Rio Tinto’s New Zealand Aluminium Smelters says it will spend $50 million on processing spent cell liner at its Tiwai Point aluminium smelter in Southland.

The company said it was a big step forward in its long-term remediation programme.

Highly toxic spent cell liner (SCL) had been stored at Mataura before a public outcry led to the company removing the material in 2021.

SCL is a byproduct of the aluminium production process.

Historically, it has been stored undercover in sheds and in a specially designed encapsulated pad on site.

Since January 2024, New Zealand Aluminium Smelters (NZAS) has worked with specialist processor Regain to safely treat SCL in Australia before it is reused in the global cement industry.

“Our new facility at Tiwai Point means this processing will now take place in New Zealand, reducing the need for this processing to happen overseas and forming a key part of the long-term remediation plan for the Tiwai site,” Rio Tinto-NZAS acting general manager Matt Black said.

Black said that SCL previously stored in the encapsulated pad would be progressively excavated, processed on-site and exported for reuse.

The project will create 20 jobs during construction and six during operations.

All consents for the facility have been received and construction is expected to begin in the second quarter of 2026.

Once operational, the plant will be run by Regain Services, which also operates a similar facility at the Tomago smelter in New South Wales.

“Processing SCL on site is a milestone in delivering on the remediation commitments we have made to Ngāi Tahu and our community,” Black said.

“The initiative builds on the remediation plan co-designed with Ngāi Tahu, guiding how legacy materials at the Tiwai site are removed, monitored and recycled, and how the whenua [land] is restored over time,” he said.

The company says Tiwai is one of the world’s lowest-carbon aluminium manufacturers.

Rio Tinto managing director of Pacific operations, Armando Torres, said the investment underscored the company’s commitment to the remediation programme.

“Building a dedicated processing facility at the smelter is another positive step forward in the remediation of the Tiwai site and reflects our shared commitment to working in partnership to protect our environment for future generations,” Te Rūnanga o Ngāi Tahu group head of strategy and environment Jacqui Caine said.

The remediation programme has already seen more than 36,000 tonnes of SCL exported for reuse since 2024, alongside major progress in returning ouvea premix and processing historical dross.

SCL is the carbon and refractory material that lines the inside of aluminium reduction cells and must be periodically replaced during the smelting process.

When removed, it becomes a regulated byproduct because it can contain carbon, fluorides and other compounds that require specialist handling.

The aluminium smelter at Tiwai is 100% owned by Rio Tinto.

Jamie Gray is an Auckland-based journalist, covering the financial markets, the primary sector and energy. He joined the Herald in 2011.