Zimbabwe’s ban on lithium ore exports, which was introduced by the government last December, has caused two million tons of stockpiles to be built up in the country. The government had laid out the ban in a bid to encourage local processing of lithium in the country, but that resulted in a large stockpile build-up, which prompted the industry to ask President Mnangagwa to review the ban as it threatens the viability of lithium mining operations.

“The unexpected ban has prejudiced standing offtake agreements between miners and international buyers, some of whom had taken loans from their respective countries to trade in these minerals,” Zimbabwe’s Miners Federation President Rushwaya said in a letter to Mnangagwa.

The ban has particularly affected small- and medium-scale miners, but it’s not clear how much lithium is contained in the stockpiled ore.

Most of the lithium from Zimbabwe, which is home to one of Africa’s largest resources of the battery metal, is shipped to China and South Africa. Nations from the U.S. to China are rushing to secure supplies of materials necessary for green-energy transition as the world turns away from fossil fuels.

Chinese companies Chengxin Lithium Group and Sinomine Resource Group are exploring a joint venture to set up a battery metals processing plant in Zimbabwe, while another Chinese firm Zhejiang Huayou Cobalt has invested $300 million to develop a processing plant at its Arcadia lithium mine.