Conversion of Low-Grade Phosphate Rock to Produce Slow-Release Fertilizer

Technology #16867

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Zhenli L. He
Peter J. Stoffella Ph.D.
Managed By
John Byatt
Assistant Director 352-392-8929

Generates Slow-Release Phosphorus From Previously Unusable Low-Grade Dolomite Phosphate Rock

This production process activates readily available phosphate rock powder with organic molecules to form a slow-release fertilizer. Phosphorus is the second limiting nutrient after nitrogen for plant growth and optimal crop yield depends on its application. However, the world’s limited sources of high-grade phosphate rock reserves are close to being depleted. Traditional methods of extracting phosphorus for use in fertilizer involves dissolving phosphate rock in concentrated sulfuric acid. However, this process is environmentally unfriendly and produces tremendous quantities of solid and aqueous wastes, including dolomite phosphate rock materials that have no further use or economic value. Furthermore, heavy rainfall can wash the highly soluble phosphate salts (incorporated into fertilizer) into waterways, leading to algal blooms.

Researchers at the University of Florida have developed an environmentally sound process for treating low- to medium-grade DPR to generate a slow-release fertilizer that releases phosphate into the soil in a controlled manner.


Process to generate slow-release phosphate fertilizers for agricultural use from discarded or previously unusable low-grade dolomite phosphate rock


  • Uses abundant, inexpensive, low-grade dolomite phosphate rock to produce high-quality fertilizers, enabling beneficial use of previously unusable by-products
  • Possesses slow-release characteristics, resulting in minimal leaching loss, enabling more efficient use of the phosphorus
  • Uses naturally occurring organic materials , making it more environmentally sound than available practices to produce phosphorus containing fertilizers


This process blends phosphate rock powder with a variety of selected organic molecular activating agents. The organic materials investigated are all abundant natural substances, such as humic acid. The interactions of activating agents with dolomite phosphate rock under optimized conditions, including mineralogical properties and particle sizes of phosphate rock, type and dosage of activating agents, moisture content and reaction time, substantially boost the availability of phosphorus in the dolomite phosphate rock and make it a slow-release phosphate fertilizers desired for agricultural use. This process creates a low cost, efficient, and environmentally friendly phosphate fertilizer with zero wastes.