China has moved to protect its supply of the world's most used industrial chemical, with ramifications for everything from food production to fashion and mobile phones.Sulphuric acid is a crucial ingredient in the manufacture of batteries, clothing and phosphate fertilisers, and is also used to treat drinking water, purify petroleum, and produce some metals and computer chips.China is a key exporter, but it relies on imported sulphur — itself a by-product of oil refining and smelting — to make it.In 2025, about half of the global sulphur supply came from the Middle East.With trade disrupted, Beijing has banned exports of…