Challenges in Limestone Processing

This article was authored by:

Chris Kozicki
Agglomeration Expert

Limestone is a versatile commodity used to create products for agricultural, environmental, and industrial purposes. Cement, paint, soil amendments, and even breakfast cereals all contain this resourceful mineral. Of course, mined limestone is not naturally found in a suitable form for many of these products. Therefore, various processing systems are needed to transform raw limestone rock material into a useful product. Common limestone processing methods that prepare the material for subsequent manufacturing stages include drying, calcining, pre-conditioning, and pelletization. The following information highlights limestone processing issues associated with these techniques, as well as general material challenges associated with limestone manufacturing.

Limestone Drying

Limestone Processing Issues: Abrasive and Prone to Clumping

A drying process is often used to precondition limestone rock for subsequent manufacturing steps. Like most rocks, limestone is abrasive as a raw material. As a result, heavy-duty rotary dryers are recommended to handle limestone’s abrasive characteristics.

Drying processes may also be used on powdered limestone, with the recommended equipment again being rotary dryers. Many limestone manufacturers address moisture issues and prevent material clumping by utilizing a drying process before storing powdered limestone for extended periods of time.

In both cases, rotary dryers are the ideal choice for their ability to handle fluctuations in feedstock size and moisture content.

Calcination of Limestone

Limestone Processing Issue: Emission Control

Rotary kilns are most often used to produce lime products in the United States. Hot combustion gases and limestone move counter currently within the refractory-lined drum of the rotary kiln, applying a high-temperature process that ultimately changes the raw material into a high-calcium lime or dolomitic lime. Particle matter pollutants are a common issue with rotary kilns, requiring the application of a particulate control system in order to counteract this problem. FEECO also offers special burners to limit air pollutant emissions such as NO2 and CO.

Limestone Pelletizing

Limestone Processing Issue: Moisture

Pelletization resolves a number of issues associated with limestone processing, from uniformity to nutrient delivery. Limestone pellets offer reduced dust, more accurate application, improved handling, and less product lost to dust. Fortunately, with such great benefits, limestone pelletization is a fairly straight-forward process.

However, there are still limestone processing problems that must be considered. For example, moisture is an important element in effectively pelletizing limestone. Throughout preconditioning, pelletization, and drying, moisture levels should be monitored and maintained to ensure optimal products are created through every stage of limestone processing.

Pre-Conditioning: A pin mixer imparts a powerful rotating motion upon limestone and its binder, creating an evenly distributed mixture with a moisture level best suited for pelletization. A successful pre-conditioning process creates an easily controllable mixture for forming limestone pellets on the subsequent disc pelletizer. Additionally, the material densification is greater than  that of a disc pelletizer alone. However, pin mixers require special abrasion resistant pins due to the potential for accelerated wear when processing limestone. Consequently, proper maintenance is important to avoid equipment breaks and prevent costly downtimes.

Pelletization: A disc pelletizer gradually grows the pre-conditioned mixture into limestone pellets using a binder and the motion of the rotating disc. Monitoring the material’s moisture level is critical at this stage, because pellet characteristics such as size and strength are secured by monitoring moisture ratios during this process.

Drying: A drying process is utilized to control moisture levels within the pelletized limestone. As an added benefit, drying adds pellet strength and prevents clumping related issues. Rotary dryers are recommended for their ability to uniformly dry pellets, handle a large throughput of material, and naturally polish the limestone as it tumbles through the drum. The resulting product is also easier to handle and store.  Knocking systems are available to reduce material clumps by dislodging material build-up inside the drum.

General Limestone Processing Challenges

Limestone processing problems are not unlike the challenges faced by many other naturally occurring materials. In addition to build-up and clumping problems, limestone composition can also vary from one region to another.


Limestone build-up has the ability to wear down equipment parts if left untreated. In order to prevent limestone maintenance issues, consistent material build-up removal (as part of an equipment’s regularly scheduled maintenance plan) is necessary.


Another potential limestone processing issue is clumping. Fortunately, a number of solutions are available to prevent limestone clumping issues:

    • As previously mentioned, a drying process reduces material clumping while adding a number of benefits to the final product’s quality.
    • Material handling equipment can also be used to correct material clumps. Screw conveyors, for example, use a flinging motion in their feed trajectory that naturally breaks apart material as it moves between equipment.
    • Anti-caking additives are available in a variety of forms based on material characteristics and desired product results. A paddle mixer or rotary coating drum is used to apply the additive to the limestone mixture/pellets.

Varying Composition

Limestone’s composition, porosity, and texture can vary for a number of reasons, especially when the material is mined from different regions around the world. Consequently, FEECO recommends testing limestone before moving forward with processing strategies.

From drying to pelletizing, and even testing and material handling, FEECO is a complete processing solutions provider for the limestone industry. By combining over 70 years of experience with superior engineering capabilities and a unique material testing facility, FEECO is able to create the best limestone processing and equipment designs for our customers. For more information on our limestone processing experience, contact us today!

About the Author . . .

Chris Kozicki is a Process Sales Engineer and agglomeration expert.

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