Last month, it declared a force majeure on customer contracts and halted mining and smelting operations at the project following a violent community unrest and a report that an employee was killed in May.
The miner said shutting one of the four furnaces at the mineral sands project would reduce the use of its stockpile of feedstock and limit the long-term impacts of a shutdown on RBM's furnaces.
"Shutting a furnace has a major impact on the business and broader community and it not a decision we have taken lightly," Sinead Kaufman, chief executive of Rio's minerals division, said.
RBM will reassess the situation to decide on restarting the furnace or potentially shutting other furnaces depending on "when the safety and security position improves," Rio said.
All operations at RBM remain halted until further notice, the miner said.
