Introduction
Two popular techniques for heating the ore are calcination and roasting. The method used to heat the ore with the air differs between them. Carbonate ores are heated primarily through the calcination process. This is possible because carbonate ores may be heated using little to no air. For sulfide ores, roasting is employed. This is because they become heated when there is air present.
Let’s look into the major differences between calcination and roasting in this article.
Calcination vs Roasting
The primary distinction between calcination and roasting is that the ore will be heated with a constrained amount of air in calcination. However, the ore will be heated in the presence of air when it is roasted. No hazardous substances will be emitted throughout the calcination process. In opposition to this, poisonous and acidic substances will be released during the roasting process.
Calcination is the heating process used to convert ore into oxide. Below its melting point, it is heated. It can be performed out from a finite quantity of air and without any air at all. It is commonly utilized to change hydroxides and carbonates into the appropriate oxides. Metal carbonates, for instance, will break down to create metal oxides. It is believed to be a method of mental purification.
One of the processes in the processing of some ores is roasting. It is a metallurgical procedure that involves high-temperature gas-solid interactions. Purification of metal components is the goal. A metal sulfide can become a metal oxide by this procedure. They can also be changed into free metal by it. A blast furnace is the type of furnace used for roasting.
Difference Between Calcination and Roasting in Tabular Form
| Parameters of Comparison | Calcination | Roasting |
| Air supply | Ore will be heated using a meager supply of air. | When there is air present, ore will heat up. |
| Gases that get released | There will be a carbon dioxide release. | The result will be sulfur dioxide. |
| The impurities | Organic moisture impurities will be eliminated. | Elimination of volatile contaminants. |
| The toxic compounds | They're not let out. | They'll be let go. |
| Usage | They’re used for carbonate ores. | They’re used for sulfide ores. |
What is Calcination?
Calcination is the thermal treatment of a solid chemical compound (such as mixed carbonate ores) in which the compound is heated to a high temperature without melting while being supplied with a limited amount of ambient oxygen (i.e., the gaseous O2 fraction of air), typically to remove impurities or volatile substances and/or cause thermal decomposition.
A calciner is a rotating steel cylinder that operates at extremely high temperatures (550–1150 °C, or 1000–2100 °F) and in a controlled environment.
Due to its most common use, the breakdown of calcium carbonate (limestone) into calcium oxide (lime) and carbon dioxide to produce cement, the process of calcination derives its name from the Latin calculate (to burn lime). Regardless of the specific minerals undergoing thermal treatment, the result of calcination is typically referred to as "calcine". Calcination is done in a variety of furnaces or reactors, including fluidized bed reactors, shaft furnaces, rotary kilns, multiple hearth furnaces, and rotary calciners.
Calcination is the heating of a solid substance to bring about the chemical separation of its constituent parts. Calcination can be used to achieve a variety of goals, including the release of chemically bound (crystalline) water, the volatilization of impurities from the source material, thermal degradation, and even phase shifts. Each of these goals in turn contributes to a wide range of industry, material, and process goals.
Industrial companies can manage a variety of end product qualities, reduce contamination in waste or process byproducts, and much more thanks to calcination. As a result, calcination has emerged as a crucial procedure in industrial process settings, with the rotary calciner serving as its foundation.
Now, according to studies, calcination is the process of heating a substance to a certain temperature and holding it there for a predetermined period in a controlled environment. So, when the material is heated to a point where one or more components chemically split into less complex building units, this is considered true calcination. This often leads to a target component oxidizing, removing a volatile component or organic matter, chemically dehydrating, and/or decomposing carbonates.
However, due to the term's extensive usage, it may occasionally be used to refer to other thermal processes like reduction, induration, heat setting, and more.
No matter the origin or composition of a material, it is frequently referred to as "calcine" when it has undergone calcination.
The calcination procedure is adaptable in that different process variables can be changed to regulate the reaction(s) and fine-tune the properties of the finished product. Here is a summary of the most important variables.
During calcination, both the procedure and material temperatures are carefully controlled and maintained. In many instances, the temperature is regulated to increase quickly or steadily, retain a substance after a certain temperature for a specified period, and/or decrease quickly or gradually.
Since the material frequently needs to be held at temperature to produce the required reaction, the retention or residence duration is strongly related to the temperature requirements. Drum speed, slope, size, and, if necessary, dams are used to limit retention time.
The calciner's controls system controls temperature, and sensors inside the machine give the operator feedback.
The processing environment expected to undertake the intended reaction is supplied by the air conditions inside the calciner. To facilitate or maximize the efficiency of the reaction, this often necessitates a careful effect on the quantity of oxygen in the kiln. In some situations, this may also require the addition of inert gas.
The calcining process can be carried out using a variety of tools, with rotary kilns being one of the most widely used.
Both direct-fired and indirect-fired rotary kilns, which are frequently referred to as calciners in this context, can be used for calcination.
In direct-fired kilns, the material is heated through direct contact with the combustion byproducts. The material and combustion byproducts are put into the spinning drum. Depending on the process objectives and the properties of the fuel, the material and combustion products may travel concurrently (parallel) or countercurrent to one another.
Indirect-fired kilns do not come into direct touch with the materials being burned or the combustion products, in contrast to direct-fired kilns. This makes it possible to have a strictly controlled or inert processing environment, which is perfect for materials that cannot be exposed to oxygen or that need a particular atmosphere for the intended reaction to take place.
