Metallurgy

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Metallurgy

• Lecturer Hong Vu, Ph.D., vun_at_vscht.cz,
  tel.5025, room A50
• Literature Chemical Metallurgy (J.J. Moore)
• Website web.vscht.cz/vun/vun.htm

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The extraction process applies one or more of
three types of metallurgy pyrometallurgy,
hydrometallurgy and electrometallury
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Substances Examples
Elements Au, Ag, Cu, As, Sb, Bi
Sulfides CuS, Cu2S, PbS, ZnS, NiS, Cu5FeS4,
CuFeS2, FeS, FeS2, MoS2
Oxides and hydroxides Fe2O3, Fe3O4, FeTiO3, FeCr2O4, TiO2, MnO2,
  SnO2, Al2O3, Al(OH)3, AlOOH, FeOOH
Halides NaCl, KCl, CaF2, Na3AlF6, KMgCl3 6 H2O,
  Cu2Cl(OH)3
Carbonates, nitrates, and borates MgCO3, CaCO3, FeCO3, MnCO3, ZnCO3,
  CaMg(CO3)2, Cu2CO3(OH)2, NaNO3, Na2B4O7 10 H2O
Sulfates, chromates, molybdates, and BaSO4, PbSO4, CaSO4, CaSO4 2 H2O, KFe3(SO4)2(OH)6
tungstenates CaWO4, FeWO4
Phosphates, arsenates, and vanadates (Ca, Ce, Nd)PO4, (Ce, La, Th)PO4
Silicates ZrSiO4, ZnSiO4, SiO2, LiAlSi2O6
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Separation according to Particle Size The
separation of particles according to size is
effected by the use of physical barriers and
screens or by the differential movement of solid
particles through fluids rake classifiers,
sedimentation classifiers, and hydrocyclones. Sepa
ration according to Density The sorting of
particles as a function of their density may be
performed in unit operations and devices such as
Humphreys Spiral, shaking tables, jigging and
tabling operations, dense-medium
separation Separation due to Surface Properties
(Flotation) Air bubbles, which are blown through
a pulp, attach selectively to the valuable
particles (e.g., various sulfides) and float to a
froth which is skimmed off and collected as
concentrate. Thr flotation process is carried out
in cells, columns, and air-sparged hydrocyclones.
Flotation cells are arranged in banks which are
interconnected so as to produce maximum
recovery. Magnetic and Electrostatic Sorting
These techniques (wet or dry) utilize the
magnetic (e.g., with magnetite), electrical
conductive, and induced electrostatic properties
of various minerals and materials to separate the
valuable mineral or material from the surrounding
gangue.
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X-Ray Sorting. When certain materials (e.g.,
diamonds) are irradiated by X-rays they become
luminous and, hence, can be detected
electronically and sorted from the gangue
material. Solid  Liquid Separation. The recovery
of solids from liquid media, either to clarify
solutions for hydrometallurgical treatment or to
dewater pulps for pyrometallurgical operations,
can be performed in drum, leaf, and sand filters,
thickeners, as well as decanting and centrifuging
processes. Gas Cleaning. Gas cyclones, bag
filters, and electrostatic precipitators are used
to clean gases or to recover valuable minerals
from flue gases from pyrometallurgical
operations, before they are vented to the
atmosphere.
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The ?otation process relies primarily on the fact
that hydrophilic particles are wetted by water,
whereas hydrophobic particles are wetted by oils
and air bubbles
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Collectors. These are used primarily to make
solids hydrophobic and promote adhesion to air
bubbles or oil droplets. Common examples are
fatty acids, sulfonates, xanthates
(dithiocarbonates), amines, and
dithiophosphates. Frothers. Frothers promote the
formation of a metastable froth phase that
facilitates the removal of particles carried by
air bubbles to the top of the ?otation cell.
Examples of frothers are pine oil, long-chain
alcohols, and polyoxypropylene Auxiliary
Reagents. These reagents include depressants,
which are used to prevent solids from becoming
hydrophobic, and activators, which promote the
adsorption of reagents onto selected solids.
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Agglomeration If the particle's size is too small
for use in subsequent metallurgical unit
operations, it is agglomerated into larger, more
suitable lumps of appropriate size and strength.
The unit operations used to achieve this
objective are briquetting, pelletizing,
sintering, and nodularizing. Briquetting. Ore
fines are mixed with a suitable binder and
mechanically pressed into a suitable shape at
room or higher temperature. The briquettes may
subsequently be hardened in a kiln. Pelletizing.
A suitable binder and water are added to the ore
fines, which are fed into a inclined rotating
drum or disk. These green pellets may
subsequently be fired in a furnace to increase
their strength. Sintering. Coal dust (5  6 ),
ore fines, and water are mixed and fed onto the
grate of a sinterstrand. The carbon in the sinter
bed is ignited, and air sucked or blown through
the bed produces an ignition front which
facilitates drying, calcination, volatilization
of the compounds in the bed, and fusion of the
materials in the bed, imparting strength to the
sinter. If sulfides are roasted and sintered, no
carbon need be added. Nodularizing. The same feed
materials used for sintering are fed to an
inclined rotating drum at an elevated temperature
to produce nodules.