Making aluminum without making CO₂

Three industrial giants are getting together to commercialize a new process for making aluminum that generates oxygen as a by-product instead of carbon dioxide.

The companies—aluminum makers Alcoa and Rio Tinto and computer icon Apple—plus the governments of Quebec and Canada will invest a combined $145 million to develop the approach and license it to the aluminum industry.

Aluminum has been made the same way since 1886, when the American chemist Charles Martin Hall and the Frenchman Paul Héroult almost simultaneously developed an electrolytic technique for reducing aluminum oxide in a bath of molten cryolite (hexafluoroaluminate). The process uses a carbon-rich anode that reacts with the generated oxygen to form CO₂.

Researchers have sought inert anodes almost since the Hall-Héroult process debuted, according to Donald R. Sadoway, a professor of materials chemistry at MIT. But to date nothing has satisfied tough anode requirements such as physical stability, electrical conductivity, and resistance to attack by fluorine and oxygen.

Alcoa has been testing an inert anode of undisclosed composition since 2009 at a technical center in Pittsburgh. Sadoway notes that Alcoa has published frequently about nickel ferrite cermet anodes, though it likely has moved beyond the metals and alloys previously disclosed.

Apple says the partnership to commercialize the technology emerged after three of its engineers went looking for a better way to produce aluminum, used extensively in its phones and computers. Seeing the potential environmental impact of the Alcoa process, the engineers brought Rio Tinto to the table, Apple says.

Converting Canada’s aluminum industry, the world’s third largest, to the new technology could eliminate greenhouse gas emissions equivalent to nearly 1.8 million light-duty vehicles, the partners say. Aluminum production’s biggest source of emissions is the electricity needed for electrolysis.

Producing oxygen on an inert anode does require more energy that producing CO₂ on a consumable carbon anode. Sadoway notes, however, that other benefits of a long-lasting anode should offset the energy gain. Plus, the process won’t generate CF₄ and C₂F₆—both potent greenhouse gases—as by-products.