Quartz, a common inorganic nonmetallic mineral, is usually
removed
or purified by beneficiation, normally flotation. Given the strong
polarity of the quartz surface, it is easy to hydrate to form a hydroxylation
layer, which makes it impossible to float quartz with sodium oleate
(OL) used alone. An ideal flotation method for quartz is preactivation
with Ca2+, followed by collection with OL. Herein, the
effects of surface hydroxylation on the adsorption of the anionic
collector OL on the quartz surface before and after Ca2+ activation are systematically investigated by density functional
theory (DFT) calculations. The results show that the displacement
adsorption of surface hydroxyl substituted by OL– is not feasible in thermodynamics, and the OL– can only bind to the H atoms of the hydroxylated quartz surface
via hydrogen bonds, namely, hydrogen binding adsorption. Due to the
electrostatic repulsion and steric hindrance effect induced by the
surface hydroxylation structure, the adsorption ability of OL– on the quartz surface mediated by hydroxyl bridges
is very weak, which is insufficient to realize quartz floating. However,
Ca2+ ions are easily adsorbed on the hydroxylated quartz
surface, providing favorable active sites for subsequent adsorption
of OL–, thus becoming a credible solution for the
industrial flotation of the strong hydrophilic mineral quartz. These
findings shed some new insights for accurately understanding the flotation
mechanism of strongly hydrophilic oxide minerals and are beneficial
to promoting the development of mineral flotation fundamentals.
Hematite, as an important iron source, usually crystallizes in the structure of rhombohedral R3̅ c in nature. To date, reports on the major exposed surface of hematite are still inconclusive. Herein, the fracture nature of hematite is studied by the density functional theory (DFT) method. The fracture surface morphology analysis predicts the fracture dominance of the (012) plane structurally. Besides, the lowest surface broken bond density (D b ) and the surface energy among all of the investigated surfaces also establish the exposure priority of the (012) surface. In addition, the ( 110) and ( 104) surfaces also show a strong fracture potential. In our proposed partition model, the exposure priority of ( 110) and ( 104) surfaces in region 2 with a lower surface energy and surface broken bond density is second only to the (012) surface. The other surfaces, except for the (012), (110), and (104) surfaces, are divided into region 3; here, the exposure of the surfaces located in this region is considered to be uncompetitive.
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.
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