Chemistry

UNIT 2: EXTRACTION OF METALS
Key unit competence
To be able to: Relate the properties of metals to their methods of extraction and uses
and suggest preventive measures to dangers associated with their extraction.
Learning objectives
At the end of this unit , students will be able to:
• Describe the extraction of copper, iron, sodium, tantalum, zinc, wolfram and
aluminium;
• Outline and explain the uses of copper, iron, tantalum, zinc, wolfram, and tin
ore (cassiterite);
• Explain the issues associated with the extraction of metals and preventive
measures;
• Relate the properties of metals to their methods of extraction.

Introductory activity
1. a. Do you know any metal and mineral extracted in Rwanda?
b. If yes, name them?
c. Give the applications of those metal and mineral .
2. Most of the metals are found in nature, not as pure metals, but as
compounds, i.e. combined with other chemical elements. Such metals are
extracted from their compounds using chemical reactions. The following
setup shows one example of a laboratory chemical reaction. Analyse it and
follow the procedure to be able to interpret the results.

  

Procedure
1. Transfer one spatula measure of copper (II) oxide to a hard-glass test-tube.
2. Carefully add one spatula of charcoal powder on top of the copper (II)
oxide without any mixing.
3. Strongly heat these two layers for 5 minutes in a Bunsen flame.
4. Allow the tube to cool and then look closely at where the two powders
meet in the test tube.
Questions
1. Describe the solid copper (II) oxide before heating.
2. Name the gas formed in the reaction.
3. Describe the solid remaining after heating.
4. Name the solid formed in the reaction.
5. Write the word and symbol equations for the reactions.
6. What does this reaction tell you about the relative reactivities of carbon
and copper?
7. Explain why this reaction is a redox reaction.

The chemical substances in the earth’s crust obtained by mining are called
minerals. Minerals, which are source of metal economically needed, are called
“Ore”. The unwanted impurities present in ore are called gangue. A native metal is
any metal that is found in its metallic form, either pure or alloyed, in nature (example:
Gold). The entire process of extraction of metal from its ore is called metallurgy.

Many metals are found in the Earth’s crust as ores. An ore is usually a compound
of the metal mixed with impurities. An ore is any naturally-occurring source of a
metal that you can economically extract the metal from. Most metals exist in in
nature as compounds, usually oxides or sulphides.

Sulphide ores cannot be converted directly into the metal. Instead they must be
converted to the oxide. This is achieved by roasting them in air. Roasting involves
heating of ore in presence of air below melting point of metal in reverberatory
furnace.

Reverberatory furnace, in zinc, copper, tin and nickel production, is a furnace used
for smelting or refining in which the fuel is not in direct contact with the ore but
heats it by a flame blown over it from another chamber. In steel making, this process,
now largely obsolete, is called the open-hearth process.

 

In this process, volatile impurities escape leaving behind metal oxide and sulphur
dioxide (metal sulphide is converted to metal oxide).

This process causes problems because of the large quantity of sulphur dioxide
produced. Sulphur dioxide is one of the principal causes of acid rain; hence SO2 is
one of the air pollutants.
However if the sulphur dioxide can be collected before being released into the
atmosphere, it can be used to make sulphuric acid.

Metals in their compounds are in oxidized form, i.e. have lost electron(s) and bear
a positive charge. In order to get them as metals, they need to gain electrons: this
process or reaction of gaining electrons is called “reduction”. Reduction of metals
can be carried out using a chemical reducing agent such as carbon (coke, charcoal)
or electricity.

When the mineral is dug up, a method must be used to separate the metal from the
rest of the ore. This is called extraction of the metal.

2.1. Relating the properties of metals to their methods of extraction
Activity 2.1
Make a research (in books or internet) in order .to:
1. Find different methods of extraction of metals referring to the reactivity.
2. Explain why the ores have to be concentrated and different ways that can
be used.
2.1.1. Methods of metal extraction according to their properties
A number of methods are used to extract metals from their ores. The best method
to use depends on a number of factors. These factors are based on the properties of the metal.
The main factor here is the reactivity of the metal (the position it takes in the reactivity
series). Let us use the following question method to clarify these factors.
• Will the method successfully extract the metal? This depends on the reactivity
of the metal.
• How much do the reactants cost? Raw materials vary widely in cost.
• What purity is needed, and are the purification methods expensive? Some
metals are not useful unless very pure, others are useful impure.
• How much energy does the process use? High temperatures and electrolysis
use a lot of energy.
• How efficiently, and in what quantities, can the metal be made? Continuous
processes are more efficient than batch processes.
• Are there any environmental considerations? Some processes produce a lot
of pollutants.

