Bauxite residue reduction with hydrogen and Metal recovery

As part of the H2020 HARARE project, the PhD candidate will work on the reduction of bauxite residue using hydrogen, which will lead to a product that builds the base for the recovery of metals. BR will be mixed with alkali sources and pelletised before roasting in H2. The aim is to convert the iron oxides in the BR to magnetite. Lower temperatures and shorter holding time are necessary for this reaction than for conversion to metallic iron. Thus, roasting at intermediate temperatures (400-800°C) will be sufficient. In addition to temperature, the parameters to be studied are different alkali sources (NaOH, Na2CO3) and vol.% of H2 (from 2 to 25 vol.%). The experimental campaign will be based upon a Design of Experiments, DoE approach, and the streams will be analysed for their chemistry, crystalline phases (both qualitatively and quantitatively) and microstructure (including pore structure and surface). The fate of REE and radioactive elements will be investigated in detail. In previous C-based smelting experiments it has been shown that REE and Th concentrate in a perovskite (CaTiO3) phase with total REE content of 31082 μg g-1, next to 4400 μg g-1 of Th. The same techniques will be used to analyse the Fe, Al, Na-depleted fraction in each process variation, including radioelement mapping. The process will be scaled to a production of 50 kg per batch (i.e. 250 kg per day). The BR cake, after dewatering in a filter press, will be mixed with the additives in a screw-mixer, followed by pelletizing in a stiff vacuum extruder and drying in a continuous microwave drier. Roasting will take place in a 230 kW induction furnace modified with a closed crucible that allows purging of H2 gas. The main parameter to be investigated will be the gas composition (fraction H2 in N2).