Activation effect of lead ions on scheelite flotation: Adsorption mechanism, AFM imaging and adsorption model

Progress in the applications of atomic force microscope (AFM) for mineralogical research

Mineral surface properties and mineral-aqueous interfacial reactions are essential factors affecting the geochemical cycle, related environmental impacts, and bioavailability of chemical elements. Compared to macroscopic analytical instruments, an atomic force microscope (AFM) provides necessary and vital information for analyzing mineral structure, especially the mineral-aqueous interfaces, and has excellent application prospects in mineralogical research. This paper presents recent advances in the study of properties of minerals such as surface roughness, crystal structure and adhesion by atomic force microscopy, as well as the progress of application and main contributions in mineral-aqueous interfaces analysis, such as mineral dissolution, redox and adsorption processes. It describes the principles, range of applications, strengths and weaknesses of using AFM in combination with IR and Raman spectroscopy instruments to characterization of minerals. Finally, according to the limitations of the AFM structure and function, this research proposes some ideas and suggestions for developing and designing AFM techniques.

Study of the Effect of Manganese Ion Addition Points on the Separation of Scheelite and Calcite by Sodium Silicate

The flotation separation (FS) of both scheelite and calcite minerals with similar physicochemical properties remains challenging, since the Ca active sites exist on their surfaces. The present work investigated the effects of different addition points of MnCl₂ on the FS of scheelite and calcite by micro-flotation tests, zeta potential measurements, UV-Vis spectrophotometer measurements, infrared spectrum analysis, and X-ray photoelectron spectroscopy (XPS) tests, and the mechanism of separation is elucidated. Interestingly, the recovery of scheelite was 91.33% and that of calcite was 8.49% when MnCl₂ was added after sodium silicate. Compared with the addition of MnCl₂ before Na₂SiO₃, the recovery of scheelite was 64.94% and that of calcite was 6.64%. The sequence of adding MnCl₂ followed by Na₂SiO₃ leads to the non-selective adsorption of Mn²⁺ on the surface of scheelite and calcite firstly, and later, sodium silicate will interact with it to produce hydrophilic silicate. This substantially enhances the hydrophilicity on the surface of both minerals, making separation impossible. In contrast, the addition of MnCl₂ after sodium silicate can promote the formation of a metal silicate and enhance the selectivity and inhibition effect on calcite. Meanwhile, under this dosing sequence, the adsorption of Mn²⁺ on the scheelite surface offered more active sites for sodium oleate, which improved the scheelite surface hydrophobicity. This leads to a great improvement of the FS effect of scheelite and calcite.

Bi-functional hydrogen and coordination bonding surfactant: A novel and promising collector for improving the separation of calcium minerals

Mono-functional chelating collectors exhibit limited selectivity in the flotation of minerals. In particular, the selective separation of calcium minerals presents a significant challenge because mono-functional chelating collectors, such as fatty acid, indistinguishably adsorb onto mineral surfaces by coordinating with the same metal cation (Ca²⁺). Thus, there is an urgent need to develop new-mode-functional collectors to separate calcium minerals and a need to understand the underlying chemoselectivity. Given the difference of the hydrogen bonding ability of anions with fluorite, calcite and scheelite surfaces, the introduction of additional hydrogen bonding functional groups into collector molecules is a novel strategy to improve selectivity. In this study, a hydrogen and coordination bonding (bi-functional) collector, 2-cyano-N-ethylcarbamoyl acetamide (CEA) was developed, which could form coordination bonds with the Ca²⁺ ions (by carbonyl groups) and hydrogen bonds with the anions (by amino groups) on calcium mineral surfaces. The results of flotation tests showed that CEA can selectively separate fluorite and calcite from scheelite at pH 7. The promising selectivity of CEA lies in both the electrical properties and the anions' hydrogen bonding ability with the three calcium minerals. The negatively charged scheelite surfaces are not conducive to coordination bonding with CEA while the positively charged fluorite and calcite surfaces are. Besides, the hydrogen bonding ability of fluorite (F^-) and calcite (CO₃^2-) with carbamido in CEA is higher than that of scheelite (WO₄^2-), and this also plays an essential role. This coordination and hydrogen bonding based surfactant design protocol has a great potential in the development of tail-made collectors/depressants for the separation of other oxidized minerals.

