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Rare earth elements (REEs) are important strategic resources, widely used in various technological fields, especially heavy rare earth elements (HREEs). China has extensive rare earth deposits, with diverse mineral types and a complete range of rare earth elements, characterized by a “heavy south, light north” resource distribution pattern. The rare earth-bearing collophane in the Zhijin area of Guizhou is a typical marine sedimentary phosphorite deposit with large reserves and a high heavy rare earth content. This study investigates the rare earth-bearing collophane in the Zhijin area using X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) to analyze its mineral composition and occurrence characteristics. In terms of flotation, a reverse flotation process for magnesium removal was adopted. By optimizing the flotation parameters, including grinding fineness, collector dosage, pH regulator dosage, and depressant dosage, the optimal flotation conditions were determined. A further mineralogical analysis was conducted on both the flotation concentrate and tailings. The results show that the main minerals in the rare earth-bearing collophane of Zhijin are fluorapatite and dolomite, with dolomite as the primary gangue mineral, and rare earth elements are mainly hosted in fluorapatite. The optimal flotation conditions were achieved when the grinding fineness was −74 μm with an 83% passing rate, XF-1 was used as the collector at a dosage of 300 g/t, sulfuric acid (H₂SO₄) as the pH regulator at 6 kg/t, and phosphoric acid (H₃PO₄) as the depressant at 3 kg/t. By employing an optimal reagent regime and implementing a reverse flotation process consisting of one roughing and one scavenging stage, a phosphate concentrate was obtained with a P₂O₅ grade of 31.61% and an REO content of 0.161%. The P₂O₅ recovery reached 84.22%, while the REO recovery was 78.65%. Compared to the raw ore, the P₂O₅ grade increased by 11.52 percentage points, and the REO content improved by 0.051 percentage points. Mineralogical analysis of the flotation concentrate and tailings revealed that dolomite was effectively removed by reverse flotation, while rare earth elements were successfully enriched in the phosphate concentrate. In conclusion, this study provides an efficient flotation separation process for rare earth-bearing collophane and dolomite, while also offering technical support for the efficient recovery of rare earth resources. This research has significant theoretical and practical implications. Full article

Rare-earth elements (REEs) are often highly concentrated in sedimentary phosphate deposits, and the microdistribution characteristics and occurrence state of rare earth in these deposits play a crucial role in the overall development and utilization of mineral resources. This study aims to analyze the microdistribution of REEs in REE-bearing phosphate deposits in the Zhijin region of Guizhou at the microstructural level and investigate their occurrence modes. Specifically, rock and mineral identification, X-ray diffraction (XRD), scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS), and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) were utilized to analyze the samples. The correlation between the distribution of REEs and phosphorus was examined. In addition, the microdistribution of REEs in specific mineral phases and the locations of their occurrence were investigated. The analysis revealed that no REEs existed independently in the deposit. Instead, the distribution of REEs was highly consistent and significantly positively correlated with that of phosphorus. In the microarea structure, REEs were predominantly found both in particles, such as bioclasts, sand debris, and agglomerates, and in phosphate cement, where the main mineral components were collophane and apatite. Conversely, the content of REEs in dolomitized sand debris edges, sparry dolomitic cement, and siliceous cement was considerably lower. Based on these findings, it is speculated that REEs primarily occur within the lattice defects of apatite or on the surface of collophanite. There is a notable contrast in the REE content between the unaltered sand debris at the periphery and the dolomitized sand debris, indicating that the dolomitization in the diagenetic stage resulted in a depletion of REE abundance in the ore. Obviously, the dominant gangue mineral, dolomite, does not serve as the primary host for REEs. Furthermore, the highest concentration of REEs was inside organisms. This finding suggests that the high content of REEs in biological soft tissue may remain under the influence of waves and tides, and REE-bearing apatite may be preferentially separated and fill the cavities of deceased organisms. The second highest content of REEs was found in the shells of organisms, indicating that small shelly organisms absorb phosphorus materials through their life activities to construct their shells, resulting in REE enrichment. Quantitative analysis through sequential extraction procedures displayed that most REEs were present in the residual state, with a smaller portion combined with organic matter. These results confirm that REEs in the Zhijin phosphate deposits primarily exist as isomorphic substitutions in the lattice defects of apatite, with a secondary occurrence as organic matter-bound REEs. Full article