Metals and Metallurgical Principles.pptx

Metals and Metallurgical Principles
ORE METAL MATERIALS

• An element is a chemical substance that cannot be broken down into other
substances by chemical reactions.
• The basic particle that constitutes a chemical element is the atom.
• Elements are identified by the number of protons in their nucleus, known as the
element's atomic number.
• Elements are classified on three categories: Metals, Non-metals and Metalloids.
• Metals are elements that are generally hard, shiny, malleable, ductile, and fusible,
with high electrical and thermal conductivity, commonly used in a wide range of
industrial and everyday applications due to their versatile properties. Eg. Iron,
copper, gold, silver ,etc.
Metals and Metallurgical
Principles
INTRODUCTION

• Non-metals are elements characterized by their lack of metallic properties,
typically being poor conductors of heat and electricity, and often found as
gases, liquids, or brittle solids, playing key roles in various chemical processes
and biological systems. Eg. Oxygen. Hydrogen, carbon, etc.
• Metalloids are elements that have properties intermediate between metals and
non-metals, often being semiconductors and found in applications such as
electronics and alloys due to their unique ability to conduct electricity better
than non-metals but not as well as metals.
• Metalloids are also called semi-metals as they are poor conductors of heat and
electricity. Eg. Arsenic, bismuth, beryllium, etc.
Principles
Introduction (Contd.....)

• The process of extracting a metal from its ore and refining it, is called
metallurgical process or simply as metallurgy.
• The actual process of extraction of a metal from its ore depends upon the nature
of the ore and the metal.
• There is no universally operational method for the extraction of metals. Certain
common steps however, are involved in all metallurgical processes.
• Metallurgy comprises of 3 steps:
a. Concentration of Ore
b. Isolation of metal from the concentrated Ore
c. Purification of the metal
Principles
METALLURGY

Principles
• Some of the types of Metallurgical processes are as follows:
a. Pyrometallurgy (pryo means heat):
Pyrometallurgy is a branch of metallurgy that involves the extraction and
purification of metals through high-temperature processes. It involves heating
ores to separate the metal from other materials through chemical reactions. This
method typically includes steps such as roasting, smelting, and refining to
separate metals from their ores.
b. Electrometallurgy :
Electrometallurgy is the method of extraction of metals from the pre by
electrolytic reduction in molten state or in aqueous solution. Electrowinning is a
process that extracts metal from a solution by using an electric current to deposit
the metal onto an electrode. It is commonly used to recover metals like gold,
silver, and copper.Generally applied for alkali and alkaline earth metals.

Principles
c. Hydrometallurgy:
Hydrometallurgy is the method of extraction of metals from the ore by
dissolving the ore with suitable reagent and subsequent precipitation of the metal
by other active electropositive metals. This method is used for the extraction of
Ag, Au from their ores which are less reactive.
For example, silver ore is leached with a dilute solution of sodium cyanide. Silver
ore is dissolved forming a complex (Sodium argentocyanide). The solution is
further treated with zinc to get the precipitate of silver.
Ag2S + 4NaCN 2Na[Ag(CN)2] +Na2S
sodium argentocyandide
2Na[Ag(CN)2] + Zn Na2[Zn(CN)4] +2Ag
sodium tetracyanozincate

Principles
Minerals:
Minerals are naturally occurring, inorganic solid substances with a specific chemical
composition and crystalline structure. They are the building blocks of rocks and can have
various properties such as color, hardness, and luster. All the Minerals are ores but all ores
are not minerals. For eg. Clay contains aluminium but it is not an ore of aluminium.the
process of taking out a minerals from mine is called mining.
Ores:
Ores are naturally occurring rocks or sediments from which valuable minerals or metals
can be extracted profitably. They contain high concentrations of specific minerals or metals
and are mined for industrial use, such as copper, gold, and iron ores.
All minerals are not suitable for extractions of metals due to:
a. Minerals may not be deposited in a large area.
b. Metal may be present in low percentage by composition in the given mineral
c. Impurities present in the minerals may not be easily removed and extraction of metal
may be difficult.

Principles
State of Minerals:
a. Native state: Elements in their native state are found in nature in their pure, un
combined form. Examples include gold, silver, and platinum, which are often found as
native metals due to their low reactivity and ability to occur in their metallic form.
These generally have alluvial impurities like sand, clay, etc.
b. Combined state: Elements in their combined state are found as part of compounds or
minerals. Most elements are found in this form, bonded with other elements. For
instance, iron is commonly found in compounds such as hematite (Fe O ) and
₂ ₃
magnetite (Fe O ), and oxygen is found in water (H O) and various minerals. Complex
₃ ₄ ₂
ores are those ores containing two or more metals, as lead zinc whereas Simple ores
contain only one metal.