Different methods of metal extraction will be considered in this unit. Some examples
are given below:
• Reduction of metal oxides with carbon
Carbon (as coke or charcoal) is cheap. It not only acts as a reducing agent, but it
also acts as the fuel to provide heat for the process. However, in some cases (for
example with aluminium) the temperature needed for carbon reduction is too high
to be economic - so a different method has to be used. Carbon may also be left in
the metal as an impurity. Sometimes this can be removed afterwards (for example,
in the extraction of iron); sometimes it cannot (for example in producing titanium),
and a different method would have to be used in cases like this.
• Electrolysis of the metal ore
This method is used to extract metals which are difficult to reduce by chemical
agents.These metals include aluminium or metals which are difficult to reduce such
as Group 1 and 2 metals.
Reduction of the metal oxide with hydrogen
Hydrogen can be used as a reducing agent, it is also used in purification of cpper.
This is the main method for the extraction of tungsten from its oxide.
Sustainable use of natural resources: As these extraction processes are expensive
and the supply of ore is not infinite, it is essential to recycle the metals as much
as possible. Recycling of metals is one way of conservation and sustainable use of
natural resources.
Metallurgical operations are sources of pollution, water and air pollution. Measures

must be taken to eliminate or at least to minimise that kind of pollution.

2.1.2. Concentrating the ore
Concentrating the ore is also called “Dressing” or “Benefaction of ore”. The ore from
which the metal will be extracted has to be prepared before extraction. Concentrating
the ore is getting rid of as much of the unwanted rocky material as possible before
the ore is converted into the metal.This simply means “Removal of gangue from
ore”. This may be done by chemical or physical means.
• By physical processes
Physical operations use physical techniques that do not change the chemical nature
of the minerals; these techniques are based on physical properties such as: density,
magnetic properties, etc… In many cases, it is possible to separate the metal
compound from unwanted rocky material by physical means.
- Mechanical sorting (Hand picking): this involves use of hands to pick the
gangue and breaking away the gangue using a hammer.
- Magnetic separation: the ore is crushed and a very strong magnet is used to
sort out magnetic materials from non-magnetic materials. This method is for
example used to separate wolframite from cassiterite where cassiterite being
non-magnetic is not attracted by the magnet.
- Washing: the ores are usually denser than the gangue, which may be washed

away in a stream of water on an inclined table. Examples of ores separated in
this way are galena and limestone; cassiterite from silicates.
- Froth flotation method: this process is important in treating many sulphide
ores like galena, zinc blende (zinc sulphide), copper pyrites, etc. Separation is
based on different abilities of mineral and gangue particles to be moistened
by water. During this process, the ore is first powdered and fed into a large
concentration tank containing water and a suitable oil (frothing agents).

                   http://(Source: https://blog.byjus.com/extraction-of-zinc/)

The mixture is agitated by blowing air through at a high pressure. The sulphide ores
rise to the surface in the froth while the gangue sinks to the bottom. The froth is
skimmed off the surface, and an acid is added to break up the froth. The concentrated
ore is filtered and dried.

• By chemical processes.
For example, pure aluminium oxide is obtained from bauxite by a process involving
a reaction with sodium hydroxide solution. Some copper ores can be converted
into copper (II) sulphate solution by leaving the crushed ore in contact with dilute
sulphuric acid for a long time and then copper can be extracted from the copper (II)
sulphate solution.
- Leaching with aqueous solvents: in this method the finely powdered ore is
treated with a suitable reagent that dissolves the ore but not impurities, for
example:
1. Bauxite is crushed and digested with sodium hydroxide solution
2. Zinc ores can be leached with dilute sulphuric acid and electrolysed

- Roasting in air and Calcination: Here the ore is powdered and roasted in air
to drive off the water (for the hydrated ores) and other volatile substances. For
example,
Carbonates decompose to release carbon dioxide.
Roasting: Sulphides release sulphur dioxide gas:
             2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g)
- Calcination: It is a process heating the ore strongly either in limited supply of air
ih the absence in air
              ZnCO₃(s) → ZnO(s) + CO₂(g)
- Smelting is the process by which a metal is obtained, either as the element or
as a simple compound, from its oxide ore by heating beyond the melting point,
ordinarily in the presence of reducing agents, such as coke.
                    CuO + C → Cu +CO

Checking up 2.1
1. What is an ore?
2. What is the difference between an ore and a mineral?
3. Are ores a finite resource?
4. Are ores renewable?
5. When is carbon used for extraction?
6. Name a metal that could be extracted from its ore using carbon.
7. When is electrolysis used for extraction?
8. What do you understand with dressing of ore, smelting, froth flotation and
gangue?
9. Name two metals that can only be extracted by electrolysis.
10. Suggest a reason why iron is extracted using carbon rather than by
electrolysis.
11. State three factors which determine the choice of reduction method
used for the extraction of metals from their ores.
12. Complete with the following words: iron, extracted, crust, gold, native,
elemental, reduced
“Metals come from the Earth’s …….. Some metals like ……. are very unreactive
and are found as ………. in their ………state. Metals such as zinc, lead and
………are found combined with oxygen in compounds. These metals can be
……… using chemical reactions. The metal oxides are ………as oxygen is
removed from the compound”.
13. Why most of metals are produced by reduction method ?

