The Challenge of Tungsten Skarn Processing by Froth Flotation: A Review

A review of flotation reagents for bastnäsite-(Ce) rare earth ore

Given the indispensability and immense value of rare earth elements for scientific and technological advancements in the 21st century, extracting high-quality rare earth resources from nature has become a global priority. Bastnäsite-(Ce) is one of the known rare earth minerals with high rare earth content and wide distribution, which occupies a pivotal position in human life and high-end production activities, making its efficient development and utilization crucial. In recent years, research on separating bastnäsite-(Ce) from gangue minerals has focused on the flotation process, with flotation reagents playing a critical role in achieving effective separation. This paper provides a detailed summary of current research on the behavior of bastnäsite-(Ce) flotation agents on minerals, their interaction with mineral surfaces during flotation separation, and outlines future prospects for further research.

Improved Flotation Separation of Scheelite from Calcite by Sulfomethylated Kraft Lignin

Low-grade and high-reserve scheelite, which is associated with calcite, has similar surface properties that cause difficulty in separation. In this study, sulfomethylated kraft lignin (SMKL) was used as a novel eco-friendly inhibitor for the flotation separation of scheelite and calcite. The flotation test results showed that 60 mg/L SMKL had a significant influence on depressing calcite flotation, while it had a slight effect on scheelite flotation. Furthermore, it enhanced the WO₃ grade of the concentrate in the artificial mixed ore to 62.02% with a recovery rate of 80.37%. The contact angle and zeta potential showed that SMKL could effectively decrease the surface floatability of calcite and caused the negative shift of minerals' surface potential. XPS and DFT calculations revealed that the sulfonic acid group of SMKL had an electron-donating ability and was easily adsorbed on the positively charged surface of calcite, which hindered the adsorption of sodium oleate on calcite. SMKL could separate calcium-bearing minerals with a high efficiency and selectivity, providing a new method for industrial production.

Flotation Separation of Scheelite from Calcite Using Sulfonated Naphthalene–Formaldehyde Condensate as Depressant

In this paper, the potential of sulfonated naphthalene formaldehyde (SNF) condensate as a depressant in the flotation separation of scheelite from calcite was verified and investigated. The results of microflotation experiments showed that SNF had a stronger depressant performance on calcite than a conventional depressant—water glass and had an excellent performance in fine-grained particles (−0.037 mm) treatment. Adsorption tests were conducted to quantitatively study the selective adsorption of SNF on the surface of scheelite and calcite. At 200 mg/L SNF, the adsorption density of SNF on the calcite surface reached 5.48 mg/g, which was more than four times than that of scheelite. In addition, compared with scheelite, the adsorption of SNF on the calcite surface had a more significant negative effect on the contact angle. Moreover, infrared (IR) measurements combined with X-ray photoelectron spectroscopy (XPS) analysis were performed to investigate the adsorption mechanisms of SNF on scheelite and calcite surfaces. The results showed that the adsorption of SNF on scheelite was more likely to be physical attraction, while the –SO3− group in SNF could chemically react with Ca species on the surface of calcite, resulting in a stronger adsorption than on scheelite.

Application of a Superplasticizer in Scheelite Selective Flotation from Calcite

The superplasticizer sulfonated acetone formaldehyde condensate (SAF) was first used as a depressant in the selective flotation of scheelite and calcite in this paper. First, single mineral flotation tests were performed to compare the depressing performance of SAF and the traditional depressant water glass. Results showed that both −0.074 + 0.037 mm and −0.037 mm particles could be well treated by SAF with more satisfactory results than that of water glass. Contact angle test results showed that SAF could amplify the wettability difference between scheelite and calcite surfaces. Then, the effect of SAF on the surface electrical properties of scheelite and calcite was studied by zeta-potential tests. SAF could negatively charge the calcite surface before adding the collector and hinder the subsequent adsorption of the collector while having little effect on the scheelite. Moreover, microscopic analysis of slurry suspensions showed that SAF could prevent calcite particles from forming hydrophobic agglomerates to achieve the dispersion of gangue minerals. Finally, the selective adsorption effect of the SAF on the calcite and scheelite surfaces was studied by surface analysis using FTIR (Fourier transform infrared) and XPS (X-ray photoelectron spectroscopy). Results showed that Ca2+ on the calcite surface was the main adsorption site for the chemisorption of sulfonic acid groups in SAF.

Adsorption mechanisms of fatty acids on fluorite unraveled by infrared spectroscopy and first-principles calculations

HYPOTHESIS

The adsorption mechanisms of fatty acids on minerals are largely debated from years, and their understanding is now required to improve flotation processing in the critical context of raw materials. Three wavenumbers have been observed in the literature for the asymmetric stretching vibration of COO^- after the adsorption of fatty acids on mineral surfaces. They have been interpreted as different adsorbed forms, such as a precipitate formation, an adsorption of sole or bridged carboxylates, an anion exchange, or adsorbed modes, such as monodentate or bidentate configurations.

EXPERIMENTS/THEORY

Diffuse reflectance infrared Fourier transform spectroscopy was combined with ab initio molecular dynamics simulations and simulation of infrared spectra. Fluorite and sodium octanoate - or longer-chain fatty acids - were used as prototypical materials for all the investigations.

FINDINGS

At low fatty acids concentration, the asymmetric stretching vibration of COO^- peaks at 1560 cm^-1 while, at higher concentration, this infrared band converts into a doublet peaking at 1535 and 1575 cm^-1. Using simulations, we assign the band at 1560 cm^-1 to the adsorption of a carboxylate molecule bridged on a sodium counter-cation and the doublet at 1535 and 1575 cm^-1 to the adsorption of the sole carboxylate anion under a monodentate or a bidentate binuclear configuration, respectively. The formation of an adsorbed layer on the mineral surface is initiated by the adsorption of a sodium carboxylate and followed by the adsorption of mixed sole anionic forms. The role of the carboxylate counter-cation is highlighted for the first time, which was totally ignored in the literature beforehand. This particularly opens the path to the development of innovative strategies to enhance the separation contrast between minerals, which is of uttermost importance for the recovery of critical raw materials.

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.