Mineral processing for erasmus students

Particle SelectionSeparation 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 mov

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

• Literature: Chemical Metallurgy (J.J Moore)

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.

Elements Au, Ag, Cu, As, Sb, Bi

Sulfides CuS, Cu 2 S, PbS, ZnS, NiS, Cu 5 FeS 4 ,

CuFeS 2 , FeS, FeS 2 , MoS 2

Oxides and hydroxides Fe 2 O 3 , Fe 3 O 4 , FeTiO 3 , FeCr 2 O 4 , TiO 2 , MnO 2 ,

SnO 2 , Al 2 O 3 , Al(OH) 3 , AlOOH, FeOOH Halides NaCl, KCl, CaF 2 , Na 3 AlF 6 , KMgCl 3 · 6 H 2 O,

Cu 2 Cl(OH) 3

Carbonates, nitrates, and borates MgCO 3 , CaCO 3 , FeCO 3 , MnCO 3 , ZnCO 3 ,

CaMg(CO 3 ) 2 , Cu 2 CO 3 (OH) 2 , NaNO 3 , Na 2 B 4 O 7 · 10 H 2 O Sulfates, chromates, molybdates, and BaSO 4 , PbSO 4 , CaSO 4 , CaSO 4 · 2 H 2 O, KFe 3 (SO 4 ) 2 (OH) 6

tungstenates CaWO 4 , FeWO 4

Phosphates, arsenates, and vanadates (Ca, Ce, Nd)PO 4 , (Ce, La, Th)PO 4

Silicates ZrSiO 4 , ZnSiO 4 , SiO 2 , LiAlSi 2 O 6

Metal ores are concentrations of above metal compounds associated with other unwanted minerals

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

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

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