OSLO – Aluminium producer Norsk Hydro needs to return soon to full output at its Alunorte alumina refinery in Brazil to avoid shutting down production lines completely, it said on Tuesday.

Last month Brazilian authorities ordered Hydro to temporarily halve its output from the plant after they said a waste spill at one of Alunorte's bauxite refuse deposits occurred after heavy rain – a claim Hydro denies.

By rotating output between the plant's seven production lines, the company has been able to avoid shutting any of them down completely, a company spokesman said on Tuesday.

"It's complicated and very time consuming to shut these production lines down completely and then restart them again. That is something we are really trying to avoid," said Hydro spokesman Halvor Molland.

"Right now we rotate the production between the seven production lines at the factory to keep them all warm. But this is not a lasting solution. We can't keep doing it like this much longer."

Alunorte, located in the northern Brazilian state of Para, is the world's largest alumina refinery.

It transforms bauxite to alumina, which is turned into aluminium at smelters. The plant has around 2,000 employees and produced a record 6.4 million tonnes of alumina in 2017.

"Right now our main focus is continuing our dialogue with the authorities. As we see it, there are no environmental arguments to be made against us getting back to full production again."

Hydro disputes accusations from Brazilian authorities regarding the contamination of water supplies in the area surrounding the plant following heavy rainfall in February.

Hydro has said the integrity at the plant is still intact and there are no indications suggesting there were ever any emissions from its bauxite depositories.

It has said some unregulated spills, including of untreated rainwater from the roof of a coal storage shed, have occurred, which were "completely unacceptable", Hydro CEO Svein Richard Brandtzaeg said on March 19.

"In our view, it should now be possible to increase production to full capacity in a safe way," said Molland.

On Monday, Hydro received a counterproposal from the Brazilian public prosecutor's office as part of its talks with authorities. Still, Hydro said the company had yet not been told what it needs to do to resume full operations.

Late on Monday, the company said it would release on April 9 conclusions from its internal review and a review it ordered from environmental consultancy SGW Services.