How did Brine Salt Purification by Recrystallization work?

Crude salt (containing NaCl + CaSO₄ + MgCl₂, etc.) → dissolved in water → insoluble impurities settle or are filtered → heated to evaporate → NaCl reaches saturation and precipitates first → Ca/Mg salts remain in the mother liquor due to higher solubility → pure NaCl is separated.

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卤水制盐提纯

Q: What did Brine Salt Purification by Recrystallization look like?

In salt pans or salt pans, brine is concentrated by evaporation and crude salt precipitates → crude salt is redissolved in fresh water → insoluble matter is filtered out → the solution is heated to evaporate, causing NaCl to recrystallize → pure white table salt is obtained.

Brine Salt Purification by Recrystallization

Recrystallization purification of sodium chloride from brine: exploiting the near-flat temperature-solubility curve of NaCl vs. the inverse solubility of calcium sulfate (gypsum) to achieve food-grade salt through sequential evaporation and fractional crystallization.

卤水制盐

Scientific Principle

Fractional crystallization via evaporation: NaCl solubility is nearly temperature-independent (~35.7 g/100g H₂O at 0°C, ~39.8 g at 100°C), so cooling is useless — instead, brine is evaporated, causing NaCl to reach saturation and crystallize first. CaSO₄ (gypsum) has inverse solubility — it precipitates when heated, so it is removed early in the process. MgCl₂ and other highly soluble salts remain in the mother liquor (bittern/卤水) and are discarded. This produces table salt of >95% purity without modern chemical processing. The Chinese salt administration (盐铁专卖) was one of the world's earliest state monopolies, funding the Han Empire's military expansion.

卤水制盐提纯

Brine Salt Purification by Recrystallization

Scientific Principle

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