Vacuum pyrolysis method for reclamation of rare earth elements from hyperaccumulator Dicranopteris dichotoma grown in contaminated soil

Abstract

Rare earth elements sources in China have been overexploited and have caused serious soil pollution. The hyperaccumulator Dicranopteris dichotoma was discovered to have the ability to remove rare earth elements from contaminated soil and was widely planted as part of the remediation process for rare earth elements contaminated soil. Therefore, abundant hazardous Dicranopteris dichotoma biomass containing a high concentration of rare earth elements was generated. However, treatment methods for Dicranopteris dichotoma have not been previously investigated. In this paper, the eco-friendly technology of vacuum-pyrolysis-condensation was proposed for disposing the biomass of this fern, it was employed to change biomass accumulated with rare earth elements in to chemical resource. Ethylene oxide was the main component of the chemical resources, constituting 49.4 wt%. However, no ethylene oxide was detected in the pyrolytic products from non-accumulated biomass. The residual ash contained 6160 mg kg−1 of rare earth elements and was suggested as a rich ‘bio-ore’ of rare earth elements. No hazardous wastes were produced in the reclamation of these hyperaccumulators. We concluded that rare earth elements strongly influenced the pyrolysis process of dicranopteris dichotoma biomass and caused the generation of ethylene oxide. This paper takes the vacuum-pyrolysis-condensation of rare earth elements accumulated Dicranopteris dichotoma as the guidance, in order to attract more attention and develop more eco-friendly disposal technologies for hyperaccumulator biomass from the remediation process of contaminated soil, recovering the biomass resources and realized its high value.