Extraction of high purity magnetite from bauxite residue

Abstract

Bauxite residue is a byproduct of the alumina industry and is characterized by high alkalinity and very fine particle size. Currently, there is a low volume utilization of bauxite residue as an additive in the construction industries, and only 3–4 % of the total volume produced annually (160 million tons) is utilized effectively. Bauxite residue is mainly composed of iron oxide along with oxides of aluminum, calcium, sodium, silicon, and titanium. A high fraction of iron in bauxite residue makes it a potential alternative source. However, recovery of high purity iron products with high recovery is technically challenging. The present work is focused on the recovery of iron from bauxite residue in the form of high purity magnetite through a hydrometallurgical approach. Bauxite residue is first neutralized after leaching with mild hydrochloric acid, followed by the leaching of iron with oxalic acid and photochemical reduction of leach liquor to obtain ferrous oxalate precipitate, which is further converted to high purity magnetite. Three different bauxite residue samples with different mineralogical compositions were used, and a comparative study is presented to illustrate the flexibility of the process toward different grades of bauxite residue.