Bayer Process Towards the Circular Economy—Metal Recovery from Bauxite Residue

Abstract

On a global basis, 150 million tons of bauxite residue (BR) are produced every year and the total inventory are estimated in 4.6 billion tons. BR still contains significant amounts of valuable metals such as Fe (6.8–71.9%), Ti (2.5–22.6%), Al (2.12–28.4%) and rare earth elements (REE) and can be considered a potential secondary source of raw materials. Its utilization to recover these metals would follow the principles of the circular economy in mining sector and environmental impact mitigation. In 2017, Brazil produced 11 million tons of alumina and around 8.8–16.5 million tons of BR. Here we evaluate the potential for wet direct magnetic iron recovery from a Brazilian BR using different magnetic field intensities. The BR had an iron concentration of 40.08% Fe2O3 where hematite was the main iron mineral phase. Particle size distribution analysis and wet sieving assessment indicated a high concentration of fines (D90 < 43.7 μm), as well as, a narrow size distribution curve. The overall iron recovery was 11.5% w/w and the magnetic product achieved 59% Fe2O3. The data showed that all the coarser particles in the feed (8.34% w/w, < 100 μm) reported to the magnetic product while the fines were in the non-magnetic fraction, proving that particle size is fundamental for wet magnetic separation of paramagnetic materials. Looking at the rough number, an iron magnetic recovery rate of 11.5% could potentially recover around 0.3–0.6 million tons of iron annually.