Hemihydrate Process (HH)

The main feature of WPA production hemihydrate method is decomposition of phosphate raw materials with a mixture of sulphuric and phosphoric acids with calcium sulphate crystallization in the form of a metastable phase - CaSO4*0,5H2O dihydrate. Standard HH process flowsheet is shown in Figure 1.

DH process flowsheet.jpg

Figure 1. HH process flowsheet

Plant production capacity is 160÷500 thousand tons of Р2О5 per year during processing of Khibiny apatite concentrate. 

General advantages of the HH process:

  • high efficiency of reaction volume usage and Р2О5 surface efficiency at filtration unit (2÷3 times higher than at dihydrate plants of the same capacity);
  • low capital and operating costs of high efficiency reaction slurry air cooling method in the foam layer;
  • long operating time of the plant (not less than 325 days per year);
  • low electricity consumption per 1 ton of Р2О5 (~ 75 kW for Khibiny apatite concentrate);
  • high content of Р2О5 in product WPA - 31÷37%;
  • low energy costs for WPA concentration (by ~ 2 times relative to WPA dihydrate process).

Main disadvantages of the HH process:

  • particular quality of the used phosphate raw materials (not lower than 70BPL);
  • relatively low process yield - up to 96÷96.5% (for Khibiny apatite concentrate);
  • high operating temperatures of operating mediums (87÷94 °C);
  • sufficiently high emission of fluorine gases at the extraction and filtration stages.

The following types of phosphate raw materials are used as suitable for HH process: Khibiny and Kovdorsky apatite concentrates, some types phosphate rocks (China, Saudi Arabia, Jordan, Syria, Australia, etc.) as well as their mixtures.

Main parameters of JSC NIUIF HH process:


Apatite concentrate KOLA

Kovdorsky apatite concentrate*

Plant modernization

New plant

Plant production capacity, thousand tons of Р2О5 per year

tons of Р2О5 per day










Reaction volume, m3




Total filtration surface, m2




Type and number of used vacuum filters

3 tilting pan filters

2-3 belt filters

2 tilting pan and 1 belt

Р2О5 content in WPA from filteration unit, %



* co-processing with other types of raw materials, plant after modernization