Industrial clay minerals exhibit incredibly diverse characteristics, lending their use in everything from consumer products such as cat litter and cosmetics, to industrial additives, catalysts, and adsorbents, to name a few.
While there are many types of clay, each with wide variation in characteristics, the majority of industrial clay mineral producers have one thing in common: they rely on a drying step to prepare a quality clay product for market.
Here’s a look at how rotary dryers are used in preparing industrial clays for market.
Clay Minerals That Require Drying
As with many mined materials, drying often contributes to easier handling and lower transportation costs, but it plays an especially critical role in allowing producers to engineer industrial clay materials and products with the qualities their market demands. The following breaks down how drying is used in processing some of the most common industrial clays.
Kaolin
Kaolin, also commonly referred to as China clay, is one of the most important clay minerals, with uses spanning a range of different industries and applications. Kaolin clay is commonly used in:
- Paper making
- Tableware and china
- Medicine
- Pigments and paints
- Rubber
- Fertilizers
- Refractories
- Fiberglass
- Technical ceramics
- Consumer products such as cosmetics, toothpaste, and creams
While drying is largely used to prepare kaolin for shipment (it is estimated that drying is employed in more than 70% of total kaolin production.1), it is a necessity if the kaolin is bound for calcination – a thermal treatment commonly used in kaolin processing to reduce impurities, enhance brightness, and improve other properties.
Bentonite Clay
Bentonite is another one of the most widely used types of industrial clay. Popular uses for bentonite clay include:
- Cat litter
- Oil and industrial spill absorbents
- Binder in iron ore pelletizing process
- Adsorbents
- Drilling mud
- Groundwater barrier
Upon extraction, most bentonites exhibit a moisture content between 25 and 35% by weight. Depending on the moisture content of the specific deposit, mined bentonite may first be allowed to dry on-site naturally in order to reduce the burden on the dryer. Natural drying typically brings this down to less than 12%. Further drying brings the moisture content to around 8%. Bentonite clay requires careful consideration in drying, because over drying the material is likely to degrade its performance.²
Ball Clay
Ball clays are favored for their high level of plasticity (they are also commonly called “plastic clays”). Ball clays are often blended with other less plastic clays such as kaolin in order to produce a product with optimized characteristics. Ball clays are commonly used in:
- Ceramics
- Refractories
- Tableware
- Tile
Mined ball clay typically exhibits a moisture content around 28%. It may be allowed to naturally dry and then sold as-is (this makes up a small portion of the ball clay market), or after natural drying, it may be further dried down to 8-10% moisture. For this type of clay, indirect drying, where the material does not come into direct contact with the drying medium, is employed.3 While ball clay is not always further dried before sale, it is recognized that drying generally produces a more refined product with improved characteristics.
As with bentonite clay, careful control over the drying process is important, as over drying leads to a reduction in product quality and subsequent value; if over dried, ball clay loses much of its plasticity, the primary characteristic for which it is employed.4
Fire Clay
Fire clays cover a range of materials that exhibit optimal properties for use in high-temperature thermal applications such as refractories, furnace linings, crucibles, and other products that must withstand extreme temperatures.
Fire clays are almost always dried or calcined (or both) prior to any further processing. An initial natural drying step is common, with some clays requiring a mechanical drying step prior to further drying. Overdrying the clay should be avoided, as this leads to excessive dust.5
Fuller’s Earth
Fuller’s earth clay materials are largely used in absorption applications, with other uses including drilling mud and fertilizers.
In this setting, drying is used to reduce the moisture content of fuller’s earth to less than 10% (down from between 40-50%).3
Here again, overdrying substantially degrades the useful properties of the material, lowering its value. Manipulation of drying parameters produces products suited to different end-use applications.6
Rotary Dryers for Industrial Clay Drying
Dryers serve as one of the first and most critical steps to reaching the many end goals required by industrial clay producers and end markets. Industrial clay producers rely on drying systems to reduce shipping costs, improve handling characteristics, prepare the clay for downstream processing, and ensure clay materials meet their specific performance standards.
Already the industry standard for aggregates, minerals, and other industrial products, it is not surprising, then, that rotary dryers are a preferred dryer system for processing clay. The high
throughput of the dryer, combined with its robust build, make it an ideal processing option for demanding, high-capacity applications.
Further, since rotary drums are already widely used for various objectives in mineral processing, and they boast simple operation, they offer easy adoption in most settings. Additional reasons for which rotary dryers are selected for clay processing applications include:
Customizability
Rotary dryers offer a high level of customization, making them applicable for a wide range of materials – perfect for the diverse nature of the clay industry, allowing producers to tailor their dryer system to their exact needs.
One common customization is the use of a combustion chamber as a means of maintaining product integrity; the combustion chamber prevents contact between the clay being processed and the burner flame, reducing the potential for overdrying the product, which, as noted, often severely impacts the quality of the end product.
Other common customizations include:
- Air flow (co-current or counter-current)
- Method of heating (direct or indirect)
- Additional components such as knocking systems and grizzlies (trommel screens)
- Custom flight (material lifter) design and pattern
- Multiple fuel sources
- Materials of construction
- Seal design
Reliability
Rotary dryers have a well-earned reputation for reliability, typically performing efficiently for decades. This is in part a result of their rugged construction, but also rests on their simple design and operation, though producers should take care to select a quality rotary dryer manufacturer.
Tolerance to Feedstock Variation
Depending on the specific clay source and pretreatment, variation in feedstock may or may not be a concern, and certainly, the more uniform the feedstock, the more uniform the end product. However, when variation in feedstock exists, be it in particle size distribution, moisture content, or otherwise, rotary dryers offer the best processing option; other dryer types such as fluid bed dryers require tight control over feedstock parameters to avoid frequent process upsets.
Clay Dryer Testing & Process Development
The variation in both clay sources and end products makes testing an important part of designing a commercial-scale clay dryer optimized for its specific application. FEECO often recommends pilot dryer testing in our Innovation Center.
Here, process experts assist in every aspect of the drying process, from assessing initial feasibility, all the way through to fine-tuning process parameters to produce an optimal product.
Conclusion
Drying is an important step in the processing of industrial clays, whether it be to reduce costs associated with shipping, or to prepare the material for its end use. Rotary dryers provide industrial clay producers with a reliable, flexible drying system tailored to their specific drying requirements.
FEECO is the leading provider of custom rotary dryers, with all dryers designed around the specific characteristics of the material to be dried. We also offer tailored dryer testing programs and comprehensive parts and service support. For more information on our clay dryers, contact us today!