Basis for a new process for producing REE oxides from Dicranopteris linearis.

• Rare earth elements can be recovered from an hyperaccumulating fern. • REEs can be precipitated as oxalate after direct extraction from the biomass. • H 2 SO 4 is used to extract REEs and to obtain a highly concentrated final solid. • Major REEs behave in the same way throughout the process. Dicranopteris linearis is a fern that grows naturally on the tailings of former rare earth element (REE) mines in southern China. It accumulates REEs in its aerial parts at concentrations that classify this plant as hyperaccumulator. The main objective of this research is to design a process to recover REEs directly from the dry biomass. This process involves three steps: (i) extraction of REEs from the dry plant by leaching with a solution containing acid and/or complexing agents, (ii) precipitation of REEs with oxalate and (iii) calcination to prepare REE oxide. A methodology based on speciation calculation made it possible to determine operating conditions for precipitation by accounting for the influence of the species present according to the extraction method. Simulations were carried out using Chess software, allowing the calculation of the composition of a multicomponent solution at thermodynamic equilibrium. These operating conditions were then validated experimentally. REE extraction from the dry plant was significantly improved under acid conditions (with H 2 SO 4) or with a strong complexing agent (ethylenediaminetetraacetic acid). After optimization of the precipitation conditions, REE precipitation yields were above 90 %. After calcination, the final solid (REE oxide) contained ca 69 % of the REEs present in the initial biomass. The use of sulphuric acid as an extracting agent resulted in the recovery of a solid composed of 52 wt % of REEs (based on metal content). Thus, this study proposes a new recovery route for these strategic elements with a REE concentration factor from soil to final solid of 2500. [ABSTRACT FROM AUTHOR]