Profile
Settings
Refer your friends
Sign out
Metals are usually extracted from oxide ores by a reduction or electrolysis process. While oxide ores are simple to reduce, sulphides and carbonates are more difficult. Only after converting carbonates and sulphides to an oxide ore can these ores be converted to metals. So, how does an individual go on doing it? The majority of the conversion is accomplished through calcination or roasting. So, on this page, we’ll learn about calcination and roasting, as well as the various issues that go along with them.
Calcination
Calcination is the process of turning ore into an oxide by heating it extremely hot, according to popular definition. In the absence of air or with restricted supplies, the ore is heated below its melting point. Carbonates and hydroxides are often converted to their corresponding oxides using this approach. Moisture as well as volatile contaminants are removed during the calcination process. Calcination is a thermal process that causes a thermal breakdown of ores and other solid materials. The reaction in calcination usually takes place at or near the thermal decomposition temperature.
The word “calcination” comes from the Latin word calculate, which means “to burn lime.” As a result, calcination is frequently used in the degradation of organic materials. As a result, calcination is mostly utilised to convert limestone (calcium carbonate) to lime (calcium oxide) and carbon dioxide.
The Chemical Reaction: CaCO3 —> CaO + CO2
Meanwhile, independent of the actual compounds undergoing thermal treatment, the products obtained from calcination are referred to as calcining.
Roasting
When we converse about roasting, we’re discussing about a metallurgical process in which ore is heated beyond its melting point in the presence of extra air and then transformed into its oxide. Roasting is a process for transforming sulphide ores, while calcination is primarily employed for oxidation of carbonates. Moisture and non-metallic adulterations are emanated as volatile gases during roasting. The roasting procedure is made up of solid-gas thermal effects include oxidation, reduction, sulfation, chlorination, in addition to pyro hydrolysis.
Roasting with sulphides, on the other hand, is a major source of air pollution, and the main disadvantage of this process is that it releases a large amount of metallic, poisonous, and acidic compounds, all of which are harmful to the environment.
When zinc sulphide is transformed to zinc oxide, this is an example of roasting.
The Chemical Reaction: 2ZnS+3O2 —> 2ZnO + 2SO2
Difference between the Two Processes: Calcination Vs Roasting
CALCINATION | ROASTING |
Calcination is a process in which ore is heated without the presence of air or with only a little amount of air. | Roasting is the procedure of heating ore to a temperature under its melting point while in the existence of air or oxygen. |
Calcination is the procedure of thermally decomposing carbonate ores. | Roasting is mainly put in use to extract sulphide minerals. |
Moisture is emitted away of an ore during calcination. | Roasting does not necessitate the dehydration of an ore. |
During calcination, carbon dioxide is released. | A huge amount of poisonous, metallic, and acidic chemicals are emitted during roasting. |
Process of Calcination
Calcination is commonly done in furnaces, retorts, or kilns and materials are frequently racked over or agitated to ensure uniformity. The reverberatory furnace is one of the most frequent calcination arrangements. The normal construction and process are described in the following sections.
Reverberatory furnaces are built in a variety of ways, but the flames and hot gases from the fire always come into close contact with the material to be calcined; however, the fuel is isolated from it.
The fire is burning on the grate at G in the illustration above. The flames travelling over the bridge at E are now deflected downward by the furnace’s low sloping roof and pass directly over the surface of the charge or calcination material on platform B. The fumes and heated gases subsequently escape into the chimney through the throat F. As a thin layer, the charge is spread out uniformly on the bed.
Calcination: It’s Purpose
Calculation is the method for determining a material’s thermal decomposition. It is accomplished by heating a substance to a temperature higher than its melting point. This high-temperature heating aids in the removal of volatile chemicals while also oxidising any quantity of the substance. As a result, calcination might be regarded as a metal purifying process. Calcination, on the other hand, is usually employed to oxidise carbonate compounds.
Roasting: It’s Purpose
Roasting is the process of heating a substance below its melting point in the presence of oxygen or air. Roasting is used in metallurgical operations to transform ores into oxides, which are then utilised to recover metals. It’s most commonly utilised to transform sulphide ores. Volatile chemicals, moisture, and contaminants are eliminated during this process.
Conclusion
The process of roasting as well as that of calcination is used for the refining of ores of sulphides, calcites and oxides. It is an efficient and effective metallurgical process. This article has provided sufficient information, in regard to the concepts related to calcination and roasting.