2.2. Methods of extraction of Copper
Activity 2.2
Use the search engine and the library:
1. To find out the name of the two main ores of Copper.
2. To describe the full process in copper metal is extracted from its ores.
3. To demonstrate how copper is useful in our daily life.
We are going to deal with the extraction of copper from its ores, its purification by
electrolysis, and some of its uses.

2.2.1. Extracting copper from its ores
There are two main copper ore types of interest, copper oxide ores and copper
sulphide ores. Both ore types can be economically mined, however, the most
common source of copper ore is the sulphide ore mineral chalcopyrite also known
as copper pyrites, which accounts for about 50 percent of copper production.

Table 2.1: Some main ores of copper

The ores typically contain low percentages of copper and have to be concentrated
by, for example, froth flotation before processing.
The method used to extract copper from its ores depends on the nature of the ore.
Sulphide ores such as chalcopyrite are converted to copper by a different method
from silicate, carbonate or sulphate ores. Copper, Cu, is mainly extracted from the
ore chalcopyrite, CuFeS₂, in a three stage process.

• In the first stage, chalcopyrite is heated with silicon dioxide and oxygen
2 CuFeS₂ + 2 SiO₂ + 4 O₂→ Cu₂S + 2 FeSiO₃ + 3 SO₂
• In the second stage, the copper (I) sulphide is roasted with oxygen at a high
temperature in a reverberatory furnace giving copper (II) oxide.
            Cu₂S + 2 O₂→2 CuO + SO₂
• In the third stage, the copper (II) oxide is reduced by heating with carbon.
            CuO + C → Cu +CO
The end product of this is called blister copper - a porous brittle form of copper,
about 98 - 99.5% pure.

2.2.2. Purification of copper
When copper is made from sulphide ores by the first method above, it is impure.
The blister copper is first treated to remove any remaining sulphur (trapped as
bubbles of sulphur dioxide in the copper - hence “blister copper”) and then cast into
anodes for refining using electrolysis(electrolytic refining).The purification uses an
electrolyte of copper (II) sulphate solution, impure copper anodes, and strips of high purity copper for the cathodes.

The diagram shows a very simplified view of a cell.

               

• Any metal in the impure anode which is below copper in the electrochemical

series (reactivity series) does not go into solution as ions. It stays as a metal and

falls to the bottom of the cell as “anode sludge” together with any unreactive

material left over from the ore. The anode sludge may contain valuable metals

such as silver and gold.

• Metals above copper in the electrochemical series (like zinc) will form ions at

the anode and go into solution. However, they will not get discharged at the

cathode provided their concentration does not get too high.

Extracting copper from other ores

Copper can be extracted from non-sulphide ores by a different process involving

three separate stages:

Step 1: Reaction of the ore (over quite a long time and on a huge scale) with a

dilute acid such as dilute sulphuric acid to produce a very dilute copper (II) sulphate

solution.

Step 2: Concentration of the copper (II) sulphate solution by solvent extraction.

The very dilute solution is brought into contact with a relatively small amount of an

organic solvent containing a substance which will bind with copper (II) ions so that

they are removed from the dilute solution. The solvent must not mix with water.

Copper (II) ions are removed again from the organic solvent by reaction with fresh

sulphuric acid, producing a much more concentrated copper (II) sulphate solution

than before.

Step 3: Electrolysis of the new solution. Copper (II) ions are deposited as copper

on the cathode. The anodes for this process were traditionally lead-based alloys, but

newer methods use titanium or stainless steel. The cathode is either a strip of very

pure copper or stainless steel.

2.3. Methods of extraction of Iron

Activity 2.3

Using your own research, use the available resources (chemistry books, notebooks,

internet...) to make a succinct summary of:

1. The main ores of iron.

2. The full process involved in the blast furnace while the iron is being

extracted (Include the diagram, the raw materials introduced and the

role of each and the equations of the main reactions occurring).

3. The main different forms of iron, its properties and their respective uses.

The common ores of iron are iron oxides, and these can be reduced to iron by

heating them with carbon in the form of coke. Coke is produced by heating coal

in the absence of air. Coke is cheap and provides both the reducing agent for the

reaction and also the heat source - as you will see below.

2.3.3. Extraction

Three substances are needed to enable extraction of iron from its ore. The combined

mixture is called the “charge”:

• Iron ore

• Limestone (calcium carbonate).

• Coke - mainly carbon.

The charge is placed into the blast furnace. Hot air is blasted through the bottom.

Several reactions take place before the iron is finally produced. This is a continuous

process that needs a high temperature. The high temperature is produced by

burning the carbon in a blast of hot air.

Oxygen in the air reacts with coke to give carbon dioxide.

2.3.5. Different forms of iron

• Pig iron (Cast iron after removing some impurities), an alloy of iron that contains

2 to 4 percent carbon, along with varying amounts of silicon and manganese

and traces of impurities such as sulfur and phosphorus.

- It is made by reducing iron ore in a blast furnace.

- It has a low tensile strength

- It is used in making gates, pipes, lamp posts where high strength is not needed.

