5. Preparation of industrial anhydrous sodium sulfate from sea salt bitter brine. At present, in order to make full use of sea water resources in order to make full use of sea water resources, mixed salt of potassium chloride, new halogen or bitter brine to produce potassium chloride, with halogen Method, new halogen method and mixed salt freezing to manufacture mirabilite .
(1) Glauber's salt with halogen method The salt-producing mother liquor - bitter brine (28 ° ~ 29 ° Be) or brine brine is evaporated to 20 ~ 23Be with a certain amount of new halogen, formulated into a sodium- magnesium ratio of 2 ° 21 ° The brine of ~23°Be is mainly composed of NaCl, MgCl ₂ , MgSO _{4 ,} etc. In the Yantian evaporation pond or the storage brine pool, Glauber's salt is naturally frozen at low temperature (-10-15 ° C) in winter.
(2) The new halogen method is used to prepare the thenardite by freezing the fresh brine which is not saturated with NaCl. The method has a high precipitation rate of the Glauber's salt, and does not use bitter brine, thereby avoiding the salt production due to the bitter brine cycle.
(3) Glauber's salt is prepared by mixing salt and frozen. The mixed salt is a by-product of the preparation of the mother liquor (bitter brine) in the production of potassium chloride (chemical composition: MgSO ₄ 30%, MgCl ₂ 29%, KCl 1%, NaCl 35%). When Na:Mg=2:1, then the Glauber's salt can be frozen. There are two kinds of freezing methods, one is to use the low temperature natural freezing in the salt field, and the other is the mechanical freezing method. Glauber's salt prepared by the natural freezing method produces industrial anhydrous sodium sulfate by a full-dissolution evaporation dehydration method due to the mixing of impurities such as sediment. The quality of the mirabilite prepared by the mechanical freezing method is high, and the anhydrous sodium sulfate product can be obtained by dehydrating and drying the mirabilite by a hot melt evaporation dehydration method or a hot melt salting out method. The hot melt evaporation dehydration method: the Glauber's salt obtained by the mechanical freezing method is sent to a hot melt tank and heated to about 70 ° C, so that a part of the sodium sulfate solution forms a saturated liquid in its own crystal water, and another part of sodium sulfate is precipitated as an anhydrous salt. The slurry is sent to a centrifuge for separation to obtain anhydrous sodium sulfate and a saturated solution. The anhydrous sodium sulfate is sent to dryness, and the saturated solution is recovered by evaporation, centrifugation, and drying. Hot-melt salting-out method: The Glauber's salt is heated and melted at 32.4 °C or higher to reduce the viscosity and facilitate the conversion. Generally, the temperature is 70-80 ° C, and an appropriate amount of NaCl is added to reduce the solubility of Na ₂ SO ₄ . The solution is precipitated, and the precipitated anhydrous sodium sulfate is subjected to centrifugal dehydration and drying to obtain a qualified product. 2 mixed salt conversion to produce nitrate. The conversion from the mixed salt to anhydrous sodium sulfate requires three different conversion reactions, which are carried out in three conversion tanks, all in a continuous countercurrent operation (Fig. 5).

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