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Conversion of Ore into Metal

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  • Last Updated : 04 Mar, 2022

Metals are minerals or substances that form naturally beneath the Earth’s surface. Metals are inorganic, which means they were formed from non-living substances. Metals are natural compounds of the earth’s crust that are found in the form of metal ores and are associated with each other as well as many other elements. They are also found naturally in rocks washed by surface and groundwater, as well as in atmospheric dust.

Metal is very strong and durable, so it is used to make a variety of items. These are used in the manufacture of automobiles, satellites, cooking utensils, and other items. The majority of metals are hard, but some are not. Sodium and potassium are knife-cuttable metals, whereas mercury is a liquid metal at room temperature. Iron is a solid element in nature.

What is an Ore?

Ore is a deposit of one or more valuable minerals in the Earth’s crust. Metals essential to industry and trade, such as copper, gold, and iron, are found in the most valuable ore deposits.

Ores are classified according to how they form. Some ores form as a result of mineral cooling and crystallization within magmas, lavas, or igneous intrusions. These are referred to as magmatic or volcanic ores. Ores of nickel, copper, and iron are typically formed from magmatic or volcanic deposits. 

Other than volcanic and activity, carbonate alkaline ores are formed by igneous processes. The carbonate alkaline group includes rare earth element ores as well as some diamonds. If ores can form as a result of igneous processes, they can also form as a result of metamorphic or sedimentary processes. Lead, zinc, and silver are frequently found in metamorphic ores, as are some iron oxides. Banded iron formations, as well as gold, platinum, zinc, tin, and even diamond-containing ores, formed in sedimentary environments.

Hydrothermal processes can result in the formation of ore. These processes involve the exposure of rocks and minerals to extremely hot water, which occurs most commonly near oceanic hydrothermal vents or hot springs. Hydrothermal processes produced the majority of the world’s gold and uranium ores.

Conversion of Concentrated Ore into Metal

Isolation of metal from concentrated ore entails refining metals from the compounds in which they are found to their original state. The concentrated ore is first converted to an oxide, and then metal extraction is accomplished by reducing the oxide to metal with a suitable reducing agent. 

The ores are concentrated in their original oxide, carbonate, sulphide, or halide forms. It is preferable to convert the metal – compounds into oxides in order to obtain pure metals from these chemicals. 

Metal oxides are easily reduced, and pure metal can be obtained. Two processes are used to convert the concentrated ores into metal oxides. These processes are calcination (heating with insufficient air) and roasting the ore (heating an inadequate quantity of air).

Calcination

Calcination is the process of converting ore into oxide by rapidly heating it. This method is frequently used to convert carbonates and hydroxides to their corresponding oxides. 

In the absence of air, carbonate ores are heated. In the absence of air and heat, CO3 is converted into CO2 and O. The metal retains the O as metal – oxide. Any water content in the ore is also removed by heating. Heating also removes any volatile impurities or gases that may be trapped in the ore. The process of converting calamine ore or zinc carbonate to ZnO by calcination is illustrated below.

[Cu(H2O)6]+2 + 4NH3 ⇢  [Cu(H2O)2(NH3)4]+2 (complex ion)

Calcinating refers to the products of calcination, regardless of the actual compounds undergoing thermal treatment.

Roasting

Roasting is a metallurgical process in which ore is converted into oxide by heating it below its melting point in the presence of excess air. 

While calcination is mostly used for carbonate oxidation, roasting is a method for converting sulphide ores.. Sulphide ores are roasted or heated in large quantities of air. Sulphide is converted to sulphur dioxide. When the metal reacts with the oxygen in the air, it forms a metal – oxide. The removal of gaseous and other volatile impurities is accomplished through heating. The following example shows how roasting converts zinc blende ore (zinc sulphide) to ZnO.

2ZnS + 3O2 ⇢  2ZnO + 2SO2

Non-metallic and moisture impurities are released as volatile gas during roasting. The roasting process includes solid-gas thermal reactions such as reduction, oxidation, chlorination, sulfation, and pyro hydrolysis. Roasting with sulphides is a major source of air pollution, and the main disadvantage of this process is that it emits a large amount of metallic, toxic, and acidic compounds that harm the environment. Other ores, such as metal–oxide ores and metal–chloride ores, are unaffected by the calcination and roasting processes. Heat treatment removes impurities and water from these ores.

Difference between Calcination and Roasting 

Calcination

Roasting

Calcination is a process in which either a limited amount of air is supplied or the ore is heated in the absence of air.

Roasting is the process of heating ore to temperatures lower than its melting point in the presence of oxygen or air.

The thermal decomposition of carbonate ores is involved in calcination.

Roasting is primarily used for sulphide minerals.

During calcination, moisture is extracted from the ore.

Roasting does not involve ore dehydration.

During calcination, carbon dioxide is produced.

A large amount of toxic, acidic, and metallic compounds are released during roasting.

CO3 is converted into CO2 and O

Here, Sulphide is converted to sulphur dioxide. 

Sample Questions

Question 1: What happens if you touch calcium metal?

Answer:

Calcium will react with water or moisture that causes heat. Calcium metal can cause severe corrosive irritation when it comes into contact with moisture in the eyes, body, or respiratory tract.

Question 2: What is the softest metal?

Answer:

Caesium is thought to be the softest metal, and lead is thought to be one of the softest metals. Mercury is a liquid at room temperature (molten). At body temperature, gallium is a liquid, and at room temperature, it is a solid (if soft).

Question 3: How does non-metals react with water?

Answer:

Nonmetals do not react with water, but they are usually very reactive in air, which is why some of them are stored in water. Phosphorus, for example, is a highly reactive nonmetal that catches fire when exposed to air, which is why it is stored in water to avoid contact with atmospheric oxygen.

Question 4: Why Does Calcination Occur in the Absence of Oxygen?

Answer:

For the Carbonate Ores, calcination is used. The ores are intensely heated in the absence of oxygen during the calcination process (air). This is done to convert metal carbonates to carbon dioxide and metal oxides. If these ores are heated in the presence of oxygen or air, no reaction occurs, and the entire process is rendered ineffective.

Question 5: What is the reduction of oxide to metal?

Solution:

Metal oxide reduction entails the removal of oxygen in order to refine metal to its free state. This is accomplished with the assistance of reducing agents such as carbon (C) and carbon monoxide (CO). Heat is applied to the metal oxide obtained from the ore.

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