Kuliah Ekstraksi 1

transcript

Kuliah Metalurgi EkstraksiKuliah Metalurgi Ekstraksi

Department of Metallurgy and MaterialsDepartment of Metallurgy and Materials

Faculty of EngineeringFaculty of Engineering

University of Indonesia University of Indonesia

Depok, 17 September 2010Depok, 17 September 2010

Prof. Dr. Ir. Johny Wahyuadi Soedarsono, DEAProf. Dr. Ir. Johny Wahyuadi Soedarsono, DEA

MetallurgicalMetallurgical EngineeringEngineering

Metallurgical engineering or metallurgy is the study of metals and is the oldest

sciences devoted to the study of engineering materials.

MetallurgyMetallurgy

Metallurgy is the science and technology of metal. It is the oldest of the sciences devoted to the study

of engineering materials. Metallurgy has evolved into three

separate groups: extractive, mechanical, and physical.

Extractive MetallurgyExtractive Metallurgy

• Extractive metallurgy is the study of the extraction and purification of metals from their ores.

• Extracting a metal from its ore is conducted in several process steps.

• For example, the extraction route from ore to refined metal includes any or all of the following process steps.

• Concentration.– Separate ore from waste rock.

• Roasting.– Heat to a high temperature to form the oxide.

• Reduction.– Commonly use carbon as coke or powdered coal.

• Refining.– Metals must be purified.

Extractive MetallurgyExtractive Metallurgy

Benefication, mineral dressing, pyrometallurgy,

hydrometallurgy, and electrometallurgy.

Mechanical MetallurgyMechanical Metallurgy

Mechanical metallurgy is the study of the techniques and mechanical forces that shape or make finished forms of

metal.

Physical MetallurgyPhysical Metallurgy• Physical metallurgy is the

study of the effect of structure on the properties of metals.

• The two structures studied in physical metallurgy are the crystal structure and micro structure.

• See figure 1-4• The crystal structure is the

arrangement of atoms in the metal.

• An atom is the smallest building block of matter that can exist alone or in combination.

• It cannot be divided without changing its basic character.

• The crystal structure is shown through modeling.

• The microstructure is the microscopic arrangement of the components, or phases, within a metal.

• The technology of heat treatment of steels is based on a specific crystal structure and microstructure change that occurs when steel is rapidly cooled from a high temperature.

• These changes lead to hardening and strengthening of steels.

Ceramic EngineeringCeramic Engineering

Ceramic engineering, or ceramics, is the study of the development and

production of products made from nonmetallic, inorganic materials by

firing at high temperatures. Ceramic materials are divided into four groups:

Ceramic Engineering Cont.Ceramic Engineering Cont.

• Clay-based materials• Refractories• Glasses• Inorganic cements

Polymer EngineeringPolymer Engineering

Polymer engineering or polymer is the study of the development and

production of synthetic organic materials. Polymer are divided into two

groups:

Polymer Engineering Cont.Polymer Engineering Cont.

• Thermoplatics• Thermosets• Polymer are used In applications such as

adhesives, building products, fibers sporting goods, and automotive and aerospace components.

Composite Engineering Composite Engineering

Composite engineering, or composites, is the study of the applicability of

combinations of materials. Composites are used to strengthen metals, ceramics,

or polymers and improve their structural usefulness.

Materials EngineeringMaterials Engineering

Materials engineering, which crosses the boundaries of all the branches of

materials sciences, is the study of the evaluation of the characteristic

properties of all materials.

Occurrence and Distribution of MetalsOccurrence and Distribution of Metals• Early history is divided into the Stone Age, Bronze

Age, and the Iron Age.• If we consider a jet engine, there are 7 metals present.

Fe is not.• A modern jet engine consists mostly of Ti and Ni with

decreasing amounts of Cr, Co, Al, Nb and Ta.• The solid portion of the earth is called the lithosphere.• Concentrated metal deposits are found beneath the

earth’s surface.• Ore: deposit that contains enough metal that we can

extract economically.