Principles Some common ores found in Nepal
Mineral Location
Nickel
Bamangaun (Dadeldhura), Beringkhola (Ilam), Bauligad (Bajhang) Khoprekhani
(Sindhuli)
Bismuth Dadeldhura and Baraghare and Mandukhola area in Makawanpur district
Tungsten Dadeldhura and Makwanpur
Iron
Dhaubadi (Nawalpur), Lalitpur (Phulchoki), Thoshe (Ramechhap), Labdhikhola
(Tanahu), Jirbang (Chitwan), and Dhuwakot (Parbat)
Silver Ganesh Himal (Rasuwa), Barghare (Makawanpur),Bering Khola (Ilam)
Zinc
Ganesh Himal area (Rasuwa), Phakuwa (Sankhuwashbha), Libangkhairang,
Damar, and Baraghare (Makawanpur), Pangum (Solukhumbu), Salimar valley
(Mugu/Humla),Phulchoki (Lalitpur), Sishakhani and Khandebas (Baglung),
Duwakot (Parbat) Bhalu Danda (Dhading), Kholakhani (Taplejung)
Copper Gyazi (Gorkha), Okharbot (Myagdi) and Wapsa (Solukhumbu)
Cinabar Khimti River
Gold
Mahakali, Chamaliya, Jamari gad, Seti, Karnali, Bheri, Rapti, Lungrikhola and
Phagumkhola (Rolpa), Kaligandaki, Myagdikhola, Modi, Madi, Marsyandi, Trishuli,
Bhudhi Gandaki, and Sunkoshi
Tin Meddi and Genera (Dadeldhura) and Mandhukhola area (Makawanpur)
Cobalt Netadarling and Tamghas (Gulmi) and Samarbhamar (Arghakhanchi)

Principles
Gangue or Matrix, Flux and Slag
• Gangue refers to the worthless minerals or materials in an ore deposit that are separated
from the valuable minerals during the extraction process.
• Flux is a substance added during the smelting or refining process to facilitate the removal
of impurities and to help the formation of slag.
Flux + Matrix Slag
• The types of flux are:
a. Acidic Flux:
Contains substances like silica or alumina that react with basic impurities to form a
slag. It is used in processes such as the extraction of iron from its ore.
b. Basic Flux:
Contains substances like lime (calcium oxide) that react with acidic impurities to form
a slag. It is commonly used in processes like steelmaking.

c. Neutral Flux:
Does not significantly alter the acidity or basicity of the slag and is used to maintain the
desired properties of the molten metal. Examples include borax and certain fluorides.
d. Reducing Flux:
Contains substances that remove oxygen from the metal ore or slag, helping to prevent
oxidation. It is used in processes where oxidation needs to be controlled.
• Slag is a by product of metal smelting that consists of the non-metallic residue left after
the extraction of the desired metal from ore.
Principles
Types of flux.(contd…)

Principles
Alloy
Alloy is a metal made by combining two or more elements, typically metals, to
achieve desirable properties such as increased strength, hardness, or resistance to
corrosion. Examples include stainless steel (iron, chromium, and nickel) and
aluminum alloys (aluminum with elements like copper or magnesium).
Alloys’ chemical properties remain the same as component elements whereas
physical properties changes.

Principles
Some important Alloys, composition and their usages

Classification of Alloys
Based on Metal Content(Iron):
a. Ferrous Alloys: Alloys containing iron as the primary metal or major metal are called
Ferrous Alloys.
Example: Steel (iron and carbon), Cast Iron (iron, carbon, and silicon).
b. Non-Ferrous Alloys: Alloys do not containing iron as the primary metal.
Example: Bronze (copper and tin), Brass (copper and zinc).
Uses of Alloying:
Enhanced Strength: Alloying improves the mechanical strength and hardness of metals,
making them suitable for structural applications.
Example: High-Strength Low-Alloy (HSLA) Steel is used in construction and
automotive industries due to its superior strength.
Improved Corrosion Resistance: Alloying can increase a metal's resistance to corrosion
and oxidation, extending its lifespan and reducing maintenance.
Example: Stainless Steel, with chromium added, is used in kitchen utensils and medical
instruments due to its resistance to rust and corrosion.
Principles

