Selective extraction of potassium from raw nepheline materials

The global aluminium industry is ever-changing and primarily relies on bauxite as its traditional source. However, due to the finite reserves of processed bauxite, alternative sources need to be found. Nephelines have emerged as potential alumina sources. In addition to alumina, nepheline processing can yield marketable products such as soda, potash, cement, and rare metals. The objective of this study was to identify the ideal conditions for selectively extracting potassium from alkaline leaching solutions while separating it from sodium alkali, aluminium, and silicon during the comprehensive processing of nepheline syenites from the Kubasadyr deposit. This approach involved a two-stage hydrothermal leaching process with an incremental calcium addition. Under optimal conditions, the potassium extraction in the alkaline solution reached 93.91 %. The resulting leaching solution served as a feedstock for potassium sulfate production through the crystallization method. The preliminary selective separation of potassium played a crucial role in mitigating its adverse effects on the extraction of aluminium, which is the primary processed product; thus, the economic viability of production was enhanced.

Mesoplankton across the North Atlantic: Composition and environmental drivers at 59.5th latitude

North Atlantic zooplankton communities vary in terms of abundance, biomass and species composition depending on various environmental factors. In this study we analyzed the influence of hydrological factors (water temperature, salinity and density) on mesoplankton and retrieve boundaries between mesoplankton assemblages across the Subpolar North Atlantic. The material was collected in July 2013 with the use of Juday plankton net vertical hauls (0-300 m layer) at 55 stations arranged along a longitudinal transect along 59.5° N during the 41-th expedition of R/V "Akademik Ioffe". Both total abundance and biomass were higher in the eastern part of the transect and greatly decreased in the western part except the Greenland shelf and slope where the values were high. Four mesoplankton assemblages were retrieved by cluster analysis: two of them (above the Rockall Plateau and the Island Basin) were associated with warm Atlantic waters, the other two assemblages (in the Irminger Basin and above the Greenland slope and shelf) inhabited cold Arctic waters. The major biogeographic boundary was linked to the Subarctic Front above the Reykjanes Ridge. The best correlations of zooplankton characteristics with the surface chlorophyll a amount were obtained when averaging the surface chlorophyll data over May and 3 latitudinal and longitudinal degrees around each station. This can be connected to the main spring phytoplankton bloom, occurring during May in this area. The exception was the western-most part of the transect above the Greenland shelf and slope that harbored separate mesoplankton assemblages with high abundance and biomass, dominated by early mesoplankton stages (e.g. young copepodites and nauplii). These assemblages were likely supported by summer subsurface phytoplankton bloom caused by a water discharge from the melting Greenland Ice Shield.

Observation of Supercavity Modes in Subwavelength Dielectric Resonators

Electromagnetic response of dielectric resonators with high refractive index is governed by optically induced electric and magnetic Mie resonances facilitating confinement of light with the amplitude enhancement. Traditionally, strong subwavelength trapping of light was associated only with plasmonic or epsilon-near-zero structures, which however suffer from material losses. Recently, an alternative localization mechanism was proposed allowing the trapping of light in individual subwavelength optical resonators with a high quality factor in the regime of a supercavity mode. Here, the experimental observation of the supercavity modes in subwavelength ceramic resonators in the radio-frequency range is presented. It is experimentally demonstrated that the regime of supercavity modes can be achieved via precise tuning of the resonator's dimensions. A huge growth of the unloaded quality factor is achieved with experimental values up to 1.25 × 10⁴ , limited only by material losses of ceramics. It is revealed that the supercavity modes can be excited efficiently both in the near- and far-field. In both cases, the supercavity mode manifests itself explicitly as a Fano resonance with characteristic peculiarities of spectral shape and radiation pattern. A comparison of supercavities made of diversified materials for the visible, infrared, THz, and radio-frequency regimes is provided.