Mining giant Adani is expected to announce a $74-million deal today to buy railway steel from Arrium's troubled Whyalla steelworks in South Australia.

It is understood Adani will contract Arrium to supply 54,000 tonnes of steel for the 400-kilometre railway line to Queensland, linking its proposed Carmichael coal mine with Abbot Point on the coast.

Acting Prime Minister Barnaby Joyce and Federal Resources Minister Matt Canavan are expected to travel to Whyalla on SA's Eyre Peninsula for the announcement later this morning.

The deal is a potential life-line for Arrium, which was placed into voluntary administration in April 2016 with debts of more than $4 billion.

About $2.8 billion is owed to Arrium's financiers, which include Australia's four big banks.

South Australian Chamber of Mines and Energy chief executive Rebecca Knol said the deal was a vital breakthrough for Arrium's administrator Korda Mentha and the city of Whyalla, which is facing massive job losses if the steelworks close.

But Indian company Adani is still to decide whether to proceed with the Carmichael mine in the Galilee Basin.

Environmentalists have been campaigning heavily against what would be Australia's biggest coal mine, and Westpac has ruled out lending money to the project, stating it would only lend to projects involving higher-quality coal.

Adani is also seeking a $900 million taxpayer-subsidised loan for the rail line to the Abbot Point coal port.

Adani said in a statement that while the contract to purchase steal had been signed, it was subject to the "normal commercial requirement that the Carmichael mine proceeds".

"There is more work to be done but this contract is a major step forward," Adani Australia chief executive officer Jeyakumar Janakaraj said.