Uses of Alloying:
Better Wear Resistance: Alloys can be designed to withstand wear and abrasion, making
them ideal for high-friction environments. Example: Bronze is used in bearings and bushings
because of its durability and resistance to wear.
Enhanced Conductivity: Alloying can modify a metal's electrical or thermal conductivity to
suit specific applications. Example: Brass, with its improved electrical conductivity, is used
in electrical connectors and terminals.
Improved Ductility and Malleability: Alloying can enhance a metal's ability to be shaped
or deformed without breaking. Example: Aluminum Alloys, such as those used in aerospace,
offer good ductility and are lightweight, making them suitable for aircraft components.
Temperature Stability:Some alloys are designed to retain their properties at high or low
temperatures. Example: Inconel alloys, used in jet engines and industrial reactors, maintain
strength and resist oxidation at high temperatures.
Principles

Specific Functional Properties of Alloying:
Alloying can impart unique properties required for specialized applications.
Example: Amalgams, such as those used in dental fillings, combine mercury with other
metals for their specific hardness and malleability
Principles
Amalgams:
Amalgams are alloys that include mercury combined with another metal or metals. They have
been used for various purposes ,one of the most notable uses being dental amalgams for
filling cavities. some examples are
a. Sodium-Amalgams (Na-Hg) b. Silver-Amalgams (Ag-Hg)
c. Zinc-Amalgams(Zn-Hg) d. Copper-Amalgams (Cu-
Hg)
Almost all metals form amalgam with mercury except some metals like iron, platinum,
tungsten and tantalum.
Dental amalgams are typically made from a mixture of mercury (about 50%) and a powdered
alloy composed of silver, tin, and copper. Other metals like zinc, indium, or palladium can

Properties: Amalgams are known for their durability, strength, and ability to withstand the
forces of chewing. They have good compressive strength and are relatively easy to manipulate
and shape.
Some Uses are:
Dental Amalgams: Used for over a century, these fillings are known for their longevity and
effectiveness in restoring teeth. They are particularly useful in posterior teeth (molars) where
chewing forces are greatest.
Industrial Applications: Amalgams are used in the extraction of gold and silver from ore.
Mercury amalgamates with these metals, making it easier to separate them from other
materials.
Principles
Amalgams:

Principles
a. Crushing and Pulverization:
Crushing: The process of reducing large chunks of materials into smaller pieces using
mechanical forces, typically involving crushers.
Process:
Feeding: Large materials, such as rocks or ores, are fed into the crusher.
Crushing: The crusher applies compressive forces to break the materials into smaller pieces.
Output: The resulting smaller pieces are then ready for further processing or use.
Pulverization: The process of grinding materials into fine powders or dust using mechanical
forces, typically involving mills.
Process:
Feeding: Smaller pieces of material from the crushing process are fed into the mill.
Grinding: The mill applies mechanical forces such as impact, compression, and attrition to
grind the material into fine powders.
Output: The resulting fine powders are then ready for further use or chemical processing.
General Principles of the extraction of Metals

Principles
b. Concentration:
Removing unwanted materials, such as sand and clay, from ore is referred to as concentration,
dressing, or benefaction. This process involves multiple steps, which are chosen based on the
differences in physical properties between the metal compounds and the gangue (waste
materials). The choice of methods also depends on factors like the type of metal, available
technology, and environmental considerations. Here are some key procedures used in this
process.
a. Gravity Separation:
The process of separating ore from gangue based on their differing gravities is known
as gravity separation. This method involves washing powdered ore with an upward
stream of running water, which carries away the lighter gangue particles while leaving
the heavier ore particles behind. The lighter gangue, being less dense, is washed out
and discarded, while the denser ore particles remain, allowing for the concentration of
the desired material. This technique is valued for its simplicity and environmentally
friendly nature, as it primarily uses water for separation, though its effectiveness
depends on the significant difference in density between the ore and gangue, and it
requires considerable water resources.

Principles
Powdered

Principles
b. Magnetic Seperation: This method uses
differences in magnetic properties to
separate ore from gangue. If either the ore
or the waste material can be attracted by a
magnet, magnetic separation is used. For
example, this is done with iron ores. The
crushed ore is moved on a conveyor belt
that passes over a magnetic roller, which
pulls out the magnetic particles and
separates them from the non-magnetic
ones.
Magnetic separation is used to extract metals that exhibit magnetic properties. This technique is
commonly employed to separate iron from its ores, such as magnetite, due to its strong
magnetic nature. It is also utilized for chromium ores like chromite and tantalum ores

Principles
c. Froth Floatation Method:
This method is used to remove gangue
from sulfide ores. The process starts by
creating a suspension of powdered ore
mixed with water, to which collectors
and froth stabilizers are added.
Collectors, such as pine oils, fatty acids,
or xanthates, make the mineral particles
less likely to wet with water, while froth
stabilizers like cresols or aniline help
maintain the froth. The oils make the
mineral particles wet, whereas the
gangue particles remain wet with water.

