Magnesium sulphate heptahydrate
There are three produce method of magnesium sulphate hepta
- It is obtained by adding sulfuric acid to natural magnesium carbonate (magnesite), removing carbon dioxide, and recrystallizing it. It is obtained by dissolving Kieserite (MgSO4·H2O) in hot water and recrystallizing it, and it is made from sea water.
- (sea water sun-dried salt bittern method)
Brine is obtained from salt in the sea water. After evaporation by the brine method, high temperature salt is produced. Its composition is MgSO4>30%, NaCI<35%, MgCl2 is about 7%, and KCl is about 0.5%. Bittern can be leached with 200g/L MgCl2 solution at 48°C. NaCl dissolves less, while MgSO4 dissolves more. After separation, the leaching solution was cooled to 10°C to precipitate crude MgSO4·7H2O, which was recrystallized twice to obtain the finished product.
- (sulfuric acid method)
In the neutralization tank, first add the magnesite slowly to the water and mother liquor, and then neutralize with sulfuric acid until the color changes from soil to red. Control pH=5, relative density 1.37～1.38 (39～40°Bé) . Filter the neutralized solution at 80°C, then adjust the pH to 4 with sulfuric acid, add an appropriate amount of seed crystals, and cool to 30°C to crystallize. After separation, the finished product is dried at 50~55℃, and the mother liquor is returned to the neutralization tank. It can also be neutralized with low-concentration sulfuric acid and 65% magnesium oxide content of bitter soil, and then filtered, precipitated, concentrated, crystallized, centrifuged, and dried to obtain magnesium sulfate heptahydrate.
Reaction chemical equation: MgO+H2SO4+6H2O→MgSO4·7H2O
Magnesium sulphate hepta chemical character:
It is stable under 48.1℃, easy to weather in warm dry air, when it is heated to 48.1℃, it loses 1 crystal water and becomes magnesium sulfate hexahydrate. At 67.5℃, it dissolves in its own crystal water At the same time, magnesium sulfate monohydrate is precipitated. At 70～80℃, 4 crystal water is lost, 5 crystal water is lost at 100℃, 6 crystal water is lost at 150℃, and all crystal water is lost at 200℃. Powdery anhydrous magnesium sulfate, the dehydrated substance is placed in moist air to re-absorb water. In a saturated solution of magnesium sulfate, hydrated crystals with 1, 2, 3, 4, 5, 6, and 12 water can be crystallized, and magnesium sulfate dodecahydrate can be precipitated in a saturated aqueous solution at -3.9 to 1.8°C. Magnesium sulfate heptahydrate is precipitated in saturated aqueous solution at -1.8～48.18℃, and magnesium sulfate hexahydrate is precipitated in saturated aqueous solution at 48.1～67.5℃. Magnesium sulfate monohydrate is precipitated when it is higher than 67.5℃. Magnesium sulfate hexahydrate is at 87～92. Dissimilar melting occurs between ℃ and produce magnesium sulfate pentahydrate or tetrahydrate. Magnesium sulfate tetrahydrate is converted into magnesium sulfate trihydrate at 106°C. Magnesium sulfate trihydrate is converted into magnesium sulfate dihydrate and dihydrate at 122～124°C. Magnesium sulfate is converted into stable magnesium sulfate monohydrate at 161～169°C.