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.


Everything you ever wanted to know about the Seoul Metro System but were too afraid to ask

Gwanghwamoon subway station on line 5 in Seoul, 2010. Image: Getty.

Seoul’s metro system carries 7m passengers a day across 1,000 miles of track. The system is as much a regional commuter railway as an urban subway system. Without technically leaving the network, one can travel from Asan over 50 miles to the south of central Seoul, all the way up to the North Korean border 20 miles north of the city.

Fares are incredibly low for a developed country. A basic fare of 1,250 won (about £1) will allow you to travel 10km; it’s only an extra 100 won (about 7p) to travel every additional 5km on most lines.

The trains are reasonably quick: maximum speeds of 62mph and average operating speeds of around 20mph make them comparable to London Underground. But the trains are much more spacious, air conditioned and have wi-fi access. Every station also has protective fences, between platform and track, to prevent suicides and accidents.

The network

The  service has a complex system of ownership and operation. The Seoul Metro Company (owned by Seoul City council) operates lines 5-8 on its own, but lines 1-4 are operated jointly with Korail, the state-owned national rail company. Meanwhile, Line 9 is operated jointly between Trans-Dev (a French company which operates many buses in northern England) and RATP (The Parisian version of TfL).

Then there’s Neotrans, owned by the Korean conglomerate Doosan, which owns and operates the driverless Sinbundang line. The Incheon city government, which borders Seoul to the west, owns and operates Incheon Line 1 and Line 2.

The Airport Express was originally built and owned by a corporation jointly owned by 11 large Korean firms, but is now mostly owned by Korail. The Uijeongbu light railway is currently being taken over by the Uijeongbu city council (that one’s north of Seoul) after the operating company went bankrupt. And the Everline people mover is operated by a joint venture owned by Bombardier and a variety of Korean companies.

Seoul’s subway map. Click to expand. Image: Wikimedia Commons.

The rest of the lines are operated by the national rail operator Korail. The fare structure is either identical or very similar for all of these lines. All buses and trains in the region are accessible with a T-money card, similar to London’s Oyster card. Fares are collected centrally and then distributed back to operators based on levels of usage.


The Korean government spends around £27bn on transport every year: that works out at 10 per cent more per person than the British government spends.  The Seoul subway’s annual loss of around £200m is covered by this budget.

The main reason the loss is much lower than TfL’s £458m is that, despite Seoul’s lower fares, it also has much lower maintenance costs. The oldest line, Line 1 is only 44 years old.

Higher levels of automation and lower crime rates also mean there are fewer staff. Workers pay is also lower: a newly qualified driver will be paid around £27,000 a year compared to £49,000 in London.

New infrastructure is paid for by central government. However, investment in the capital does not cause the same regional rivalries as it does in the UK for a variety of reasons. Firstly, investment is not so heavily concentrated in the capital. Five other cities have subways; the second city of Busan has an extensive five-line network.

What’s more, while investment is still skewed towards Seoul, it’s a much bigger city than London, and South Korea is physically a much smaller country than the UK (about the size of Scotland and Wales combined). Some 40 per cent of the national population lives on the Seoul network – and everyone else who lives on the mainland can be in Seoul within 3 hours.

Finally, politically the biggest divide in South Korea is between the south-west and the south-east (the recently ousted President Park Geun-Hye won just 11 per cent of the vote in the south west, while winning 69 per cent in the south-east). Seoul is seen as neutral territory.  


A driverless train on the Shinbundang Line. Image: Wikicommons.

The system is far from perfect. Seoul’s network is highly radial. It’s incredibly cheap and easy to travel from outer lying areas to the centre, and around the centre itself. But travelling from one of Seoul’s satellite cities to another by public transport is often difficult. A journey from central Goyang (population: 1m) to central Incheon (population: 3m) is around 30 minutes by car. By public transport, it takes around 2 hours. There is no real equivalent of the London Overground.

There is also a lack of fast commuter services. The four-track Seoul Line 1 offers express services to Incheon and Cheonan, and some commuter towns south of the city are covered by intercity services. But most large cities of hundreds of thousands of people within commuting distance (places comparable to Reading or Milton Keynes) are reliant on the subway network, and do not have a fast rail link that takes commuters directly to the city centre.

This is changing however with the construction of a system modelled on the Paris RER and London’s Crossrail. The GTX will operate at maximum speed of 110Mph. The first line (of three planned) is scheduled to open in 2023, and will extend from the new town of Ilsan on the North Korean border to the new town of Dongtan about 25km south of the city centre.

The system will stop much less regularly than Crossrail or the RER resulting in drastic cuts in journey times. For example, the time from llsan to Gangnam (of Gangnam Style fame) will be cut from around 1hr30 to just 17 minutes. When the three-line network is complete most of the major cities in the region will have a direct fast link to Seoul Station, the focal point of the GTX as well as the national rail network. A very good public transport network is going to get even better.