• Wrought iron is a soft, ductile, fibrous variety that is produced from a semifused

mass of relatively pure iron globules (haematite) partially surrounded by

slag. It usually contains less than 0.1 percent carbon and 1 or 2 percent slag.

- It is purer than cast iron.

- It is fibrous and tough

- It can be welded (joined by hammering when red hot)

- It is malleable and ductile

- It is used for making sheets, wire and nails.

- Steel is an alloy of iron, carbon, manganese, nickel and vanadium.

2.3.6. Alloys of iron and their uses

Checking up 2.3

1. Iron is extracted using the Blast Furnace

a. What is introduced into the top of the blast furnace?

b. What is the source of heat used in the blast furnace? Write the involved

equation

c. What is the main reducing agent and how is it produced? (give an equation)

d. How is the iron oxide reduced by this reducing agent? (give an equation)

e. What is the other reducing agent and how does it reduce the iron oxide?

(give an equation)

2. The blast furnace is a continuous process. What does this mean and why

is it advantageous?

2.4. Methods of extraction of tin

Activity 2.4

Make a research using the appropriate books and internet to:

1. Find out the main tin ore and state 2 regions in Rwanda where it is mined.

2. Describe the process taken to extract tin from its principal ore.

3. State three properties and uses of tin.

prevent corrosion. In modern times tin is used in many alloys. The first alloy,

used in large scale since 3000 BC, was bronze, an alloy of tin and copper.

Most notably tin/lead soft solders, typically containing 60% or more of tin.

• Another large application for tin is corrosion-resistant tin plating of steel.

• Because of its low toxicity, tin-plated metal is also used for food packaging,

giving the name to tin cans, which are made mostly of steel.

• Due to its resistance to atmospheric corrosion and low melting point, it can be

used to make sheet glass.

Checking up 2.4

1. Name the main ore of tin.

2. Explain the extraction of tin from tin oxide.

3. Tin metal is obtained by removing oxygen from the metal oxide. What

name do we give to this chemical reaction?

4. Explain why tin is said to be very useful.

2.5. Methods of extraction of Zinc

Activity 2.5

Use the library or other search engine to

1. Find out the main ores of zinc.

2. Describe all steps followed to obtain the purified zinc from its sulphide

ore.

3. Demonstrate how zinc is so useful.

 

concentrated zinc sulphide ores settles on the surface leaving behind the impurities

in water.

b. Process of roasting

The concentrated ore is then treated at 900oC in the presence of excess air, on the

base of a reverberatory furnace.This process of heating is called roasting. During

this process, zinc oxide is obtained from the zinc sulphide ore. The equation for this

process is:

Checking up 2.5

1. Recall 2 uses of zinc (refer to unit 1)

2. Describe the extraction of zinc from zinc oxide.

3. Zinc is extracted by removing oxygen from zinc oxide.

a. What name is given to a reaction in which oxygen is removed from a

substance?

b. Explain how oxygen can be removed from zinc oxide to make zinc.

4. Describe different methods by which the impurities in zinc extracted can

be removed.

2.6. Methods of extraction of Sodium

Activity 2.6

You are requested to use all resources about sodium (books, internet, textbooks).

1. Discuss on the importance of sodium and its compound in Chemistry

and in everyday life.

2. Sodium metal does not occur in Free State in nature. Explain why these

statement?

3. Use the available resources to describe the way this valuable metal can be

obtained at large scale (include the mining process, separation methods

from its compounds, reaction equations where necessary, the main

drawbacks that can be encountered during this process and the way to

overcome them).

On industrial scale sodium metal is extracted by “Down’s Process”. Down’s Process is

based on the electrolysis of fused salt (NaCl). This compound is found all around

the world, dissolved in sea water. It is also mined from the ore called rock salt, which

is made up mainly of sodium chloride (NaCl).

2.6.1. Extraction using Down’s Cell

The salt is found mixed with insoluble impurities of sand and bits of rock. Once the

dissolved rock salt has been filtered, we are left with a solution of sodium chloride

in water. You might think that this could be electrolysed to extract the sodium.

However, because sodium is more reactive than the hydrogen in the water,

hydrogen would be produced at the cathode instead of sodium. Instead, sodium

chloride is crystallized out of the solution and melted. The molten sodium chloride

is then electrolysed to extract the sodium metal. This is carried out in a Down’s cell as

shown in figure below.

2.6.4. Uses of sodium

• Molten sodium is used as a coolant in some types of nuclear reactor. Its high

thermal conductivity and low melting temperature and the fact that its boiling

temperature is much higher than that of water make sodium suitable for this

purpose.

• Sodium wire is used in electrical circuits for special applications. It is very

flexible and has a high electrical conductivity. The wire is coated with plastics

to exclude moisture.

• In countries that experience very cold winter, NaCl is spread on the roads to

de-ice the roads.

Checking up 2.6

1. Why is sodium not extracted by carbon reduction process? What is the

method used?

