Urea-Gypsum Fertilisers: Reducing Two Major Environmental Challenges in our Industry – A Review of Production Technologies

Phosphoric acid is a major feedstock for phosphate fertiliser, but, for every tonne of acid produced, an average of 5.4t of phosphogypsum (PG) is created. The outcome is that the annual PG output of International Fertiliser Association (IFA) members is in the range ~225-245 million tonnes. This amount and its contaminants pose a significant challenge for the industry to achieve better sustainability performance.

Urea is the most widely used nitrogen fertiliser with some 200 million tonnes sold annually but suffers from significant nitrogen losses through ammonia volatilisation, CO2 loss, as well as N2O emissions and nitrate leaching. The emissions of CO2 and N2O contribute significantly to the carbon footprint of urea fertilisers.

These two issues form possibly the two major environmental challenges in our industry.

Urea with gypsum represents a potential next-generation fertiliser. It can deliver improved agronomic performance and higher nitrogen use efficiencies. And, because of the large volume of urea use, it can potentially contribute significantly to the reuse of PG.

This paper shows potential and proven novel production pathways to produce urea-gypsum fertilisers. Some production pathways start with solid urea products while others use urea solution or urea melt as the feedstock; several production methodologies are proven at commercial scale. Coating with gypsum, a core of granules with gypsum and inhibitors and co-crystals can all increase nitrogen use efficiency, primarily through reducing the rate of dissolution and thus of urea hydrolysis, and may in some cases increase the product quality. One proven production method also integrates phosphate producing a unique ‘USP’ granular fertiliser, containing four nutrients: urea (N), phosphate, sulphur and calcium, with the option to add other nutrients such as potassium and micro-nutrients.

By recycling industrial gypsum wastes and reducing nitrogen losses, the use of urea-gypsum fertilisers aligns with global goals for climate-smart, resource-efficient agriculture.