Behavior and mechanism of different fraction lead leach with several typical sulfate lixiviants in the weathered crust elution-deposited rare earth ore

An eco-friendly and high-yield extraction of rare earth from the leaching solution of ion adsorbed minerals

Ion-adsorbed rare earth minerals are rich in medium and heavy rare earth (RE), which are important strategic resources. In this article, a novel approach for the extraction of RE from ion adsorbed minerals was developed. Through a comprehensive assessment of their extraction and separation performance, the hydrophobic deep eutectic solvents (HDES) with a composition of trioctylphosphine oxide (TOPO): dodecanol (LA): 2-thiophenoyltrifluoroacetone (HTTA) = 1:1:1 was determined as the optimal configuration. Under optimized conditions, only RE were extracted by the HDES, while Al, Ca, Mg were not extracted at all. The HDES based extraction obviated the need for diluent such as kerosene, eliminating the generation of impurity removal residues. The RE in the stripping solution could be successfully enriched by saponified lauric acid, achieving an impressive precipitation rate of 99.7%. The RE precipitate underwent further enrichment, resulting in a RE concentration of 176 g/L (REO = 210 g/L). Unlike industrial precipitants such as oxalic acid and ammonium bicarbonate, lauric acid can be effectively recycled, thereby avoiding a large amount of wastewater and carbon dioxide emissions. The obtained RE solution product exhibits high yield and purity, this study provides an eco-friendly and high-yield approach for extracting RE.

Interactive effects of ammonium sulfate and lead on alfalfa in rare earth tailings: Physiological responses and toxicity thresholds

Ion-adsorption rare earth ore contains significant levels of leaching agents and heavy metals, leading to substantial co-contamination. This presents significant challenges for ecological rehabilitation, yet there is limited understanding of the toxicity thresholds associated with the co-contamination of ammonium sulfate (AS) and lead (Pb) on pioneer plants. Here, we investigated the toxicity thresholds of various aspects of alfalfa, including growth, ultrastructural changes, metabolism, antioxidant system response, and Pb accumulation. The results indicated that the co-contamination of AS-Pb decreased the dry weight of shoot and root by 26 %-77 % and 18 %-92 %, respectively, leading to irregular root cell morphology and nucleus disintegration. The high concentration and combined exposures to AS and Pb induced oxidative stress on alfalfa, which stimulated the defense of the antioxidative system and resulted in an increase in proline levels and a decrease in soluble sugars. Structural equation modeling analysis and integrated biomarker response elucidated that the soluble sugars, proline, and POD were the key physiological indicators of alfalfa under stresses and indicated that co-exposure induced more severe oxidative stress in alfalfa. The toxicity thresholds under single exposure were 496 (EC5), 566 (EC10), 719 (EC25), 940 (EC50) mg kg-1 for AS and 505 (EC5), 539 (EC10), 605 (EC25), 678 (EC50) mg kg-1 for Pb. This study showed that AS-Pb pollution notably influenced plant growth performance and had negative impacts on the growth processes, metabolite levels, and the antioxidant system in plants. Our findings contribute to a theoretical foundation and research necessity for evaluating ecological risks in mining areas and assessing the suitability of ecological restoration strategies.

Non-negligible N2O emission hotspots: Rivers impacted by ion-adsorption rare earth mining

Rare earth mining causes severe riverine nitrogen pollution, but its effect on nitrous oxide (N2O) emissions and the associated nitrogen transformation processes remain unclear. Here, we characterized N2O fluxes from China's largest ion-adsorption rare earth mining watershed and elucidated the mechanisms that drove N2O production and consumption using advanced isotope mapping and molecular biology techniques. Compared to the undisturbed river, the mining-affected river exhibited higher N2O fluxes (7.96 ± 10.18 mmol m-2d-1 vs. 2.88 ± 8.27 mmol m-2d-1, P = 0.002), confirming that mining-affected rivers are N2O emission hotspots. Flux variations scaled with high nitrogen supply (resulting from mining activities), and were mainly attributed to changes in water chemistry (i.e., pH, and metal concentrations), sediment property (i.e., particle size), and hydrogeomorphic factors (e.g., river order and slope). Coupled nitrification-denitrification and N2O reduction were the dominant processes controlling the N2O dynamics. Of these, the contribution of incomplete denitrification to N2O production was greater than that of nitrification, especially in the heavily mining-affected reaches. Co-occurrence network analysis identified Thiomonas and Rhodanobacter as the key genus closely associated with N2O production, suggesting their potential roles for denitrification. This is the first study to elucidate N2O emission and influential mechanisms in mining-affected rivers using combined isotopic and molecular techniques. The discovery of this study enhances our understanding of the distinctive processes driving N2O production and consumption in highly anthropogenically disturbed aquatic systems, and also provides the foundation for accurate assessment of N2O emissions from mining-affected rivers on regional and global scales.

Pollution caused by mining reshaped the structure and function of bacterial communities in China's largest ion-adsorption rare earth mine watershed

Ion-adsorption rare earth mining results in the production of high levels of nitrogen, multiple metals, and strong acidic mine drainage (AMD), the impacts of which on microbial assembly and ecological functions remain unclear. To address this knowledge gap, we collected river sediments from the watershed of China's largest ion-adsorption rare earth mine and analyzed the bacterial community's structure, function, and assembly mechanisms. Results showed that bacterial community assembly was weakly affected by spatial dispersion, and dispersal limitation and homogeneous selection were the dominant ecological processes, with the latter increasing with pollution gradients. Bacterial alpha diversity decreased with pollution, which was mainly influenced by lead (Pb), pH, rare earth elements (REEs), and electrical conductivity (EC). However, bacteria developed survival strategies (i.e., enhanced acid tolerance and interspecific competition) to adapt to extreme environments, sustaining species diversity and community stability. Community structure and function showed a consistent response to the polluted environment (r = 0.662, P = 0.001). Enhanced environmental selection reshaped key microbial-mediated biogeochemical processes in the mining area, in particular weakening the potential for microbial denitrification. These findings provide new insights into the ecological response of microbes to compound pollution and offer theoretical support for proposing effective remediation and management strategies for polluted areas.