Advances in Alumina production from Anorthosite with Integrated CO₂ Storage – A feasibility study

The main purpose of the project is to assess the technical and economic potential for a new technology for the production of alumina from Anorthosite and at the same time store CO₂. Anorthosite is a silicate rock comprising approx. 30 % alumina, and is therefore a potential source of alumina for the aluminium industry and other applications. The technology dissolves Anorthosite in a mineral acid under moderate process conditions to extract the alumina. The rock also consists of approx. 14 per cent calcium, which is bound to carbonate from CO₂, forming calcium carbonate as an integrated part of the process. This can present a long-term storage medium for CO₂. Silica is formed as a potential commercial by-product of the process. In the production of approx. 3 million tonnes Anorthosite annually, approx. 1 million tonnes of alumina can be extracted, 1.5 million tonnes silica and around 500 000 tonnes of CO₂ can be stored.

The project period was concluded in December 2013, after about 1.5 years duration. Important milestones during the project period have been:

1. Optimisation of process parameters in the laboratory at the Institute for Energy Technology.
2. Verification of the acid bath process in pilot tests at the Herøya Industry Park in partnership with Bilfinger.
3. Testing of an innovative new process step to store CO₂ in the form of calcium carbonate and at the same time regenerate acid for further use in the process.
4. Implementation of a technical and economic analysis to assess costs in connection with investment and operation of a full-scale process.
5. Implementation of preliminary life-cycle analysis (LCA) for the process in order to assess the overall CO₂ balance of the technology.

The project has been successful in demonstrating that AI3+ and Ca2+ from Anorthosite can be efficiently extracted from the rock using a bath process, both in lab scale and pilot. Alumina from the Anorthosite has also been produced in laboratory tests. The technology provides possible storage of substantial volumes of CO₂ in the form of calcium carbonate which, at the same time, is a decisive process step for recycling acid.

The technical and economic analysis shows that it is possible to achieve a positive current value for the production of approx. 1 million tonnes alumina annually with moderate investments. The study also shows that the economy is particularly sensitive in regards to acid and energy consumption. The project economy can largely be improved through increased recycling of acid and energy recovery. These are aspects of the project that will be optimised and improved in the further project work. The alumina production process itself will also be optimised and tested in pilot-scale trials.

The preliminary CO₂ balance and life cycle analysis of the technology show that the process has potential for reduced CO₂ emissions compared with conventional alumina production technology. The technology also has environmental advantages as regards generation of residual mass and waste products from the process.