水氯镁石电解制备高纯氢氧化镁的反应过程与电流效率损失机理研究

A large of brine with rich magnesium chloride is uncontrolled emission from potassium fertilizer extraction which use salt lakes brine as raw materials. The brine is to be formed to bischoffite by dried and evaporated naturally; it is not only cause magnesium resources waste, but also cause serious damage to the ecological environment of Salt Lake, and it is be called "magnesium harm". The market demand of high-purity magnesium hydroxide is increasing year by year, because of its excellent performances. In order to solve magnesium pollution and obtain high value-added product, a novel electrolysis preparation of high-purity magnesium hydroxide process is developed, which use bischofite as raw materials. The mechanisms of electrode reaction，mass transfer and growth for Mg(OH)2 will be investigated based on thermodynamics, electrochemistry, kinetics, crystallography，fluid mechanics and also combined with advanced material structure testing technology. Effects of electrolysis process conditions and impurity ions (Li+, Na+, K+, Ca2+ and BO33-) on current efficiency and performances of Mg(OH)2 will be explored. Simultaneous optimization method for current efficiency and performances of Mg(OH)2 will be obtained. Theory system of electrolysis preparation of high-purity Mg(OH)2 will be established. Previous fundamental research will provide the theoretical basis for comprehensive utilization and safe disposal of salt lakes bischofite.

盐湖资源提钾过程中无节制排放大量富含氯化镁的卤水，经自然蒸发形成水氯镁石，不仅造成镁资源浪费，而且对盐湖生态环境造成严重破坏，业内称之为“镁害”。而高纯氢氧化镁由于其优良性能，市场需求量逐年递增。据此，本项目提出一种水氯镁石电解制备高纯氢氧化镁的新工艺以期实现增值化消除“镁害”。基于热力学、电化学、动力学、晶体学、流体力学结合先进的物质结构测试技术，明晰氯化镁电解的电极过程、传质规律、Mg(OH)2生长机制；揭示电解工艺条件、Li+/Na+/K+/Ca2+/BO33-非镁阳离子对电流效率及Mg(OH)2物性特征的影响规律；掌握电流效率与Mg(OH)2物性特征同步优化的调控机制。建立较为完善的盐湖提钾水氯镁石电解法制备高纯氢氧化镁的基础理论体系，为实现盐湖水氯镁石的综合利用和无害化处理提供理论基础。

盐湖提钾过程中排放的大量含氯化镁废卤水，经自然蒸发形成水氯镁石，不仅造成镁资源浪费，而且对盐湖生态环境造成严重破坏，业内称之为“镁害”。而高纯氢氧化镁由于其优良性能，市场需求量逐年递增。据此，本项目提出一种水氯镁石电解制备高纯氢氧化镁的新工艺以期实现增值化消除“镁害”。研究了电解工艺条件、杂质离子对电流效率及Mg(OH)2物性特征的影响规律。电流效率低的原因有：低Mg2+浓度时，OH-与Mg2+结合生成Mg(OH)64-；电解温度低时，溶液粘度高，离子扩散速度慢；电流密度低时，氢氧化镁生长速率慢；但较高的Mg2+浓度（＞0.5mol/L）、电流密度（＞0.05A/cm2）及温度（＞40℃）又会使产物氢氧化镁聚集严重粘结极板；Ca2+，BO33-严重影响电解过程及氢氧化镁纯度；Na+、K+、Li+对电流效率及产物纯度影响不显著，SO42-能使氢氧化镁以多孔网状生长，且观察到以层岛复合状和完整光滑界面机制进行生长；.成核过程研究发现：温度越高氢氧化镁成核诱导期越短，温度恒定时电流密度是成核过程的主导因素，结晶初期高电流密度及温度会促进晶核形成，相同电流密度条件下升高温度有利于晶体长大；活性剂PEG对氢氧化镁晶体生长有规范作用，但浓度大于0.6g/L时，会形成复杂络合物覆盖电极活性位点；氢氧化镁在500℃/保温时间1h直接煅烧所得氧化镁活性最高，平均粒径27.6nm，比表面积51.15m2/g；.数值模拟研究发现，气体流动受极板放置深度影响，增大极板放置深度更有利于传质。气泡上浮过程中存在横向弥散行为，气泡幕覆盖极板表面，产生不利影响；形成了水氯镁石电解制备氢氧化镁扩试平台，优化条件下可达电流效率84%，电耗8105 kWh/t，产物氢氧化镁粒度均匀，纯度99.4%，白度95.8，从工艺及装备方面为工业级水氯镁石电解槽提供设计依据。基于上述研究成果建立了较为完善的盐湖提钾水氯镁石电解法制备高纯氢氧化镁的基础理论体系，为实现盐湖水氯镁石的综合利用和无害化处理提供理论基础。

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