Bayer Process Towards the Circular Economy—Soil Conditioners from Bauxite Residue

Large-scale bauxite residue (BR) reuse is still a challenge for alumina producers worldwide. Agronomic applications for BR can be a sustainable and economically viable option for soil fertility improvement in countries where agriculture plays a crucial economic role, such as Brazil. This study reports a biological approach to partial BR alkalinity neutralization, allowing its safe application as a soil conditioner for fertility improvement in acidic tropical soils. Microcosm tests were established to assess the effect of incorporating local agro-industrial organic residues into the BR to generate acidity, while highly fertile undisturbed soil was added as a microbial inoculum. BR amendment with organic residues exhibited a fast pH neutralisation (from 10 to 6.5 at the second day of incubation). Results confirmed that the locally available organic residues and the soil added to BR improved its physical and chemical characteristics, allowing further research into its agronomic effects.