metallurgy and ore production

8/17/2019 Metallurgy and Ore Production

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•

field of materials science that deals with the physical and chemicof metallic elements, their intermetallic compounds, and thewhich are called alloys

• essential to today’s society since applying the concept of scieproduction of metals and the engineering of metal components ato improve the quality of our lives


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Uses and Economics

Weapons made from metals were used by the Egyptians, specifically miron in about 3000 BC.

Many applications, practices, and devices associated or involved in mewere established in ancient China, such as the innovation of the blast cast iron, hydraulic-powered trip hammers, and double acting piston


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History: Bronze

True bronze appeared between 3000 and 2500BC, beginning in Euphrates delta. Bronze culture spread through trade and the mpeople from the Middle East to Egypt, Europe, and possibly China.


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History: Iron

In 1400BC in Anatolia, iron was assuming considerable importanceIn 1200 –1000BC, it was being fashioned on quite a large scale intoinitially dagger blades. For this reason, 1200 BC has been taken as theof the Iron Age.

Carbon-containing iron had the further great advantage that it coulstill harder by quenching.


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History: Brass

An alloy of copper and zinc without tinAppeared in Egypt about 30 BC, and was rapidly adopted throughout world for currency. It was made by the calamine process.


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History: Lead

By 500 BC, rich lead-bearing silver mines was opened in Greece.Lead was removed from the silver by cupellation. A stream of amolten mass preferentially oxidized the lead. Its oxide was removed skimming the molten surface; the remainder was absorbed into cupel. Silver metal and any gold were retained on the cupel.


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History: Gold and Silver

Native gold itself often contained quite considerable quantities of silver was converted into silver chloride, which passed into the mleaving a purified gold.

Gold and silver, together with lead, were used for artistic and religioupersonal adornment, household utensils, and equipment for the chas


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History: Ferrous Metals

The crucible process for making steel, introduced in England in 1740bar iron and added materials were placed in clay crucibles heated byresulted in the first reliable steel made by a puddling process.


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History: Light Metals

Henri-Étienne Sainte-Claire Deville◦ most successful in the production of light metals

◦ In 1855, he developed a method by which cryolite was reduced metal to aluminum and sodium fluoride.

Charles M. Hall & Paul-Louis-Toussaint Héroult◦ announced identical processes for aluminum extraction, which

based on electrolysis


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Welding•

introduced during the 20th centuryThe metal in a join can also be melted by an electric arc, and a proccarbon as a negative electrode and the workpiece as a positive firstcommercial interest about 1902. Striking an arc from a coated metawhich melts into the join, was introduced in 1910.


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Metallography- the study of the composition and microscopic structure of metals

This study was appreciated throughout Europe, with particular attepaid to the structure of steel.


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Extractive Metallurgy• Removing valuable metals from an ore

and refining the extracted raw metals inta purer form

• Converts the compound into a type that

can be more readily treated


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Common practice is to convert metallsulfides to oxides, sulfates, or chlorides;

oxides to sulfates or chlorides; andcarbonates to oxides

1. PYROMETALLURGY

2. HYDROMETALLURGY


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A. PYROMETALLURGY• ROASTING

Compounds are converted at temperatures just below their melting points

• SMELTING

All the constituents of an ore or concentrateare completely melted and separated into twliquid layers, one containing the valuablemetals and the other the waste rock.


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Common processes:

1. Oxidation

Metals having a great affinity for oxygselectively combine with it to form metaloxides; these can be treated further in order

obtain a pure metal or can be separated andiscarded as a waste product.


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2. Reduction

A metallic oxide compound is fed intofurnace along with a reducing agent such carbon. The metal releases its combined oxyge

which recombines with the carbon to form a ne

carbonaceous oxide and leaves the metal in uncombined form.


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Smelting• Liberates the metallic element from i

compound as an impure molten metal anseparates it from the waste rock part of thcharge, which becomes a molten slag.

• Types:

1. Reduction smelting2. Matte smelting

3.Electrolytic smelting


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• Reduction SmeltingBoth the metallic charge fed into the smelter and the sla

formed from the process are oxidesBlast furnace -reduction of iron oxide, zinc oxide, and

lead oxide

• Matte SmeltingSlag + Metallic charge = Matte

Melt and recombine the charge into a homogeneousmatte of metallic copper, nickel, cobalt, and iron sulfideand to give an iron and silicon oxide slag

• Electrolytic Smeltingelectric current is passed through the bath to dissociate

the metallic compound; the metal released collects at thcathode, while a gas is given off at the anode.