2. What difficulties arise in the extraction of sodium from its ore?

3. Choose the suitable answer. In sodium extraction, fused (molten) NaCl is

used rather than the dissolved (aqueous) NaCl because:

a. Obtaining molten NaCl is easy than obtaining aqueous NaCl.

b. In molten NaCl, the ions are free to move and not in aqueous NaCl.

c. Molten sodium NaCl is an electrolyte and not the aqueous NaCl.

2.7. Methods of extraction of Aluminium

Activity 2.7

Research in library textbook or search engine about aluminium and its extraction

and make a good summary containing the following:

1. The main ores of aluminium.

2. Why aluminium extraction is suitable to be done by electrolytic method

rather than reduction with carbon.

3. The way the main ore is purified to have the pure aluminium oxide

4. The process by which aluminium is extracted from the purified ore

by electrolytic method (include the diagram, reaction equations at

electrodes and the way to solve some difficulties which may arise during

this extraction process)

5. The properties of aluminium which makes it to be very important in our

daily uses and the uses of aluminium.

min (Al, Cu, Mg and Mn). Aluminium alloys are used in aircraft and other transportation

vehicles because of its low density.

• It is used as jewellery because it is a shiny metal, it has a good appearance.

• Resists corrosion because of the strong thin layer of aluminium oxide on its

surface. This layer can be strengthened further by anodising the aluminium.

• It is used for making window frames.

• Aluminium foil is used for wrapping cigarettes, food, etc because it reflects

light.

• Drink cans because it is not toxic.

• Aluminium utensils are extensively used for household purposes.

• Aluminium is used to produce metals such as chromium and manganese from

their ores (aluminothermic process).

2.7.4. Recycling of aluminium

Aluminum is one of the most recycled materials in the world. This is due to high

cost of new aluminium that involves high cost of electricity needed to produce

aluminium. Recycled aluminium cost less in production and constitutes another

way of sustainable management of our natural resources.

• The consumer throws aluminium cans and foil into a recycle bin.

• The aluminium is then collected and taken to a treatment plant.

• In the treatment plant the aluminium is sorted and cleaned ready for

reprocessing.

• It then goes through a re-melt process and turns into molten aluminium, this

removes the coatings and inks that may be present on the aluminium.

• The aluminium is then made into large blocks called ingots.

• The ingots are sent to mills where they are rolled out, this gives the aluminium

greater flexibility and strength.

• This is then made into aluminium products such as cans, chocolate wrapping

and ready meal packaging.

• In as little as 6 weeks, the recycled aluminium products are then sent back to

the shops ready to be used again.

Checking up 2.7

Consider the electrolytic extraction of aluminium.

1. How is aluminium ore called?

2. Explain why cryolithe is added to aluminium oxide

3. Describe the process by which the ore of aluminium is purified.

4. Write half-equations for the reactions at each electrode, and write an

overall equation for the reaction.

5. State what each electrode is made of.

6. Explain why

a. The anodes need to be regularly replaced.

b. The electrolysis of aluminium oxide is expensive.

c. Aluminium is recycled.

7. Give three uses of aluminium and the properties responsible for each use.

2.8. Methods of extraction of Wolfram (Tungsten)

Activity 2.8

1. Visit the nearby mining sites of wolfram and make a field report.

2. Research using internet and some books and make a summary about the

following:

a. The ores of wolfram.

b. Where in Rwanda do we find wolfram?

c. How wolfram extraction differs from that of zinc in terms of reduction.

d. Full description of the extraction process of tungsten from its ore.

e. The main uses of tungsten.

Tungsten ore is a rock from which the element tungsten can be economically

2.8.2. The extraction process

2.8.3. Advantages and disadvantages of the process

a. Advantages:

• It produces very pure tungsten

• Hydrogen is a cheap reagent

b. Disadvantages:

• The energy cost are high

• Using a flammable gas such as hydrogen at high temperatures is very dangerous

2.8.4. Uses

• Tungsten is mostly used in light bulb filaments which heat up to 2000ºC, when

many other metals would vaporise, particularly at the pressures found inside

light bulbs. This is because it has a very high melting point.

• Tungsten has the highest melting point of all metals and is alloyed with

other metals to strengthen them. Tungsten and its alloys are used in many

high-temperature applications, such as arc-welding electrodes and heating

elements in high-temperature furnaces.

• Tungsten carbide (WC) is extremely hard and is very important to the metalworking,

mining and petroleum industries. It is made by mixing tungsten

powder and carbon powder and heating to 2200°C. It makes excellent cutting

and drilling tools, including a new ‘painless’ dental drill which spins at ultrahigh

speeds.

• Calcium and magnesium tungstates are widely used in fluorescent lighting.

Tungsten mill products are either tungsten metal products, such as lighting

filaments, electrodes, electrical and electronic contacts, wires, sheets, rods etc

or tungsten alloys.

• Due to tungsten’s ability to keep its shape at high temperatures, tungsten

filaments are now also used in a variety of household applications, including

lamps, floodlights, heating elements in electrical furnaces, microwave ovens,

x-ray tubes and cathode-ray tubes (CRTs) in computer monitors and television

sets.

