It's a major boost for Portland and the plant which had been operating under the fear of closure for years, and has prompted intervention from state and federal governments to keep it operational.

Alcoa will restart one of its pot lines which has sat idle since 2009 and will mean the site will operate at about 95 per cent capacity.

Alcoa's vice-president of operations and Alcoa Australia president Michael Gollschewski said restarting the idle capacity after 12 years improved the smelter's cost structure, competitiveness and longer term sustainability.

The process to restart the capacity will begin immediately, with metal production expected to start in the third quarter of 2022. It will add another 35,000 metric tons per year to the plant's capacity.

The project would add an extra 30 permanent roles to the smelter's 680-strong workforce which consists of both direct employees and contractors.

There will be about 50 temporary jobs created during the construction phase.

"Portland Aluminium has long enjoyed the support of the local community and with this project we are pleased to be able to create further positive social impact through additional employment and local expenditure," Mr Gollschewski said.

Energy to operate the restored capacity will be supplied under a new four-year agreement with power generator AGL.

It will supplement the earlier announced five-year energy agreements with AGL, Alinta Energy and Origin that came into force on August 1.

In March, a $160 million deal was announced by Prime Minister Scott Morrison which saved the smelter for another five years.

AGL chief operating officer Markus Brokhof said AGL welcomed Alcoa's decision to restart the pots which would allow AGL to continue playing a role in supporting the smelter's operations.

"The Portland smelter is one of AGL's largest wholesale customers in Victoria and provides critical stability to the state's energy network," he said.

"This restart will continue to support the communities in which the Portland smelter operates, as well as providing essential jobs and security to Victoria's electricity supply."

It will cost about $28 million to restart the potline, of which Alcoa Corporation's share is about $9 million. The rest of the funding will come from the smelter's joint venture partners, not governments.

Once the restart is complete, Portland Aluminium will operate at about 95 percent of its total capacity, and Alcoa Corporation's share of consolidated operating capacity will be about 186,000 metric tons per year.

Portland Aluminium is an unincorporated joint venture, and Alcoa Corporation has 197,000 metric tons per year of consolidated capacity of the smelter's total capacity of 358,000 metric tons per year.

Alcoa has also recently restarted 268,000 metric tons of yearly capacity at its Brazil smelter.

CORONAVIRUS STORIES:

We have removed our paywall from our stories about the coronavirus. This is a rapidly changing situation and we aim to make sure our readers are as informed as possible. If you would like to support our journalists you can subscribe here.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can access our trusted content:

Have you signed up to The Standard's daily newsletter and breaking news emails? You can register below and make sure you are up to date with everything that's happening in the south-west.