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Occurrence of Metals, Minerals and Ores

  • Last Updated : 20 Oct, 2021

Metals are a crucial element of our existence, even if we don’t realize it. Since the industrial era, we have had a heavy reliance on metals. From construction to jewellery, we use them for everything. But where do we acquire these metals from? Let us look into their occurrence. Before studying the occurrence of metals, let’s first take a look at the reactive series of the metals, as the occurrence of metals is related to the reactivity series of metals.

Why is hydrogen placed in the reactivity series of metals?

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Despite the fact that hydrogen is not a metal, it is included in the reactivity series of metals. This is because, like metals, hydrogen loses electrons and forms the positive ion H+ .

Occurrence of Metals

The earth’s crust is a key source of metals. Metal salts such as sodium chloride and magnesium chloride, among others, are found in seawater. Metals are not found in a free state in nature. As a result, the majority of metals are found in compounds with other elements, referred to as the combined state. The compounds of these metals found in nature are sulphides, oxides, carbonates, chloride, and some other metal compounds. Metals are present in these compounds in the form of positive ions or cations. Only a few metals, such as copper, silver, gold, and platinum, exist in a free state as metals. When a metal is discovered as a free state, it is referred to as being in its “native state.” Copper, silver, gold, and platinum are all found in nature in their native state. Copper and silver metals occur in the free state as well as in the combined state in nature.



Why do some metals occur in a combined state and others in a free state?

Potassium, sodium, calcium, magnesium, and aluminium, which are at the top of the reactivity series, are so reactive that they are never found as free elements in nature. They are always found in a combined state. Metals like zinc, iron, and lead, which are in the middle of the reactivity series, are moderately reactive metals that can also be found in the combined state. 

All of the metals in the reactivity series above copper are only found in nature in form of their compounds. Copper, silver, gold, and platinum are among the least reactive or unreactive metals and are thus found in their free state as metals. Only a small amount of copper and silver are found in a free state. They are generally found as sulphides or oxides in their combined state.

What are Minerals?

A mineral is distinct from synthetic equivalents made in the laboratory by the fact that it must be developed through natural processes. Artificial minerals, such as emeralds, sapphires, diamonds, and other valuable gemstones, are regularly produced in industrial and research facilities and are almost identical to their natural counterparts. A mineral is a single solid substance of uniform composition that cannot be physically divided into simpler chemical compounds, according to its definition as a homogeneous solid. 

Minerals have a regular geometric form and a highly ordered interior atomic structure. Minerals are classified as crystalline solids because of this property. Crystalline solids can express their structured internal framework through a well-developed external form, known as crystal form or morphology, under the right conditions. Solids that do not show such ordered internal arrangement are known as amorphous. The mineral formation can be divided into four groups as given below.

  • Minerals crystallise from a melt in igneous or magmatic rocks.
  • Minerals are formed as a result of sedimentation, a process in which the raw materials are particles from other rocks that have been weathered or eroded.
  • Metamorphic refers to the formation of new minerals at the expense of older ones as a result of changes in temperature, pressure, or both on an existing rock type.
  • Minerals are chemically precipitated from hot solutions within the Earth’s crust in a hydrothermal process.

The first three steps produce a variety of rocks with distinct mineral grains tightly intergrown in an interlocking weave. Hydrothermal and very low-temperature liquids tend to follow fracture zones in rocks, creating open spaces for mineral chemical precipitation. The majority of the exceptional mineral specimens have been obtained from such open spaces, which are partially filled by minerals deposited from solutions. Allowing a mineral in the process of growth (as a result of precipitation) to develop in free space generally results in a well-developed crystal shape, which contributes to the visual appeal of a specimen. 

Thus, minerals are natural materials in which metals or their compounds can be found in the earth. Some minerals may contain a considerable amount of metal, whereas others may only contain a small percentage. Some minerals may be free of unwanted impurities, while others may include some unwanted impurities that restrict metal extraction. As a result, all minerals can not be used to extract metals.

What are Ores?

Ores are the minerals from which metals can be extracted efficiently and profitably. A previous meaning limited the term ore to metallic mineral deposits, although it has since been expanded to cover non-metallics in some cases. Only roughly 100 of the more than 2,800 mineral species have been recognised as ore minerals. Hematite, magnetite, limonite, and siderite are the main sources of iron; chalcopyrite, bornite, and chalcocite are the main sources of copper; and sphalerite and galena are the main sources of zinc and lead, respectively. No ore deposit is made up of a single ore mineral. 

The ore is invariably mixed with gangue, which is a term for undesired or non-valuable rocks and minerals. In most cases, the ore and gangue are mined together—that is, a mass of ore and gangue is extracted from the host rock by either mechanical or human means. The ore is then separated from the gangue via a series of activities known as mineral processing, or ore dressing. Smelting, roasting, or leaching processes are used to extract the necessary metallic element from the ore. Some metals, such as copper, uranium, and gold, can now be extracted from host rock without drilling or blasting because of advances in hydrometallurgy. 



In some cases, special bacteria are used as part of the process. Metals can be refined or alloyed with other metals once they’ve been recovered, as in a copper refinery or steel mill. Mining, processing, and refining are all processes in the process of extracting metal from an ore deposit. There are no unwanted impurities in ore, and it includes a high percentage of metal. As a result, all ores are minerals, but not all minerals are ores.

The following table lists some of the most common ores:

  Metal (to be extracted) Name of ore Name of the compound in ore Formula of ore
1. Sodium Rock salt Sodium Chloride NaCl
2. Aluminium Bauxite Aluminium oxide Al2O3.2H2O
3. Iron Haematite Iron (III) oxide Fe2O3
4. Manganese Pyrolusite Manganese dioxide MnO2
5. Mercury Cinnabar Mercury (II) sulphide HgS
6. Zinc
  1. Zinc blende
  2. Calamine

Zinc sulphide

Zinc carbonate

ZnS

ZnCO3

7. Copper
  1. Cuprite
  2. Copper glance

Copper (I) oxide

Copper (I) Sulphide

Cu2O

Cu2S

Solved Questions

Question 1: Why do most of the metals do not occur in their free state?



Answer:

The most reactive metals are those at the top of the reactivity series, and are so reactive that they are never found as free elements in nature.

Question 2: Define the term gangue.

Answer:

The unwanted impurities or non-valuable rocks, earthy particles present in an ore are called gangue.

Question 3: Among the metals magnesium and mercury, which occur in a combined state and which occur in a free state?

Answer:

The metals above hydrogen in the reactivity series are so reactive that they are never found as free elements in nature, whereas the metals which are at the bottom of the reactivity series below hydrogen, are least reactive so they occur in a free state. Since magnesium exists above hydrogen in the reactivity series, so it occurs in a combined state and mercury exists below hydrogen in the reactivity series, so it occurs in a free state.

Question 4: Name a metal that occurs in a free state as well as in a combined state?

Answer:

Copper is a metal that exists both in its free and mixed states. Only a small quantity of copper exists in its free state. In its combined state, it usually exists as its sulphides or oxides.

Question 5: Name the metal which is extracted from the cinnabar ore.

Answer: 

The metal that is extracted from the cinnabar ore is mercury.

Question 6: What is hydrometallurgy?

Answer:

Hydrometallurgy is the process of extracting metal from ore by making an aqueous solution of a metal salt and recovering the metal from it.




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