Potential of Ligand-Promoted Dissolution at Mild pH for the Selective Recovery of Rare Earth Elements in Bauxite Residues

Abstract

In a context of overexploitation of natural resources, a circular economy and particularly the extraction of resources from secondary sources, are essential to sustain a number of key technologies including renewable energies. Among secondary sources, bauxite residue contains critical elements including rare earth elements (REEs) (712mg/kg). We investigated the use of soft and selective dissolution protocols at mild pHs (2-6) as an alternative to pyroand hydrometallurgy for the recovery of REEs through ligand-promoted dissolution. This approach depends on the detailed characterization of the waste and the speciation of targeted elements. We assessed dissolution using low molecular weight organic acids (LMWOAs) and their conjugate bases. Citric acid/citrate showed satisfactory dissolution of REEs (up to 50% of light REEs) up to a pH of nearly 5, while tartaric acid/tartrate showed the best dissolution selectivity (enrichment factor up to 21.5 compared to Fe, Al and Ti). Almost no heavy REEs were dissolved in any of the conditions tested, probably due to the high chemical stability of their bearing phases. Indeed, heavy REEs were found as discrete phosphate particles. SynopsisLigand-promoted dissolution, an interesting mechanism for the development of selective recovery processes of REEs from bauxite residue in mild pH conditions.

Yttrium speciation variability in bauxite residues of various origins, ages and storage conditions

“…In both cases, Y-rich particles were found, co-localized with similar elements. Yttrium was found colocalized with other HREEs (Gd, Dy, Ho, Er, Yb), which supports the classification of Y as HREEs and validates using it as a proxy for HREEs (Borst et al, 2020;Lallemand et al, 2022;Pingitore et al, 2014).…”

“…Yttrium was used as a proxy for HREEs thanks to its similar physico-chemical behaviour (Borst et al, 2020;Lallemand et al, 2022;Pingitore et al, 2014). Improving knowledge of the REE speciation in BRs and the factors that influence it will pave the way for the development of extraction processes that account for the specificity of the targeted BRs in terms of origin, storage conditions and time (Deady et al, 2014).…”

Preparation and Application of Polyaluminum Ferric Sulfate from Red Mud: Behaviors of Leaching, Polymerizing, and Coagulation

“…The red mud dump can produce strong alkaline leachate, which can also harm people and animals near the dump . Therefore, many researchers have used red mud, fly ash, and coal gangue to prepare geopolymers and roadbed materials and achieved some good application results. , However, it is worth noting that the red mud contains many available chemical components such as aluminum, iron, and scandium, in which the content of aluminum and iron accounts for 40–60% of the total amount. , Efficient recovery of aluminum and iron from red mud is an important way for its comprehensive utilization of “reduction, recycling, and harmlessness”. At present, the extraction of aluminum and iron from red mud mainly involves magnetization roasting-magnetic separation for the recovery of iron and alkali roasting-alkali leaching for the recovery of aluminum.…”

“…3,4 However, it is worth noting that the red mud contains many available chemical components such as aluminum, iron, and scandium, in which the content of aluminum and iron accounts for 40−60% of the total amount. 5,6 Efficient recovery of aluminum and iron from red mud is an important way for its comprehensive utilization of "reduction, recycling, and harmlessness". At present, the extraction of aluminum and iron from red mud mainly involves magnetization roasting-magnetic separation for the recovery of iron and alkali roasting-alkali leaching for the recovery of aluminum.…”

Efficient dealkalization of red mud and recovery of valuable metals by a sulfur-oxidizing bacterium

“…Chemical extraction of REEs from RM has been performed using H 2 SO 4 , HCl, HNO 3 , and SO 2 gas (Abhilash and Meshram, 2019 ), and attempts have also been made to selectively extract metals such as Ti (Deng et al, 2017 ). The reported methods for metal extraction from RM include the following: acid leaching (Agatzini-Leonardou et al, 2008 ; Pepper et al, 2016 ; Kong et al, 2017 ; Li et al, 2021 ; Lallemand et al, 2022 ), roasting combined with water leaching (Zhu et al, 2015 ; Borra et al, 2016 ), bioleaching using fungi (Qu and Lian, 2013 ; Vakilchap et al, 2016 ; Pedram et al, 2020 ; Ilyas et al, 2021 ), chemoorganotrophic bacteria (Abhilash et al, 2021 ; Kiskira et al, 2021 ), and microalgae (CíŽková et al, 2019 ). Also, a combination of washing and electrodialysis has been used to treat RM and extract metals, respectively (Zhang et al, 2019 ).…”