Bentonite clay, with its extraordinary properties, is one of the most important clay minerals in modern industry. The clay has become a mainstay not only in the products industries and consumers rely on, but the processes as well, lending its diverse qualities to each and every application in a unique way. For this reason, bentonite has earned the nickname, “Clay of a Thousand Uses.”
This diversity in application requires equally diverse processing methods to produce a bentonite product with the desired characteristics. As such, there is not a one-size-fits-all approach to processing bentonite; each industry and even individual use case is likely to have its own requirements. This is further complicated by bentonite’s significant variation – even within the same deposit. As such, bentonite process development testing is a key aspect of developing a successful processing operation.
Bentonite Characteristics
Bentonite is a member of the smectite group of minerals and is primarily made up of montmorillonite. As a smectite, bentonite exhibits a combination of several important characteristics that have lent it to such widespread use.
Key properties of the smectite group include:¹
- 2:1 Expandable layers
- High layer exchange
- High base exchange capacity
- Thin flakes
- Considerable surface area
- Significant absorption capacity
- Large swelling capacity
- High viscosity
- Thixotropic quality
While there are a few outliers, most bentonites fall under one of two categories, either sodium bentonite (Na-Bentonite) or calcium bentonite (Ca-Bentonite). Each exhibits a variation on the properties listed above and is therefore better suited to different applications; sodium bentonite is typically selected when swelling capacity is important, while calcium bentonite provides a superior absorbent.
Other types of bentonite include sulfur bentonite and potassium bentonite.
Bentonite Clay Applications
Bentonite’s unique properties have become a cornerstone of several applications:
Binder in Iron Ore Pelletizing
Bentonite is the most commonly employed binder in the iron ore pelletizing, or “balling” process used in the production of steel. The importance of iron ore pelletizing has been on the rise in recent years as high-grade sources of iron ore diminish, buyer preferences change, and producers look to operate more sustainably.
Sodium bentonite is selected for this application because it exhibits an incredible dry strength and is necessary in only a very small amount.¹
Foundry Sands
As with iron ore pelletizing, bentonite also serves as a binder in the foundry sands industry, playing a critical role in producing moulds that will yield cast products of the desired quality.
As a binder, bentonite lends excellent green and dry compression strength, hot strength, flowability, permeability, and durability to the sand used to form moulds.¹
The Na-bentonites found in the western United States are also known for their ability to hold up well during the pouring of molten materials, improving clay utilization and even fostering fewer defects.²
Drilling Mud
Drilling mud is tasked with a number of objectives in the drilling process. Among them: keeping the drill bit cool and lubricated, controlling pressure, bringing drill cuttings to the surface, and more.
Bentonite is commonly chosen for this application because of a few key characteristics, namely, its ability to swell upon hydration, its high viscosity when paired with water, and its thixotropic nature, which promotes rapid gel formation when the drill stops, suspending cuttings, and then resumes a fluid state when drilling restarts. Other important properties of bentonite in drilling mud include a high gel strength and low permeability as a filter cake.¹
As swelling is a critical quality in this setting, drilling muds primarily employ sodium bentonite.
Sorbents
Bentonite serves as a common sorbent, capable of acting both as an adsorbent or absorbent. The fine particle size, large surface area, favorable surface charge, and base exchange capacity make calcium bentonite an excellent sorbent.³
For these qualities, along with its ability to absorb impressive amounts of water, bentonite is used as a cat litter and industrial spill absorbent.
In animal feed production, bentonite is used as a binding agent, but plays an absorbent role as well, absorbing bacteria in the digestive tract. Similarly, when used as a landfill liner, bentonite absorbs heavy metals and organic compounds, helping to prevent contamination of surrounding water sources.³
As an adsorbent, bentonite’s ability to remove toxic compounds has seen it utilized in water treatment applications, such as the removal of heavy metals. It is also an important tool in clarifying wine, thanks to its ability to capture high amounts of protein.
Barrier
As a result of their incredible swelling ability, which fills pores and voids thereby preventing permeation, sodium bentonites are widely used in geological barrier applications, such as landfills, ponds and impoundments, dams, and more.¹
As a barrier, bentonite works as a sealant, creating a watertight barrier and preventing the exchange of material or water both inwards and outwards.
Additional Uses for Bentonite
Applications employing bentonite continue to grow. Common additional uses for this diverse clay mineral include refractory, fertilizer or pesticide carriers, decolorizing agents, adhesives, catalysts, cosmetics, and more.
Bentonite Process Development Testing
The diverse nature of bentonite, paired with its potential for variation make a thorough process development program such as those carried out in the FEECO Innovation Center crucial to those producing bentonite products. While there are many variations on bentonite processing, testing is particularly important to two aspects: drying and agglomeration.
Drying Bentonite
Bentonite, as mined, typically contains between 25-35% moisture and requires drying to 5% to 12%. This is often accomplished through the use of a rotary drum dryer.
While drying can be a fairly straightforward task in mineral processing, bentonite requires special attention, as overdrying risks diminished performance of the clay.
For this reason, process experts in the FEECO Innovation Center utilize a pilot-scale rotary dryer to assess how the specific source of bentonite will respond to drying, gathering the data necessary for the design of a commercial-scale bentonite dryer.
Dryer testing often centers around identifying key process parameters such as:
- Temperature profiles
- Retention time
- Feed and product rates
- Rotational speed
- Gas sampling & analysis
- And more…
Agglomerating Bentonite
Producers are also frequently looking to agglomerate bentonite for its end use or for making it easier to handle and more flowable in the production setting. All materials respond in their own way to agglomeration and bentonite is no exception, especially considering the variation that can occur between and within sources.
The Innovation Center offers testing at both batch- and continuous pilot-scale for agglomeration processes utilizing a single piece of equipment (typically a disc pelletizer or pin mixer), or a combination of several pieces of equipment, including the rotary dryer. Depending on the goals of the process and what is already known, agglomeration testing typically centers around:
- Type(s) of equipment used
- Binder type and spray rate
- Spray locations
- Equipment speed
- Material feed rate
- Product yield
- And more…
Whether for drying or agglomeration, testing programs like these give producers the opportunity to assess the feasibility of their intended process, while also addressing potential production challenges and gathering the data necessary for scale-up. It also allows the fine-tuning of key product parameters such as:
- Particle size distribution (PSD)
- Bulk density
- Green/wet strength
- Dry crush strength
- Attrition
- Moisture content
- Flowability
- And more…
Conclusion
Bentonite clay is an incredibly diverse material with an array of properties that make it advantageous in numerous settings. Combined with its potential for variation, reaching the particle characteristics required of the intended application often necessitates thorough testing.
The FEECO Innovation Center is equipped with both the expertise and equipment to assist bentonite producers in meeting their production goals and evaluating their intended process. For more information on testing the drying or agglomeration process for bentonite, contact us today!