Gambar 1. Mineral dan ikutannya

Evolution of metalsEvolution of metals

Copper

Bronze

Cast Iron Steels

AlloySteels Light

Alloys

Super Alloys

Ti-, Zr- Alloys

GlassyMetals

Special Steels andNew superalloys

Stone ageBronze age

Iron age

Age of advanced materialsSteel technologies

Occurrence and Distribution of MetalsOccurrence and Distribution of Metals

The Iron Triad: Iron, Cobalt and NickelThe Iron Triad: Iron, Cobalt and Nickel• Iron – annual worldwide production over 500 million tons.

– Most important metal in modern civilization.

– 4.7% natural abundance.

• Cobalt – 0.0020% natural abundance.

– Deposits are reasonably concentrated.

– Primarily used in alloys, Co5Sm makes a good magnet.

• Nickel – 24th most abundant element.

– Primarily used in alloys, but also for electroplating.

Occurrence and Distribution of MetalsOccurrence and Distribution of MetalsMineralsMinerals• Ore: deposit that contains enough metal that we can

extract economically.• Most metals are found in minerals.• Names of minerals are usually based on the location

of their discovery.• Other minerals are named after their colors:

malachite comes from the Greek malache (the name of the tree with very green leaves).

• Most important ores are oxide, sulfide and carbonate minerals.

Occurrence and Distribution of MetalsOccurrence and Distribution of MetalsMineralsMinerals

Occurrence and Distribution of MetalsOccurrence and Distribution of MetalsMetallurgyMetallurgy• Metallurgy is the science and technology of extracting

metals from minerals.• There are five important steps:– Mining (getting the ore out of the ground);

– Concentrating (preparing it for further treatment);

– Reduction (to obtain the free metal in the zero oxidation state);

– Refining (to obtain the pure metal); and

– Mixing with other metals (to form an alloy).

Hydrometallurgicalmetal production

Materialsciences

Mining &Enrichment

Metallurgy:introduction

Electro-metallurgy

Extractivemetallurgy

OresMining

EnrichmentCrushingScreeningMechanicalseparation

Properties ofmetals

Physicalmetallurgy

Hot and coldrolling

Hydrometallurgy

Pyrometallurgy

e.g.zinc

nickel

Electrowinning

Cementation

Ionexchange

Chemicalprecipitation

Solventextraction

Similarmethods

Reactionkinetics

Thermo-dynamics

Theory

Metalrecovery

Impurityremoval

Fluiddynamics

Heattransfer

Masstransfer

Transportphenomena

Methods

Leaching

Iron andsteel

Sulphide-ores (e.g. Cu)

e.g. Roasting

Pyrometall.pretreatment

Pyrometallurgicalmetal production

e.g.iron/steel

copper

Sintering

Coking

Blastfurnace

Sulphurremoval

Ladletreatments

Converters(LD/AOD/...)

Casting

Flashsmelting

Converters(PS)

Electricfurnaces

AcidicBasic

Organic

Solvents

How to choose a process?How to choose a process?

Pyromet. unit operationsPyromet. unit operationsHydromet. unit operationsHydromet. unit operations

Electro-chem. unit operationsElectro-chem. unit operations

Production chainProduction chain ProductsProductsRaw materialsRaw materials

ResiduesResidues

MarketsMarketsTransportTransport

EnergyEnergy

Water neededWater needed

• the mineral must first be separated from the surrounding ore material by physical means

• extractive metallurgy are the chemical processes that separate a metal from its mineral

• refining are the processes that purify the metal for use

SeparationSeparation

• first step is to crush the ore into small particles• the mineral is then separated from the gangue by

physical means– using cyclonic winds to separate by density

– froth flotation in which the mineral is treated with a wetting agent to make it more attracted to the froth

Alternative MethodsAlternative Methods

• Many ores contain several metals and it is not always necessary to separate them.– Fe(CrO2)2 can be reduced to ferrochrome and can be

added directly to iron to produce steel.

– V2O5 and MnO2 are also added to iron to produce other types of steel.

• Titanium cannot be produced by reduction with C.– In the Kroll process Mg is used.

Mining Companies’ Raison d'êtreMining Companies’ Raison d'être

1.Survival

2.Profitability: Stable earnings

Earnings growth

Disposals

3.Growth

Mining Basics - TheoryMining Basics - Theory

• Turnings rock in the ground into profits!

• The fundamental value of a mineral deposit ultimately depends entirely on its capacity to support an economically viable mining operation in the future

Pyrometallurgical ProcessesPyrometallurgical Processes

• The roasting – reduction process is known as pyrometallurgy.

