CALCIUM SULFATE HEMIHYDRATE

Description

Phosphogypsum is a moist, fine powder with a free water content of ca. 20 – 30 % and considerable amounts of impurities, the exact impurities and their amounts depending on the rock and the specific process. The radioactive substances present in small amounts in sedimentary phosphate rock are partly transferred to the phosphogypsum as 226Ra, leading to slightly increased radioactivity of such gypsums. About 1.7 t of gypsum is obtained per tonne of raw phosphate, corresponding to 5 t of gypsum per tonne of phosphorus pentoxide produced.

The Uses of CALCIUM SULFATE HEMIHYDRATE

Anhydrous: insoluble anhydrite is used in cement formulations and as a paper filler. Soluble anhydride, because of its strong tendency to absorb moisture, is useful as a drying agent for solids, organic liquids and gases; the desiccant used in laboratory and industry is known under the name Drierite. This material can be regenerated repeatedly and reused without noticeable decrease in its desiccating efficiency. The hemihydrate is used for wall plasters; wallboard; tiles and blocks for the building industry; moldings; statuary; in the paper industry. The dihydrate is used in the manufacture of portland cement; in soil treatment to neutralize alkali carbonates and to prevent loss of volatile and dissolved nitrogenous compounds by volatilization and leaching; for the manufacture of plaster of Paris, artificial marble; as a white pigment, filler or glaze in paints, enamels, pharmaceuticals, paper, insecticide dusts, yeast manufacture, water treatment, polishing powders; in the manufacture of sulfuric acid, CaC2, (NH4)2SO4, porous polymers. Pharmaceutic aid (in plaster casts).

Definition

A powdered mixture of calcium silicates and aluminates, which is made by heating limestone (CaCO3) with clay, and grinding the result. When mixed with water, reactions occur with the water (hence the name hydraulic cement) and a hard solid aluminosilicate is formed.

Definition

calcium sulphate: A white solidcompound, CaSO₄; r.d. 2.96; 1450°C.It occurs naturally as the mineralanhydrite, which has a rhombicstructure, transforming to a monoclinicform at 200°C. More commonly,it is found as the dihydrate,gypsum, CaSO₄.2H₂O (monoclinic;r.d. 2.32). When heated, gypsumloses water at 128°C to give thehemihydrate, 2CaSO₄.2H₂O, betterknown as plaster of Paris. Calciumsulphate is sparingly soluble in waterand is a cause of permanent hardnessof water. It is used in the manufacture of certain paints, ceramics,and paper. The naturally occurringforms are used in the manufacture ofsulphuric acid.

General Description

White or nearly white, odorless, crystalline solid.

Reactivity Profile

CALCIUM SULFATE HEMIHYDRATE is generally of low reactivity. Can serve as an oxidizing agent under forcing conditions. Incompatible with aluminum (at high temperatures) and diazomethane.

Agricultural Uses

Calcium sulphate (CaSO₄) is a white solid that occurs naturally as a mineral anhydrite. It is found more commonly as dihydrate, called gypsum (CaSO₄·2H₂O). When heated, gypsum loses water at 128°C to give a hemihydrate (2CaSO₄·H₂O), also known as plaster of Paris.
Calcium sulphate is sparingly soluble in water and makes water permanently hard. CaSO₄ is used in the manufacture of certain paints, ceramics and paper. Its naturally occurring form is used in sulphuric acid manufacture.
Gypsum is the cheapest and the most useful material in reclamation of sodic soils.Calcium, solubilized from gypsum, replaces sodium, leaving behind the watersoluble sodium sulphate, which is leached out as a result of the following reactions in the soil:
Since both reactions are reversible, adequate leaching arrangements have to be made to remove sodium sulphate.
The application of about 40 t/ha of gypsum in Nevada (USA) was seen to increase water infiltration and the depth of water penetration substantially. These two measures increased hay yield up to 2.3 t/ha per year.
Gypsum requirement (GR) is the amount of gypsum necessary to be added to reclaim soil and is calculated using the formula:
The gypsum requirement is equivalent to (Na_x)×4.50 metric tons of gypsum per hectare for a 30 cm fixed depth, where Na, is the milliequivalent of exchangeable sodium to be replaced by calcium from the added gypsum.