Melting is a common phrase that we come across in day-to-day life. Technically, the physical process by which a substance transits from the solid to the liquid phase by application of heat is described as melting. But, people most often confuse melting with smelting. Though both the terms sound similar and their processes seem to match each other, both are different.
Smelting is the process of extracting metal from its ore by heating beyond the melting point. The base metal is extracted from the ore by a process involving heat and melting. This process uses heat and a chemical-reducing agent for decomposing the raw ore, eliminating other elements and leaving just the metal. Broadly, smelting is described as a form of extractive metallurgy for separating metal from its ore.
Smelting vs. Melting
Though smelting and melting are different, the processes share a similarity; both involve heating. Given the fact that scientifically both processes are different, here we bring a broad comparison of smelting and melting that distinguishes the processes from each other.
Ores are naturally occurring solid materials from which valuable minerals or metals can be extracted. Smelting is broadly used in industrial sectors for extracting metals in their purest form from ores. This process involves chemicals and raw ores being heated to melt. Basically, the temperature is set beyond the melting point which helps to extract the metals from the raw materials in their purest form and the chemicals (reducing agents) used to wash out the residues like gases and slag (waste). This process just leaves the metal behind.
Smelting involves two main steps:
The 2 major steps involved in smelting – roasting and reduction are outlined below in summary in the next part of the article.
Roasting: In this step, the ore is heated beyond the melting point in the presence of excess air or oxygen. Generally, it is done at a high temperature above their melting point. This either reduces or oxidizes the metal. Roasting is done inside a furnace with high temperature which powers the reaction of combustion with redox reactions.
Reduction: In this step, the oxygen atoms are removed from the raw material. Generally, the reduction is done by carbon monoxide. The chemicals or reducing agents are used for washing out other elements from the ores. Most commonly, carbon monoxide or carbon dioxide are used as reducing agents. Limestone is commonly used for washing the impurities from the ores as waste.
As said, smelting is used for extracting a metal in its purest form from the raw ores, this process is used in the production of valuable metals like gold, silver, and other metals like copper, iron, etc.
Melting is a much simpler process by which a substance changes its phase from solid to liquid. This phase transition process is also called fusion. Heat is applied to the solid substance up to its melting point. This increases the internal energy of the substance. For the applied heat, the tight packing ions or molecules of the substance start loosening. A solid substance with a well-ordered structure reduces its configuration.
When the solid melts, the volume increases as the liquid has no tightly packed ions or molecules. Moreover, the density of the substance increases, with a few exceptions. The melting point of pure crystalline solid substances is fixed. However, impure substances melt at different temperatures and not at the melting point. The temperature at which impure substances start melting varies depending on the type and amount of impurities present in them.
In the process, the viscosity of the substance in its liquid state also changes when the applied temperature increases. The viscosity or the thickness of the liquid varies with the output requirements.
Generally, melting is done to mold a substance into a particular shape so that it can be used in various ways. We come across the melting process in our everyday life including in the kitchen. For instance, wax melts and molds into a candle of any desired shape and size or any other product as required.