• Large quantities of waste material is produced in concentrating low grade ore.

• High energy consumption.• Gaseous emission must be controlled.

Pyrometallurgical unit operationsPyrometallurgical unit operations

Raw materialRaw materialpretreatmentpretreatment

MetalMetalrefiningrefining

MetalMetalextractioextractio

Production of Production of metalsmetals

Raw materialsRaw materials ProductsProducts

ReductioReductionn

and and oxidizingoxidizing

Thermal Thermal pretreatmepretreatme

Metal Metal raffinatioraffinatio

MatteMatteproductionproduction

ReductionReductionof oxidesof oxides

CompositionCompositioncontrolcontrol

Impurity removalImpurity removal

TemperatureTemperaturecontrolcontrol

SinteringSintering

DryingDrying

CalcinationCalcination

CokingCoking RoastingRoastingPelletizingPelletizing

DryingDrying• Dangerous to charge wet materials to the high

temperature processes– The moisture that is allowed depends on the further

processing

• Mechanical moisture removal prefered– Thermal drying requires a lot of energy

• Counter-current drum-driers are common in the drying of metallurgical raw materials

• Utilisation of the process waste heat streams

SinteringSintering• Problems in processing fine materials– Gas permeability

– Dusting

• Thermal agglomeration– Partial melting

– Minimisation of the surface energyas a driving force for agglomeration

• Chemical and mineralogical changes in material• Drum-, batch- or belt-sintering– Pretreatment: Micropelletising

PelletizingPelletizing• Feeding of concentrates, binding materials and

water into the rotating and sloped pelletising drum or plate

• Capillar forces caused by moisture as cohesive force

• Aftertreatments in order to achieve wanted properties– Sintering

– Shaft furnace

• Small pellets are fed backto the process

CalcinationCalcination

• Thermal disintegration of a compound (which leads into a formation of gaseous product)– Thermal conductivity (endothermic reactions)

– Removal of gas from the reaction surface

• e.g. calcination of limestone to produce burned lime

Use of lime in iron and steelmaking slags– CaCO3 = CaO + CO2 HR >> 0

– Counter-current shaft furnace or rotating drum

• Other examples– Disintegration of CaMg(CO2)2 or Al(OH)2

CokingCoking• Pyrolysis of coal in order to modify it to be more

suitable for metallurgical processes– Removal of water and volatile components

– Agglomeration of coal particles

– Porous coke as a result

• Dry or wet quenching• Several by-products– Reducing gas (H2, CO)

– Raw materials for chem. industry

RoastingRoasting• A process in which an anion of a solid compound

is changed without changing the valency of the cation

• High temperature processing of the sulphide ores without agglomeration– Often used as a pretreatment for the

hydrometallurgical processes

• Examples– Oxidising roasting

– Sulphating roasting

– Chlorine/Fluor/Alkalines/...

Oxidising roastingOxidising roasting

• Difficulties to reduce sulphide ores using carbon– e.g. 2 ZnS + C = 2 Zn + CS2 or ZnS + CO = Zn + COS

– Equilibrium is strongly on the reactants’ side

• Roasting of sulphides into the oxides– MeS + 3/2 O2 = MeO + SO2

– Used e.g. in the production of lead, copper, zinc, cobalt, nickel and iron when using sulphide ores as raw materials

– SO2 SO3 H2SO4

• Fluidized bed, sintering or shaft furnace roasting– Products are either fine material or porous agglomerates

Sulphating roastingSulphating roasting• Used in separation of metals from complex

materials– Some metals react to sulphates that are soluble to water

• MeS + 3/2 O2 = MeO + SO2

• SO2 + 1/2 O2 = SO3

• MeO + SO3 = MeSO4

– Some are left as oxides (non-soluble)

• A pretreatment for hydrometallurgical processes• Usually fluidized bed roasting• Often used to remove iron from more valuable

metals (Cu, Ni, Zn, Co)– When T > 600 C Ferrisulphate is not stable

Reduction of oxidesReduction of oxides

• MeO + R = Me + RO– Me is a metal

– R is a reducing component (an element or a compound which forms an oxide which is more stable than MeO in the considered temperature)

• Carbo-thermal reduction– MeO + C = Me + CO

– In practice:• MeO + CO = Me + CO2

• C + CO2 = 2 CO (= Boudouard reaction)

