Interest in lithium, used in batteries, is strong as electric vehicles gain popularity, but projects can take years to bring online.

Rio discovered the 136 million-tonne reserve of jadarite, named after the Jadar Valley, in 2004 and has invested $90 million so far on developing the mineral.

Rio Tinto says the project is expected to start producing in 2023 assuming the necessary approvals are obtained, which the MOU is designed to accelerate.

Rio Tinto Salt, Uranium and Borates Division Managing Director Simon Trott, who signed the agreement on behalf of the company, said it brought "Serbia and Rio Tinto closer to becoming a leading source of global lithium and borate production".

Minister of Mining and Energy Aleksandar Antic, who signed the accord on behalf of Serbia, said the deal would "speed up the activities related to the process of opening a mine and the beginning of the exploitation of lithium, which will have capital effect on the development of Serbia".

Jadarite contains borates, used in ceramics, fertilisers and other chemical compounds, as well as lithium.

Rio Tinto said it expected to make a final investment decision and start construction in 2020 and then the first production, based on a processing technology developed by Rio, is expected to commence in 2023.