A rotating paddle agitates the mixture and introduces air, creating froth that carries the mineral
particles. This froth is then skimmed off, dried, and the ore particles are recovered. In some
cases, two sulfide ores can be separated by adjusting the oil-to-water ratio or using
depressants. For example, sodium cyanide (NaCN) can be used as a depressant to prevent zinc
sulfide (ZnS) from rising with the froth while allowing lead sulfide (PbS) to be collected in the

Principles
d. Leaching :
Leaching is a chemical process that extracts valuable metals or minerals from ores by
dissolving them in a solvent. The material is prepared, mixed with a solvent that dissolves the
desired components, and then the solution is separated from the residue or precipitate to
recover the metals. This method is used in mining, environmental clean up, and agriculture
but requires careful handling of potentially toxic solvents to manage environmental and
health risks.
For Eg. Bauxite(Al2O3.2H2O) ore is concentrated by leaching it with a 45% caustic soda
solution and forms soluble sodium meta aluminate. It is also given by Baeyers method.
Al2O3.2H2O + 2NaOH 2NaAlO2+ 3H2O
This solution is filtered to remove insoluble impurities like silica and other oxides. The
filtrate is diluted with water and agitated for several hours to get precipitate of aluminium
hydroxide.
NaAlO2+ 2H2O Al(OH)3 + NaOH
The precipitate is seperated and ignited to get Al O .

Principles
c. Conversion of concentrated ores into reducible form:
This process involves the conversion of metals ore in to reducible form(Metal Oxide). It is
easy to obtain metal from their oxides so this process is carried out. This step can be done by
two processes:
a. Calcination: The concentrated ore obtained is heated strongly in the absence of air or a
limited supply of air below its melting point. This process is called Calcination process.
This process is suitable for only oxide or hydroxide or carbonate ores.
b. Roasting: It is the process in which the concentrated ore obtained is heated strongly in
the presence of air or a limited supply of air below its melting point. This process is only
suitable for sulphide ores.
The changes during this processes are:
i. It removes volatile impurities like CO2, SO2, moisture, etc.
ii. It directly removes water.
iii. The ore becomes porous and easy to handle in succeeding steps.
These processes are done in a special type of vessel known as reverberatory furnace.
In some conditions Calcination is carried out in an open-hearth furnace, shaft furnace,
blast furnace, etc.

Principles

c. Conversion of concentrated ores into Metal form:
Reduction process is used for converting metal – oxides into metal. Reduction of the metal
oxide usually involves heating it with some other substance acting as a reducing agent (C or
H2 or Al or CO or even another metal). The reduction reaction chosen depends on the
chemical reaction or reactivity of metals. Generally reduction by heat, chemical reduction or
electrolytic reduction processes are utilized.
I. Carbon Reduction (Smelting):
In this process the reducing agent (e.g., carbon) combines with the oxygen of the metal
oxide. Oxides of Zn, Fe, Ni, Sn, Pb are reduced by heating them with carbon. Metal – oxide
is mixed with coke, a source of carbon, and heated in a furnace. The heating process is
carried above the melting point of the metal. Carbon reacts with oxygen and free metal is
obtained.
Principles

Carbon Reduction (Smelting)(Contd…)
Some metal oxides get reduced easily
while others are very difficult to be
reduced (reduction means electron gain
or electronation). In any case, heating
is required. To understand the variation
in the temperature requirement for
thermal reductions (pyrometallurgy)
and to predict which element will suit
as the reducing agent for a given metal
oxide (MxOy ), Gibbs energy
interpretations are made.
Principles
Reduction in Blast Furnace

Principles
ii. Reduction by Al:
This process is called the Thermite process. Al is more reactive than carbon. Some metal –
oxides that cannot be reduced by coke are reduced by Al. Al itself attracts oxygen from the
metal – oxide and becomes aluminum oxide and this frees the metal. Mn(Manganese), Sn(Tin)
and Cr(Chromium) metal oxides are extracted and reduced by Al.

