It comes after the company received Foreign Investment Review Board approval.  

Rio announced the acquisition from Sentient Equity Partners' Rincon Mining, just before Christmas.

Rincon is a large undeveloped lithium brine project located in the heart of the lithium triangle in the Salta Province of Argentina, an emerging hub for greenfield projects.

The project is a long life, scaleable resource capable of producing battery grade lithium carbonate. It has the potential to have one of the lowest carbon footprints in the industry.

A July 2021 NI 43-101 resource estimated measured and indicated contained lithium carbonate equivalent of 5.8 million tonnes, as well as just under 6Mt in inferred.

The project has reserves of almost 2Mt of contained LCE, sufficient for a 40-year mine life.

"Rincon strengthens our battery materials business and positions Rio Tinto to meet the double-digit growth in demand for lithium over the next decade, at a time when supply is constrained," Rio CEO Jakob Stausholm said.

"We will be working with local communities, the province of Salta and the government of Argentina as we develop this project to the highest ESG standards."

Rio said the direct lithium extraction technology proposed for the project has the potential to significantly increase lithium recoveries as compared to solar evaporation ponds.

A pilot plant is currently running at the site and further work will focus on continuing to optimise the process and recoveries.

Rio said market fundamentals for battery grade lithium carbonate were strong, with lithium demand forecast to grow 25-35% per annum over the next decade with a significant supply demand deficit expected from the second half of this decade.

Rio shares opened 0.4% lower at A$118.