Rio Tinto has partnered with the Australian Renewable Energy Agency (ARENA) to study whether hydrogen can replace natural gas in alumina refineries to reduce emissions.

Rio Tinto will conduct a $1.2-million feasibility study, equally funded with ARENA through a $580,000 grant, into using clean hydrogen to replace natural gas in the calcination stage of producing alumina at the Yarwun alumina refinery in Gladstone. Calcination is the final stage of the Bayer process for producing alumina from bauxite; alumina is then used for the production of aluminum metal through the Hall–Héroult electrochemical smelting process.

Yarwun alumina refinery

Calcination heats hydrated alumina (aluminum hydroxide) from the preceding precipitation stage at temperatures up to 1100 ˚C to form anhydrous alumina (aluminium oxide, Al2O₃). Calcination is an energy-intensive process, for which the current predominant fuel is natural gas.

A fifth-generation (circa 2011) alumina calciner. Klett and Perander (2015)

In a 2017 open-access paper exploring the use of concentrated solar thermal (CST) radiation for alumina calcination, Davis et al. noted that the process heat requirements of modern industrial calciners and estimated resulting CO₂ emissions (calculated from the combustion of methane) are approximately 3 GJ per tonne-alumina and 165 kg-CO₂ per tonne-alumina product, respectively, with natural gas as the predominant fuel.

The Rio Tinto-ARENA study program includes work to be done at Rio Tinto’s Bundoora Technical Development Center in Melbourne, where Rio Tinto’s in-house development capability has now been extended to hydrogen.

If we can replace fossil fuels with clean hydrogen in the refining process for alumina, this will reduce emissions in the energy and emissions intensive refining stage of the aluminum supply chain. Exploring these new clean energy technologies and methods is a crucial step towards producing green aluminum.

This study will investigate a potential technology that can contribute to the decarbonization of the Australian alumina industry. If successful, the technical and commercial lessons from Rio Tinto’s study could lead to the implementation of hydrogen calcination technology, not only in Australia, but also internationally.

—ARENA CEO Darren Miller

The study comprises two distinct work packages:

• Preliminary engineering and design study conducted to understand the construction and operational requirements of a potential demonstration project at the Yarwun alumina refinery.

• Simulating the calcination process using a lab scale reactor at the Bundoora Technical Development Center.

Once complete, the study will inform the viability of a potential demonstration project. Rio Tinto has lodged patents for the hydrogen calcination process.

Rio Tinto is aiming to reach net zero emissions across its operations by 2050. Across the company, it is targeting a 15% reduction in absolute emissions and a 30% reduction in emissions intensity by 2030, from a 2018 baseline.

Resources

• Dominic Davis, Fabian Müller, Woei L. Saw, Aldo Steinfeld and Graham J. Nathan (2017) “Solar-driven alumina calcination for CO₂ mitigation and improved product quality” Green Chem., 19, 2992-3005 doi: 10.1039/C7GC00585G

• Klett C., Perander L. (2015) “Alumina Calcination: A Mature Technology Under Review from Supplier Perspective.” In: Hyland M. (eds) Light Metals 2015. Springer, Cham. doi: 10.1007/978-3-319-48248-4_15