The extraction of alumina from bauxite is significantly impacted by the silica content of the ore — specifically the presence of silica in kaolinite (Al2Si2O5(OH)4). This is because traditional bauxite-beneficiation methods, such as washing, flotation and particle-size separation, also typically result in the loss of alumina bound in the kaolinite structure. This reduces alumina yield, increases operating costs and creates “red mud” residue that must be subsequently managed. A new alumina refining technology (diagram) developed by IB2 (L’Isle sur la Sorgue, France; www.ib2-bauxite.com) addresses these challenges by selectively removing silica from kaolinite while preserving its alumina content, which helps to optimize the use of low-grade bauxite deposits. “A key benefit of this approach is the conversion of the extracted silica into a high-value product called tobermorite, which is widely used in the cement and construction industries. Additionally, stabilizing silica as tobermorite reduces the environmental risks associated with red mud disposal by preventing silica leaching,” explains Yves Occello, founder and CEO of IB2.
The technology’s selective separation is achieved via a carefully controlled reaction for the change of the mineralogical phases. This promotes the liberation of silica and its subsequent conversion to tobermorite. The process is operated under optimized temperature and reaction kinetics to minimize alumina loss.
“While traditional bauxite processing requires 2.5 to 3.0 tons of raw bauxite per ton of alumina, IB2 reduces this to approximately 1.7 tons, even when using low-grade ore. This results in a significant reduction in red mud generation, alleviating environmental and storage constraints, and an improvement in ore utilization that allows for better use of lower-grade bauxites,” adds Occello. Furthermore, the tests confirmed a 50–70% reduction in caustic soda consumption compared to conventional refining and the successful conversion of extracted silica to tobermorite with a purity suitable for cement applications.
IB2 has validated the process through extensive pilot testing in Germany, Belgium and China, at throughputs of around 30–40 kg/h. At these pilot plants, silica-removal efficiencies exceeding 90% were demonstrated, while maintaining alumina recoveries greater than 95%. “The next phase is to scale up the process, with commercial deployments planned in China, Kazakhstan, Saudi Arabia and India. The technology has already been adopted by the Senze Group in China,” says Occello.