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Refining• Final procedure for removing the last

small amounts of impurities left after themajor extraction steps have beencompleted

• Types

1. Fire refining2.Electrolytic refining

3.Chemical refining


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• Fire RefiningOxygen or air is added to the impure liquid metal; the

impurities oxidize before the metal and are removed as aoxide slag or a volatile oxide gas

• Electrolytic Refining Anode – metal to be refinedCathode – another materialMetal ions dissolve from the anode and deposit at the ca

• Chemical RefiningNickel carbonyl processImpure nickel metal reacted with carbon monoxide gas

form nickel carbonyl gas. This gas is then decomposed thigh-purity nickel metal.


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B. HYDROMETALLURGY

• LeachingMetallic compounds are selectively

dissolved from an ore by an aqueous solven

• ElectrowinningMetallic ions are deposited onto anelectrode by an electric current passedthrough the solution


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•Conversion

•Leaching

•Recovery


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Conversion• “subjected to preliminary operations” before

leaching or electrowinning

• Examples:

1. Sulfide ores (insoluble in sulfuric acid) can bconverted to quite soluble forms by oxidizinor sulfatizing roasts.

2. Oxide ores and concentrates can be given acontrolled reducing roast to produce a calcicontaining a reduced metal that will dissolveasily in the leaching solution.


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LeachingMain methods:

• Simple Leaching

At ambient temperature andatmospheric pressure

• Pressure Leaching

Pressure and temperature are increasein order to accelerate the operation


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Recovery

• Pregnant solution from leachingoperations is treated in a variety of ways precipitate the dissolved metal values andrecover them in solid form

• Types

1. Electrolytic deposition2. Solvent extraction

3. Chemical precipitation


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Electrolytic Deposition• Insoluble anodes, and cathodes made of either

strippable inert material or a thin sheet of thedeposited metal, are inserted into a tankcontaining leach solution.

• As current is passed, the solution dissociates an

metal ions deposit at the cathode.

• This common method is used for copper, zinc,nickel, and cobalt.


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Solvent Extraction

• Takes dilute, low-value metal solutions andconcentrates them into small volumes and highmetal contents, rendering them satisfactory forelectrolytic treatment

• Low-grade copper ores are processed in thismanner


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Chemical precipitation

• Methods:

• 1. Displacement reaction takes place in which a more active metal replaces a lessactive metal in solution.

• 2. Changing the acidity of a solution is acommon method of precipitation


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PHYSICAL METALLURGY

• the science of making useful products out of metals

• considerations for the desired finished product:

shape, properties and cost


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Structures and Properties of Metals

1. Metallic crystal structures

2. Mechanical Properties

3. Electrical Properties

4. Magnetic Properties

5. Chemical Properties


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1. Metallic crystal structures

a. hexagonal close-packed symmetry (hcp)

examples: metals as magnesium, cadmium, zinc, and alpha tita

b. cubic symmetry or face-centered symmetry (fcp)

- cubes with atoms at the corners and at the center of each fac

examples: aluminium, copper, nickel, gamma iron, gold, and sil

c. body-centered cubic (bcc)

- cubes with atoms at the corners and an atom in the center of

examples: alpha iron, tungsten, chromium, and beta titanium


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2. Mechanical properties

• yield stress

- determined by the resistance to slipping of one plane of atomanother

• ductility

• toughness


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3. Electrical properties

• Conductivity of a given metal is decreased by phenomena that d

scatter, the moving electrons – which can destroy the local perfethe atomic arrangement

• Conductivity of a metal increases substantially with falling temp


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4. Magnetic properties

• Ferromagnetism is the strong magnetic property of metals.

• Iron, cobalt and nickel are the most prominent ferromagnetic m

• Hard metal: slow magnetization loss; useful as a permanent ma

• Soft metal: fast magnetization loss; useful in electrical transform


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5. Chemical properties

• Almost any metal will oxidize in air, the only exception being gol

• A special property of metal surfaces is their ability to catalyse chreactions.


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Alloying• Done by melting the base metal in vacuum chambers and then a

alloying agent, which was melted in air, since mixing is difficult istate

• Done with electricity, either by:

- induction heating (in a crucible) or by

- arc melting (melted droplets drip from the arc onto a water-co

pedestal and are immediately solidified)

• Purification is often carried out at the same time with being caravoid contamination.


