Wednesday, 27 July 2016

Vanadium: the 'beautiful metal' that stores energy

Helena I. Gomes,  and Helen Abigail Baxter.
An unheralded metal could become a crucial part of the renewables revolution. Vanadium is used in new batteries which can store large amounts of energy almost indefinitely, perfect for remote wind or solar farms. And what’s more there is loads of the stuff simply lying around in industrial dumps.

Don’t let the dumpster diving put you off – never mind gold or silver, vanadium may just be the most beautiful metal of all. It’s the 22nd most abundant element in the Earth’s crust, though it’s rarely found naturally in its metallic form. Instead, vanadium can be found in more than 100 different minerals.

Colours of vanadium. Steffen Kristensen

Once extracted and dissolved in water, various forms of vanadium turn into bright, bold colours. It’s even named after “Vanadis”, the old Norse name for the Scandinavian goddess of beauty, Freyja.
Vanadium is not only beautiful, but also strong. Adding small percentages of it creates exceptionally light, tough and more resilient steel alloys. Henry Ford was the first to use it on an industrial scale, in the 1908 Model T car chassis, and today the vast majority of vanadium is used in structural steel, mainly to build bridges and buildings.

Vanadium flow batteries

The unique properties of vanadium make it ideal for a new type of batteries that may revolutionise energy systems in the near future – redox flow batteries.

Batteries store energy and generate electricity by a reaction between two different materials – typically solid zinc and manganese. In flow batteries, these materials are liquid and have different electric charges. Both are pumped into a “cell” where the electric current is generated. A tiny membrane separates the two liquids, so they are able to react but don’t come into direct contact.
Vanadium is used in these batteries as it can convert back and forth from its various different states, which can carry different positive charges. As only one material is used, the risk of cross contamination is eliminated. The liquids have an indefinite life, so the replacement costs are low and there are no waste disposal problems. Also, the battery is extended to a potentially infinite lifetime.

Vanadium flow batteries.

In flow batteries, the energy production and capacity are independent. Energy is stored in tanks, whereas the capacity depends only on the amount of liquid stored. This provides a great design flexibility that other batteries do not allow. They are also safer, as the two liquids don’t mix causing a sudden release of energy. Even President Obama is impressed.

The new energy reservoir

Vanadium flow batteries are too big and heavy to replace the lithium batteries found in your phone, however. These batteries are instead used for large stationary long-term energy storage, or to supply remote areas, or provide backup power. They’re the basis for a more efficient, reliable, and cleaner electrical energy market.

Energy storage is one of the main factors limiting the spread of renewables. When solar and wind power is produced at the wrong time of day we need to store it to use it during the evening demand peaks. Studies have shown that vanadium batteries can be a sustainable solution.

When we can create huge stores of energy to access as required, we will be liberated from the need to maintain rapidly-accessible energy generation such as coal or gas. Vanadium batteries can be a reservoir of energy much in the same way as we use actual reservoirs to store rainwater for later use.

Strengthened with vanadium. The Henry Ford / Life magazine

The ability to store electricity would reduce reliance on gas and coal. In turn this would increase fuel security and cut CO2 emissions, helping to meet agreed emissions targets. No wonder then that the EU considers vanadium a critical metal for strategic energy technologies.

The hunt for vanadium

The metal is mined, and supplies are currently dominated by China, South Africa, Russia and the US. Vanadium has a medium risk of supply shortage and a high political risk.

However, as vanadium can be a byproduct of other sorts of mining, about 70% of the vanadium above ground is unused, left in industrial wastes such as mine tailings, debris or steel slags. In fact, a study I published with colleagues last year estimated that 43% of the annual global production of vanadium could be recovered from alkaline wastes, such as steel slag, red mud, fly ashes from coal energy production, and construction and demolition waste.

But there isn’t yet a firmly established technology to recover this vanadium. Certain bacteria and fungi can extract more vanadium from industrial wastes, and various solutions for turning this into useful metal are under development. But we still need to come up with a better way to reach potential sources of this beautiful metal.

The Conversation
Helena I. Gomes, Postdoctoral researcher in Environmental Sciences, University of Hull and Helen Abigail Baxter, Post Doc Research Assistant, Department of Geography Environment and Earth Sciences, University of Hull

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

Tuesday, 19 July 2016

Wealth in waste? Using industrial leftovers to offset climate emissions

Helena I. GomesMike 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: 
The Conversation
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.