JAKARTA, March 18 (Reuters) - Nickel miner PT Vale Indonesia is exploring a potential investment in a high-pressure acid leaching plant in Sulawesi island, with an estimated cost of 30 trillion rupiah ($1.91 billion), its investment ministry said on Monday.

The plant, named "SOA HPAL", will be the company's third such project to turn nickel ore into mixed hydroxide precipitate (MHP) - a material used to make electric vehicle batteries, according to presentation material shown by Indonesia's Investment Minister Bahlil Lahadalia.

A Vale Indonesia spokesperson declined to comment.

The plant could have an annual output capacity of 60,000 metric tons of nickel in MHP, the ministry said, adding Vale Indonesia is completing its final stage of exploration and it will partner with automakers.

Vale Indonesia already has two HPAL plants under construction in Sulawesi Island, in Pomalaa and Sorowako. Both projects are in partnership with Zhejiang Huayou Cobalt.

U.S. carmaker Ford is involved in the $4.5 billion Pomalaa plant.

Last month, Indonesia's state mining company MIND ID agreed to acquire a 14% stake in Vale Indonesia from Vale Canada and Japan's Sumitomo Metal Mining to become a top shareholder. ($1 = 15,685.0000 rupiah) (Reporting by Stefanno Sulaiman, Editing by Louise Heavens)