From the New York Times:
Strong buying by China has helped lift commodity prices around the world this spring, but growing evidence suggests that a sizable portion of this buying has been to build stockpiles in China, and may not be sustainable.
Commodities and shipping executives describe Chinese stockpiling in recent months of a range of other commodities as well, including aluminum, copper, nickel, tin, zinc, canola and soybeans. Starting in April, China began stockpiling significant quantities of crude oil.
China’s goals vary by commodity. Chinese companies have bought iron ore heavily on the spot market in anticipation of higher prices in annual contract talks now nearing completion. The Chinese government has been stockpiling oil and some metals for strategic reasons, and bought huge quantities of aluminum and canola to insulate domestic producers of these goods from falling global prices over the winter.
Those extra purchases beyond China’s daily needs have helped reverse the price collapse in commodities that followed the economic downturn, but could also limit the scale of the rebound.