Abstract:

There are abundant magnesium resources in salt lake brine, and the primary utilization form at present is mainly to extract crystalline magnesium chloride. In order to improve the efficiency of the process, the scheme of directly separating high-purity crystalline magnesium sulfate by adding brine and changing temperature was put forward in this paper, and the changes of magnesium sulfate crystal micro-morphology and the influence of cooling rate on crystal morphology during the non-equilibrium dynamic cooling process of MgSO₄ saturated brine, MgSO₄-NaCl co-saturated brine and MgSO₄-NaCl-MgCl₂ co-saturated brine were investigated. The results show that the rate of crystal formation in the non-equilibrium dynamic cooling process of MgSO₄ saturated brine is related to the cooling rate. At the cooling rate of -1.02℃/min, MgSO₄ saturated brine can form MgSO₄·7H₂O crystal with a radial diameter of about 1300 μm after cooling for 30 min. However, when NaCl exists in brine, the final crystal form is MgSO₄·6H₂O, and most of them are irregular blocks. MgCl₂ in brine can promote the crystal to form prismatic MgSO₄·6H₂O. Under the action of NaCl and MgCl₂, MgSO₄-NaCl-MgCl₂ co-saturated brine can precipitate a complete crystal form of high-purity crystalline magnesium sulfate after cooling for 15 h. It is assumed that the initial crystal nucleus determines the crystal form, but the interference of Na⁺ on crystal growth makes the crystals diversified in morphology.

Key words: magnesium sulfate, salt lake tail brine, crystallization, separation, microstructure

摘要：

盐湖老卤中镁资源储量丰富，现阶段的初级利用形式主要是提取结晶氯化镁。为提高过程效益，提出了兑卤及变温直接分离高纯结晶硫酸镁的方案，并分别考察MgSO₄饱和卤水、MgSO₄-NaCl共饱和卤水、MgSO₄-NaCl-MgCl₂共饱和卤水在非平衡动态降温过程中硫酸镁晶体微观形貌的变化以及降温速率对晶体形貌的影响。结果表明，MgSO₄饱和卤水非平衡动态降温过程中晶体形成的速率与降温速率有关，在-1.02℃/min的降温速率下，MgSO₄饱和卤水降温30 min后即可形成径向约1300 μm的MgSO₄·7H₂O晶体；但是，当卤水中存在NaCl时，最终的晶体形式为MgSO₄·6H₂O，且多为不规则的块状；卤水中的MgCl₂能促使晶体形成棱柱状的MgSO₄·6H₂O。在NaCl和MgCl₂的作用下，MgSO₄-NaCl-MgCl₂共饱和卤水降温15 h后可以析出完整晶型的高纯结晶硫酸镁。

关键词: 硫酸镁, 盐湖老卤, 结晶, 分离, 显微结构