We use different types of matter in our daily life. These substances are classified into two types, pure and impure. Elements and compounds are pure substances whereas a mixture is an impure substance. Scientists have discovered 118 elements now. These elements are classified as metals, nonmetals, and metalloids on the basis of their properties. Most of the elements are metals among the 118 elements in the modern periodic table whereas some are non-metals and only a few are metalloids. Metals are extracted from ores. Before knowing about the extraction of metals from ores, let’s discuss the properties of metals, nonmetals, and metalloids.
Properties of Metals
The following are the properties of metals.
- Electrical Conductivity: Metals are excellent conductors of electricity. So, metal wires are used for electrical wiring, circuits, and various electronic devices.
- Thermal Conductivity: Metals are also a good conductor of heat. They have high thermal conductivity, hence are used to make utensils and other appliances.
- Malleability: Metals can be easily beaten or rolled into thin sheets without breaking. This property is known as malleability. So, metals are used to make large pipes and other sheets.
- Ductility: Metals also possess the property of ductility, which means they can be drawn into thin wires without losing their integrity. It helps in manufacture of the wire
- Luster: Many metals have a shiny appearance due to their ability to reflect light. This property is called luster. Luster makes metal attractive, so is used for making jewelry.
- High Melting and Boiling Points: Metals generally have high melting and boiling points compared to nonmetals.
Properties of Non-Metals
Following are some of the properties of non-metals.
- Poor Conductors: Nonmetals are poor conductors of electricity. So, non-metals are suitable for making insulators in wires.
- Brittle and Non-Malleable: Nonmetals are usually brittle and cannot be used to make thin sheets or modify according to usage.
- Low Density: Nonmetals typically have lower densities compared to metals. So, most of the nonmetals float on water.
- Dull Appearance: Nonmetals usually have a dull or non-lustrous appearance. They do not reflect light and don’t have luster properties.
- Low Melting and Boiling Points: Nonmetals generally have lower melting and boiling points compared to metals.
Properties of Metalloids
Following are some of the properties of metalloids.
- Semiconductivity: Metalliods can conduct electricity to some extent but not as effectively as metals. Their electrical conductivity can be controlled or modified by factors such as temperature or the presence of impurities, making them essential in electronic devices and semiconductor technology.
- Brittle and Hard: Metalloids generally have a brittle and hard nature, similar to nonmetals. While they may possess metallic luster, they lack the malleability and ductility characteristic of most metals.
- Semi-Metallic Luster: Metalloids exhibit a semi-metallic luster, which means they can appear shiny like metals but not as brilliantly reflective.
In this article, we will discuss how metals are found in nature and how these metals can be purified.
Minerals
Almost all metals, except some, are found in the form of compounds on the earth’s crust. These elements and compounds which are found naturally are called minerals. Minerals are the sources of metals. The rocks found on the earth’s surface are mainly made of metallic and nonmetallic matter. Some rocks are made of one or more types of minerals. Nonreactive metals like gold, silver, etc are found in a pure state in nature whereas reactive metals like sodium, potassium, calcium, iron, etc are found in the form of compounds. Almost all minerals are inorganic, pure, solid, and crystalline in nature. In this way, the pure, solid, and crystalline compounds found in nature are called minerals. They have a fixed chemical formula. The earth’s crust is composed of about 90% of silicate minerals. Besides this, sulfide, oxide, carbonate, sulfate, and phosphate ores are also found on it. Minerals like hematite, cuprite, granite, limestone, talc, red clay, coal, etc are found in different parts of Nepal. Dang, Salyan, Rolpa, Gulmi, Pyuthan, Lalitpur, Palpa, Nawalparasi are some places where minerals are found in Nepal.
Ore
A lot of impurities are found in the ores obtained from the mines. Metals can be obtained from these ores only after removing these impurities.
The process of removing impurities from the ores depends upon the physical and chemical properties of the substances found in them.
Different amounts of metals are found in different minerals. Some minerals contain more amounts of metals from which the metals can be extracted easily and economically whereas some minerals contain less amount of metals and thus metals cannot be extracted easily and economically from them. The mineral from which a metal can be extracted in a large amount at a low cost is called the ore of that metal. The minerals from which a metal cannot be taken out easily are not ores. The metals used in our daily life are obtained from different ores.
Some Ores of Iron
Some ores of iron are as follows
- Hematite (Fe2O3)
- Magnetite (Fe3O4)
- Siderite (FeCO3)
- Limonite (2Fe2O3.3H2O)
- Iron Pyrite (FeS2)
Among them, hematite is the chief ore of iron. It contains a maximum amount of iron (about 75%)
Some Ores of Alumunium
Some of the ores of aluminum are given below
- Bauxite (2Al2O3.2H2O)
- Cryolite (Na3 AlF6)
- Corundum (Al2O3)
Among these ores, Bauxite is the chief ore of aluminum which contains about 40-60% of aluminum.
Some Ores of Copper
Some of the ores of copper are as follows:
- Chalcocite or Copper Glance (Cu2S)
- Copper Pyrite or chalcopyrite (CuFeS2)
- Cuprite (Cu2O)
- Malachite [Cu2 (OH)2CO3]
Copper Pyrite or chalcopyrite is the main ore of copper which contains about 34.5% of copper.
Some Ores of Silver
Some of the ores of silver are as follows.
- Argentite (Ag2S)
- Horn Silver (AgCl)
- Ruby Silver (Ag2Sb2S3)
- Silver Copper glance (Ag(Cu)2S)
Among these, the chief ore of silver is argentite which consists of about 87% of silver.
Some Ores of Gold
Gold is found in a pure state in nature or the ores of gold contain it in pure form. Gold is a nonreactive metal so it is found in a pure state. It is found mainly in rocks and alluvial soil formed from rocks.
