Borate Caking: Understanding and Prevention

:: Tuesday, August 3, 2021 :: Posted By Emmanuel Laval

U.S. Borax refined borate products are well known for their resistance to caking, which happens when particles clump together into crystallized masses. At our U.S.-based production facilities in Boron, California, and Wilmington (at the Port of Los Angeles), we take great care throughout the processes of refining, production, and packaging to ensure that our products are easy to handle, free-flowing, and easy to use in a wide variety of formulations and applications.

However, no borate product is immune to caking. Because of the inherent properties of borates, caking can cause multiple problems in some industrial applications:

  • Caked borates are difficult to incorporate evenly
  • Caking interferes with the flowability of the product during processing
  • In applications that require fine or powder-grade particles, manufacturers must take the extra step of crushing or milling the material before it can be used if it is caked

To prevent these issues, it helps to understand why borate caking happens.

  • Compaction: When weight is applied to the material, it compresses, which can cause particles to clump together
  • Moisture: Just like with table salt, exposure to water or humidity can cause the highly soluble borate particles to stick together
  • Heat: Exposure to high temperatures and temperature variations can release crystalline water that is present in the borate, creating the conditions for caking

Preventing caking due to compaction is fairly straightforward. We recommend using racks to store bags in warehouses or storing in a single layer on the floor. Avoid stacking packaging during transportation and storage. When powder and granular pallets are loaded and stacked into containers, pallets of borates in powder form should be placed on top of pallets of borates in granular form, since powdered borates are more prone to caking from compaction.

Caking due to moisture and temperature changes is a bit more complicated and can be tricky to prevent because it can actually happen inside of sealed containers. Let’s take a closer look.

How moisture causes caking in borates

Anhydrous borates, which have already been dehydrated and have no water content—such as Dehybor®—will cake only if they come into contact with moisture from an external source, such as humidity in the atmosphere or water that condenses on the inside of a storage facility.

When water contacts a dehydrated borate, the highly soluble particles dissolve and essentially melt together. When the water later evaporates, those particles stay bonded and form large crystals of many tightly bonded particles.

Hydrated borates—such as Neobor® and Optibor®—contain water of hydration for different properties and purposes. These borate products can cake inside of sealed containers if the temperature inside of the container fluctuates enough to cause the water to release as water vapor.

In a sealed container, that water doesn't disappear. It hangs out in the container until the temperature lowers, at which point it condenses back into water—and you get the same process that happens with anhydrous borate.

The higher the number of water molecules, the lower the temperature that water will start to escape through dehydration. Some borates, particularly decahydrates, can actually lose water at room temperature—causing caking.

How to prevent borate caking

To prevent caking in borates, it’s important to minimize compaction and ensure that no water can contact the material. Most U.S. Borax products are packed in lined paper bags that keep moisture out. But some industrial customers purchase borates in bulk, and they must take extra care to transport and store the material in a way that minimizes caking.

Recommendations for packaged borates:

  • Take care not to damage packaging during transportation or storage.
  • Pay attention to the temperature at which hydrated borates start to dehydrate and store them below that temperature. (For example, Neobor should be stored below 85°F or 29°C.)
  • Limit temperature fluctuations in the storage facility, as hydrated borates can still cake inside of sealed packaging with enough temperature fluctuation.
  • In storage, the widest temperature variation usually happens near or on container walls. So if you’re storing borates on the edges of containers, you’ll need to be especially careful about temperature fluctuations.
  • Sustained elevated temperatures are worse than temperature cycles, so if you discover that the temperature has risen in a storage container, it’s important to get it back down as soon as possible.

Recommendations for bulk borates:

  • Prevent cross-contamination of sodium borate with non-sodium borate products by using dedicated storage equipment and/or rigorously cleaning between uses. For example, accidentally mixing Optibor with Neobor can cause caking due to the formation of sodium pentaborate.
  • If storing borates in a steel silo, install an air dryer to keep moisture out.
  • The hardness of the caked lumps generally increases with the number of temperature cycles. Because it’s difficult to completely prevent temperature changes, if you store products for many years, you’re likely to end up with hard caking. Use your oldest products first and consider switching to just-in-time inventory.

U.S. Borax products are designed and packaged to ensure a long usable shelf life. Following these recommendations will help ensure you get the best results from our high-quality products.

Have more questions? Our technical support team is here to help. Contact us any time




U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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