In this instance, the interior of the drum is shut off and heated externally. The material is heated through contact with the drum's shell rather than coming into touch with combustion byproducts. Although significantly less effective, this strategy is required for particular materials and process objectives.
Now, testing is a critical step in creating an effective and efficient calcination process for a particular application due to the variety of calcination objectives, and the wide range of materials, each with distinct properties, and end product goals.
Several batches- and pilot-scale test kilns (direct and indirect) are available from the FEECO Innovation Center for testing research and development activities, including demonstrating proof of concept, proof of product, and proof of process. Producers can also acquire crucial process information about their material for scaling up and designing a commercial-scale calciner during the testing process, such as:
- Gas analysis and sampling
- Criteria for pretreatment
- Process variables
- Use of burner fuel
- Calculator size
- Emissions
Calcination is a variety of heat treatments that allows producers to remove volatile components, improve product qualities, remove crystalline water, and more through the chemical separation of constituents. The crucial calcination parameters of temperature, retention period and processing environment are frequently developed by testing.
Now, the most well-known instance of the common process of calcination is the separation of calcium carbonate into calcium oxide and carbon dioxide during the manufacture of cement from limestone. Among the other uses of calcination are:
- Preparing the catalyst
- Diatomaceous digesting the earth
- Clay Kaolin processing
- Spodumene to Lithium Conversion
- Expanded clay aggregate production
- Production of color
- Aluminum and alumina production
What is Roasting?
Sulfide ore is heated to a high temperature while being exposed to air during the roasting process. It is a stage in the refinement of some ores. To purify the metal component, roasting is frequently a metallurgical process that involves gas-solid interactions at high temperatures (s). The ore has frequently already undergone partial purification, such as froth flotation, before roasting. To speed up the procedure, the concentrate is combined with other components. Although the technology helps make some ores viable, it can also be a significant source of air pollution.
Thermal gas-solid processes, such as oxidation, reduction, chlorination, sulfation, and pyrohydrolysis, make up roasting. When roasting, extremely hot air is used to treat the ore or ore concentrate. Sulfide minerals typically undergo this procedure. The sulfide is changed into oxide and emitted as sulfur dioxide during roasting.
Sulfur dioxide (SO2), a gaseous byproduct of sulfide roasting, is frequently used to make sulfuric acid. Many sulfide minerals also contain additional elements that are discharged into the environment, such as arsenic.
Wood was typically burned on top of ore to begin roasting before the turn of the 20th century. The ore would be heated to a point where its sulfur content would act as fuel, allowing the roasting process to continue without the need for additional fuel sources. This method of early sulfide roasting involved "open hearth" roasters that required manual stirring (a process known as "rabbling") with rake-like implements to expose unroasted ore to oxygen as the reaction progressed.
Large amounts of metallic, acidic, and other hazardous chemicals were produced during this process. The results of this include region that, even after 60–80 years, are still entirely lifeless. These regions frequently exactly match the roast bed area and might be several hundred meters wide and kilometers long. The process of roasting is exothermic. However, its major downside is the quantity of metallic, poisonous, and acidic components it produces. It might damage the ecosystem. Zinc sulfide will become zinc oxide when it is heated. Sulfide minerals typically undergo this procedure. This procedure is used since directly reducing sulfide is not the optimum approach. When the ore is exposed to the air in this situation, it will experience extremely high temperatures.
As a result, the ore sometimes reacts and produces an oxide. Metal is also formed by it. Air is used in excess, as opposed to a limited amount during calcination. As a result, carbonate ores cannot be used. Due to the possibility of sulfur gas escaping during removal, this technique is mostly utilized with sulfide ores. Air will no longer escape during roasting.
Main Differences Between Calcination and Roasting In Points
Now, let’s get to know the major points of differentiation between calcination and roasting with the help of the following points:
- Thermal treatment or breakdown of carbonate ores is accomplished through calcination. On the other hand, sulfide ores are treated or thermally decomposed when they are roasted.
- The calcination process does not result in the emission of toxic substances. On the other hand, during the roasting process, poisonous and acidic substances will be emitted.
- Organic contaminants with moisture are eliminated during the calcination process. On the other hand, volatile contaminants are eliminated during the roasting process.
- Carbon dioxide and metal oxide will both be created during the calcination process. On the other side, while roasting, metal oxide and sulfur dioxide will be formed.
- The ore will be heated during calcination with a constrained air supply. On the other hand, during roasting, the air is present and the ore is heated.
Conclusion
Ore is heated using both calcination and roasting so that carbonate and sulfide ores can be heated. To ensure that the ore is effectively separated, this procedure should be carefully carried out and the procedures should be correctly carried out. The procedure is carried out in a blast furnace. The impurities in the ore are also helped to be removed by this process.
However, calcination will release hazardous chemicals, which is seen to be a benefit. However, the roasting process releases both acidic and poisonous chemicals, which benefits ores that contain sulfur dioxide. Both of these metals will yield chemical compounds in addition to metal oxide.
References
- Calcination. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Calcination
- Carlson, C. (n.d.). What Is Calcination? Retrieved from FEECO INTERNATIONAL: https://feeco.com/what-is-calcination/
- Roasting (metallurgy). (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Roasting_(metallurgy)
