent it isn’t completely covered by ice sheets, it is a mountainous area and there are many glaciers feeding into ice sheets and the surrounding sea. 

Map of Antarctica showing the 3 ice sheets, with an inset highlighting the Antarctic Peninsula (Source: Antarctic Digital Database)

The Antarctic Peninsula has over 400 glaciers and current thinking is that climate change is causing a rapid reduction of these, however there is very little detailed long-term information to support this. Most of the glaciers are inaccessible thereby preventing collection of measurements in the field and so remote techniques have to be used to determine how these may have altered. Satellite imagery has been used to reconstruct glacial change since the 1990s but the impact of change over the 20^th Century is still unknown for the majority of glaciers. Fortunately we do have an archive of aerial photography of the Antarctic Peninsula at BAS dating back to the 1940s.  We can use this data source to not only visually compare differences in glacier extent during this period but also calculate the volumetric change using photogrammetry.  My December blog post covers use of this technique: What’s in a photo?

Normally photogrammetry requires: (1) two overlapping photographs of an area, (2) details on the camera used, and (3) some identifiable points on the ground that you know the co-ordinates of, to create a 3D model of the overlap area that can then be used to take measurements. In the case of the Antarctic Peninsula we don’t have any ground measurements for large areas, so using the standard technique wasn’t possible and therefore we had to come up with a new way to undertake photogrammetry with no available ground control.

The BAS Twin Otter that the aerial photography is flown from (left) and the camera and storage set up inside the plane (right) (Photos courtesy of the BAS Photo Repository)

New aerial photography in Antarctica is flown by the BAS using a digital camera mounted in a Twin Otter plane with the camera set into a holding that records the exact position, height and rotation of the camera at the instant that each photograph is taken (shown in the pics above). Using this information I can create a high resolution digital elevation model, or 3D model of the surface, using photogrammetry without the need for ground control measurements, thus allowing us to undertake this research in even the most inaccessible areas. The accuracy of this technique (with the potential for 40 cm resolution, so every pixel in the image equates to 40 cm on the ground) far exceeds that offered by current satellite imagery (with a resolution of 15 m). This results in clearly definable features on the subsequently processed photography. I can therefore look at the modern digital elevation model and identify co-ordinates for rock outcrops and mountain peaks that won’t have changed through time. This can then be reverse engineered to create ground control points for the historic aerial photos without ever having to set foot on the glacier! So as long as I have contemporary aerial photography of a glacier I can use this to process older photography from the same area, allowing us to fully utilise the rich archive of historic air photography stored in the BAS archives.

The Moider glacier on the Antarctic Peninsula in (a) 1947 and (b) 2005 showing the thinning and retreat at the glacier front, and (c) the digital elevation model produced from the 2005 imagery.

Preliminary results show dramatic mass change in the study glaciers over the last few decades, and I am currently processing these results in further detail and extending the study sites. I will be blogging about these results in the near future so watch this space…

This research is part of the NERC funded grant: Ref NE/K004867/1: “The spatial and temporal distribution of 20^th Century Antarctic Peninsula glacier mass change and its drivers”