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Metallurgy

1. Increasing strength

2. Increasing corrosion resistance

3. Reducing costs

4. Lowering melting points


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Casting• consists of pouring molten metal into a mold, where it solidifies

shape of the mold

• particularly valuable for the economical production of complex ranging from mass-produced parts for automobiles to one-of-a-production of statues, jewellery, or massive machinery

1 Sand Casting


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1. Sand Casting

• used for making cast-iron and steel parts of medium to large size in smoothness and dimensional precision are not of primary importan

• Full-mold or evaporative pattern casting – injection molding of poly

• Shell-molding casting – mixture of sand and thermosetting resin bin

2. Metal molds

• A die of the desire shape is machined from cast iron or steel

• Permanent metal molding - process where the metal flows into the

gravity

• Die casting - process where molten metal is forced in under pressur

3 Investment casting


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3. Investment casting

• involves drying of refractory slurry on a pattern made of wax and p

series of layers is applied and dried to make a ceramic shell, and th

is then melted or burned out to provide the mold

4. Centrifugal casting

• used for the casting of small precious-metal objects

•

Metal is forced into the mold by spinning• used to produce long, hollow objects without resorting to cores


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5. Continuous casting

• metal is poured into a short, reciprocating, water-cooled mold and seven as it is withdrawn from the other side of the mold

• used in the steel industry because it eliminates the cost of reheatingand rolling them to the proportions of the billets, blooms, and slabscontinuous casting


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Metallurgy

1. Grain size

2. Segregation

3. Porosity


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Metalworking• Cold working - performed below the recrystallization temperatu

hardens metal and makes the part stronger

1. Rolling


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g

• With high-speed computer control, several stands of rolls are combseries, with thick sheet entering the first stand and thin sheet beingfrom the last stand at linear speeds of more than 100 kilometres (6per hour.

2. Extrusion

• converts a billet of metal into a length of uniform cross section by fbillet to flow through the orifice of a die, and products may have eisimple or a complex cross section

• Forward extrusion: the ram and the die are on the opposite sides oworkpiece

• Impact extrusion: the workpiece is at the bottom of the hole, and afitting ram is pushed against it

3. Drawing


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3. Drawing

• consists of pulling metal through a die

• Wire drawing – limited die diameter reduction, but several dies in sbe used to obtain the desired reduction

• Deep drawing – starts with a disk of metal and ends up with a cup bthe metal through a hole (die)

4. Sheet metal forming

•

Stretch forming - the sheet is formed over a lock while the workpiectension; the metal is stretched just beyond its yield point to retain n

• Bending – done by pressing between two dies

• Shearing - cutting operation similar to that used for cloth

5. Forging


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• shaping of a piece of metal by pushing with open or close dies

• usually done hot in order to reduce the required force and increasemetal’s plasticity

• Open-die forging - done by hammering a part between two flat fac

• Closed-die forging - shaping of hot metal within the walls of two diecome together to enclose the workpiece on all sides

• Two closed-die forging

• Coining - the desired imprint is formed on a smooth metal disk thpressed in a closed die; involves small strains and is done cold to surface definition and smoothness

• Upsetting - involves a flow of the metal back upon itself


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Metallurgy

1. Provides control over and improvement of mechanical properties

2. Increases strain hardening

3. Better deep-drawing properties

4. Increases ability to undergo strain


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Powder Metallurgy• Metal processing technology in which parts are produced fro

powders.

• Certain metals that are difficult to fabricate by other methods canby PM.

• Minimal waste - 97% of starting powders are converted into produ


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Production of Metal PowdersPowders are often produced by chemically reducing a powdered

example, iron oxide reduced with carbon or hydrogen. The resuaggregate is then milled and sieved to obtain the desired powder. Pcan be made by electrodepositing the metal at a high current densitby milling to break up the deposit.

Powder Metallurgy Production


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Powder Metallurgy ProductionProcess


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Applications• Production of high-melting-point metals such as platinum, tun

tantalum.• Production of small, complex parts for automobiles and appliances

• Production of porous-metal bearings and filters.


