Concerns over stockpile of hazardous waste at New Zealand aluminium smelter

CONCERNS have been raised over a stockpile of hazardous waste at Rio Tinto’s Tiwai Point aluminium smelter. The company says it is working on solutions to deal with it.

New Zealand’s Aluminium Smelter (NZAS) is a joint venture between Rio Tinto and Japan’s Sumitomo Chemical Company, with Rio Tinto owning the majority. The smelter was supposed to close this year due to a combination of a decline in aluminium prices and a failure to negotiate a lower price for power with its supplier, but this has been delayed until 2024.

A report by RNZ, New Zealand’s public radio broadcaster, raised concerns over the stockpiling of cyanide-laced hazardous waste at the smelter, claiming that there is a lack of clarity over NZAS’ plans for the waste, which goes against international industry guidelines.

The waste is spent cell liner (SCL) waste – also called spent pot lining (SPL) – which contains chemicals including fluoride and cyanide. There is a risk of producing explosive gases if it is mixed with water. The RNZ report notes that the waste is stored 85 m from a rapidly eroding beach.

RNZ also reported that the New Zealand Government has suspended talks with Rio Tinto over how the smelter will shut down until more detail is given on what will be done with the waste.

A spokesperson for Rio Tinto told The Chemical Engineer: “At Tiwai Point we are carefully storing the waste produced by our aluminium smelter. It is extremely closely monitored, as is the coastal erosion on the Peninsula. We are confident the waste material is securely and safely stored while we work on the best end-user solution. This material is often used in cement making and this is a great end use as it ultimately provides a zero-waste solution. Currently there are no cement manufacturers in New Zealand able to take the material, so as part of our detailed closure study we are exploring other options and in particular would hope to find a local end user. We don’t have all the answers right now but we are working hard to ensure we deliver the best result in the end. The best solutions can sometimes take time and in the meantime we know the material at Tiwai, as confirmed by Worksafe inspectors who visited in late February, is safe and well monitored.”

The company said that until 2016 some of the SCL waste was used in Holcim’s Westport plant for cement production. With the closure of that plant, NZAS has not been able to identify new end users for the waste in New Zealand, which has led to some of the waste being exported. It said that there is currently 181,000 t of SCL stored on site, with around 58,000 t being exported over the last ten years. NZAS is currently exploring other possible options for reusing the waste in other industrial processes and said it welcomes input from any possible end users within New Zealand.