Metallurgy
Metallurgy is the process involved in the extraction of pure metals from their ores. Some of the processes involved in the metallurgy process are.
Mining
For extracting metals, the ores of the metals are first taken out from their mines by digging into the earth’s surface. This process of extracting useful substances and minerals from the earth’s geological surface is called mining. Mining is done to take out coal, petroleum, gold, and ores of different metals from the Earth’s crust. Then metals are extracted from their ores through different steps.
Metallurgy is the science that deals with the properties, production, and purification of metals. It also includes the stepwise extraction process of metals from their respective ores.
General Steps of Metallurgy
These are some of the general steps of metallurgy.
Grinding
This is the first step of metal extraction. The process of crushing the ores into small particles form with the help of a roller of the machines is called grinding.
Concentration
The grounded or crushed ores contain impurities like mud, sand, rocks, etc. which is known as gangue. So these impurities must be removed first. Concentration is done to remove the impurities from the ores. Thus the process of removing the impurities from the ores thereby increasing the percentage of metals in them is called concentration. A specific method is used to remove these impurities from the ores according to their properties. For example, if the density of ore and impurities is different then the hydraulic or gravity separation method is used. Similarly, magnetic separation is used if one of them is magnetic and the other is a non-magnetic substance. If either ore or impurities are hydrophilic or hydrophobic, a froth floatation process is used to concentrate the ore.
Activity
Use of the magnetic method to separate the mixture of magnetic and non-magnetic substances.
Materials required: Iron dust, aluminum dust, sand, and a magnet
Method/Procedure: Make a mixture of iron dust, aluminum dust, and sand. Bring a magnet near the mixture.
Observation
What do you see? Why does it happen?
In this way, the magnet attracts iron dust (magnetic substance) but does not attract aluminum, and sand (non-magnetic substances) and they get separated.
Conclusion
Hence the mixture of magnetic and non-magnetic substances can be separated by a magnetic method using a magnet.
Oxidation
It is easier to obtain the metals from their oxides, so the concentrated ores are changed into metal oxide. There are two processes for the oxidation of metals.
a. Roasting
It is the process of strongly heating the ore to its oxides by passing air or in the presence of oxygen. This process is done for the non-oxide ores. Generally roasting is done to convert sulphide ores to their oxide ores. For example, Zinc sulfide (ZnS) is converted to Zinc oxide (ZnO) by the process of roasting.
b. Calcination
It is the process of strongly heating the ores to their oxides in the absence of air or without passing oxygen. Calcination is done to convert carbonate ores to their oxides. For example, calcium carbonate is converted to calcium oxide by using a calcination process.
Reduction
It is the process of removing oxygen from the metal oxide. The metal oxides like copper oxide, lead oxide, and iron oxide are treated with reducing agents like carbon, carbon monoxide, hydrogen, etc. which remove oxygen from these metal oxides.
But zinc oxide can be reduced by carbon only. Silver oxide and mercury oxide are unstable and they are reduced when heated. The oxides of reactive metals like sodium, potassium, calcium, magnesium, aluminum, etc. are very stable and they can be reduced only by the electrolysis method.
Smelting
After oxidation, metal oxides are reacted with reducing agents like carbon, coke, or hydrogen above the melting point of the metals. In this process, metals are separated from their oxides in the molten form, and the remaining impurities are separated in the form of gases or slag. This process of heating metals beyond their melting points along with a reducing agent is called smelting.
Refining
The metals obtained after the reduction process may still contain some impurities. So to obtain metals in a pure state, refining is done. Metals can be refined through various processes like distillation, electro-refining, etc. In this way, pure metals can be obtained after refining through various methods.
a. Distillation
In this method, the impurities present in metals are removed by boiling. This process is done when either the metals or impurities would change to vapor when heated. It is used for the purification of metals that possess a low boiling point and get vaporized such as mercury.
b. Electro-refining
Electro-refining is one of the processes of refining the metals obtained from the reduction process. For electro-refining, the electrolysis method is used. This process is used to obtain metals like iron, silver, copper, gold, etc. in a pure state. The metals obtained by this process are about 99% pure. In this method, a voltameter (a vessel to perform electrolysis) is taken and impure metal is connected to the anode (positive terminal of cell) whereas pure metal is connected to the cathode (negative terminal of cell). In this method, one of the salts of the metal to be refined is used as an electrolyte. For example, do the activity of purifying impure copper by the method of electro-refining.
Activity
Purifying impure copper by the method of electro-refining
Materials Required: voltameter, impure copper, pure copper plate, battery, copper sulfate solution, or solution of any other copper salts.
Method:
Take the solution of copper sulfate in the voltameter. Connect impure copper to the positive terminal of the battery and the pure copper plate to the negative terminal of the battery as shown in the figure. Thus making impure copper an anode and pure copper a cathode. Now pass electricity into the voltameter.
Observation
What do you see? Why and how does it happen?
The impure copper plate in the anode erodes and pure copper gets deposited on the cathode.
Conclusion
In this way, we can get pure copper from its impure form through the process of electrolysis.
In conclusion, metals are essential natural resources that are mostly found in the form of compounds called minerals in the Earth’s crust. To obtain pure metals from these minerals, a series of steps in metallurgy are followed. The process involves grinding the ores into small particles, concentrating the ores to remove impurities, and then converting the ores into metal oxides through processes like roasting and calcination. The metal oxides are then reduced using suitable reducing agents, and the metals are extracted in their molten form through smelting. However, the obtained metals may still contain impurities, which are further removed through refining processes like distillation or electro-refining to obtain pure metals.
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