• Metallothermal reduction– MeO + M = Me + MO

• Gas reduction– Usually H2 and CO (separately or as a mixture)

• MeO + H2 = Me + H2O

• MeO + CO = Me + CO2

The largest industrial CO2-emissionsin Finland and Sweden (Mt)

Specific and total CO2-emissionsof the Finnish steel industry

Matte productionMatte production

• Separation of metals from the sulphides– ”Worthless” metal is oxidised Oxidic slag

– Wanted metal is still as a sulphide Matte

• Matte is further refined Metal• Used e.g. in the production of copper, nickel and

lead– 2 CuS + O2 = Cu2S + SO2

– FeS2 + O2 = FeS + SO2

– 2 FeS + 3 O2 + SiO2 = Fe2SiO4 + 2 SO2

Removal of impurities (from iron/steel)Removal of impurities (from iron/steel)

• Carbon removal (hot metal crude steel)– To achieve wanted properties

– Decarburization in BOF-converters• Removal of other oxidising impurities/elements (Si, Mn, P)

• Oxygen blowing Oxide formation Slag/Gases

• Temperature is increased– Scrap melting

– Vacuum treatment• Burning of carbon is more efficient

in lowered pressure

• Partial pressure of CO can also belowered using inert gases

Removal of impurities (from iron/steel)Removal of impurities (from iron/steel)

• Deoksidation / Oxygen removal– Solubility of oxygen in steel melt is appr. 0,2 % (T > 1500

– Solubility decreases when temperature is decreased• Causes CO formation, oxidation of alloying elements, etc.

– Alloying, diffusion or vacuum deoxidation

• Gas removal– Solubilities of gases decrease when T is decreased (cf. O)

– Gas removal is based on decreasing the partial pressure of the concerned element in the gas phase (vacuum, inert gas)

• Sulphur removal– Formation of CaS Into the slag

Composition control (Steel)Composition control (Steel)

• Alloying of steel is made mainly in the BOF-converters after the blowing

• More accurate alloying in the steel ladle– Lumps

– Powder injection

– Wire injection

• Stirring– Inductive

– Using an inert gas

Temperature controlTemperature control

• Increased significance due to continuous casting

• Optimisation of a tap temperature• Inductive heating• Use of fuels• Plasma heaters• Chemical heating (Al, Si)• Electric arcs• Insulation• Scrap cooling• Stirring

PyrometallurgyPyrometallurgy• Pyrometallurgy: using high temperatures to obtain

the free metal.• Several steps are employed:– Calcination is heating of ore to cause decomposition and

elimination of a volatile product:

PbCO3(s) PbO(s) + CO2(g)– Roasting is heating which causes chemical reactions

between the ore and the furnace atmosphere:

2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g)

2MoS2(s) + 7O2(g) 2MoO3(s) + 4SO2(g)– Smelting is a melting process that causes materials to

separate into two or more layers.

PyrometallurgyPyrometallurgy– Slag consists mostly of molten silicates in addition to

aluminates, phosphates, fluorides, and other inorganic materials.

– Refining is the process during which a crude, impure metal is converted into a pure metal.

The Pyrometallurgy of IronThe Pyrometallurgy of Iron• Most important sources of iron are hematite Fe2O3

and magnetite Fe3O4.

• Reduction occurs in a blast furnace.• The ore, limestone and coke are added to the top of

the blast furnace.• Coke is coal that has been heated to drive off the

volatile components.

PyrometallurgyPyrometallurgyThe Pyrometallurgy of IronThe Pyrometallurgy of Iron

PyrometallurgyPyrometallurgyThe Pyrometallurgy of IronThe Pyrometallurgy of Iron• Coke reacts with oxygen to form CO (the reducing

agent):

2C(s) + O2(g) 2CO(g), H = -221 kJ

• CO is also produced by the reaction of water vapor in the air with C:

C(s) + H2O(g) CO(g) + H2(g), H = +131 kJ

Since this reaction is endothermic, if the blast furnace gets too hot, water vapor is added to cool it down without interrupting the chemistry.

