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Publication: Fertilizer International 510
Date: September - October 2022
Expert: Jevis Bao, R&D Director, Arkema China

The origin and importance of colour

When the industrial production of fertilizers first began, their natural colour was largely a reflectionof their original constituents and the manufacturing process. In single superphosphate (SSP) and calcium superphosphate manufacture, for example, grey-to-dark colour phosphate rock is reacted with sul- phuric acid or phosphoric acid to generate large concentrations of light-coloured calcium sulphate and calcium phosphate. Unsurprisingly, this colour combination results in grey fertilizer granules.

The light grey or green colour of diammonium phosphate (DAP) from Idaho, meanwhile, primarily comes from the phosphoric acid that is reacted with ammonia during its manufacture. Urea and carbonyl diamide, in contrast, are white in colour due to the absence of impurities in their ammonia and carbon dioxide starting materials.

During the first half of the 20th century, it became possible to manufacture many more types of fertilizer in greater quantities due to rapid advances in production technology – a transformation that propelled the fertilizer sector from its relatively modest origins into a fully-fledged standalone industry.

By the end of the last century, the fertilizer industry had developed a sophisticated range of complex speciality fertilizers suitable for many different agricultural applications globally. At the same time, the use of colourants emerged as an increasingly important way to brand or dif- ferentiate individual fertilizer types. DAP fertilizers from Florida and North Carolina, for example, became very popular and widely recognised as ‘magic granules’ in North American agriculture due to their signature natural dark brown colour.

Today, colour is an important differentiator for fertilizers. Producers use colourants:
  • To differentiate their fertilizers from those of other producers
  • To meet regional and customer colour preferences
  • As functional additives or coatings to reduce dust formation and prevent caking.

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Read about the project in Fertilizer International.