HH Process

05 Hh Process 05

The Prayon Hemihydrate (HH) Process

The Prayon Hemihydrate (HH) Process is sought for its simplicity and the high P2O5 strength in the product acid.

It consists of an attack of the phosphate rock under hemihydrate conditions cooled by a specific flash cooler designed to limit the scaling. The square compartment reactor fitted with Prayon agitators provides the best available conditions on the market in terms of lifetime, maintenance and reaction efficiency. Hemihydrate slurry is filtered on a Prayon tilting pan filter to recover the phosphoric acid.

Depending on the rock processed, the ex-filter acid strength is typically 40-42% P2O5 and the typical P2O5 recovery efficiency is 92-94%.


  • low investment
  • flexibility to process all types of phosphate (sedimentary and igneous)
  • limited grinding of the rock
  • high strength phosphoric acid


  • where low-cost rock is accessible
  • where energy cost is high
  • where gypsum disposal is possible
  • where water and steam supply are a challenge