The Value of Refined Borates

Rising fertilizer costs make it tempting to buy cheaper boron. However, these unrefined borate sources fall short when it comes to performance. Ultimately, that means buying more and applying more.

In contrast, refined borates are a better value because they deliver better results.

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


Refined boron is more available to crops

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

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

Compare: Granulated ulexite vs. refined Granubor

Granulated ulexite is a sodium-calcium borate product that you’ll commonly find in the marketplace. However, this borate is less refined meaning it’s only partially water soluble and therefore not as available to crops. 
%B Average15.0%Inconsistent B levels
Particle SizeAverage 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)]
Particle HardnessSuperior particle hardness and strengthInsufficient hardness, degradation prone
Water Solubility100% solubleLimited availability (only 30-40% soluble)
Release RateEven release rateUneven Release Rate
PurityNo added ingredients, fillers, or coatingsLess pure, may contain high levels of heavy metals
ConsistencyUniform particle sizes, minimal segregationIrregular Sizing; Higher Segregation Rate

Additional Resources

Arsenic in fertilizers
Arsenic (As) is a naturally occurring, toxic heavy metal dispersed in the environment through a variety of industrial, mining, and agricultural activities. Hi... Read More
Availability of boron to plants
Soil plays a major role in determining the availability of boron in plants. Boron is taken up by plant roots from the soil solution. Learn about the science b... Read More
An Agricultural Borates Primer
The majority of researchers and farmers have recognized the importance of boron in agriculture. Boron is necessary for proper plant nutrition. Learn More

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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