Key Takeaways & Executive Findings
- •• NaOL significantly enhances flotation recovery of brucite over diaspore and limonite at pH 11 with 40 mg/L collector. • Surface analysis (contact angle, zeta potential, XPS) confirms stronger adsorption of NaOL on brucite due to exposed Mg2+ sites from weak interlayer bonding. • DFT calculations reveal higher adsorption energy and stable chemical adsorption via covalent O–metal bonds on brucite surface. • Molecular-level insights guide the design of selective collectors for efficient separation of hydroxide minerals.
Abstract
Brucite, diaspore, and limonite, as typical hydroxide minerals, exhibit similar surface properties due to their high content of −OH. This study investigated the effect of traditional anionic collector sodium oleate (NaOL) on the flotation performance and surface properties of brucite, diaspore, and limonite. The flotation experiment results show that adding 40 mg/L NaOL at pH 11 can significantly increase the flotation recovery of brucite compared to diaspore and limonite. The results of contact angle, zeta potential, and XPS indicate that NaOL can exhibit strong adsorption on the surfaces of the three minerals, but the adsorption effect on the brucite surface is stronger than that on diaspore and limonite, resulting in differences in floatability among the three minerals. This is mainly due to the weak interlayer interaction force of brucite, which can expose more Mg2+ sites during the grinding process, resulting in brucite being able to adsorb more oleate ions. DFT calculations further indicate that sodium oleate has greater adsorption energy on the brucite surface and can stably undergo chemical adsorption through covalent bonding between O in the carboxyl group and metal sites on the surface of hydroxides. This study provides molecular-level insights into the design of highly efficient selective collectors for metal hydroxide minerals.
1. Introduction
Hydroxide minerals, as important carriers of metallic elements, are the main sources of strategic resources such as magnesium, iron, and aluminum [1−3]. Brucite (Mg(OH)2), as a high magnesium mineral, is a key raw material for the production of refractory materials, flame retardants, and magnesium alloys [4−6]. Diaspore (AlO(OH)) is one of the main constituent minerals of bauxite, widely used in metallurgy and construction fields, and is an important industrial raw material [7]. Limonite (FeO(OH)·nH2O), as a typical product of iron ore oxidation zone, is an important supplementary raw material for the steel industry [8]. The industrial value of these minerals is not only reflected in the field of metal smelting, but their unique surface physicochemical properties (such as high hydroxyl density and layered crystal structure) also demonstrate great potential in wastewater treatment, aerospace, and new energy materials [9−12].
However, the effective separation of hydroxide minerals is limited by the complexity of their surface features. The Mg sites exposed on the cleavage plane of brucite (011) alternate with hydroxyl groups (—OH) to form a strongly polar surface [13]. The coordination mode between Al and hydroxyl groups in the chain structure of diaspore results in highly anisotropic surface charge distribution [14]. Limonite produces a large number of hydroxylation sites due to the hydrolysis of surface Fe atoms [15]. These characteristics make the interaction mechanism between mineral surfaces and flotation agents significantly different from that of oxidized minerals or silicate minerals. For example, hydroxyl groups (—OH) can participate in hydrogen bonding formation, and may also affect the ionization state of adsorbent molecules through proton transfer [16, 17]. Therefore, studying the adsorption law of reagents on the surface of hydroxides can provide a theoretical basis for improving the efficiency of resource recovery.
Sodium oleate (NaOL), an anionic collector, is widely used for flotation separation of oxidized minerals and hydroxide minerals due to its advantages of wide source, low cost, and environmental friendliness [18, 19]. The carboxylic acid group (—COO−) in NaOL molecules can undergo physical or chemical reactions with metal sites on mineral surfaces through chemical adsorption, electrostatic interactions, or hydrogen bonding, forming hydrophobic oleic acid metal soaps (such as Mg(OL)2 and Fe(OL)3) [20, 21]. In recent years, a large number of researchers have studied the flotation separation of hydroxides and gangue minerals. FU et al [22] studied the entrainment behavior of fine-grained serpentine in the recovery process of brucite. Under the action of calcium lignosulfonate, the entrainment rate of fine-grained serpentine decreased from...
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YAO Jin, DU Wei-fan, GONG Xiu-feng, YIN Wan-zhong, YU Jian-wei, ZHAO Xu (2026). Insights into the adsorption properties of NaOL on hydroxide mineral surfaces: Experiments and DFT calculations. Journal of Central South University. https://doi.org/10.1007/s11771-026-6270-x
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Frequently Asked Questions
What is the main finding of this study?
The study reveals that sodium oleate (NaOL) exhibits stronger adsorption on brucite surfaces compared to diaspore and limonite, leading to higher flotation recovery of brucite. This is attributed to the weak interlayer forces in brucite, which expose more Mg2+ sites for oleate adsorption, and DFT calculations confirm stable chemical adsorption via covalent O–metal bonds.
How does NaOL interact with hydroxide mineral surfaces?
NaOL interacts through chemical adsorption, electrostatic interactions, or hydrogen bonding with metal sites on the mineral surfaces. The carboxyl group of NaOL forms covalent bonds with metal ions (e.g., Mg2+, Al3+, Fe3+), creating hydrophobic metal oleate complexes.
Why is brucite more floatable than diaspore and limonite with NaOL?
Brucite has a layered structure with weak interlayer bonding, which upon grinding exposes more Mg2+ sites on the surface. These sites readily adsorb oleate ions, increasing hydrophobicity and flotation recovery. In contrast, diaspore and limonite have stronger surface bonding and fewer exposed active sites, resulting in lower adsorption and floatability.
What methods were used to investigate the adsorption properties?
The study employed flotation experiments, contact angle measurements, zeta potential analysis, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations to characterize the adsorption behavior and surface interactions.
What is the significance of this research for mineral processing?
The findings provide molecular-level insights into the selective adsorption of collectors on hydroxide minerals, which can guide the design of more efficient and selective flotation reagents for the separation of valuable hydroxide minerals from gangue, improving resource recovery and processing efficiency.
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