• The metal tolerance to intense heat also makes it ideal for thermocouples and

electrical contacts in electric arc furnaces and welding equipment.

Checking up 2.8

1. Nowadays, there is a special reduction method used to extract Tungsten

from its ores.

a. State 2 main ores of tungsten.

b. Write the balanced equation of the reduction reaction of tungsten (II)

oxide.

2. Suggest the reason why ore concentrating plants are always located in

close proximity to the mine.

3. Give 2 widely known physical properties of tungsten and the uses

associated to these properties.

2.9. Methods of extraction of tantalum

Activity 2.9

1. Visit the nearby mining sites of tantalum and make a field report.

2. The picture below shows the miners at work in Rwanda. The metal being

extracted here is very important in modern area. According to Merchant

and Consulting Ltd (2018), Rwanda is the world’s largest producer of this

metal which is called “tantalum”.

Research using any relevant source of information about tantalum:

a. To find out the physical properties of tantalum metal and its main uses.

b. To make a description of the extraction of tantalum from its main ore

tantalite.

Tantalum is a hard, heavy, shiny, grayish-blue metal that is very stable, almost

impervious (impermeable) to air, water and all but a few acids. It has the third highest

melting point of all elements (over 3000 oC), and its primary use is in capacitors for

electronic applications, and for vacuum furnace parts.

It is classified as a “refractory” metal, which means it can sustain high temperatures

and resist corrosion. It is a good conductor of heat and electricity, which makes it

useful in various electronics. Pure tantalum can be drawn into fine wire filament,

which is used to evaporate other metals.

2.9.1. Where tantalum is found

Tantalum is found in hard rock deposits such as granites, carbonites and pegmatites

(igneous rock that consists of coarse granite). The chief tantalum ores are tantalite

[(Fe, Mn)

 

Tantalum is an important component in many modern technologies, and is used in

capacitors for everything from computers to mobile phones.

Despite its importance in the world today, tantalum mining takes place in very few

countries and mining it is difficult. Only four countries produced tantalum in 2016,

and most was mined in the Democratic Republic of Congo (DRC). Rwanda, Brazil

and China were the other top countries for tantalum mining in that year. Sites are

being identified for future development, and existing sites are being evaluated for

expansion.

2.9.2. How tantalum is mined

Tantalum comes from the processing and refining of tantalite. Tantalite is the

common name for any mineral ore containing tantalum. Most tantalum mines are

open pit; some are underground.

The process of mining tantalum involves blasting, crushing and transporting the

resulting ore to begin the process of freeing the tantalum. Before transportation, the

ore is concentrated at or near the mine site, to increase the percentage (by weight)

of tantalum oxide and niobium. The material is concentrated through wet gravity

techniques, gravity, electrostatic and electromagnetic processes.

2.9.3. How tantalum is processed

The tantalum concentrate is transported to the processor for chemical processing.

The concentrate is then treated with a mixture of hydrofluoric and sulphuric acids

at high temperatures. This causes the tantalum and niobium to dissolve as fluorides.

Numerous impurities are also dissolved. Other elements, such as silicon, iron,

manganese, titanium, zirconium, uranium and thorium, are generally present and

processed for other uses.

The concentrate is broken down into a slurry (A slurry is a watery mixture of insoluble

matter such as mud, lime, or plaster of Paris). The slurry is filtered and further

processed by solvent extraction. Using methyl isobutyl ketone (MIBK), or liquid ion

exchange using an amine extract in kerosenes, produces highly purified solutions of

tantalum and niobium. In this way, the tantalum oxide is obtained which is finally

reduced with molten sodium to produce tantalum metal in powder form.

It can then be compacted (as it is for capacitors) to final shape, or may be melted

(and refined) in an electron beam furnace.

2.9.4. Uses for tantalum

• Tantalum is used to make electrolytic conductors, aircraft engines, vacuum

furnace parts, nuclear reactors and missile parts.

• Tantalum is unaffected by body fluids, and is non-irritating, which makes it

useful for surgical appliances.

• It is common in the production of cell phones, personal computers, igniter

chips in car air bags, cutting tools, drill bits, teeth for excavators, bullets and

heat shields.

• Because the metal is an electrical conductor, it is useful in many consumer

electronics, such as microprocessors for plasma televisions.

Checking up 2.9

In pairs, answer the following questions:

1. Where tantalum is found in Rwanda?

2. How tantalum is mined.

3. How tantalum is processed

4. Give 3 uses of tantalum.

5. What is the role of methyl isobutyl ketone (MIBK) in tantalum processing?

2.10. Dangers associated with extraction of metals

Activity 2.10

If you have ever visited a mining site, remember all the processes involved and

suggest all possible common dangers associated with the extraction of metals.

The following are some of the dangers associated with metals extraction. Especially,

these hazards are found in smelting and refining and in addition mining.

