硫酸锰溶液中镁离子的行为及复盐结晶法除镁技术调控机制

The salts crystallization method with magnesium ammonium sulfate was proposed in this project, and it was low cost, no pollution and the by-products were easy to comprehensive utilization, the method could solve the common problem in electrolytic manganese production. It is the problem that the concentration of impurity ion magnesium was higher than that of the main metal ion manganese. By researching the effect of Mg2+ on the physical and chemical properties and solution structure of manganese sulfate solution for electrolytic manganese and the electrolytic process, the behavior of magnesium ions in manganese sulfate solution would be elucidated, and the harm of magnesium ion to electrolytic manganese production would be quantified. The solubility of ammonium sulfate and magnesium sulfate in manganese sulfate solution was determined by equilibrium method. Using Raman, XRD, SEM, TEM and other advanced detection methods and solution crystallization theory, the crystal state, crystal size and morphology were studied, the nucleation time, and growth process were recorded. As a result, the mechanism and dynamic behavior of salts crystallization with ammonium magnesium sulfate would be explored. Basing on the previous two, combining with electrolytic manganese production practices, by controlling the crystallization parameters, applying outfield and adding seeds, the technical regulation mechanism for the salts crystallization of magnesium ammonium sulfate would be obtained, and the technology prototype of removing magnesium with salts crystallization would be formed. The results of the project would be of great significance to solve the harm of magnesium ion in the production of electrolytic manganese, to promote the sustainable development of electrolytic manganese industry, and to improve the scientific and technology of manganese metallurgy.

项目提出了低成本、无污染、副产物易综合利用的硫酸铵镁复盐结晶除镁的方法，以解决电解锰生产工业的共性问题：杂质离子镁的浓度高于主体金属离子锰的浓度。项目拟通过镁离子对电解锰用硫酸锰溶液的物化性质、溶液结构和电解过程的影响研究，阐明镁离子在硫酸锰溶液中的行为，量化镁离子对电解锰生产的危害；采用平衡法测定硫酸铵和硫酸镁在硫酸锰溶液中的溶解度，利用Raman、XRD、SEM和TEM等先进检测手段和溶液结晶理论，研究结晶晶态、晶体粒度、形貌，记录成核时间、核的长大过程，探索硫酸铵镁复盐结晶的机理及动力学行为；在前两者的基础上，结合电解锰生产实践，采用控制结晶参数、施加外场和添加晶种等手段，获得硫酸铵镁复盐结晶的技术调控机制，形成复盐结晶法除镁的技术原型。项目成果对解决电解锰生产中镁离子的危害、促进电解锰产业的持续发展、完善锰冶金科学技术具有重要意义。

针对电解锰系统镁离子浓度高、对生产造成诸多负面影响的事实，本项目开展了如下研究。系统研究了镁离子在电解锰生产系统中的平衡分布。当锰矿中含有100g镁，有38.19g的Mg进入浸出液中，除铁和除重金属后，进入到锰电解液中的Mg约为29.5g，电解时Mg在阳极液、阴极液、金属锰及阳极泥中的含量分别为25.71g、3.23g、0.09g和0.018g；研究了镁离子对电解金属锰用硫酸锰溶液的物化性质及其对电解过程的影响，量化了镁离子对电解锰生产系统的危害。随着Mg2+浓度的增加，不同温度梯度下的硫酸锰电解液的密度、电导率以及粘度逐渐增加，而表面张力逐渐下降。随着电解液中Mg2+浓度的增加，电流效率呈现出逐渐下降的趋势；在Mg2+浓度较低时及电沉积早期，锰晶粒主要以棱锥体首先铺满整个阴极板，到电沉积中期，逐渐以大小相似的多边形颗粒形式存在，随着Mg2+浓度的增加以及电沉积时间的延长，条纹和金字塔顶逐渐不规则，随Mg2+浓度从10 g/L增加到30 g/L，晶粒生长速率由13.213 μm/h增加到18.785 μm/h。不同Mg2+浓度时电解锰溶液的循环伏安曲线基本特征不变，但随着Mg2+浓度的增加，阴极电流曲线斜率逐渐降低，氧化峰电流曲线斜率逐渐降低。电化学阻抗谱说明Mg2+浓度的增加使得溶液与电极界面间电荷转移的难度增加；系统研究了硫酸镁、硫酸铵在硫酸锰溶液中的溶解度，并用Apelblat半经验公式进行拟合。利用ΔL定律模型对铵、镁、锰复盐蒸发结晶动力学进行了系统研究，并在此基础上讨论了电解锰生产条件下Mn2+浓度、Mg2+浓度、硫酸铵浓度、结晶温度、转速、保温时间、有无晶种等因素对铵、镁、锰复盐结晶过程和晶体粒度和质量的影响规律。获得较为适宜的结晶工艺条件：Mn2+浓度为28g/L、Mg2+浓度为20g/L、硫酸铵浓度为110g/L、结晶温度为328K、转速为90rpm、结晶时间为3600s且添加8%晶种。在此条件下锰、镁、铵结晶率分别为68.05%，97.59%，94.81%。本项目的研究系统阐明了镁离子对电解锰生产的危害程度，揭示硫酸锰溶液中硫酸铵镁复盐结晶机理及动力学行为，在此基础上探寻复盐结晶法除镁的调控技术，为电解锰生产健康发展提供理论指导。