A new method for recovering rare earth elements from the hyperaccumulating fern Dicranopteris linearis from China

Hyperaccumulator plants are new alternative sources for elements of interest e.g., nickel, rare-earth elements (REEs), as concentrations in their aerial parts are higher than in common low-grade ores. The fern Dicranopteris linearis naturally grows on former mine tailings in Southern China and is classified as a REE hyperaccumulator. The efficient recovery of REEs is fundamental to ensure economic viability and to limit the environmental impact of the process. This study presents a novel approach for the treatment of the Dicranopteris biomass after incineration to ash to drastically improve the ?bio-ore? grade and to generate heat. Ash structure and composition is described, and challenges for efficient recovery of REEs are discussed. A pre-processing step, aiming at rendering the REEs available for extraction, was designed to dissolve aluminum (Al) using concentrated sodium hydroxide (6 M) at an average temperature (80 ?C). The operating parameters were investigated through experiment methodology design and parametric studies to build an empirical model. Additional experiments revealed that the formation of insoluble aluminosilicate compounds limited the removal of aluminium. Rinsing the REE-rich residue proved to be effective to increase the REE concentration and was carefully designed. Subsequently, the REEs were extracted under mildly acidic conditions using nitric acid (25 ?C, pH 4.8), producing a valuable solution devoid of aluminium and containing 74% of the REEs.