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Phosphoric acid

Dihydrate Process (DH)

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Dihydrate Process (DH)

The main feature of WPA production dihydrate method is decomposition of phosphate raw materials with a mixture of sulphuric and phosphoric acids with calcium sulphate crystallization in the form of a stable phase - CaSO₄*2H₂O dihydrate. Standard DH process flowsheet is shown in Figure 1.

DH process flowsheet.jpg

Figure 1. DH process flowsheet

Plant unit production capacity is up to 300 thousand tons of Р₂О₅ per year or more.

General advantages of the DH process:

there are almost no restrictions on the quality of the used phosphate raw materials;
relatively high process yield - up to 98%;
long operating time of plants and equipment (320÷330 days per year);
relatively low operating temperatures of operating medium (80÷85 °C);
relatively low emission of fluorine gases at the extraction and filtration stages;
high yield of by-product - fluorosilicic acid at concentration stage.

Main disadvantages of DH process:

low efficiency of reaction volume usage and low Р₂О₅ surface efficiency at filtration unit;
low content of Р₂О₅ in WPA - 24÷28%.

JSC NIUIF developed high efficiency dihydrate process, which allows to significantly improve efficiency and increase the content of Р₂О₅ in WPA from filtration unit.

The improvement of the DH process for phosphate raw materials - Khibiny apatite concentrate is:

process temperature increase up to 85÷95 °C;
the use of aluminum containing modifier-additives;
reducing slurry hold-up time in the extractor to 2.5÷3.5 h (in the usual DH process - 5÷6 h);
increasing the content of Р₂О₅ in WPA up to 30÷33%;
air cooling of the reaction slurry.

Increasing Р₂О₅content in WPA can significantly reduce the energy consumption for its concentration. The average process yield of Р₂О₅ in the improved process reaches 97.5÷97.7%. The implementation of the process is relevant for new plants with a unit capacity of about 300 thousand tons of Р₂О₅ per year, the modernization of operating plants is also possible.

Main parameters of JSC NIUIF high efficiency dihydrate process

Parameter	Apatite concentrate KOLA	Karatau Phosphate rock
Plant production capacity, thousand tons of Р₂О₅ per year	300÷450*	up to 220
Reaction volume, m³	1200÷3200*	1100
Total filtration surface, m²	250÷390*	250
Р₂О₅ content in WPA from filtration unit, %	30÷33	25÷27

*for modernization of operating plants