The mixture of roasted or calcined ore and aluminium is called thermite is mixed with
barium peroxide and suitable flux in a crucible. Burning Magnesium is introduced to crucible
for ignition, large amount of energy is released. Metallic oxide is reduced to metal in molten
form and collected in bottom.
Principles

Principles
iii. Reduction by electrolysis:
Some consideration for this process are:
a. Reactivity of the Metal: Choose electrolytes and conditions to prevent re-oxidation and
side reactions based on metal reactivity.
b. Electrodes: Select inert, conductive materials like graphite, platinum, or coated metals to
avoid degradation and participation in the reaction.
c. Addition of Flux: Use fluxes to enhance conductivity, remove impurities, and ensure
smooth deposition of the reduced metal for higher purity and quality.
Highly reactive metal – oxides and metal – chlorides are not easy to be reduced by chemical
reactions. Metals such as Na, K, Mn, Ca have to be freed from their ores by electrolytic
processes. These metals are so reactive that they themselves are powerful reducing agents.
Molten metal – oxides or chlorides form the electrolyte in an electrochemical cell. The
cathode of the cell provides the electrons needed for the metal to free itself from the metal –
oxide or metal – chloride bonds. In the electrolysis, metals atoms get deposited on the
cathode electrodes, which then have to carefully removed and stored.

iii. Reduction by heat (Self Reduction):
Metals that are unreactive, like Hg, can be reduced from their ores by heating them. Mercury
ore cinnabar is actually mercury sulphide. This can be heated at 300°C so that S is removed
as SO2 and HgO is obtained. Hg is a very unreactive metal. HgO dissociates into Hg and
oxygen soon.
Principles

c. Refining:
A metal extracted by any method is usually contaminated with some impurity like trace
amount of others metals, unreduced oxides, residual slag or flux and non-metals like carbon,
silicon, etc. For obtaining metals of high purity, several techniques are used depending upon
the differences in properties of the metal and the impurity. Some of them are listed below.
(a) Distillation (b) Liquation (c) Electrolytic refining
(d) Zone refining (e) Poling (f) Oxidation
a. Distillation: This is very useful for low boiling metals like zinc and mercury. The impure
metal is evaporated to obtain the pure metal as distillate. Distillation purifies metals by
heating them until they vaporize, separating them from impurities with higher boiling points
that remain in the furnace. The metal vapor is then directed into a cooler area where it
condenses back into a liquid or solid form, which is collected as the purified metal.
Impurities are left behind in the distillation apparatus, and the process can be repeated to
achieve higher purity levels. This method is especially effective for metals with significantly
different boiling points from their impurities, such as zinc, mercury, and cadmium.
Principles

(b) Liquation: In this method, a
low melting metal like tin can be
made to flow on a sloping surface.
In this way it is separated from
higher melting impurities. This
method is used when the metal to be
extracted has lower melting point
than the impurties or gangue.
Principles
In this method:
• The crude or impure metal obtained after extraction process is placed on the sloping hearth
of a reverberatory furnace and heated in the absence of air slightly above the melting point
of the metal.
• Metal melts and flows away leaving non-fusible impurities (oxides) behind.
• This method is employed for low melting metals like Bi, Sn, Pb, Hg.

(c) Electrolytic refining: In this method, the impure metal is made to act as anode. A strip of
the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath
containing soluble salt of the same metal. The more basic metal remains in the solution and the
less basic ones go to the anode mud. This process is also explained using the concept of
electrode potential, over potential, and Gibbs energy which you have seen in previous sections.
Principles

Principles
As shown in the figure above :The reactions involved are:
Anode: M → Mn+
+ ne–
Cathode: Mn+
+ ne– → M
Eg. Copper is refined using an electrolytic method. Anodes are of impure copper and pure
copper strips are taken as cathode. The electrolyte is acidified solution of copper sulphate
and the net result of electrolysis is the transfer of copper in pure form from the anode to the
cathode:
Anode: Cu → Cu2+
+ 2 e–
Cathode: Cu2+
+ 2e– → Cu
Impurities from the blister copper deposit as anode mud which contains antimony, selenium,
tellurium, silver, gold and platinum; recovery of these elements may meet the cost of
refining. Zinc may also be refined this way.

Principles
(d) Zone refining : This method is based on the principle that the impurities are more soluble
in the melt than in the solid state of the metal. A circular mobile heater is fixed at one end of a
rod of the impure metal. The molten zone moves along with the heater which is moved
forward. As the heater moves forward, the pure metal crystallises out of the melt and the
impurities pass on into the adjacent molten zone. The process is repeated several times and the
heater is moved in the same direction. At one end, impurities get concentrated. This end is cut
off. This method is very useful for producing semiconductor and other metals of very high
purity, e.g., germanium, silicon, boron, gallium and indium.

Principles
Poling: Poling is a method used to purify metals that have oxidized impurities. It is typically
used to purify metals like copper or tin that are in the impure form of a copper oxide or tin
oxide. A log of wood which is still green is used to stir the liquid metal.

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