The smelter went into maintenance that was scheduled for about 30 days, but has been extended due to a lack of oxygen supply from a neighboring oxygen plant.
Broker AMT has been appointed by the LME as a liquidity provider for its steel contracts, giving a boost to the market as the first ring trader in that role.
Carmakers seeking to boost sales of electric cars are struggling to get their hands on cobalt, a scarce but vital component in the production of batteries.
Relations with Congolese authorities have grown increasingly strained in recent months as the government pushes for foreign investors to contribute more.