PyrometallurgyPyrometallurgyThe Pyrometallurgy of IronThe Pyrometallurgy of Iron• At around 250C limestone is calcinated (heated to

decomposition and elimination of volatiles).• Also around 250C iron oxides are reduced by CO:

Fe3O4(s) + 4CO(g) 3Fe(s) + 4CO2(g), H = -15 kJ

Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(g), H = +150 kJ

• Molten iron is produced lower down the furnace and removed at the bottom.

• Slag (molten silicate materials) is removed from above the molten iron.

PyrometallurgyPyrometallurgyThe Pyrometallurgy of IronThe Pyrometallurgy of Iron• If iron is going to be made into steel it is poured

directly into a basic oxygen furnace.• The molten iron is converted to steel, an alloy of iron.

• To remove impurities, O2 is blown through the molten mixture.

• The oxygen oxidizes the impurities.

Formation of SteelFormation of Steel• Steel is an alloy of iron.• From the blast furnace, the iron is poured into a

converter.

PyrometallurgyPyrometallurgyFormation of SteelFormation of Steel• A converter consists of a steel shell encasing a

refractory brick liner.• After treatment in the blast furnace, there are

impurities in the iron, which must be removed by oxidation.

• Air cannot be present in the converter because the nitrogen will form iron nitride (causes the steel to be brittle).

• Oxygen diluted with Ar is used as the oxidizing agent.

SteelSteel

• Three fundamental changes from pig iron.– Reduction of the C content.

• 3-4% in pig iron

• 0-1.5% in steel.

– Removal, through slag formation, of:• Si, Mn, P (about 1% in pig iron)

• Other minor impurities.

– Addition of alloying elements.• Cr, Ni, Mn, V, Mo, and W.

– Give the steel its desired properties.

PyrometallurgyPyrometallurgyFormation of SteelFormation of Steel

• When oxygen emerges from the converter, then all the impurities have been oxidized and the iron is poured into a ladle.

Impacts of smeltingImpacts of smelting

• acid rain. The smelting of sulfide ores results in the emission of sulfur dioxide gas, which reacts chemically in the atmosphere to form a sulfuric acid . As this acid rain falls to the earth, it increases the acidity of soils, streams, and lakes, harming the health of vegetation and fish and wildlife populations.

* Copper and selenium, for example, which can be released from copper smelters, are essential to organisms as trace elements, but they are toxic if they are overabundant.

* These metals can contaminate the soil in the vicinity of smelters, destroying much of the vegetation. In addition, particulate matter emitted from smelters may include oxides of such toxic metals as arsenic (cumulative poison), cadmium (heart disease), and mercury (nerve damage).

SolutionsSolutions• Older smelters emitted most of the sulfur dioxide

generated, and now almost all of it is captured prior to emission using new technologies, such as electrostatic precipitators, which capture dust particles and return them to the process.

• Raw material substitution or elimination, such as recycling lead batteries and aluminum cans, decreases the need to process ore, which reduces pollution.

Hydrometallurgical ProcessesHydrometallurgical Processes

• Leaching: Metal ions are extracted from the ore by a liquid.– Acids, bases and salts may be used.

– Oxidation and reduction may also be involved.

• Purification and concentration.– Adsorption of impurities on activated charcoal or by

ion exchange.

• Precipitation.– Desired ions are precipitated or reduced to the free

metal.

– Electroanalytical methods are often used.

HydrometallurgyHydrometallurgy• Hydrometallurgy is the extraction of metals from ores

using water.• Leaching is the selective dissolution of the desired

mineral.• Typical leaching agents are dilute acids, bases, salts,

and sometimes water.• Gold can be extracted from low-grade ore by

cyanidation:– NaCN is sprayed over the crushed ore and the gold is

oxidized:

4Au(s) + 8CN-(aq) + O2(g) + 2H2O(l) 4Au(CN)2-(aq) + 4OH-

HydrometallurgyHydrometallurgy– The gold is then obtained by reduction:

2Au(CN)2-(aq) + Zn(s) Zn(CN)4

2-(aq) + 2Au(s)

The Hydrometallurgy of AluminumThe Hydrometallurgy of Aluminum• Aluminum is the second most useful metal.

• Bauxite is a mineral that contains Al as Al2O3.xH2O.

• Bayer process:– The crushed ore is digested in 30% NaOH (by mass) at 150

- 230C and high pressure (30 atm to prevent boiling).

