Digging deep with phosphorus
A compact news update from Ma ’ aden about investments in a phosphate fertilizer project in Saudi Arabia recently caught SSW ’ s attention , prompting desk research into how such fertilizers are produced . The standard process relies on aggressive chemicals hence a wide range of corrosion resistant alloys are normally required , especially when considering the likelihood for contamination . And , with global food consumption on an upward trend , demand for such fertilizers seems set to grow .
By KCI Editorial
Production chain The production chain for most commercial phosphate fertilizers starts with phosphate rock . Significant reserves of high-quality phosphate rock can be found in Morocco , China and US , making these countries the most important suppliers in the phosphate industry . The extracted rock
Phosphates vs phosphorus
Phosphates are a naturally occurring form of the element phosphorus . Together with nitrogen and potassium , phosphorus is one of the three primary nutrients required for photosynthesis and crop growth . is first ground before being passed through recovery units to mechanically separate out sand , clay and other impurities . In the US , this process is often referred to as phosphate beneficiation . The crushed , concentrated phosphate rock is then mixed in a reactor with sulphuric acid . The two react to form a weak phosphoric acid . This particular step is widely known as the wet phosphoric acid process – WPA for short . As an aside , engineers may refer to the actual breaking down of geological matter using acids as digestion . The weak phosphoric acid ( 40-55 %) thus produced can then be used as the starting point to produce solid and liquid phosphate fertilizers ( see box below ). SSP is the easiest to produce : the semi-solid resulting from the phosphate rock / sulphuric acid reaction is simply allowed to cool and cure . It is then milled and screened to the appropriate size .
A quick guide to phosphate fertilizers : MAP = mono-ammonium phosphate DAP = di-ammonium phosphate SSP = single superphosphate TSP = triple superphosphate
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