Difference Between Melting and Smelting

Main Difference – Melting vs Smelting

Although the two terms melting and smelting sound similar, they are different terms that have different applications. Melting is the process of liquefying a solid substance by heating. It is the process by which a substance changes from the solid phase to the liquid phase. Smelting is the process by which a metal is obtained at temperatures beyond the melting point from its ore. Both processes involve heating a substance into a higher temperature. The main difference between melting and smelting is that melting converts a solid substance into a liquid whereas smelting converts an ore to its purest form.

Key Areas Covered

1. What is Melting
     – Definition, Melting Point, Melting of Pure and Impure Compounds
2. What is Smelting
     – Definition, Steps and Requirements
3. What is the Difference Between Melting and Smelting
     – Comparison of Key Differences

Key Terms: Density, Heat, Internal Energy, Melting, Melting Point, Phase, Smelting, Temperature, Volume

What is Melting

Melting is the process by which a substance changes from the solid phase to the liquid phase. Melting is also called fusion. It is a phase transition process. During melting, the internal energy of the substance increases. Melting is done typically by providing heat.

While melting, the tight packing of ions or molecules starts to loosen. A solid substance has a well-ordered structure than a liquid. During melting, it becomes a less ordered structure. When a solid melts, the volume increases because the liquid has no tight packing like in the solid. Therefore, the density is decreased. But there are some exceptions too. Ex: Melting of ice cubes form water. But the density of ice cubes is lower than water (density has increased). Therefore, ice floats on water.

Figure 1: Ice Melting

For pure, crystalline solid substances, melting occurs at a fixed temperature. This temperature is known as the melting point. The melting of an impure substance occurs at a different temperature, not at the melting point. The temperature in which the impure substance starts to melt can be varied depending on the type and the amount of the impurities present.

What is Smelting

Smelting is the process by which a metal is obtained at temperatures beyond the melting point from its ore. An ore is a naturally occurring solid material from which a metal or valuable mineral can be extracted profitably. From smelting, an ore can be converted into its purest form. We can obtain a pure element or a smaller compound from an ore via smelting process.

The most common applications of smelting include the production of silver, iron, copper and other metals from their ores. The smelting process has two requirements.

• Heat treatment
• Reducing agent

Coke (carbon) is often used as a reducing agent. Carbon can remove oxygen from the ore by forming carbon monoxide and carbon dioxide.

Figure 2: A Phosphate Smelting Furnace

The smelting process has two main steps as follows:

Roasting

Heating the ore in the presence of excess air or oxygen.

Reduction

A reducing environment removes the oxygen atoms from the raw material. This is usually done by carbon monoxide which is a product of incomplete combustion of coke (carbon).

Difference Between Melting and Smelting

Definition

Melting: Melting is the process by which a substance changes from the solid phase to the liquid phase.

Smelting: Smelting is the process by which a metal is obtained at temperatures beyond the melting point from its ore.

Temperature

Melting: Melting of a pure substance occurs at a fixed temperature called the melting point.

Smelting: Smelting includes a step known as roasting that is done at high temperatures.

Melting Point

Melting: Melting occurs at the melting point of a (pure) substance.

Smelting: Smelting is done at temperatures beyond the melting point of ore.

Final Outcome

Melting: Melting gives a liquid out of a solid substance.

Smelting: Smelting gives a pure element or a simple compound from an impure ore.

Conclusion

Melting and smelting are two different chemical terms that describe two different processes. The main difference between melting and smelting is that melting converts a solid substance into a liquid whereas smelting converts an ore to its purest form.

Reference:

1. Helmenstine, Anne Marie. “What Is the Definition of Melting?” ThoughtCo, Available here.
2. “Melting.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 22 Nov. 2016, Available here.
3. “Smelting.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 30 Nov. 2016, Available here.

Image Courtesy:

1. “TVA phosphate smelting furnace” By Alfred T. Palmer – available from the United States Library of Congress’s Prints and Photographs division (Public Domain) via Commons Wikimedia
2. “570500” (Public Domain) via Pixabay

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