Evaluation on rare earth elements and microbial communities in abandoned rare earth tailings

Abstract

Rare earth elements (REEs) tailings present a pressing issue in terms of resource waste, with a lack of effective methods for evaluating and recycling these resources. This study aimed to establish an evaluation system and assess the potential for reutilization of REEs tailings. The study measured the contents of 14 REEs in two layers (0–15 cm, L1 and 15–30 cm, L2) of the tailings across different abandoned durations of 1.5-year (1.5-Y), 7-year (7-Y), 10-year (10-Y), and 14-year (14-Y), as well as an unmined site (CK), using inductively coupled plasma mass spectrometry (ICP-MS). Additionally, the characteristics and functions of microbial communities in the tailings were investigated; The amplified 16S rRNA gene and ITS gene were used to detect bacteria and fungi respectively. Results showed that total REEs content in surface tailings increased from 851.46 μg/g at 1.5-Y to 2133.81 μg/g at 14-Y, which can be attributed to vertical migration. The residue degree of REEs in the tailings ranged from 10.03 % to 21.57 %. The maximal fold to extraction ultimate value of REEs ranged from 1.31 (Ce) to 4.54 (Nd), while the maximal rate to initial ore value of REEs ranged from 0.279 (Ce) to 0.610 (Nd). Moreover, the maximal phyto-remining potential index ranged from 0.365 (Ce) to 2.768 (Nd), with values above 1.0 indicating potential for phyto-remining. Bradyrhizobium showed a positive correlation with all 14 individual REEs, whereas Burkholderia exhibited negative correlations with all 14 individual REEs among bacteria, In terms of fungi, Sagenomella, Suillus, and Trichoderma were positively correlated with all 14 tested REEs, while Chalara, Cenococcum, and Pseudotomentella displayed negative correlations with all 14 tested REEs. The REEs content significantly influenced the microbial communities in the tailings, particularly impacting fungal species during ecological restoration. The REEs tailings demonstrated promising potential for phyto-remining. These findings offer valuable insights into the recycling of REEs tailings.