The flotation of bastnaesite, as a major mineral source of rare earth elements, attracting much attention in the mineral processing field, is challenging owing to the natural flotability of calcium-bearing minerals. To promote the application of flotation, we systematically investigated the flotation behavior of bastnaesite, barite, and calcite, with salicylhydroxamic acid (SHA) as the collector through micro-flotation experiments, zeta-potential measurements, Fourier transform infrared (FT-IR) analyses, X-ray photoelectron spectroscopy (XPS) analyses, and solution chemistry analyses. Micro-flotation experiments confirm that the flotability of bastnaesite is high at pH 6.5–8.5, while calcite floats at pH 8.0–9.5, and barite has little flotation response. The results of FT-IR, XPS, and zeta-potential measurements indicate that there is chemical adsorption of SHA on the bastnaesite surface, and physical adsorption also occurs. However, as for barite and calcite, there is only physical adsorption of SHA on the surfaces. The solution chemistry results show that SHA anions can interact with RE³⁺, REOH²⁺, and RE(OH)₂⁺ on bastnaesite surfaces in aqueous suspensions, resulting in bastnaesite flotation.

As a solid waste, kaolinite-type pyrite flotation tailings (KPFT) are a type of low-quality kaolin that contain impurities, such as iron and titanium. In this study, KPFT were calcined at 800 °C for two hours. The calcined production (CKPFT), which is mainly metakaolin, was used as the silicon and aluminum source to synthesize 4A zeolite (Na₁₂[(AlO₂)₁₂(SiO₂)₁₂]·27H₂O) via hydrothermal synthesis. The optimal hydrothermal synthesis conditions were determined from X-ray diffraction phase analysis, relative crystallinity (RC), and cation ion exchange capacity (CEC). The optimal hydrothermal synthesis conditions were determined to be a ratio of 5 g CKPFT, 6.5 g NaOH, 65 mL H₂O, crystallization temperature 110 °C, and crystallization time of three hours. Under the optimal hydrothermal synthesis conditions, the RC and CEC of the synthesized 4A zeolite were 40.77% and 210.32 mg CaCO₃·g⁻¹, respectively. Further characterizations including pore size distribution, scanning electron microscopy, energy dispersive X-ray, thermogravimetry-differential scanning calorimetry, and Fourier transform infrared spectroscopy were performed. The results revealed that impurities in KPFT do not affect the synthesis of 4A zeolite. The surface morphology of the synthesized 4A zeolite was composed of chamfered-edged cubes with a particle size of one to three μm that was thermally stable up to approximately 890 °C.

The activation mechanism of lead ions (Pb²⁺) in perovskite flotation with an octyl hydroxamic acid collector was systematically investigated using microflotation experiments, zeta-potential measurements, adsorption tests, Fourier transform infrared (FT-IR) analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The results of microflotation experiments and adsorption tests indicate that the presence of Pb²⁺ can promote the adsorption of octyl hydroxamic acid (OHA) on the perovskite surface and enhance the flotability of perovskite under weakly acidic conditions. The maximum recovery of 79.62% was obtained at pH 6.5 in the presence of Pb²⁺, and the maximum recovery of 57.93% was obtained at pH 5.7 without Pb²⁺. At pHs below 7, lead species are mainly present as Pb²⁺ and PbOH⁺ in the solution; besides this, the relative content of titanium increases on the perovskite surface. The adsorption of Pb²⁺ and PbOH⁺ on the perovskite surface makes the zeta-potential of perovskite shift positively, and increases the number of activated sites on the perovskite surface. FT-IR and XPS analyses confirm that OHA chemisorbs on the surface of Pb²⁺-activated perovskite and forms hydrophobic Pb-OHA complexes, which improve the flotability of perovskite.