As an ecological transition zone, the ecosystem of the Qin River Basin in the middle reaches of the Yellow River is of great significance to the regional ecological balance. With the rapid socio-economic development, land use changes are significant, and the spatial and temporal patterns of ecosystems are evolving. Exploring its dynamics and driving mechanisms is crucial to the ecological protection and sustainable development of watersheds. This research systematically examines the spatiotemporal dynamics and driving mechanisms of ecosystem patterns in the middle Yellow River’s Qin River Basin (1990–2020). Quantitative assessments integrating ecosystem transition metrics and redundancy analysis reveal three critical insights: (1) dominance of agricultural land and woodland (74.81% combined coverage), with grassland (18.58%) and other land types (6.61%) constituting secondary components; (2) dynamic interconversion between woodland and grassland accompanied by urban encroachment on agricultural land, manifesting as net reductions in woodland (−13.74%), farmland (−6.60%), and wetland (−38.64%) contrasting with grassland (+43.34%) and built-up area (+116.63%) expansion; (3) quantified anthropogenic drivers showing agricultural intensification (45.03%) and ecological protection measures (36.50%) as primary forces, while urbanization account for 18.47% of observed changes. The first two RDA ordination axes significantly (p < 0.01) explain 68.3% of the variance in ecosystem evolution, particularly linking land-use changes to socioeconomic indicators. Based on these findings, the study proposes integrated watershed management strategies emphasizing scientific land-use optimization, controlled urban expansion, and systematic ecological rehabilitation to enhance landscape stability in this ecologically sensitive region. The conclusions of this study have important reference value for other ecologically sensitive watersheds in land use planning, ecological protection policy making, and ecological restoration practice, which can provide a theoretical basis and practical guidance.

Acid leaching and alkali roasting were used to remove impurities such as Ca and Si in Baiyun Obo rare earth concentrate. The effects of acid–base treatment on the physical and chemical properties of the samples were analyzed by scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller characterization, X-ray photoelectron spectroscopy, H₂-temperature-programmed reduction, NH₃-temperature-programmed desorption (TPD), and NO-TPD. Results showed that the content of Ce₇O₁₂ in the rare earth concentrates increased and the dispersion was uniform. The grains became smaller, the specific surface area of rare earth concentrates increased, and the active sites were more exposed. Ce coexisted in the form of Ce³⁺ and Ce⁴⁺, whereas Fe coexisted in the form of Fe³⁺ and Fe²⁺. The content of Fe³⁺ was increased. The acid–base-treated rare earth concentrates had a denitration efficiency of 87.4% at a reaction temperature of 400 °C.

To achieve high-value utilization of rare earth resources and meet the demands for nitrogen oxide (NO _x ) pollution control, this study focuses on the Ce-rich Bayan Obo rare earth mineral, aiming to develop efficient mineral-based denitration catalysts and elucidate the underlying mechanisms. Although this type of mineral is rich in Ce with catalytic potential, the associated Ca severely restricts the intrinsic activity of Ce and the overall denitration performance. In this work, acid leaching was applied to selectively remove Ca, and combined with multiple characterization techniques, we systematically clarified how Ca removal optimizes the speciation and surface properties of Ce, thereby significantly enhancing the selective catalytic reduction (NH ₃ -SCR) activity. The results indicate that the modified catalyst exhibits a notably increased specific surface area, an optimized Ce ³⁺ /Ce ⁴⁺ redox pair ratio, an increased oxygen vacancy concentration, and a predominant presence of Ce species in low-polymerization states. The NO _x conversion rate at 350 °C was dramatically improved from 18.9% for the raw ore to 82.1%, while maintaining excellent N ₂ selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy ( in situ DRIFTS) further confirmed that Ca removal exposes more Ce active sites and enhances the synergistic effect between Brønsted and Lewis acid sites. The established correlation system of ‘Ca removal–Ce speciation–denitration reaction mechanism’ in this work provides a solid theoretical foundation for the design of high-performance rare earth mineral-based catalysts.