拜耳法赤泥电场驱动酸法脱碱耦合动力学与过程强化调控

Red mud is the alkaline solid waste produced in the production of alumina from bauxite. The premise of large-scale harmless treatment and resource utilization is to effectively remove the alkali in red mud. The effect of acid dealkalization of red mud is obvious. However, it needs to provide H+ source and further treat the secondary waste of sodium salt. Aimed at addressing this problem, this project intended to integrate electric field into the acid dealkalization process of red mud, and Bayer red mud electrochemical dealkalization technology was proposed. Through the priority electrolysis of H2O of red mud leaching solution, H+ was produced by oxidation in the anode area to remove the alkali of red mud, and OH- was generated in the cathode area to form caustic solution, which was returned to Bayer process for recycling. Based on the thermodynamics and kinetics of H+ producing by electrolytic anodization of red mud leaching solution, as well as the kinetics of replacement reaction between H+ and Na+ in the dealkalization process of activated red mud, the control law of electrode reaction and non electrode reaction rate in the process of red mud electrochemical dealkalization was revealed. The kinetic law of the coupling process of red mud electrochemical dealkalization was revealed through the rate coordination of the electrode process and the non electrode process, and the strengthening regulation mechanism of red mud electrochemical dealkalization process was established. The basic research carried out in this project will promote the theoretical deepening of multi field coupling and the application of electric field in alumina industry, which expands the scientific frontier in the field of red mud dealkalization.

赤泥是铝土矿生产氧化铝产生的碱性废渣，赤泥大规模无害化、资源化的前提是有效去除赤泥中的碱。赤泥酸法脱碱效果显著，但一方面需要提供H+来源，另一方面产生钠盐二次废物需要进一步处理。为解决上述问题，本研究将电场融入到赤泥酸法脱碱过程中，提出拜耳法赤泥电化学脱碱技术，通过赤泥浸出液电解过程中H2O的优先放电，阳极区氧化制H+实现赤泥脱碱，阴极区产生OH-形成苛性碱溶液返回拜耳法流程循环利用。本项目通过赤泥浸出液电解阳极氧化制H+过程热力学与动力学以及活化赤泥脱碱过程H+与Na+置换反应动力学研究，揭示赤泥电化学脱碱过程电极反应和非电极反应速率控制规律。通过电极过程与非电极过程的速率协同揭示赤泥电化学脱碱耦合过程动力学规律，建立赤泥电化学脱碱过程强化调控机制。本项目开展的基础研究将推动多场耦合作用的理论深化和电场在氧化铝行业的应用，拓展赤泥脱碱领域的科学前沿。

利用电化学手段进行赤泥脱碱及苛性碱的回收一直以来在氧化铝行业存在研究空白。项目通过赤泥浸出液电解反应H2O在复杂体系优先放电的热力学与动力学研究，揭示了静态赤泥电化学脱碱过程电极反应特征和控制规律。首先，依照赤泥离子浸出特征分别绘制了Na-Al-H2O、Fe-H2O、Ca-Al-H2O体系的E-pH图，分析了阴阳两极可能发生的氧化还原反应及电极电势，明确不同pH和不同温度下H2O优先氧化还原的优势区域。其次，通过不同电解阳极的循环伏安曲线和极化曲线的测定和分析计算阳极氧化的反应速率常数等动力学参数。研究了不同阳极材料下电解过程的槽电压、阴阳极pH和体系温度的变化情况。随着电解反应的进行，金属阳离子逐渐从阳极区迁移至阴极区，槽电压和矿浆温度逐渐升高。阳极矿浆中的水分子被氧化，生成O2和H+，阳极赤泥矿浆pH从碱性逐渐降至酸性，pH最终维持在3.5左右；阴极水被还原产生H2和OH-，pH急速上升，最终稳定在12左右。通过电极反应与非电极反应的速率协同揭示赤泥电化学脱碱耦合过程动力学规律，建立赤泥电化学脱碱过程强化调控机制。理论及试验证明了通过强化传质可进一步优化静态电解的赤泥脱碱指标，较静态的赤泥电化学脱碱效率提升近20%，阴极浸出液TDC浓度提升至到12.46 g/L。本项目开展的基础研究推动了赤泥电化学脱碱的理论深化，拓展赤泥脱碱领域的科学前沿，填补了电化学手段加速赤泥脱碱的科学技术空白。