Chemists might have found a way to avoid the use of one of the most toxic substances in wide use: hydrogen fluoride.

Made from the mineral fluorspar (CaF2), hydrogen fluoride (HF) is used in both gaseous and liquid form.

A small splash of HF on skin is enough to be fatal – and coming into the contact with the gas can cause blindness, severe burns, and serious lung damage.

But hydrogen fluoride is also the only effective way to make fluorine-containing substances. These fluorochemicals are crucial in a range of products including refrigerants, lithium batteries, pharmaceuticals, agrochemicals, and non-stick materials.

A team of UK chemists has figured out a way to make fluorochemicals with just fluorspar, which is much less dangerous.

“The direct use of CaF2 for fluorination is a holy grail in the field, and a solution to this problem has been sought for decades,” says Professor Véronique Gouverneur, a chemist at the University of Oxford and senior author on a paper describing the research, published in Science.

“This study represents an important step in this direction because the method developed in Oxford has the potential to be implemented anywhere in academia and industry.”

Their method, inspired by the biomineralization that builds up teeth and bones in nature, involves grinding CaF2 in a ball mill for three hours with a salt — powdered potassium phosphate.

This generates a powder containing fluorine and potassium, which they’ve called Fluoromix

Using high precision techniques, such as X-ray diffraction, the researchers unlocked key insights into the composition of Fluoromix and structures of the fluorinating species. This diagram shows structures of crystalline constituents of Fluoromix, which serve as fluorinating reagents. Credit: Professor Michael Hayward.

The researchers have shown that their fluorspar-based Fluoromix can create more than 50 different fluorochemicals, with the potential for making many more.

Gouverneur says that the method could also minimise carbon emissions by shortening supply chains, since it skips a step in the fluorspar-to-fluorochemical pipeline.

The ball milling technique, which is the hallmark of a field called mechanochemistry, also dodges the sulphuric acid and high energy cost needed to turn CaF2 into HF.

“This seemingly simple process represents a highly effective solution to a complex problem; however, big questions on how this reaction worked remained,” says co-lead author Calum Patel, a PhD student at the University of Oxford.

“Collaboration was key to answering these questions and advancing our understanding of this new, unexplored area of fluorine chemistry.”

The researchers have spun out a company called FluoRok, which is commercialising their technology.

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