Could worthless mining waste help suck CO₂ out of the atmosphere?

Mining: actually good? Image: Getty.

The Paris Agreement commits nations to limiting global warming to less than 2˚C by the end of the century. However, it is becoming increasingly apparent that, to meet such a massive challenge, societies will need to do more than simply reduce and limit carbon emissions. It seems likely that large scale removal of greenhouse gases from the atmosphere may be called for: so-called “negative emissions”. The Conversation

One possibility is to use waste material from mining to trap CO₂ into new minerals, locking it out of the atmosphere. The idea is to exploit and accelerate the same geological processes that have regulated Earth’s climate and surface environment over the 4.5bn years of its existence.

Across the world, deep and open-pit mining operations have left behind huge piles of worthless rubble – the “overburden” of rock or soil that once lay above the useful coal or metal ore. Often, this rubble is stored in dumps alongside tiny fragments of mining waste – the “tailings” or “fines” left over after processing the ore. The fine-grained waste is particularly reactive, chemically, since more surface is exposed.

A lot of energy is spent on extracting and crushing all this waste. However, breaking rocks into smaller pieces exposes more fresh surfaces, which can react with CO₂. In this sense, energy used in mining could itself be harvested and used to reduce atmospheric carbon.

This is one of the four themes of a new £8.6m research programme launched by the UK’s Natural Environment Research Council, which will investigate new ways to reverse emissions and remove greenhouse gases from the atmosphere.

Spoil tips from current and historic mining operations, such as this gold mine in Kazakhstan, could provide new ways to draw CO₂ from the atmosphere. Image: Ainur Seitkan, Earth Sciences, University of Cambridge.

The process we want to speed up is the “carbonate-silicate cycle”, also known as the slow carbon cycle. Natural silicate rocks like granite and basalt, common at Earth’s surface, play a key part in regulating carbon in the atmosphere and oceans by removing CO₂ from the atmosphere and turning it into carbonate rocks like chalk and limestone.

Atmospheric CO₂ and water can react with the silicate rocks to dissolve elements they contain like calcium and magnesium into the water, which also soaks up the CO₂ as bicarbonate. This weak solution is the natural river water that flows to the oceans, which hold more than 60 times more carbon than the atmosphere. It is here, in the oceans, that the calcium and bicarbonate can recombine, over millions of years, and crystallise as calcite or chalk, often instigated by marine organisms as they build their shells.


Today, rivers deliver hundreds of millions of tonnes of carbon each year into the oceans, but this is still around 30 times less than the rate of carbon emission into the atmosphere due to fossil fuel burning. Given immense geological time scales, these processes would return atmospheric CO₂ to its normal steady state. But we don’t have time: the blip in CO₂ emissions from industrialisation easily unbalances nature’s best efforts.

The natural process takes millions of years – but can we do it in decades? Scientists looking at accelerated mine waste dissolution will attempt to answer a number of pressing questions. The group at Cambridge which I lead will be investigating whether we can speed up the process of silicate minerals from pre-existing mine waste being dissolved into water. We may even be able to harness friendly microbes to enhance the reaction rates.

Another part of the same project, conducted by colleagues in Oxford, Southampton and Cardiff, will study how the calcium and magnesium released from the silicate mine waste can react back into minerals like calcite, to lock CO₂ back into solid minerals into the geological future.

Whether this can be done effectively without requiring further fossil fuel energy, and at a scale that is viable and effective, remains to be seen. But accelerating the reaction rates in mining wastes should help us move at least some way towards reaching our climate targets.

Simon Redfern is professor in earth sciences at the University of Cambridge.

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

 
 
 
 

Seville has built its entire public transport system in 10 years. How has it done?

Just another sunny day in Seville. Image: Claude Lynch.

Seville, the fourth largest urban centre in Spain, was recently voted Lonely Planet’s number one city to visit in 2018. The award made a point of mentioning Seville’s impressive network of bicycles and trams, but it neglected to mention that it’s actually their ten year anniversary. The city’s metro opened just two years later.

This makes now an excellent time to look back on Seville’s public transport network – especially because almost all of it was completed in the middle of the global financial crisis. So, is it a good model for modern public transport? Let’s find out.

Cycle Hire

Seville, like any good metropolis, features a cycle hire scheme: Sevici, which is a clever portmanteau of the words ‘Seville’ and ‘bici’, short for bicicleta, the Spanish for, you guessed it, bicycle.

The service, launched in 2007, is run as a public-private partnership. Users can pay a flat weekly fee of €13.33 (£11.81) for unlimited rentals, as long as all the journeys last 30 minutes or less. For the fanatics, there’s a year-long subscription for €33. This makes Sevici cheaper than the London equivalent (£90) but slightly more than that of Paris (€29).

However, the reason why the bike hire scheme has gained particular praise in recent years is down to Seville’s network of cycle paths, snaking around the town centre and into the suburbs. The sheer scale of the scheme, 75 miles of track in total, has prompted comparisons to Amsterdam.

But there is a meaningful distinction between the two cases. First, cycling culture is such a big deal for the Amsterdammers that it has its own Wikipedia page. In Seville, cycling culture is a growing trend, but one that faces an uphill struggle, despite the city’s flatness. Around half of the cycle paths are on a pavement shared by pedestrians; pedestrians often ignore that the space is designed specifically for cycles.

A Sevici station in the town centre. Image: Claude Lynch.

Surprisingly, cyclists will also find exactly the opposite problem: the fact that bicycles enjoy the privilege of so many segregated spaces mean that, if they dare enter the road, motorists are not obliged to show them the same level of respect – because why would they need to enter the road in the first place?

