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.

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:

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