The flotation separation of scheelite and calcite by froth flotation is difficulty as these two minerals have similar physicochemical characteristics. To solve this problem, the role of calcium lignosulphonate (CLS) in the flotation separation of scheelite from calcite has been studied and the separation mechanism has been discussed. The micro-flotation tests show that calcium lignosulphonate has strong depression effect to calcite and the depression effect decreased with the increase in pH. However, its depressive effect to scheelite is weak at pH 6–9. A concentrate with WO 3 grade of 65.02%, and WO 3 recovery of 79.64% was achieved in the flotation separation of mixed mineral, while calcium lignosulphonate was used. The reason is that the adsorption amount of calcium lignosulphonate on scheelite surface is far less than that of calcite according to adsorption tests. The interaction mechanism of calcite and CLS was studied by XPS and the results shows that the interaction between calcite and CLS were chemisorptions, and this interaction that SO 3 group were involved hindered the absorption between Ol − and the Ca 2+ on the surface of calcite, it also shows that a small amount of Ca(OH) 2 was generated on the surface of calcite in the presence of CLS, the coefficient of these two mechanisms brings about the depression effect for calcite.
As promising optical materials, the structures of scheelite- and zircon-type ZrGeO4 have been investigated by Raman spectroscopy at pressures up to 51.6 GPa using diamond anvil cells. For scheelite-type ZrGeO4, two reversible phase transitions at 16.2 and 41.2 GPa were identified from the Raman spectral profiles and pressure dependence of the Raman shift upon compression. The first transition can be interpreted as the change of the tetragonal scheelite structure to the monoclinic fergusonite structure. By comparison with a previously reported isomorphic crystal, we infer that the second high pressure phase likely has a monoclinic structure. The zircon-type ZrGeO4 initially transforms to a scheelite structure at ∼10.1 GPa, while such phase transformation is completed at around 24.6 GPa, and remains stable up to 37.6 GPa. Moreover, the zircon-to-scheelite phase transition is irreversible, and the high pressure scheelite structure cannot be recovered upon decompression. These phase transitions for different starting ZrGeO4 materials were unambiguously identified for the first time, and their contrasting structural stabilities as well as the transition mechanisms can be understood from the intrinsic characteristics of the crystal lattices. These results contribute to the understanding of the pressure behavior of very sparsely reported germinate compounds in the ABO4 family.
The harmonic generation effect, a distinct nonlinear optical phenomenon , exhibits unique properties and has critical applications across multiple fields. However, harmonic generation during optical measurements can introduce significant interference or experimental errors. Here, we investigated the photoluminescence (PL) characteristics of Dy 3+ doped CaWO 4 phosphors under near-infrared (NIR) irradiation. Both characteristic yellow and blue emissions of Dy 3+ and a series of NIR-induced harmonic generation were observed. The study demonstrated that Dy 3+ emissions were excited by harmonic generation originating from the dual-grating configuration of a spectrophotometer. Leveraging the divergent temperature-dependent intensity evolution between Dy 3+ emissions and 1.5th harmonic generation, we proposed a novel ratiometric thermometric strategy based on the luminescence intensity ratio (LIR). This new thermometry achieved optimal temperature sensitivity, with a maximum absolute sensitivity of 74.57 × 10 −4 K −1 and relative sensitivity of 2.21 % K −1 , surpassing conventional ratiometric thermometry relying on thermally coupled energy levels. These findings not only clarified the origin of multiplex harmonic generation and its impact on spectral measurement but also harness harmonic generation for innovative applications in optical thermometry.
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