Secure and sustainable future for silica, alumina and calcium carbonate
Alumina, silica and calcium carbonate are three materials in increasing demand for application in areas including transport, energy, construction and coatings, to name just a few. Their economic importance and projected market growth are considerable. However, the European market is at risk of a domestic supply shortage – particularly in the case of bauxite ore to produce alumina. This critical raw material is vital to aluminium production via the intermediate alumina. In addition to supply challenges, the production of these raw materials has high environmental impact. This includes tremendous global CO2 emissions, significant solid waste and huge volumes of water to discharge waste. The ambitious EU-funded AlSiCal project developed a pioneering approach for the green co-production of silica, alumina and calcium carbonate in a single process from a single unconventional source available in Europe, with minimum waste and net-zero CO2 emissions.
Hydrochloric acid chemistry turns unconventional materials into ‘gold’
AlSiCAl focused on rock high in silica content such as anorthosite and strategically investigated and benchmarked process alternatives. The most promising was selected and further refined. According to AlSiCAl coordinator Asunción Aranda, formerly of the Institute for Energy Technology: “The chosen technology is based on hydrochloric acid (HCl) chemistry. The selected rock is dissolved in HCl and silica is separated and purified from the solution. This is followed by the chemical separation and calcination of alumina, and finally the precipitation of calcium carbonate.” The entire process was validated at laboratory scale for anorthosite. One of the three core steps – dissolution and silica production – has also been validated at pilot scale.
Minimum waste, net-negative CO2 emissions
The AlSiCal technology unlocks currently unexploited mineral resources in Europe, securing a domestic supply of certain strategic raw materials. It could substantially reinforce the entire European aluminium industry value chain – from mine to market – creating jobs in the process. It also makes a significant contribution to sustainability and environmental goals. It enables alumina and aluminium production without generating bauxite residue and achieves high resource efficiency by co-producing valuable raw materials with minimal waste generation. It also operates with net-negative CO2 emissions by efficiently transforming CO2 into the valuable raw material known as precipitated calcium carbonate. Finally, the process is designed for easy electrification and it slashes water contamination.
Culmination of years of stalled progress
Alumina production from alternative sources and secondary materials readily available in Europe has long been a goal of European metallurgy. AlSiCal is the successful culmination of efforts to reach this goal, beginning in the 1970s and 1980s in countries such as Norway and the USA. At the time, none of the technologies proposed could simultaneously satisfy technological, environmental, economic and social goals. “Shaping the evolution of our initial concept into a tangible, feasible and robust technology during the AlSiCal project has been one of the most exciting innovation journeys of many of our partners and stakeholders,” notes Aranda. AlSiCal has created a public database of global anorthosite deposits and has developed reactors and process models for the technology. Together with its many publications, its innovative tools and the knowledge generated regarding the social dimension of mining and mineral processing technologies, AlSiCal will strengthen Europe’s green minerals and metals transition. Further upscaling and optimisation of AlSiCAl’s pioneering technology will accelerate industrial deployment.
Keywords
AlSiCal, silica, CO2, alumina, raw materials, bauxite, calcium carbonate, zero waste, co-production, aluminium, mining, critical raw material
