Nat Sulph: From Mirabilite and Thenardite to Pharmaceutical-Grade Sodium Sulphate
At a glance
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Chemical name |
Sodium sulphate |
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Chemical formula |
Na₂SO₄ |
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Water solubility |
Freely soluble |
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Natural minerals |
Thenardite, Na₂SO₄, and mirabilite, Na₂SO₄·10H₂O |
Sodium sulphate occurs naturally in evaporite deposits, salt lakes, and arid environments. Its anhydrous mineral form is thenardite, Na₂SO₄. Its best-known hydrated form is mirabilite, Na₂SO₄·10H₂O, historically called Glauber’s salt.
Pharmaceutical-grade sodium sulphate may be purified from these natural sources or manufactured from purified sodium and sulphate compounds. The required hydration state is controlled during crystallization and drying.
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Mineral connection: Ten waters and a temperature-sensitive crystal Mirabilite contains ten structural water molecules for every Na₂SO₄ unit. In the sodium sulphate–water system, the stable crystalline form changes near 32.4°C: below this transition, the decahydrate is favoured under the appropriate solution conditions; above it, anhydrous sodium sulphate is favoured. Mirabilite was historically known as Glauber’s salt after the 17th-century chemist Johann Rudolf Glauber, who described it after studying mineral spring water. |
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Body connection: Sulphur in vitamins and coenzymes Sulphur is incorporated into important biological molecules, including thiamine, vitamin B₁, C₁₂H₁₇N₄OS⁺, and biotin, vitamin B₇, C₁₀H₁₆N₂O₃S. These sulphur-containing vitamins and coenzymes help enzymes carry out reactions required for normal metabolism. |
Route one: Purification from natural deposits or brines
Sodium sulphate-bearing ore or brine may also contain sodium chloride, potassium salts, calcium salts, magnesium salts, clay, moisture, and insoluble particles. Mined material is crushed where necessary, dissolved or leached, and filtered.
Selective crystallization and recrystallization exploit differences in solubility to separate sodium sulphate from neighbouring salts. Temperature control is especially important because it influences whether Na₂SO₄ crystallizes in an anhydrous or hydrated form.
Throughout purification, the goal is to preserve or deliberately establish the specified sodium sulphate form while reducing unwanted mineral and elemental impurities.
Route two: Chemically manufactured sodium sulphate
Purified sodium compounds derived from halite or brine can be neutralized with purified sulphuric acid.
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2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O |
Sodium carbonate provides another possible route:
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Na₂CO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O |
Both reactions produce sodium sulphate. The product remains dissolved until concentration and temperature are adjusted to produce the desired crystals.
Controlling the hydration state
Manufacturers may target anhydrous Na₂SO₄ or a specified hydrate. Temperature, concentration, cooling rate, residence time, and drying conditions determine whether water becomes incorporated into the crystal lattice or is removed.
The crystals are separated, washed, dried, milled or classified, and tested for identity, assay, moisture, hydration state, chloride, calcium, magnesium, heavy metals, and other elemental impurities.