MgCl26H2O-Mg(OH)2-MgO技术路线制备高纯镁砂过程基础研究

Utilization of magnesium resources has become a technical bottleneck for salt lake industrial development. In this project, an efficient green technology is developed for the utilization of magnesium resources in salt lake, in which the discarded bischofite as raw material reacts with sodium hydroxide to prepare magnesium hydroxide precursor, the precursor is calcined to get active magnesia, and then fused magnesia with high-purity is produced after the high-temperature melt crystallization of active magnesia. The research focuses on the key scientific issues in each process as follows. First, an interface model between magnesium hydroxide crystal and the solvent layer under the micro-environment of high concentration electrolyte, is developed using the surface-docking method. The crystallization kinetics of magnesium hydroxide is investigated using this interface model, and crystal morphology control and the crystallizer structure scale-up design is also studied thoroughly. Second, a particle fast reaction model considering the physicochemical processes, such as drying, crusting, thermal decomposition, crystal morphology transition, etc., is developed to illuminate the pyrolysis mechanism of magnesium hydroxide and the coupling effects of drying-reaction-transfer-flowbehavior during dynamic calcination. Third, solid state physics mechanism of magnesia melting process considering the influence of impurities, defects, and additives is investigated, and the melt-crystallization regulation method is developed to produce high purity fused magnesia with large particle size. In conclusion, according to the investigation of key scientific issues for each process, the revealing of the coupled effects of reaction-transfer-fluid flow on complex reactive crystallization, the construction of multi-scale regulation method, atheoretical foundation will beestablished for the new green technology to produce high-purity fused magnesia using the discarded bischofite as raw material, that is in favor of the high-value utilization of magnesium resources from brine.

盐湖镁资源的利用已成为盐湖工业发展的瓶颈。本课题以盐湖废弃水氯镁石为原料，烧碱法制备氢氧化镁前驱体，动态煅烧获得活性氧化镁，高温熔融结晶制备高纯镁砂，开展高效绿色工艺基础研究。用Surface-docking方法构建高浓度电解质体系微观环境下氢氧化镁晶体与溶剂层的界面作用模型，研究氢氧化镁结晶过程动力学，实现氢氧化镁晶体形貌调控和结晶器设计的最优化；获得包含颗粒干燥、结壳、热分解、晶型转变等物理化学过程的颗粒快速反应模型，揭示动态煅烧过程中干燥-反应-传递-流动行为的耦合规律与热解机理；研究镁砂熔炼过程杂质、缺陷和添加剂行为以及镁砂结晶过程的固体物理学机制，获得高纯度大晶粒度镁砂结晶过程的控制理论与方法。通过对过程关键科学问题研究，揭示复杂反应结晶过程反应-传递-流动行为的影响及其耦合规律，建立多尺度调控方法，为开发高纯电熔镁砂制备新技术与新方法，实现盐湖镁资源高值化综合利用奠定理论基础。

我国盐湖氯化钾工业副产大量水氯镁石废弃物，如何实现水氯镁石高效利用已成为盐湖循环经济产业发展的关键。本项目以MgCl2•6H2O→Mg(OH)2→MgO工艺制备高纯镁砂为主线，同时较为系统地研究了水氯镁石直接喷雾热解制备MgO并副产高纯HCl工艺，探索了水氯镁石与CO2反应制备碳酸镁前驱体工艺的可行性，重点围绕高纯Mg(OH)2制备、轻质活性MgO热解制备、高纯电熔镁砂烧结制备三个关键单元开展了系统性的应用基础理论、工艺优化与过程开发研究。. 项目采用碱法反应结晶制备高纯Mg(OH)2前驱体，优选NaOH作为矿化剂，通过耦合水热改性工艺有效提高了产品纯度与过滤性能，并实现了工艺系统优化。优化后Mg(OH)2一次平均颗粒尺寸由0.12μm增加到0.73μm，团聚指数由92.25减小到2.59，纯度由98.12%增加至99.66%。同时，基于流体力学模拟分析，设计了年产14万吨氢氧化镁的DTB型反应结晶器，并完成了装置工程建设。在此基础上，利用Mg(OH)2高温煅烧热解制备轻质活性MgO，采用多升温速率法测定了微米级Mg(OH)2颗粒热解反应动力学，确定了Mg(OH)2主分解过程为反应动力学控制，反应活化能为129.4 kJ•mol-1，指前因子为1.820×1010 min-1。同时，结合流体动力学模拟，围绕水氯镁石直接喷雾热解技术设计了颗粒干燥-煅烧-气固分离一体化热解炉，通过炉内多相传递反应特性分析，对热解炉关键几何尺寸与操作条件进行了优化，并完成了中试实验验证。针对热解煅烧获得的轻质活性MgO，进一步开展了高纯镁砂烧结制备工艺研究，获得了高纯、高密度烧结镁砂的最优操作条件，明确了轻质MgO中杂质NaCl、Mg2SO4、K2SO4和B元素的控制上限分别为0.2 wt%、0.15 wt%、0.15 wt%和0.014 wt%。此外，相关动力学研究结果表明，MgO烧结初期为体积扩散控制，TiO2加入后其动力学转向界面扩散控制，晶粒生长活化能由556.9 kJ•mol-1降至272.8 kJ•mol-1，是理想的镁砂烧结助剂。. 本项目立足于盐湖资源循环利用实际应用需求，聚焦于关键工艺过程的应用性基础科学问题，基于多种技术路线的对比探讨，建立了高纯镁砂生产技术的理论体系与工艺基础，为盐湖镁资源综合利用的相关工艺过程开发提供了理论与技术支撑。