– Al2O3 dissolves:

Al2O3.H2O(s) + 2H2O(l) + 2OH-(aq) 2Al(OH)4-(aq)

– The aluminate solution is separated by lowering the pH.

– The aluminate solution is calcined and reduced to produce the metal.

ElectrometallurgyElectrometallurgyElectrometallurgy of SodiumElectrometallurgy of Sodium• Electrometallurgy is the process of obtaining metals

through electrolysis.• Two different starting materials: molten salt or

aqueous solution.• Sodium is produced by electrolysis of molten NaCl in

a Downs cell.

• CaCl2 is used to lower the melting point of NaCl from 804C to 600C.

• An iron screen is used to separate Na and Cl (so that NaCl is not re-formed).

ElectrometallurgyElectrometallurgyElectrometallurgy of SodiumElectrometallurgy of Sodium

• At the cathode (iron): 2Na+(aq) + 2e- 2Na(l)

• At the anode (carbon): 2Cl-(aq) Cl2(g) + 2e-

ElectrometallurgyElectrometallurgyElectrometallurgy of AluminumElectrometallurgy of Aluminum• Hall process electrolysis cell is used to produce

aluminum.

• Al2O3 melts at 2000C and it is impractical to perform electrolysis on the molten salt.

• Hall: use purified Al2O3 in molten cryolite (Na3AlF6, melting point 1012C).

• Anode: C(s) + 2O2-(l) CO2(g) + 4e-

• Cathode: 3e- + Al3+(l) Al(l)• The graphite rods are consumed in the reaction.

• Bayer process: bauxite (~ 50 % Al2O3) is concentrated to produce aluminum oxide.

ElectrometallurgyElectrometallurgyElectrometallurgy of AluminumElectrometallurgy of Aluminum

ElectrometallurgyElectrometallurgyElectrometallurgy of AluminumElectrometallurgy of Aluminum• To produce 1000 kg of Al, we need 4000 kg of bauxite,

70 kg of cryolite, 450 kg of C anodes and 56 109J of energy.

ElectrometallurgyElectrometallurgyElectrorefining of CopperElectrorefining of Copper• Because of its good conductivity, Cu is used to make

electrical wiring.• Impurities reduce conductivity, therefore pure copper

is required in the electronics industry.• Slabs of impure Cu are used as anodes, thin sheets of

pure Cu are the cathodes.• Acidic copper sulfate is used as the electrolyte.• The voltage across the electrodes is designed to

produce copper at the cathode.• The metallic impurities do not plate out on the

cathode.

ElectrometallurgyElectrometallurgyElectrorefining of CopperElectrorefining of Copper• Metal ions are collected in the sludge at the bottom of

the cell.• Copper sludge provides about 25 % of US silver

production and 13 % of US gold production.

Metallic BondingMetallic BondingPhysical Properties of MetalsPhysical Properties of Metals• Important physical properties of pure metals:

malleable, ductile, good conductors, and feel cold.• Most metals are solids with the atoms in a close

packed arrangement.• In Cu, each atom is surrounded by 12 neighbors.• There are not enough electrons for the metal atoms to

be covalently bonded to each other.

Metallic BondingMetallic BondingElectron-Sea Model for Metallic BondingElectron-Sea Model for Metallic Bonding• We use a delocalized model for electrons in a metal.– The metal nuclei are seen to exist in a seal of electrons.

– No electrons are localized between any two metal atoms.

– Therefore, the electrons can flow freely through the metal.

– Without any definite bonds, the metals are easy to deform (and are malleable and ductile).

• Problems with the electron sea model:– As the number of electrons increase, the strength of

bonding should increase and the melting point should increase.

– But: group 6B metals have the highest melting points (center of the transition metals).

Metallic BondingMetallic BondingElectron-Sea Model for Metallic BondingElectron-Sea Model for Metallic Bonding

Metallic BondingMetallic BondingMolecular-Orbital Model for MetalsMolecular-Orbital Model for Metals• Delocalized bonding requires the atomic orbitals on

one atom to interact with atomic orbitals on neighboring atoms.

• Example: graphite electrons are delocalized over a whole plane, benzene molecules have electrons delocalized over a ring.

• Recall: the number of molecular orbitals is equal to the number of atomic orbitals.

• In metals there is a very large number of orbitals.• As the number of orbitals increase, their energy

spacing decreases and they band together.

