Jadar is at prefeasibility stage after Rio committed a further $US20 million to the project in February.

The company has already spent $70 million.

Rio Tinto Minerals CEO and president Dean Gehring said Jadar was an attractive investment opportunity for the company.

“The Jadar project is strategically important for Rio Tinto Minerals and will complement our existing operations,” he told a Rio corporate publication released overnight.

Jadar was discovered by the company in 2004 and is named after a new mineral uncovered at the project, jadarite.

Serbia is the only known source of jadarite, a mineral which is made up of both lithium and borates.

Rio said Jadar is one of the largest lithium deposits in the world and could produce more than 10% of the world’s lithium.

The PFS is focused on refining the company’s knowledge of the orebody, including processing.

Rio general manager of Serbia Richard Storrie said since jadarite was a new mineral, the production process would be unique.

The company has been running pilot tests in California and Melbourne.

“Having successfully piloted a batch process we’re next testing integrated, continuous production,” Storrie said.

But the environmental and social impact assessment, a key part of the PFS, won’t be completed until 2018.

After that, Rio will make a decision on a move to a full feasibility study.

“Jadar would enable us to offer multiple supply sources to our existing boric acid customers,” Rio Diamonds & Minerals CEO Alan Davies said.

“The world will need a lot more lithium in the future for electric cars.”

Goldman Sachs is expecting electric cars to make up 22% of all vehicles by 2025, up from less than 3% today.