The Value of Refined Borates

Not All Boron Sources Are Created Equal

Research shows that not all boron sources are equal in their ability to provide plants with soluble boron throughout the season.

In the tests below, all samples were of similar particle size. Granubor compared to ulexite from Peru and Chile

Our Purification Process

U.S. Borax products are fully refined to remove impurities and maximize potential plant uptake. This process results in a pure, natural product that provides optimized nutrition throughout the growing season.

The U.S. Borax refining process involves several important steps:
  1. We mine high-quality sodium-borate ore that is naturally low in calcium and other contaminants
  2. We dissolve the ore in water
  3. We settle the dissolved borate liquor to remove impurities
  4. We cool the liquor and then further wash and filter the resulting crystal slurry
  5. We dry the refined slurry to produce dry borate crystals
  6. We check our products for purity, solubility, consistency, and optimal granulation
  7. We constantly conduct and review field tests and other research to improve our products and services

Production Process of Refined Borates at U.S. Borax 

U.S. Borax borate refinement process

Crude Ulexite Ore from Other Borate Providers

Most other borates go through only minimal (if any) processing. These products are merely washed, dried and calcinated, and granulated. As a result, they are typically less soluble, contain more contaminants, are inconsistently sized, and provide less reliable boron availability rates than refined boron.

Ulexite borate refinement process


Other impurities, such as arsenic, also compromise the quality of some borate products. Our studies of fertilizer samples show arsenic content of as much as 157 ppm in samples of Turkish 10% boron ore, while Chilean 10% boron ore can contain as much as 1,500 ppm. By comparison, U.S. Borax refined Granubor® contains less than 5 ppm.


Supplier % of B Water Solubility B CaO Arsenic content (ppm)
Turkish 15% 5.4% 19% 141
Turkish 15% 5.4% 0% <20
Turkish 14% 4.7% 0% 151
Turkish 10% 7.4% 21% 157
Chilean 10% (granular) 5.2% 22% 1500
Peruvian 10% (granular) 5.9% 12% 962
Granubor 15% 15% 0% <5

What is granulated ulexite?

A sodium-calcium borate product that is only partially water soluble and therefore not as available to crops.
%B Average 15.0%Inconsistent B levels
Particle Size Average size: 2.4mm (4.75mm to 1.40mm, 95% retained guaranteed)Average size: 1.4mm [4.75 mm to 1.40mm, 85% typical with up to 15% <1.40mm (dust)]
Water Solubility 100% solubleIncomplete dissolution
Research > 30 years of worldwide field tests and researchLimited field tests
Purity No added ingredients, fillers, or coatingsCan contain high levels of arsenic, aluminum, and barium

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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