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Neutralized gypsum as granules (acid fluoride)
Gypsum as by-product is produced during Hydrofluoric Acid manufacturing process.
Neutralized pulp in granules (gypsum) is anhydrous calcium sulfate (anhydride). This product is used as an additive to a natural gypsum in cement industry to produce alabaster binding material and dry pack mortar, including self-leveling floor. Anhydrous cement forms gypsum rock when reacting with water. Unlike natural gypsum, hardening of anhydrous cement takes longer time, and the produced gypsum rock has higher strength, exceeding the strength of the best grades of natural gypsum. When hardening, anhydrous cement produced of gypsum as resulted from hydrofluoric acid manufacturing does not shrink, has low density, high sound absorption, fire-resistance and excellent sanitary characteristics. One of the advantages of the gypsum is low cost.
The results of industrial and laboratory tests of fluorogypsum (acid fluoride) are as follows:
- Density of fluorogypsum as dried up to constant weight shows 1,500 ÷ 1,650 kg/m3 vs. 1,100 ÷ 1,350 kg/m3 GOST density for gypsum;
- Strength of fluorogypsum as dried up to constant weight shows 10 ÷ 26 MPa (100 ÷ 260 kgf/cm2) vs. 5 MPa (50 kgf/cm2) under GOST in compression conditions;
- Water extract рН does not exceed 6.4 due to use of limestone (СаСО3) milled to grain size of less than 0.2 mm as a neutralizing agent;
Grain size distribution of the neutralized gypsum is shown in the table:
|Index designation||Standard value|
|Mass fraction of sulfur oxide (VI), SO3, %, min.||45|
|Mass fraction of sulphuric acid, H2SO4, %, max.||2,5|
|Mass fraction of moisture, H2O, %, max.||4|
The product is not consolidated.
- Due to insignificant content of fluorine in the form of calcium fluoride, the anhydride produced can be classified as category B (over 20 minute hardening);
- No free sulfuric acid is allowed upon neutralization.