Washington-backed mining firm USA Rare Earths agreed to buy Brazil’s Serra Verde for $2.8 billion, the latest in a string of acquisitions as the US looks to reduce its dependence on Chinese exports.

China controls the majority of the world’s supply, and Beijing’s brief export restrictions last year on the minerals — critical for the defense and energy sectors — sent shudders through US industry.

Eyeing an opportunity, Brazil has sought to attract foreign investment: Its president recently said the country had the world’s second-largest reserves of rare earths despite just a third having been mapped. But persistent tensions between Brasília and Washington could hinder further integration; on Monday the US ordered Brazil’s Washington-based security attaché to leave the country.