The role of microorganisms in rare earth elements bioaccumulation

Author

Maedeh Soleimanifar, New Jersey Institute of Technology

Document Type

Dissertation

Date of Award

12-31-2021

Degree Name

Doctor of Philosophy in Environmental Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Lucia Rodriguez-Freire

Second Advisor

Michel Boufadel

Third Advisor

Lisa Axe

Fourth Advisor

Mengyan Li

Fifth Advisor

Jose Manuel Cerrato Corrales

Abstract

Rare earth elements (REE) are valuable raw materials in our modern life. Extensive REE application from electronic devices to medical instruments and wind turbines, and non-uniform distribution of these resources around the world, make them strategically and economically important for countries. Current REE physical and chemical mining and recycling methods could have negative environmental consequences, and biologically-mediated techniques could be applied to overcome this issue.

In this research, the first objective is to investigate the bioextraction of cerium oxide and neodymium oxide nanoparticles (REE-NP) by a pure culture Methylobacterium extorquens AM1 (ATCC®14718™). Results show that adding up to 1,000 ppm CeO₂ or Nd₂O₃ nanoparticles (REE-NP) does not inhibit bacterial growth. STEM-EDS ultrafine structure images confirm the incorporation of REE-NP by the bacteria. Furthermore, ICP-MS REE results show limited dissolution of REE, and analysis of washed digested cells confirms 45 μg/gcen cerium and 154 μg/gcen neodymium accumulation by M extorquens AM1. M extorquens is able to grow in high concentrations of REE-NP and bioaccumulates them.

In the second objective, the effect of biostimulation and bioaugmentation on phytorecovery of REE-NP is studied by exposing ryegrass seeds to nanoparticles in hydroponic environments in two different sets of experiments: bioaugmentation (using CeO₂ nanoparticles and M extorquens AM1), and biostimulation (using CeO₂ or Nd₂O₃ nanoparticles and endogenous microorganisms). Ryegrass accumulates REE in the root systems, and the biostimulation increases the REE accumulation rate. In the bioaugmentation experiment, another REE-utilizing bacterium, Bacillus subtilis, is enriched more than M extorquens in control samples (no M extorquens AM1), and associated with higher Ce extraction in both natural (165 μg/gdried-plant) and surface-sterilized seeds (136 μg/gdried-plant). Also, REE phytoextraction is higher in biostimulation experiments; 705 μg/gdried-plant Ce and 19,641 μg/gdried-plant Nd. Microscopy studies confirm Nd nanoparticles on the surface and inside the roots in the biostimulation experiments. Hence, promoting microbial growth increases REE phytoextraction efficiency.

Finally, in the third objective, the biorecovery of REE from REE-enriched mine waste pile (> 8000 ppm total REE) is studied. Mine waste bioaugmentation and biostimulation are investigated by adding an enrichment solution of 70% M extorquens AM1, and methylamine hydrochloride with and without mineral medium to support microbial growth. The greatest REE cellular accumulation is obtained in the bioaugmented experiment with only methylamine hydrochloride (without mineral medium), with 557 μg/gcell total REE, the higher concentration of Ce (215 μg/gcell), followed by La (163 μz/gcell) and Nd (73 μs/gcell). However, non-bioaugmented mine waste with only methylamine hydrochloride mobilizes the highest REE concentration with limited bacterial growth. Hence, the addition of M extorquens and an exogenous carbon source and electron donor promotes REE biouptake over REE dissolution in this system.

The outcome of this research aims to a better understanding of bio-interaction between bacteria and REE, and leads to designing new systems in order to remediate wastes while extracting valuable materials.

Recommended Citation

Soleimanifar, Maedeh, "The role of microorganisms in rare earth elements bioaccumulation" (2021). Dissertations. 1766.
https://digitalcommons.njit.edu/dissertations/1766