Progressive Hydrophilic Processes of the Pyrite Surface in High-Alkaline Lime Systems.

Pyrite, as a disturbing gangue mineral in the beneficiation of valuable sulfide minerals and coal resources, is usually required to be depressed for floating in flotation practice. Specifically, the depression of pyrite is achieved by causing its surface to be hydrophilic with the assistance of depressants, normally with inexpensive lime used. Accordingly, the progressive hydrophilic processes of the pyrite surface in high-alkaline lime systems were studied in detail using density functional theory (DFT) calculations in this work. The calculation results suggested that the pyrite surface is prone to hydroxylation in the high-alkaline lime system, and the hydroxylation behavior of the pyrite surface is beneficial to the adsorption of monohydroxy calcium species in thermodynamics. Adsorbed monohydroxy calcium on the hydroxylated pyrite surface can further adsorb water molecules. Meanwhile, the adsorbed water molecules form a complex hydrogen-bonding network structure with each other and with the hydroxylated pyrite surface, which makes the pyrite surface further hydrophilic. Eventually, with the adsorption of water molecules, the adsorbed calcium (Ca) cation on the hydroxylated pyrite surface will complete its coordination shell surrounded by six ligand oxygens, which leads to the formation of a hydrophilic hydrated calcium film on the pyrite surface, thus achieving the hydrophilization of pyrite.

Magnetic Zr-Based Metal-Organic Frameworks: A Highly Efficient Au (III) Trapper for Gold Recycling.

In this work, the magnetic Zr-based MOF composites with excellent retrievability were prepared using Fe3O4@SiO2 as the core and UiO-66-NH2 as the shell. Fe3O4@SiO2 core could introduce mesopores and result in capillary condensation in MOF composites, which aggravated with the dosage of Fe3O4@SiO2. The as-synthesized MOF composites could be rapidly retrieved from aqueous solution via magnetic separation in 10 seconds. pH imposed an important effect on Au (III) adsorption by governing the ion exchange and electrostatic interaction between Au (III) anions and adsorbents, and the optimal adsorption happened at pH 7. The adsorption process fitted well with the pseudo-second order kinetics model and Langmuir adsorption model. The maximum adsorption capacity of Au (III) by FSUN-10 and FSUN-50 at 298 K were determined to be 611.18 mg∙g-1 and 463.85 mg∙g-1, respectively. Additionally, Au (III) uptakes increased with temperature. Beyond experiments, the adsorption mechanisms were thoroughly studied through systematic characterization, molecular dynamics simulation (MDS) and density functional theory (DFT) study. It was verified that Au (III) was adsorbed via coordination to hydroxyl and amino groups and was reduced to Au (I) and Au (0) by amino groups. The diffusion coefficient of Au (III) along UiO-66-NH2 was calculated to be 5.8 × 10-5 cm2∙s-1. Moreover, the magnetic Zr-based MOF composites exhibit great industrial value in gold recycling with high adsorption selectivity and good recyclability.

Effects of the Goethite Surface Hydration Microstructure on the Adsorption of the Collectors Dodecylamine and Sodium Oleate.

Dodecylamine (DDA) and sodium oleate (OL) are commonly used collectors in the reverse flotation and the direct flotation of goethite. However, the flotation mechanisms of DDA and OL on the goethite surface remain unclear. In this study, the first-principles density functional theory calculations were used to reveal the role of the hydration of the goethite surface and its effects on flotation reagents from a microscopic perspective. The calculation results showed that DDA was adsorbed on the surface of goethite by hydrogen bonds in the absence of hydration. However, the existence of the hydration microstructure hindered the formation of hydrogen bonds and made it difficult for DDA to be adsorbed on the goethite surface. In the OL system, oleate ions are chemically adsorbed on the surface Fe sites of goethite in the absence of hydration, while in the presence of hydration, the oleate ions were adsorbed on the H-terminal hydration surface of goethite by hydrogen bonds. This work sheds new light on the roles of the hydration microstructure and the adsorption mechanism of the flotation reagent on the oxide minerals.

Structures of Pb-BHA Complexes Adsorbed on Scheelite Surface.

Previous studies have shown that Pb-BHA complexes (lead complexes of benzohydroxamic acid) have better collecting ability and can be used in flotation experiments with BHA acting as a collector and lead ions acting as activators. However, the structures of Pb-BHA complexes adsorbed on a mineral surface remain unclear. In this work, the adsorption behavior of Pb-BHA complexes on the scheelite surface was studied by flotation experiments and adsorption capacity measurements, and the structures of the adsorbed Pb-BHA complexes were determined using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The adsorption capacity results showed that more BHA was adsorbed on the scheelite surface in Pb-BHA flotation, and the XPS and TOF-SIMS analysis showed that the species of Pb-BHA complexes adsorbed on the scheelite surface were similar in activation flotation and Pb-BHA flotation. Therefore, the different contents of the complexes on the scheelite surface were responsible for the flotation behavior. XPS and TOF-SIMS showed that BHA combined with lead ions to form complexes with different structures, such as five- and four-membered ring structures. Structure fragment inference based on the measurements indicated that lead ions formed monomer complexes with two BHAs, and that lead hydroxide polymers with a certain degree of polymerization bonded with oxygen atoms in the complexes. The Pb-BHA complexes combine with oxygen atoms on the scheelite surface to form an adsorbate, rendering the surface hydrophobic.