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The New Zealand Aluminium Smelter (NZAS) will begin to export thousands of tonnes of hazardous substance in June.

The waste is being stockpiled at Tiwai Point smelter site in light of a potential closure.

NZAS yesterday released the findings of its preliminary closure study, outlining the detailed work the company plans to carry out to remediate the site as part of any future closure.

While Rio Tinto announced in February it believed there was a long-term future for the Bluff operation past its previously signalled closure date of 2024, NZAS chief executive and site general manager Chris Blenkiron said it was committed to cleaning up the site regardless of the outcome.

"While we do see a positive long-term future for the smelter to operate beyond 2024, we have progressed this study to understand what work is needed to remediate the site and provide reassurance to the Southland community," he said.

Among the measures planned to be taken was the relocation of the existing landfill to a new lined and capped landfill with a higher elevation to address the long-term risk of sea-level rise and coastal erosion.

It also included the demolition of the majority of assets, the remediation of contaminated soils to an industrial level and removal and recycling of all spent cell lining material from site.

This removal was intended to be achieved via direct export to various international locations and/or via an onsite processing plant by a third-party contractor, the study states.

The company has 220,000 tonnes of spent cell lining on its site near Bluff, a material which contains both cyanide and fluoride, and 55,000 tonnes of dross residue to be processed.

The study stated commercial contracts were in place for 42,000 tonnes of dross to be processed and recycled.

"These contracts cover 100% of ouvea and MRP landfilled dross residue."

Other commercial contracts were in place for up to 30,000 tonnes a year to be exported for processing and recycling offshore.

Export permits were being confirmed and the first shipment estimated to take place in June.

"We are also in the process of updating our financial accounts and will release the updated rehabilitation and closure provision in May 2022."