The Original "White Gold"

Why salt is just as relevant for the 21st century world as it was for our ancestors

Photo by Jason Tuinstra on Unsplash

I’ve written the following article for Der Pragmaticus, a brilliant Austrian publication. If you speak German, you can and should read the original, which can be found here. For those who can’t, here’s a version in English:

What do the following items have in common: a computer chip, a sheet of paper, a solar panel, a battery and the pipes that carry the water away from your kitchen sink?

The answer is that you cannot make any of them without salt.

If I asked you to think of the substances without which civilisation as we know it wouldn’t be able to function, I suspect salt wouldn’t feature very high up on your list.

Sure, we all know we need salt to keep our bodies functioning - in much the same way as we need water. You might also know that, for a long time, salt was one of the most precious substances in the world. Making salt from seawater, or from brine springs issuing from the ground, was a time-consuming, energy-intensive process, so those who could control salt production were often disproportionately powerful. It was no accident that salt was one of the first materials in the world to be taxed by governments and coveted by despots. Those who controlled the salt could control their people.

That, however, is all history. Today, after centuries of improvements in its extraction and production, salt is one of our cheapest staples. But it still mostly comes from under the ground. And it still remains as important as it ever was.

The salt you sprinkle over your chips is only the start of it, because actually the majority of salt we extract from the ground each year goes somewhere else: into the chemicals sector, where it is turned into a variety of substances that make the modern world go round.

Some of the salt is pumped, in the form of brine, into electrolysers, where it is turned into a variety of chemicals, including chlorine and caustic soda (sodium hydroxide). Together these form the building blocks for much of the world's pharmaceuticals. The vast majority of drugs sold today rely on chemicals that began their lives as salt.

Some of the salt goes to plants where it is converted into soda ash (sodium carbonate), another one of those little-appreciated chemicals without which much of what we take for granted wouldn’t be possible. You can’t make glass without soda ash, nor could you make paper or soap.

It was not for nothing that, thousands of years ago, the Romans named their goddess of health Salus - the name echoing the Latin for salt: sal. It was not for nothing that they gave each of their soldiers a ration of salt (which is where we get the modern word “salary”). Salt was integral to life back then.

But it is just as integral to our lives today - the main difference being that we no longer spend much time talking about it. Sometimes the degree of dependence is stark. I recently visited a plant where a chemicals firm passes salt water through an electrolyser which breaks the compound apart, turning it into the chlorine which purifies 98 per cent of Britain’s tap water.

“If this place goes down unexpectedly then within seven days this country is rationing drinking water,” whispered one of the men working there. All across the world we depend on such places - these forgotten parts of the salt diaspora.

That our lives still perch precariously on this common substance was as much of a surprise to me as it probably is to you. A few years ago I set out to write a book about the most important substances to the modern economy and at first I never considered including sodium chloride.

I knew that if one wanted to understand the materials we all depend on, I would have to tell the story of sand: of how we use silicon to make glass, to shore up the built world in the form of concrete and to provide the physical underpinnings for that most advanced of all human creations, the silicon chip.

I knew that since everything in the modern world is either made out of, or with, steel, it would be important to include iron (the primary element in steel alloys). I knew that the electrical revolution would never have happened without the copper carrying power into our homes and around the world, and that we will never reduce carbon emissions without mining a lot more copper, for the cables going into wind turbines and the insides of electric cars.

I knew that those electric cars will only work if they contain energy-dense batteries, and that the most energy dense of all the metals you could put inside batteries is lithium. I knew too that while it’s tempting to believe we have reduced our reliance on fossil fuels such as oil and gas, we remain extremely dependent on them today, and are likely to remain dependent on them for decades to come - even if we burn slightly less of them. So there would have to be a place for a fossil fuel like oil or gas in my list.

But the more I travelled into what I came to think of as the “Material World” - the weird and wonderful place encompassing the stuff we get from the ground and the processes we use to turn it into amazing things - the more often I found myself encountering the tang of salt. I realised that none of these five other materials would be of much use without it.

Consider lithium - that most famed of all the critical materials we’ll need in the coming decades. The world’s biggest reserves of lithium are to be found in the “lithium triangle” in Chile, Argentina and Bolivia, in the form of underground reservoirs of concentrated liquid solutions.

How are these brines (which, it turns out, contain table salt as well as lithium) extracted from the ground? The same way as we produce salt. The vast lithium ponds in the Salar de Atacama in Chile follow much the same technique as the salt makers of Mallorca or Ibiza have been using for centuries - guiding the solution into evaporation ponds and allowing the water to evaporate under the baking sun. The main difference is that the finished product here is not something to be sprinkled on food, but to be sprinkled on the cathodes which go into lithium ion batteries.

Nor can you can actually turn the lithium into a stable battery-ready compound without using chemicals derived from salt (react it with soda ash to get lithium carbonate, with caustic soda to get lithium hydroxide). The world’s most modern technology depends upon one of the most ancient.

For thousands of years people trod salt routes, traversing Europe on old pathways connecting brine springs and the sea with major towns. But even today we walk the same routes. Look at a map of Britain or America and you find that many of the biggest chemicals firms, from the remnants of ICI to DuPont, are to be found on top of the biggest salt deposits - Cheshire in the UK, Detroit in the US.

Salt is also there, invisibly, inside one of the world’s most commonplace (and controversial) plastics - PVC. Polyvinyl chloride is made in part from oil but in part from the chlorine we get from salt. Indeed, there’s a theory that part of the reason we made so much PVC over the years was that it was a handy way of sopping up the excess chlorine produced when we rip salt apart in electrolysers to create caustic soda.

That computer chip I mentioned at the beginning of the article couldn’t be made without polysilicon - an extremely pure form of silicon. And to make polysilicon you need to carry out an extremely complex and energy-intensive process which depends, along the way, on hydrogen chloride, which we obtain from, yes, salt. And, since solar panels are also made from polysilicon, the same thing goes for them too.

It’s possible too, that salt could be at the centre of another energy revolution, for it could be the basis of a novel form of power storage. While lithium remains the chemical of choice in most high-energy batteries, the big new thing in energy storage these days is sodium ion batteries. These are batteries made in part from the sodium, which in turn comes from salt.

And while there are some serious questions marks about how easily we’ll be able to get hold of the lithium and, for that matter, the specialised sand we need for semiconductors, we will never run short of salt. If you were to remove all the sodium chloride from the oceans and spread it evenly over the land, you would glaze the entire world in a salt crust over 500 feet thick. That is before one considers the reserves under the ground, which are similarly copious.

But it turns out the stuff under the ground is not evenly distributed. Britain, Germany and Poland have large underground deposits of salt; Italy, Belgium and Switzerland have much less. So what? Well, it turns out that salt reserves will be central to another of the potential industries of the future: hydrogen.

For one of the other qualities of salt - from a geological perspective - is that it is much better than pretty much any other type of rock you find under the ground at storing liquids and gases. In the coming years we will need somewhere to store hydrogen - the green fuel which could keep our grids humming even when renewables aren't generating. And depleted salt caverns, of the kind you find under the ground after we've been mining it, are the single best storage space we know of. These caverns could also be perfect for storing compressed air, which could serve as another source of energy storage.

The upshot is that those parts of the world with large salt resources could use them as vast storage vessels in the coming centuries. These nations could be the batteries of Europe.

It’s a helpful reminder that even as we embrace the new technologies of the future, we won’t stop relying on the older ones. The minerals we’ve mined for thousands of years to help improve our lives will carry on being mined to enhance our descendants’ lives too.