Metallurgy

• Lecturer : Hong Vu, Ph.D., vun@vscht.cz, tel.:5025, room A50

• Literature: Chemical Metallurgy (J.J. Moore)

• Website: web.vscht.cz/vun/vun.htm

What is Metallurgy ?

The extraction process applies one or more of three types of metallurgy : pyrometallurgy, hydrometallurgy and electrometallury

Most metals occur in nature in mineral form, although a small number of metals (e.g., Cu, Ag, Au, Hg, Pt) may occur in their metallic state.

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

Metal ores are concentrations of above metal compounds associated with other unwanted minerals (gangue) such as silicates

Comminuation (size reduction): crushing and grinding

Particle Selection

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.

Separation 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.

Particle Selection

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.

Flotation

The flotation process relies primarily on the fact that hydrophilic particles

are wetted by water, whereas hydrophobic particles are wetted by oils and

air bubbles

Flotation Reagents

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 flotation 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.

Flotation Cells

Application of Flotation

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Final Operations

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.