膜电解在碱溶碳分法氧化铝生产工艺中的应用

Application of membrane electrolysis in alumina production by alkali-dissolution and carbonization-precipitation

对碱溶碳分法氧化铝生产工艺中直接影响离子交换膜电解效果的碳分母液除杂方案、电解槽结构设计、阳极评选、阳极区碳酸钠电解液浓度及电解深度、阴极区氢氧化钠浓度、操作温度、电流密度等关键技术及要素进行了初步的设计、研究和评估。研究表明:碳分母液中少量残留的铝酸根可以通过添加适量碳酸氢钠下调pH值至10.2以下,絮凝析出再滤除,然后直接移接氯碱厂的电解技术方法。电解碳酸钠生产氢氧化钠和碳酸氢钠的适宜的操作条件为:阳极Na2CO3溶液浓度1.5～1.8mol/L,阴极NaOH溶液浓度5～7mol/L,电解温度80～85℃,电流密度1000～2500A/m2,电解深度85～90%。采用析氧过电位较低的镍涂钌电极作阳极替代钛涂钌阳极,可以降低槽压400mV,但其耐过钝化腐蚀性能有待研究提高。

The factors that directly affect ion exchange membrane electrolysis in alumina production by alkali-dissolution and carbonization-precipitation, such as the purification of the mother liquid, the design of the electrolysis cell, the electrode materials, the concentration of sodium carbonate, the electrolysis extent, the concentration of sodium hydroxide, the operating temperature and the current density, have been investigated. Aluminates in the mother liquid can be precipitated and filtered by adding sufficient sodium bicarbonate to regulate the pH value to under 10.2. The electrolysis technology used in the chlor-alkali industry can then be directly employed. Suitable operating conditions for preparation of NaOH and NaHCO3 by membrane electrolysis of Na2CO3 were found to be as follows： Na2CO3 anolyte with concentration of 1.5 - 1.8 mol/L, NaOH catholyte with concentration of 5- 7 mol/L, temperature of 80℃, current density of 1000- 2500 A/m2, and electrolysis extent of 85 % - 90 %. The cell voltage was decreased by 400 mV when the Ru-Ti anode was replaced by Ru-Ni, which has lower overpotential of oxygen evolution, but the resistance of the latter to transpassive corrosion needs to be improved.