Rio Tinto Group’s aluminum boss sees prices for the lightweight metal heading for an “extremely” volatile period, with uncertainty over when China will curb production helping to keep investors on edge. “That’s really where the uncertainty is at the moment,” Alfredo Barrios said in an interview at Bloomberg’s Toronto office. “There’s no doubt that if you look at the supply side, if you look at the environmental issues, sooner or later that will change. But when is a question mark.” China has ordered curbs on steel and aluminum output in as many as 28 northern cities during the winter heating season...