Are we running out of sand?

BY JON EVANS

We’re used to the idea that fossil fuels are running out. But so too, potentially, are lots of other natural resources we have taken for granted. How long, for example, before we run out of copper, phosphorus and sand? Jon Evans reports

While sunning ourselves on a strip of sand that stretches out of sight in both directions, it may be difficult to believe we are running out of these tiny grains. But we are. And it’s not just sand. Increasingly, scientists are warning that several natural substances that have hitherto seemed limitless could soon start to run out.

We’re not talking about so-called critical minerals like lithium and cobalt, which are essential to the functioning of our modern technologies but mined in comparatively small quantities in only a few regions of the world (see C&I, 2024, 88(6), 22). And we’re not talking about resources that have long been forecast to be running out, such as fossil fuels. We’re talking about things present in great abundance in many regions of the world, that have been extracted at large scales for many years. Things like sand, and the commonly used metals copper and aluminium, and phosphorus.

For all these natural substances, demand is already immense and is forecast to continue growing ever more rapidly for the foreseeable future. Although we currently still have abundant deposits of these substances, we are working our way through them at an ever-faster rate. Just like with fossil fuels, we are using them at a much greater rate than they can possibly be replaced and so we will eventually run out. The question is ‘when?’.

Take sand. Its major industrial use is as a component of concrete, one of the most widely used materials on Earth, with around 30bn t/year produced. Together with gravel, sand forms the aggregate that is bound together with cement to produce concrete. On top of this, sand is also an important component in the production of asphalt, glass and electronics. As a result, 50bn t of sand and gravel are currently used each year, making it the second most used material in the world after water. And this figure is only predicted to grow, to 82bn t by 2060, driven by increased urbanisation.

Even so, you might argue, there’s a lot of sand in the world. Not just on beaches, but also in all the deserts of the world. Surely that should last quite a long time, even at high rates of use. Unfortunately, not all sand is suitable for use in concrete, which requires sand particles with sharp edges so they can bind well with cement. Desert sand grains have been weathered so much that they are too fine, round and polished to be used in concrete.

Much of the suitable sand is found on beaches and riverbanks, where large-scale extraction is often far from ideal. It can lead to more erosion and less protection from floods and storm surges, as well as the loss of critical habitat for a wide range of species of animal and plant. So, while the demand for sand continues to grow, the deposits that can be used without causing problems are quite restricted. Some researchers have suggested the world could be running out of usable sand by 2050.

The UN Environment Programme (UNEP) has already raised concerns. In 2022, UNEP published a report – Sand and Sustainability: 10 strategic recommendations to avert a crisis – offering guidance for improving the management and extraction of sand, including recognising sand as a strategic resource and accurately mapping and monitoring sand resources.

‘Our sand resources are not infinite, and we need to use them wisely,’ said Pascal Peduzzi, a UNEP Director and Programme Coordinator for the report. ‘If we can get a grip on how to manage the most extracted solid material in the world, we can avert a crisis and move toward a circular economy.’

Copper bottom

For the metals copper and aluminium, the shift to green energy technologies is the main driving force behind rapidly growing demand. ‘Aluminium and copper are produced in vast quantities globally, so their supply is not an immediate concern,’ explains Kathryn Moore, Senior Lecturer in critical and green technology metals at Exeter University, UK. ‘But they’re so important for the low-carbon transition – aluminium for lightweighting everything to reduce carbon footprints and copper as the de facto electrical conductor for everything – and they’re going to be needed in such vast quantities that it’s a question of how far we go before we start running into trouble.’

According to consultancy firm Wood Mackenzie, we could start running into trouble soon, at least for copper. In 2022, it published a report called Red metal, green demand: Copper’s critical role in achieving net zero, which predicted that demand might start to exceed supply within 20 years. The report forecast that meeting the UN’s goal of restricting the rise in global temperatures to 1.5°C of pre-industrial levels will require 18.4m t of extra copper production over the next 20 years, or a 60% increase on current levels. It doubts this is achievable, given that copper production has only grown by 11.7m t over the past 20 years.

As for phosphorus, it’s the increasing global population that is driving up demand. Phosphorus, along with ammonia, is a major component of fertiliser. But whereas ammonia is mainly derived from nitrogen in the atmosphere, phosphorus is derived from phosphate-rich sedimentary rocks. The largest deposits are found in Morocco and the Western Sahara, with global reserves estimated to be just under 70,000m t, which some researchers have predicted could be used up in 50-100 years.

