Chromium (Cr), a toxic heavy metal, poses significant environmental and health risks when industrial effluents containing Cr are discharged untreated. Addressing this challenge, this study developed a selective chromium removal strategy using IRA-900 resin in a sulfuric acid system with sodium phosphite (NaH₂PO₃) as a complexing agent. In the NaH₂PO₃-H₂SO₄ system, IRA-900 resin exhibited exceptional selectivity for Cr³⁺ with minimal co-adsorption of competing ions. The adsorption process followed the Langmuir isotherm model (R² > 0.99), indicating monolayer chemisorption dominated by homogeneous active sites, and achieved a maximum capacity of 103.56 mg·g⁻¹. Characterization via XPS, FT-IR, and SEM-EDS revealed a two-step mechanism: Cr³⁺ reacts with H₂PO₃⁻ to form an anionic complex, and then the complex undergoes electrostatic interaction and ion exchange with chloride ions (Cl⁻) on the quaternary ammonium groups of the resin. The chromium-loaded resin demonstrated remarkable structural stability, resisting Cr³⁺ desorption under conventional elution conditions. This property provides a novel pathway for chromium solidification in industrial wastewater, effectively minimizing secondary pollution risks. This work advances the design of ligand-assisted ion-exchange systems for targeted heavy metal removal, offering both high selectivity and environmental compatibility in wastewater treatment.

To investigate the rationality of water-use efficiency in agroforestry systems within this region, this study utilised the medicinal and edible plant Sophora japonica cv.jinhuai as a foundation. Five mixed planting models were established, incorporating Ardisia gigantifolia, Melicope pteleifolia, Camellia limonia, Belamcanda chinensis, Isatidis radix, and Pilea basicordata. Water-use efficiency (WUE) was analysed by measuring the carbon-stable isotope composition (δ¹³C) of plant leaves. Compared to previous studies that primarily focused on δ¹³C in single species or simple composite systems, this research innovatively evaluates the water-use efficiency (WUE) performance of different composite patterns and their impact on system stability at both the species and system levels, integrating the theory of fitness differentiation. Results indicate that the ranges of δ¹³C and WUE for the five mixed cropping systems were −27.0633‰ to 31.2188‰ and 27.7191 to 50.0365 μmol/mol, respectively. WUE ranking was: Sophora japonica cv.jinhuai—Camellia limonia—Pilea basicordata (SCP) > Sophora japonica cv.jinhuai—Camellia limonia (SC) > Sophora japonica cv.jinhuai—Belamcanda chinensis + Isatidis radix (SBI) > Sophora japonica cv.jinhuai—Melicope pteleifolia (SM) > Sophora japonica cv.jinhuai—Ardisia gigantifolia (SA). At the species level, the Sophora japonica cv.jinhuai—Camellia limonia—Pilea basicordata (SCP) composite planting model is better suited to karst arid environments, while the Sophora japonica cv.jinhuai—Ardisia gigantifolia (SA) composite planting model exhibits lower overall plant water-use efficiency (WUE) and weaker drought resistance. At the system level, Sophora japonica cv. jinhuai exhibited significantly higher water-use efficiency (WUE) than understory medicinal plants in most composite patterns, with pronounced differences in species fitness and poor system stability. The Sophora japonica cv.jinhuai—Camellia limonia—Pilea basicordata (SCP) model exhibited the highest WUE. Furthermore, no significant difference in WUE was observed between Sophora japonica cv.jinhuai and Pilea basicordata, indicating relatively high fitness matching and good coordination in water use. These species can coexist stably, suggesting promising application potential in karst arid environments. Therefore, this study not only evaluated the water-use performance of each species within the composite model but also identified SCP as the most suitable agroforestry configuration for karst regions from a system stability perspective. This provides a scientifically grounded basis for optimising agroforestry practices in these areas, integrating both species-level and system-level perspectives. It should be clarified that the WUE calculated based on δ¹³C in this study is a relative indicator rather than an absolute physiological measurement. Its reliability depends on the core assumptions and parameter settings of the isotope model.

Germanium is a strategically critical metal with indispensable applications in infrared optics, fiber-optic communications, and semiconductor devices. Although previous reviews have extensively addressed the hydrometallurgical recovery of germanium from specific enriched materials and the associated extraction efficiencies, a systematic and integrated understanding of its migration behavior, occurrence states, and phase transformations across the entire zinc smelting process is still lacking. This review fills this gap by investigating the migration and enrichment characteristics of germanium in zinc smelting residues and by constructing a comprehensive framework encompassing occurrence, roasting, leaching, separation, and purification, covering the entire route from zinc concentrate to high-purity germanium production. By establishing this integrated analytical framework that traces the migration and enrichment pathways throughout the whole process chain, this review provides a valuable technical reference for elucidating the migration patterns of germanium in complex smelting systems, devising efficient recovery strategies, and advancing the sustainable utilization of germanium resources.