Bioleaching Of Rare Earth Elements From Bastnaesite-bearing Rock By Microbes And Its Mechanism

In this study,pristine strain types were isolated from various environmental samples,collected from different rare earth mining areas to explore the microbial diversity and ecological functions in the rare earth mineral environment.The results are as follows:(1)224 strains were isolated from rare earth minerals of different sources using different culture media,of which 164 actinomycetes were identified,belonging to 11 orders,13 families and 20 genera,accounting 73.2% of the total isolates.(2)The isolated strain exhibited a relatively good ecological function,with the capacity of dephosphorization,tolerance to high concentration of rare earth elements and adsorption of rare earth elements.Secondly,the bioleaching efficiency and mechanism of rare earth elements from bastnasite by pristine isolates are explored.The use of microorganisms to leach rare earth elements from tailings is a green energy-saving method,but it is not clear whether actinomycetes have the ability to leach rare earth elements.According to the experimental results of the preliminary experiments,two actinomycetes derived from rare earth mining area and two actinomycetes from the surrounding environment were selected.Those actinomycetes from different regions were investigated in detail for leaching of rare earth elements from bastnasite under different culture conditions.Results are as follows:(1)The main rare earth elements in bastnasite are Ce and La,and all four strains can extract rare earth elements from bastnasite.In the eutrophic medium containing bastnasite,the ability of four strains to leach rare earth elements is about 56-342 ?g/L.In the oligotrophic medium containing bastnasite,only Streptomyces sp.FXJ1.172 was able to grow and leach rare earth elements,and the total rare earth element leaching ability reached 548 ?g/L.(2)All strains exhibited a relatively low leaching efficiency for rare earth elements,ranking from 0.008 to 0.08%.One possible cause responsible for the low leaching efficiency is that the leached rare earth elements formed a new precipitate,or some of the rare earth elements were readsorbed onto the mineral surface.(3)At the same pH,microbes mediated bioleaching of leach rare earth elements is much higher than that of abiotic control,indicating that pH is not a major factor in the bioleaching process of rare earth elements.(4)metabolites analysis showed that the four actinomycetes possibly leach rare earth elements via secreting organic acids,complex ligands and siderophores.SEM-EDS experiments demonstrated that the bioleached rare earth elements can be resorbed onto the surface of microbes.A multiple lines of evidence indicated that the leached rare earth elements are mainly derived from bastnasite.Therefore,the experiments in this study show that actinomycetes have the ability to selectively leach and adsorb rare earth elements,which can be utilized for further applicatiuon of bioleaching rare earth elements from tailings or low-grade ore.