This all points to a rather alarming scenario. That perhaps within just 50 years we could start to run out of sand, phosphorus and copper, which would clearly have a major impact on our ability to build, grow crops and adopt low-carbon technologies. This is, however, very much a worst-case scenario and based on highly speculative figures. In the case of sand, we don’t really know how much sand is potentially available for industrial purposes, which is why one of the recommendations of the UNEP report is to map and monitor sand resources. For copper and phosphorus, the difficulty is determining exactly what counts as a useable deposit.

Mining companies distinguish between reserves and resources. Reserves are deposits that currently are or could be profitably mined, while resources are deposits that could potentially be mined in the future, depending on the economics. Mining companies report figures for both reserves and resources and move their deposits between the two. Thus, resources can be moved into reserves, if a company plans to expand the mined area, while reserves can be moved back into resources if the company subsequently abandons its plans, often because of the economic situation.

This movement between reserves and resources can make it hard to accurately determine how much of a substance can realistically be extracted and thus how long we have before it runs out. In 2020, a team of researchers from the US and Australia used figures on global reserves and resources of 29 metals and minerals, provided by mining companies to the US Geological Survey, to determine whether deposits of these metals were gradually being depleted (Commun. Earth & Environ., 2020, 1, 13). To do this, they calculated how the ratio between the amounts of stated reserves and annual rate of production varied for these metals over the past 65 years. If this ratio fell that would indicate that reserves were gradually being depleted. But what they discovered was that this ratio generally stayed the same over time, indicating resources were being converted into new reserves at the same rate existing reserves were being used up. This was the case for both copper and bauxite, the mined mineral from which aluminium is derived.

Rather than the deposits of metals such as copper running out in 50 years, the researchers predict that they should last for the foreseeable future, as resources continue to bolster reserves. It is a similar case for phosphorus. Whereas reserves of phosphorus rock are estimated to be just under 70,000m t, global phosphate resources are thought to be around 300bn t. Indeed, the latest forecasts suggest the world’s phosphate deposits could last for almost 300 years.

Economics and ESG

But it’s not just the size of global deposits that determines when a substance will run out. Various other factors also play a role. Economics is one such factor, because deposits will only be mined if it is economic and practical to do so.

Global phosphate reserves may be 300bn t, but much of that cannot be extracted under current economic and technological conditions, including the large deposits thought to exist in the continental shelves at the bottom of the Atlantic and Pacific oceans.

Economic factors also influence the movement between reserves and resources. But so, increasingly, do environmental, social and governance factors. Indeed, in their study, the US and Australian researchers predict these factors will place more restrictions on the supply of the 29 metals and minerals over the coming decades than the depletion of reserves. Greater emphasis on limiting the detrimental effects of mining on the local environment, biodiversity and populace could prevent certain deposits from being exploited or make exploiting them prohibitively expensive.

That could quickly change, however, if this results in shortages of these metals or minerals, especially as that would lead to an increase in prices, which would change the economics of exploiting them. This shows why it is so difficult to accurately predict when we might begin to run out of things like sand, copper and phosphorus, because the whole situation is highly fluid. A deposit that isn’t economic or practical to mine under current conditions may well be economic or practical to mine in the future.

These forecasts are also based on current rates of use either staying the same or growing. But what if we could reduce these rates and eke out our deposits for longer? Recycling is one option, and some recycling of sand, copper and aluminium does already take place. But there is much scope for boosting these efforts.

For example, researchers are working on ways to extract copper and aluminium from the more than 50m t of electronic waste produced globally each year. One possibility is to dissolve the waste in an acid and then extract the metals from the resulting liquid leachate. In recent work, researchers from Austria showed this could be done by simply absorbing the metals with spent brewer’s yeast, a cheap brewing waste material (Front. Bioeng. & Biotech., 2024, 12, 1345112.).

Other researchers are exploring various ways to extract phosphorous from sewage sludge, where it can end up after being washed from fields. One possibility involves heating the sludge in the presence of a catalyst. Known as hydrothermal liquefaction, this process converts organic compounds in the sludge into a liquid biofuel, while the other components, including phosphorus, form a solid hydrochar. Phosphorus accounts for around 10% of this hydrochar, which is similar to its concentration in phosphate rock, and can be recovered by leaching with an acid.

Another option is to find alternatives for these natural substances. For example, a team led by Satish Nagarajaiah at Rice University, US, recently tried making concrete with graphene made from coal-derived metallurgical coke, rather than sand and gravel (ACS App. Mater. & Interfaces, 2024, 16, 1474). They found the resulting concrete was 25% lighter than conventional concrete, while being 32% tougher and 21% stronger.

‘The fact we’re on the brink of a “sand crisis” motivates us to look for alternatives, and metallurgical coke, which costs about the same as sand at about 10% of the cost of concrete, could help not only make better-quality concrete, but also eventually translate into significant savings,’ Nagarajaiah said.

Then we can keep the sand where it belongs – on the beach.