Metallic BondingMetallic BondingMolecular-Orbital Model for MetalsMolecular-Orbital Model for Metals

Metallic BondingMetallic BondingMolecular-Orbital Model for MetalsMolecular-Orbital Model for Metals• The number of electrons do not completely fill the

band of orbitals.• Therefore, electrons can be promoted to unoccupied

energy bands.• Since the energy differences between orbitals are

small, the promotion of electrons occurs at low energy costs.

• As we move across the transition metal series, the antibonding band starts becoming filled.

Metallic BondingMetallic BondingMolecular-Orbital Model for MetalsMolecular-Orbital Model for Metals• Therefore, the first half of the transition metal series

have only bonding-bonding interactions, the second half has bonding-antibonding interactions.

• We expect the middle of the transition metal series to have the highest melting points.

• The energy gap between bands is called the band gap.• The electron sea model is a qualitative interpretation

of band theory (molecular-orbital model for metals).

AlloysAlloys• Alloys have more than one element with

characteristics of metals.• Pure metals and alloys have different physical

properties.• In jewelry an alloy of gold and copper is used (the

alloy is harder than soft gold).• Solution alloys are homogeneous mixtures.• Heterogeneous alloys: components are not dispersed

uniformly (e.g. pearlite steel has two phases: almost pure Fe and cementite, Fe3C).

AlloysAlloys

AlloysAlloys• There are two types of solution alloy:– substitutional alloys (the solute atoms take the positions of

the solvent);

– interstitial alloys (the solute occupies interstitial sites in the metallic lattice).

• Substitutional alloys:– atoms must have similar atomic radii,

– elements must have similar bonding characteristics.

• Interstitial alloys:– one element must have a significantly smaller radius than

the other (in order to fit into the interstitial site), e.g. a nonmetal.

AlloysAlloys• Interstitial alloys:– The alloy is much stronger than the pure metal (increased

bonding between nonmetal and metal).

– Example steel (contains up to 3 % carbon).

Transition MetalsTransition MetalsPhysical PropertiesPhysical Properties• Transition metals occupy the d block of the periodic

table.• Almost all have two s electrons (exceptions group 6B

and group 1B).• Most of these elements are very important in modern

technology.• Physical properties of transition metals can be

classified into two groups: atomic properties (e.g. size) and bulk properties (e.g. melting point).

• The atomic trends tend to be smooth for the transition metals.

Transition MetalsTransition MetalsPhysical PropertiesPhysical Properties

Transition MetalsTransition MetalsPhysical PropertiesPhysical Properties• Most of the trends in bulk properties are less smooth

than the atomic properties.• The trends in atomic properties of the transition

metals can be exemplified with atomic radius.• Atomic radius decreases and reaches a minimum

around group 8B (Fe, Co, Ni) and then increases for groups 1 and 2.

• This trend is again understood in terms of effective nuclear charge.

• The increase in size of the Cu and Zn triads is rationalized in terms of the completely filled d orbital.

Transition MetalsTransition MetalsPhysical PropertiesPhysical Properties

Transition MetalsTransition MetalsPhysical PropertiesPhysical Properties• In general atomic size increases down a group.– An important exception: Hf has almost the same radius as

Zr (group 4B): we would expect Hf to be larger than Zr.

– Between La and Hf the 4f shell fills (Lanthanides).

– As 4f orbitals fill, the effective nuclear charge increases and the lanthanides contract smoothly.

– The Lanthanide Contraction balances the increase in size we anticipate between Hf and Zr.

– The second and third series are usually about the same size, with the first series being smaller.

– Second and third series metals are very similar in their properties (e.g. Hf and Zr are always found together in ores and are very difficult to separate).

Transition MetalsTransition MetalsElectron Configurations and Oxidation StatesElectron Configurations and Oxidation States• Even though the (n - 1)d orbital is filled after the ns

orbital, electrons are lost from the orbital with highest n first.

• That is, transition metals lose s electrons before the d electrons.

• Example: Fe: [Ar]3d64s2, Fe2+: [Ar]3d6.• d-Electrons are responsible for some important

properties:– transition metals have more than one oxidation state,

– transition metal compounds are colored (caused by electronic transitions),

Transition MetalsTransition MetalsElectron Configurations and Oxidation StatesElectron Configurations and Oxidation States

Transition MetalsTransition MetalsElectron Configurations and Oxidation StatesElectron Configurations and Oxidation States– transition metal compounds have magnetic properties.