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Applications


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Heat Treatment of Metals• Heat treating can soften or harden a metal depending on the co

the alloy.• Hardening heat treatments involve heating to a sufficiently high te

to dissolve solute-rich precipitates. Alloys are heated above transformation temperature for the material, then cooled rapidlycause the soft initial material to transform to a much hardestructure. Alloys may be air cooled, or cooled by quenching in oi

another liquid, depending upon the amount of alloying elemematerial.


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Heat Treatment of Metals• Softening heat treatments involve recrystallization of the metal b

at an elevated temperature. If the alloy is slowly cooled, a coarsewill form and it will yield a soft structure.


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MetallographyA field of metallurgy that deals with the evaluation of the micros

metals with the use of microscopes.Optical microscopy◦ Simplest and oldest type of metallography wherein the surface of t

given a mirror-like finish and the light reflected from it is exmagnifications of 50 to 1500x.


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MetallographyElectron microscopy

◦ a scanning electron microscope (SEM) with a magnification range20,000x is used. A narrow beam of electrons scans the surface oand forms a corresponding image from the backscattered esecondary electrons.


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Testing Mechanical PropertiesThe most common mechanical properties are yield stress, elongation

and toughness.Tensile test is used to test the yield stress and elongation of a metal. loaded until it undergoes plastic strain. If the tensile test is contyielding, the load reaches a maximum as the strain localizes anddeveloped. The final length minus the initial length divided by the inis the elongation.


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Testing Mechanical PropertiesBrinell hardness test

◦ a 10-millimetre-diameter ball is pushed a short distance into a a 3,000-kilogram load. The load divided by the contact area is the h

Charpy Test◦ employs a small bar of metal with a V-shaped groove cut on one s

hammer is swung so as to strike the bar on the side opposite the genergy absorbed in driving the hammer through the bar is the toug


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EXTRACTIVE METALLURGY OF CO

• Copper is mostly extracted from ores containin


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copper sulphides, copper oxides or coppercarbonates.

• Copper ores are generally poor and contain

between 1.5 and 5% copper.

• The extraction of copper from its sulphide oresis done by eliminating the gangue, iron, sulphuand minor impurities by the following steps.

1. Concentration


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separate the copper mineral from the gangu

ore is first crushed and finely ground

It is made into slurry with water and then feinto a froth flotation cell

The ore particles are lifted up by air bubble while the gangues remain in the cell.

The froth containing the ore is thickened an

filtered. The pulp is dried to about 6% moisture.

2. Roasting


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remove excess sulphur

carried out in a multiple hearth furnace or in afluidized bed

The dry pulp is fed into the roaster at 600 to700 OC.

The burning of the sulphide ores supplies theheat to maintain the temperature at whichroasting takes place

3. Matte Smelting


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the concentrate is smelted in a furnace toproduce a mixture of copper and iron, calledmatte

carried out at about 1350 oC.

the roasted ore is in powder form and cannottherefore be smelted conveniently in a blastfurnace

It is done in a long reverberatory furnace heate by coal dust.

4.Fire Refining h bli i f d i f h


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The blister copper is fed into a furnace wheresome of the copper is oxidized into Cu2O whichdissolves in the molten copper

A pole of green wood is then thrust in andhydrogen from the wood reduces the excessoxygen.

Poling is continued until proper surfacecharacteristics of the cooled samples areobtained.

The product is called tough pitch. It has goodelectrical conductivity. It is cast into slabs.

5. Electrolytic RefiningTough pitch copper is not fit for gas welding


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Tough pitch copper is not fit for gas-weldinguntil it is deoxidized further.

It is made into impure copper anodes which ar

immersed in a 5 to 10% sulfuric acid bathcontaining copper sulphate.

Pure copper foil serves as the cathode wherecopper deposits.

Cathodes produced as a result of the electrolyt

refining process contain 99.9% of copper whichis used for manufacturing copper and copperalloys products.


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Mineral Ores and Production

An ore is a mineral deposit which can be profitably exploited.

It may contain three groups of minerals namely:

1. valuable minerals of the metal which is being sought

2. compounds of associated metals which may be of secondary val

3. gangue minerals of minimum value


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Ore Dressing

• - a process in which ores are pre-treated, mainly physically, subjected to the main chemical treatment steps.

These may include:

1. Size Reduction to such a size as will release or expose all valuab

2. Sorting to separate particles of ore minerals from gangue (nminerals or different ores from one another.

3. Agglomeration may be carried out sometimes before a roasting

metallurgy and ore production

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