1. Injuries

Metal extraction industry has a higher rate of injuries than most other industries.

Sources of these injuries include: splattering and spills of molten metaland slag

resulting in burns; gas explosions and explosions from contact of molten metal

with water; collisions with moving vehicles; falls of heavy objects; falls from a

height,slipping and tripping injuries from obstruction of floors and passageways.

Precautions

Adequate training, appropriate personal protective equipment (PPE) [for example,

hard hats, safety shoes, work gloves and protective clothing]; good storage,

housekeeping and equipment maintenance; traffic rules for moving equipment

(including defined routes and an effective signal and warning system); and a fall

protection programme.

2. Heat illnesses

Heat stress illnesses such as heat stroke are a common hazard, primarily due to

infrared radiation from furnaces and molten metal. This is especially a problem when

strenuous work must be done in hot environments.

Prevention of heat illnesses

Water screens or air curtains in front of furnaces, spot cooling, enclosed airconditioned

booths, heat-protective clothing and air-cooled suits, allowing

sufficient time for acclimatization, work breaks in cool areas and an adequate supply

of beverages for frequent drinking.

3. Pollutions

Mining operations are major contributors to the pollution of our environment such

as: air pollution, water pollution, degradation of landscape, etc.

Exposure to a wide variety of hazardous dusts, fumes, gases and other chemicals

can occur during smelting and refining operations. Crushing and grinding ore in

particular can result in high exposures to silica and toxic metal dusts (containing

lead, arsenic and cadmium, for example). There can also be dust exposures during

furnace maintenance operations. During smelting operations, metal fumes can

be a major problem especially risk of developing respiratory system illness. In

metallurgical operations, the carbon dioxide released has more dangers especially

the global warming because it is a greenhouse gas.

Control

Dust and fume emissions can be controlled by enclosure, automation of processes,

local and dilution exhaust ventilation, wetting down of materials, reduced handling

of materials and other process changes. Where these are not adequate, respiratory

protection would be needed.

Many smelting operations involve the production of large amounts of sulphur

dioxide from sulphide ores and carbon monoxide from combustion processes.

Dilution and local exhaust ventilation (LEV) are essential.

Sulphuric acid is produced as a by-product of smelting operations and is used in

electrolytic refining and leaching of metals. Exposure can occur both to the liquid

and to sulphuric acid mists. Skin and eye protection and LEV are needed.

The extraction of some metals can have special dangers. Examples include fluorides

in aluminium smelting, arsenic in copper, etc.

These processes require their own special precautions

Other dangers

• Glare and infrared radiation from furnaces and molten metal can cause eye

damage including cataracts. Proper goggles and face shields should be worn.

High levels of infrared radiation may also cause skin burns unless protective

clothing is worn.

• High noise levels from crushing and grinding ore, gas discharge blowers and

high-power electric furnaces can cause hearing loss. If the source of the noise

cannot be enclosed or isolated, then hearing protectors should be worn. A

hearing conservation program including audiometric testing and training

should be instituted.

• Electrical hazards can occur during electrolytic processes. Precautions include

proper electrical maintenance with lockout/tagout procedures; insulated

gloves, clothing and tools; and ground fault circuit interrupters where

needed.

• Manual lifting and handling of materials can cause back and upper extremity

injuries. Mechanical lifting aids and proper training in lifting methods can

reduce this problem.

CASE OF RWANDA

According to Rwanda Environment Management Authority (REMA), mining

activities often impact significantly on the environment. For instance, sand

collecting and quarrying are already shown some significant environmental

impacts, including resource depletion, energy consumption, waste generation

and emissions of air pollutants. The dangers to human life and health associated

with mining include the displacement of people, land use changes, dust and

noise pollution.

In fact, the preparation of ores which uses a lot of water constitutes a major

pollutant of stream water in Rwanda. For example, the waters draining the

mining sectors of Rutongo and Gatumba pollute the rivers of Nyabarongo

and Nyabugogo by sediments of clay and sand which they transport over long

distances. It is this considerable mineral load which partly gives them the brown

colour that is characteristic of the rivers in Rwanda. Mining and quarrying

produce massive rejects which appear in nature in the form of enormous lots of

earth and rocks. Erosion from rain water transports the mineral residue towards

the valleys where streams are filled and covered by the residue which may be

toxic to biodiversity.

Checking up 2.10

1. State 5 sources of injuries associated with the extractions of metals

2. Give 3 ways you can prevent from heat illnesses.

3. Describe 2 ways you can control the dangers associated with the

chemicals in extraction of metals.

4. Suggest a way of protecting mining workers against the risk of lung

disease due to dust at their working place?

2.11. Preventive measures associated with metal extractions

Activity 2.11

We already know that there are many dangers associated with the extraction of

metals.

Recommend measures that must be taken to prevent from these dangers (risks).

Effort should be made by mining componies or planned for the future, to eliminate

or minimize the environmental problems associated with metal extractions include:

1. The potential sources of air contaminants should be enclosed and isolated

2. Brief, for any operation related to metal extraction, measures must be

adopted to protect the workers in particular and the environment in

general by:

• Elimination or reduction of air polluting gases.