• Note all oxidation states for metals are positive.• The 2+ oxidation state is common because it

corresponds to the loss of both s electrons. (Exception: Sc where the 3+ oxidation state is isoelectronic with Ar.)

• The maximum common oxidation state is +7 for Mn.• For the second and third series, the maximum

oxidation state is +8 for Ru and Os (RuO4 and OsO4).

Transition MetalsTransition MetalsMagnetismMagnetism• Magnetism provides important bonding information.• There are three types of magnetic behavior (shown

here in order):– Diamagnetic (no atoms or ions with magnetic moments);

– Paramagnetic (magnetic moments not aligned outside a magnetic field);

– Ferromagnetic (coupled magnetic centers aligned in a common direction).

• Electron spin generates a magnetic field with a magnetic moment.

Transition MetalsTransition MetalsMagnetismMagnetism

Transition MetalsTransition MetalsMagnetismMagnetism• When two spins are opposing the magnetic fields

cancel (diamagnetic).– Diamagnetic substances are weakly repelled by external

magnetic fields.

• When spins are unpaired, the magnetic fields do not cancel (paramagnetic).

• Generally, the unpaired electrons in a solid are not influenced by adjacent unpaired electrons. That is, the magnetic moments are randomly oriented.

• When paramagnetic materials are placed in a magnetic field, the electrons become aligned.

Transition MetalsTransition MetalsMagnetismMagnetism• Ferromagnetism is a special case of paramagnetism

where the magnetic moments are permanently aligned (e.g. Fe, Co and Ni).

• Ferromagnetic oxides are used in magnetic recording tape (e.g. CrO2 and Fe3O4).

Chemistry of Selected Transition MetalsChemistry of Selected Transition MetalsChromiumChromium• In the absence of air, Cr reacts with acid to form a

solution of blue Cr2+:

Cr(s) + 2H+(aq) Cr2+(aq) + H2(g)

• In the presence of air, the Cr2+ readily oxidizes to Cr3+:

4Cr2+(aq) + O2(g) + 4H+(aq) 4Cr3+(aq) + 2H2O(l)

• In the presence of Cl-, Cr3+forms the green Cr(H2O)4Cl2

+ ion.

Chemistry of Selected Transition MetalsChemistry of Selected Transition MetalsChromiumChromium• In aqueous solution, Cr is usually present in the 6+

oxidation state.

• In base chromate, CrO42-, is the most stable ion.

• In acid dichromate, Cr2O72-, is the most stable ion.

• Chromate is a much darker yellow than dichromate.

IronIron• In aqueous solution iron is present in the +2 (ferrous)

or +3 (ferric oxidation states).• Iron reacts with nonoxidizing agents to form Fe2+(aq).• In the presence of air, Fe2+ is oxidized to Fe3+.

Chemistry of Selected Transition MetalsChemistry of Selected Transition Metals

IronIron• As with most metal ions, in water iron

forms complex ions, Fe(H2O)6n+.

• In acidic solution Fe(H2O)63+ is stable, but

in base Fe(OH)3 precipitates.

• If NaOH is added to a solution of Fe3+(aq) and the brownish Fe(OH)3 precipitate is formed.

Chemistry of Selected Transition MetalsChemistry of Selected Transition MetalsCopperCopper• In aqueous solution copper has two dominant

oxidation states: +1 (cuprous) and +2 (cupric).• Cu+ has a 3d 10electronic configuration.• Cu(I) salts tend to be white and insoluble in water.• Cu(I) disproportionates:

2Cu+(aq) Cu2+(aq) + Cu(s)• Cu(II) is the more common oxidation state.

• Blue vitriol is CuSO4.5H2O.

Chemistry of Selected Transition MetalsChemistry of Selected Transition MetalsCopperCopper• In aqueous solution, four water molecules are

coordinated to the Cu and one is hydrogen bonded to the sulfate.

• Water soluble copper(II) salts include Cu(NO3)2, CuSO4, and CuCl2.

• However, Cu(OH)2 is insoluble and can be precipitated by adding NaOH to a solution containing Cu2+ ions.

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