New Zealand’s Aluminium Smelter (NZAS) chief executive and general manager Stew Hamilton has resigned. 

The smelter, at Tiwai Point, Bluff, has been under fire recently after it was revealed more than 100,000 tonnes of hazardous spent cell liner (SCL) waste is stored next to an eroding beach.

The, last week, the Rio Tinto-owned company said an independent audit had revealed there is 217,000 tonnes of SCL stored across the whole, some 58,000 tonnes more than the company stated in March. 

NZAS plans to close the smelter at the end of 2024 and the Government is pushing for more assurances about how it will clean up the site. 

Hamilton, who has been with Rio Tinto for 22 years and took over as chief executive of NZ Aluminium Smelters in 2018, has accepted a new position with Mercury Energy. 

He will leave in July.

Daniel van der Westhuizen, Rio Tinto's Acting Managing Director Pacific Operations, thanked him for the "significant contribution" he has made to the business.

"The smelter has been going through a very public period of transition, and Stew's commitment and leadership has been hugely valued throughout this time.

"On behalf of the entire team, we wish Stew and his family all the best for this new phase of their lives and wish them well for the future.

"We will now conduct a thorough recruitment process for a new chief executive and general manager to carry on Stew's responsibilities of running NZAS safely and with a commitment to responsible eventual closure of the operation."

Hamilton said that "while this is an exciting new challenge, it has been a hard decision to leave NZAS.

"Having started my career at NZAS as a graduate engineer I feel like I have been a part of the NZAS family for most of my professional life, and am very grateful for the support and friendship the team has shared with me.

"I came back to NZAS in 2018 to lead a team that runs one of the best operations in New Zealand and around the world. The last few years have been very challenging and I am proud of what the team has achieved over that time.

"I continue to be inspired by the team’s incredible commitment to safety, to looking after each other and ability to keep focusing on making some of the best, lowest carbon, purest aluminium in the world. 

"I leave in confidence that the Tiwai team will continue to perform at the highest level."