This problem is only compounded by the Mediterranean driving style, one that takes a more cavalier attitude to objects in the road than that of the northern Europeans. While none of this makes cycling in Seville a write-off – it remains the cycling capital of Spain – budding tourists should bear in mind that the cycle paths do not extend far into the old town proper, making them a utility, for the most part, for budding commuters.

Metro

The metro system in Seville consists of a single metro line that travels from Ciudad Expo in the west to Olivar de Quintos in the east. It has three zones, which create a simple and straightforward fare system, based on the number of journeys and number of “saltos” (jumps) between zones, and nothing more.

The need-to-know for tourists, however, is that only three of the metro stations realistically serve areas with attractions: Plaza de Cuba, Puerta de Jerez, and Prado de San Sebastian. Given that a walk between these is only a few minutes slower than by metro, it shows the metro service for what it is: a service for commuters coming from the west or east of town into the city centre.

Some of the behaviour on the network is worth noting, too. Manspreading is still dangerously common. There are no signs telling you to “stand on the right”, so people queue in a huff instead. Additionally, there is no etiquette when it comes to letting passengers debark before you get on, which makes things precarious in rush hour – or if you dare bring your bike on with you.

On the plus side, that’s something you can do; all trains have spaces reserved for bikes and prams (and they’re far more sophisticated than the kind you see on London buses). Trains are also now fitted with USB charging ports for your phone. This comes in addition to platform edge doors, total wheelchair access, and smart cards as standard. Snazzy, then – but still not much good for tourists.

Platform edge doors at Puerta Jerez. Image: Claude Lynch.

The original plan for Seville’s metro, launched in the 70s, would have had far more stations running through the city centre; it’s just that the ambitious plans were never launched, due in equal measure to a series of sinkholes and financial crises. The same kind of problems led to Seville’s metro network being opened far behind schedule, with expansion far down the list of priorities.

Still, the project, for which Sevillanos waited 40 years, is impressive – but it doesn’t feel like the best way to cater to an east-west slice of Seville’s comparatively small urban population of 1m. Tyne and Wear, one of the few British cities comparable in terms terms of size and ambition, used former railways lines for much of its metro network, and gets far more users as a result. Seville doesn’t have that luxury; or where it does, it refuses to use it in tandem.

You only need to look east, to Valencia, to see a much larger metro in practice; indeed, perhaps Seville’s metro wouldn’t look much different today if it had started at the same time as Valencia, like they wanted to. As a result, Seville´s metro ends up on the smaller side, outclassed on this fantastic list by the likes of Warsaw, Nizhny Novgorod, and, inexplicably, Pyongyang.

Seville: a less impressive metro than Pyongyang. Intriguing. Image: Neil Freeman.

Tramway

The tram travels from the high rise suburb-cum-transport hub of San Bernardo to the Plaza Nueva, in the south of the Seville’s old town. This route runs through a further metro station and narrowly avoids a third before snaking up past the Cathedral.

This seems like a nice idea in principle, but the problem is that it’s only really functional for tourists, as tram services are rare and slow to a crawl into the town centre, anticipating pedestrians, single tracks, and other obstacles (such as horse-drawn carriages; seriously). While it benefits from segregated lanes for most of the route, it lacks the raison d'être of the metro due to the fact that it only has a meagre 2km of track.

The tram travelling down a pedestrianised street with a bicycle path to the right. Image: Claude Lynch.

However, staring at a map long enough offers signs as to why the tram exists as it does. There’s no history of trams in Seville; the tracks were dug specifically for the new line. A little digging reveals that it’s again tied into the first plans for Seville’s metro, which aspired to run through the old town. Part of the reason the scheme was shelved was the immense cost brought about by having to dig through centuries-old foundations.

The solution, then, was to avoid digging altogether. However, because this means the tram is just doing the job the metro couldn’t be bothered to do, it makes it a far less useful service; one that could easily be replaced by a greater number of bike locks and, maybe, just maybe, additional horses.


So what has changed since Seville’s transport revolution?

For one thing, traffic from motor vehicles in Seville peaked in 2007 and has decreased every year since, at least until 2016. What is more promising is that the areas with the best public transport coverage have seen continued decreases in traffic on their roads, which implies that something is working.

Seville’s public transport network is less than 15 years old. The fact that the network was built from scratch, in a city with no heritage of cycling, tunnels, or tramways, meant that it could (or rather, had to) be built to spec. This is where comparisons to Amsterdam, Tyne and Wear, or any other city realistically fall out of favour; the case of Seville is special, because it’s all absolutely brand new.

As a result, it’s not unbecoming to claim that each mode of transport was built with a specific purpose. The metro, designed for the commuter; the tramway, for tourists; and cycling, a mix of the two. In a city with neither a cultural nor a physical precedent of any kind for such radical urban transportation, the outcome was surprisingly positive – the rarely realised “build it, and they will come”.

However, it bears mentioning that the ambitious nature of all three schemes has led to scaling back and curtailment in the wake of the economic crisis. This bodes poorly for the future, given that the Sevici bikes are already nearing the end of their lifetime, the cycle lanes are rapidly losing sheen, and upgrades to the tramway are downright necessary to spare it from obsolescence.

The conclusion we can draw from all this, then, appears to be a double-edged one. Ambition is not necessarily limited by a lack of resources, as alternatives may well present themselves. And yet, as is so often the case, when the money stops, so do the tracks.

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