• Avoiding water and soil pollution.

• Protect the landscape.

• Using cleaner production techniques i.e Minimize sources of pollution and use

of energy.

3. Adopt technology that minimizes wastes produced through process-reengineering/

recycling

Checking up 2.11

1. 1.In extraction of metals, the best and least costly preventive measures

are those taken at the planning stage of a new process of extraction.

Explain the main aspects that should be taken into account.

2. 2.what are the main sources of pollution in metallurgy?

END UNIT ASSESSMENT

1. Which metal is extracted from Bauxite?

a. Tin

b. Tantalum

c. Copper

d. Aluminum

2. Brass is

a. An Element

b. A Compound

c. A Mixture

d. An Alloy

3. Bronze is an alloy of

a. Copper and Zinc

b. Lead and Copper

c. Copper and Tin

d. Barium, Zinc and Iron

4. Which of the following metals is often found in pure state?

a. Copper

b. Iron

c. Gold

d. Aluminum

5. Which metal is extracted from Haematite?

a. Tin

b. Iron

c. Manganese

d. Cadmium

6. Rocks rich in metals with economic value are known as

a. Metalloids

b. Ores

c. Allotropes

d. Slag

7. An alloy is a

a. Compound of three elements

b. Homogeneus mixture of two or more metals

c. Heterogeneous mixture

d. Element in impure form

8. If a metal ore is called "pyrites" then it most probably has

a. Chlorine

b. Oxygen

c. Sulphur

d. Nitrogen

9. Often to prevent corrosion, metals are galvanized by covering them with a

layer of

a. Copper

b. Sodium

c. Zinc

d. Tin

10. What is not true about Tantalum?

a. It is classified as a "refractory" metal

b. Tantalum oxide is reduced with molten sodium to produce tantalum

metal in powder form.

c. Its ore minerals include scheelite

d. It is found in hard rock deposits such as granites, carbonites and

pegmatites

11. Complete with the terms applied in the Extraction of iron from haematite

in industry (Blast Furnace).

a. Raw materials: ___________________________________

A mixture of ___________, __________ and _____________ is added at

the top of the furnace. ________ air is blown into the furnace from the

bottom. A chain of chemical reactions occur:

b. Carbon reacts with oxygen in air to form ______________.

Equation: _______________________________________________

c. The hot carbon dioxide rises in the furnace and is reduced by _________

to form __________. Equation: ____________________________

d. Carbon monoxide is a ____________ agent. It ___________ iron(III) oxide

in haematite to form hot molten ___________.

Equation: ______________________________________________

The hot molten iron is then rum out from the bottom of the furnace.

e. The formula of limestone: ________________

Limestone breaks up into____________ and_______________ when

heated.

Equation: ________________________________________________

f. Calcium oxide helps to remove ___________ (the impurities) to form a

liquid ‘_______’. Equation: ________________________________

12. a. By giving reagents and conditions, state three different methods

of extracting metals starting from their oxides. In each case, write

equation(s) to illustrate the extraction of an appropriate metal.

b. i. Why are metals more usually extracted from their oxides rather than

from any other compound?

ii. State two environmental problems associated with the extraction of metals

from their oxides or sulphides and give the chemical responsible for each

problem.

13. a. Give the ores of iron.

b. Explain the extraction of iron from its ores.

14. a. Give 2 or 3 uses of aluminium, copper, zinc, and iron.

b. Give two reasons why the extraction of aluminium is expensive.

15. Tungsten is prepared in a pure form by high temperature reduction of

tungsten (VI) oxide with hydrogen.

a. Construct an equation for this reaction.

b. Suggest why carbon is not used as the reducing agent.

c. Suggest one advantage (other than purity of the product) and one

disadvantage of using hydrogen as the reducing agent on an industrial

scale.

16. Zinc and copper are extracted in the same way as iron (in blast furnace)

but exist as their sulphide ores.

a. How is the sulphide ore converted into an oxide and what is the problem

with this process? (give an equation)

b. Why can aluminium not be extracted in this way?

c. Why can tungsten not be extracted in this way?

17. Copper is a widely used metal. The main ore of copper contains copper

sulphide. Copper can be extracted from copper sulfide in a three stage

process.

a. In the first stage of extraction the copper sulfide is heated in air.

i. Balance the symbol equation for the reaction. Cu2S + O2 → CuO +

SO2

ii. Explain why there would be an environmental problem if the gas from

this reaction were allowed to escape into the atmosphere.

b. In the second stage copper oxide, CuO, is reduced using carbon.

Describe and explain what happens during this reaction.

c. During the third stage the copper can be purified as shown in the

diagram.

i. What is the name of the type of process used for this purification?

ii. Give one use of purified copper.

d. Copper-rich ores are running out. New ways of extracting copper from

low grade ores are being researched. Recycling of copper may be better

than extracting copper from its ores. Explain why.