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Bastnaesite is an important rare earth mineral and is usually beneficiated by flotation. Sodium silicate is commonly used to depress calcium-bearing gangue minerals, however it can also depress bastnaesite when Ca2+ ions exist in the pulp. In this study, the effect of Ca2+ ions and sodium silicate individually or in combination on bastnaesite flotation was studied through micro-flotation, zeta potential, fluorescence spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Micro-flotation results show that the combination of Ca2+ ions and sodium silicate depresses bastnaesite more severely due to their synergistic effect. Zeta potential results show that the combination renders the surface potential of bastnaesite negatively shifted more significantly. Fluorescence spectroscopy shows that the combination decreases the surface hydrophobicity of bastnaesite more severely. XPS shows that the combination increases the adsorption of sodium silicate on bastnaesite by forming hydrophilic Ca-SiO3 precipitate, which causes more serious depression on bastnaesite flotation.

A series of yttria-stabilized zirconia single-crystals doped with 0.000–0.250 mol% Tb4O7 was prepared by the optical floating-zone method. As shown by XRD and Raman spectroscopy, all of the crystals had a cubic-phase structure. These were initially orange–yellow in color, which is indicative of the presence of Tb4+ ions, but they then became colorless after being annealed in a H2/Ar atmosphere as a result of the reduction of Tb4+ to Tb3+. The absorption spectra of the unannealed samples show both the 4f8→4f75d1 transition of Tb3+ ions and the Tb4+ charge-transfer band. In addition, the transmittance of the crystals was increased by annealing. Under irradiation with 300 nm of light, all of the single-crystal samples showed seven emission peaks in the visible region, corresponding to the decay from the 5D3,4 excited state of Tb3+ to the 7FJ (J = 6–0) states. The most intense emission was at 544 nm, which corresponds to the typical strong green emission from the 5D4→7F5 transition in Tb3+ ions.

Single crystals of Ho2O3-doped Y2O3 stabilized ZrO2 (YSZ) with different Y2O3 and Ho2O3 contents were grown by the optical floating zone method. XRD and Raman spectra were measured and showed that crystal samples all had tetragonal structures. Measurements of positron annihilation lifetime spectra indicated that the increase in Y2O3 concentration led to the increases of defects and mean positron lifetime, which enhanced the scattering of light and reduced the luminous intensity and the quantum yield (QY) of the crystal. Under the excitation at 446 nm, photoluminescence (PL) spectra of Ho2O3-doped YSZ crystals showed emission peaks at 540, 551, 670, and 757 nm corresponding to Ho3+ transitions from 5S2, 5F4, 5F5, and 5I4 excited states to the 5I8 ground state, respectively. At low Ho2O3-doped concentrations (0.10–0.50 mol%), the overall emission intensity increased with Ho2O3 contents, reached the maximum value at 0.50 mol%, then decreased with higher Ho2O3 contents, probably as a result of increased non-radiative relaxation caused by increased interactions between Ho3+ ions. Quenching of the PL occurred at Ho2O3 concentrations > 0.5 mol% and due to the electric dipole–dipole interaction. The calculated chromaticity coordinates (CIE) were approximately (0.307, 0.683) and the color purity achieved 99.6%. The results showed that Ho2O3: YSZ crystals were suitable for green light-emitting devices.

Parisite (CaCe2(CO3)3F2) and bastnaesite (CeCO3F), important rare earth minerals, have different elemental compositions and crystal structures. Their flotation behavioral differences under commonly used sodium silicate (SS) depressant and hydroxamate collector are important for rare earth ore beneficiation, which is still unknown. In this study, the effect of sodium silicate on bastnaesite and parisite flotation with octyl hydroxamic acid (OHA) as collector was comparatively investigated through microflotation, zeta potential measurements, X-ray photoelectron spectroscopy (XPS), and mineral crystal computational analysis. The results indicated that the inhibition effect of SS on parisite was significantly stronger than that on bastnaesite. SS had little effect on the adsorption of OHA on bastnaesite surface, rendering a slight inhibition on bastnaesite flotation. However, SS strongly hindered the adsorption of OHA on parisite surface, rendering the heavy inhibition on parisite flotation. The inhibition mechanism of SS on parisite was due to the reaction of the calcium species with silicate, thereby forming Ca-SiO3 hydrophilic complex on parisite surfaces. This hydrophilic complex hindered the adsorption of OHA and increased the hydrophilicity on parisite surface, thus, causing significant inhibition on parisite flotation.