Laboratory Testing of Scheelite Flotation from Raw Ore in Sangdong Mine for Process Development

Tungsten is an essential metal for the manufacture of special alloys, which is in constant demand due to the development of the industry. The recovery of scheelite from undeveloped tungsten ore in South Korea was investigated to improve the flotation performance for high grade and recovery of concentrate. To investigate the interaction between the flotation reagents and the minerals, the adsorption experiments of oleic acid as a collector on Ca-bearing minerals, such as scheelite, calcite, and fluorite were carried out. This reaction was confirmed chemical adsorption by analysis of zeta potential and FTIR analysis. The batch test was performed using a raw ore to enhance the grade and recovery of the scheelite concentrate. It was obtained at the optimal conditions for high WO3 grade and recovery of scheelite concentrate by using a simple process. In particular, the sodium carbonate used as a pH modifier was investigated to increase scheelite flotation performance by supporting the selective depression of Ca-bearing gangue minerals. Furthermore, a locked cycle test (LCT) was carried out based on batch test results for the design of a continuous pilot plant.

Preparation of PVA/tetra-ZnO composite with framework-supported pore-channel structure and the removal research of lead ions

Polyvinyl alcohol (PVA) filled with different kinds of ZnO whisker was prepared by chemical cross-linking reaction. It was found that the ZnO whiskers dispersed uniformly after being modified by 3-aminopropyltriethoxysilane (APTES). The PVA/tetrapod-shaped ZnO (PVA/tetra-ZnO) composites showed better adsorption performance than other kinds of PVA/ZnO composites. The framework-supported pore-channel structure was beneficial for the transmission and adsorption of heavy metal ions, and the formation of "brush" pore-channel of PVA/tetra-ZnO composites can effectively retain and capture the heavy metal ions. The PVA/tetra-ZnO composites presented well adsorption on Pb(II), Cd(II), and Cr(III) ions than Ni(II) and showed relatively selective removal on Pb(II) and Cr(III) ions. The adsorbed heavy metal ions presented gradient distribution with high content in the out layer and low content in the inner layer. Pb(II) adsorption capacity q_e increased gradually with the increase of initial solution concentration and contact time which tended to be stable at 400 mg/L and 800 min. The maximal adsorption capacity q_m obtained by nonlinear fitting reached to about 116 mg/g which was very close to the experiment data. Adsorption isotherm results indicated the monolayer adsorption process of the Langmuir model and the adsorption kinetics data fitted well to the pseudo-second-order model. The adsorption process was spontaneous and the high temperature was in favor of adsorption. The adsorption mechanism was explored as the combination of coordination and ion exchange. Besides, the PVA/tetra-ZnO composites exhibited better stress stability, thermo stability, and favorable regeneration than neat PVA.

Effect of Sodium Oleate on the Adsorption Morphology and Mechanism of Nanobubbles on the Mica Surface

Nanobubbles promote the flotation of fine-grained minerals. In the associated mechanism, the aggregation of fine particles is first promoted, which increases the probability of collision between particles and bubbles. However, the interaction between nanobubbles and mineral particles is often neglected, especially when the surface properties of the nanobubbles are modified by flotation collectors. In this study, the interaction mechanism between nanobubbles and the mica surface is investigated by nanoparticle tracking analysis, zeta potential measurement, and atomic force microscopy. The results reveal that the hydrophobic group of sodium oleate points toward the inside of the nanobubble and the hydrophilic group faces outward after the interaction of sodium oleate molecules and nanobubbles. A surfactant micelle with nanobubbles as the core is formed, thus considerably reducing the concentration of sodium oleate to form micelles. The adsorption of the modified nanobubbles on the mineral surface is carried out by the specific adsorption of the exposed hydrophilic group and the mineral surface. This adsorption method is superior to the hydrophobic interaction between the nanobubbles and the hydrophobic mineral surface. Further, the nanobubbles are highly selective for the activation sites on the mineral surface in the adsorption mode. This study will help understand the interaction between nanobubbles and collectors to further apply nanobubbles to treat fine-grained mineral particles.