Sulphur supply on the decline

While sewage is something we aim to avoid, our re-use of waste water may soon be an important way of combating another oncoming crisis: a lack of phosphorus for fertiliser. Because as fossil fuel use declines in line with emissions targets, the supplies of sulphur this industry produces as a by-product will also dry up. That means we’ll be short of sulphuric acid, which we currently use to make fertiliser from phosphate-rich rocks, as UCLs’ Simon Day explains…

Simon - Sulphur is critical to the production of phosphate fertilisers. Phosphate rock, which is the obvious raw material, is inert and can't be used by plants to any great extent. But if that phosphate rock is treated with sulphuric acid to produce things like phosphoric acid, hydrogen phosphate, phosphate salts like ammonium, so on, those are the usable fertilisers. So sulphur in the form of sulphuric acid is absolutely critical to the production of those fertilisers. And because sulphuric acid is essentially a waste product of the fossil fuel industries, which those industries are essentially giving away, that makes phosphate fertilisers very cheap compared to what its price was say 40 or 50 years ago. And consequently, there's a tendency to overuse it and we see the environmental damage as a result.

Will - So we're moving away from our use of fossil fuels?

Simon - So we are anticipating over the next few decades, if we're going to get net zero by 2050, a very great reduction of extraction of fossil fuels from the ground. Therefore the processing of those fossil fuels, which begins with the separation of the sulphur component of the fuels, means that over the next 30 years, we can anticipate a dramatic collapse to maybe a fifth, maybe a tenth, of the current supply of sulphur. And at the same time, because populations are increasing, we're looking at an increase in the demand for phosphate fertilisers, and therefore an increase in demand for sulphur to produce those phosphate fertilisers. And also many of the metals that we're going to rely on to enable the transition away from fossil fuels like metals for batteries, metals for electric motors, which also require large amounts of sulphuric acid for their extraction. We need to look at recycling phosphate that we've taken out of the fields in the food that we eat and get that phosphate back to the fields.