Impurity Behavior in Aluminum Extraction by Low-Temperature Molten Salt Electrolysis
Shuxing Huan, Yaowu Wang, Kejia Liu, Jianping Peng, Yuezhong Di
Abstract
Alumina-containing waste can potentially be used to produce a coarse Al–Si alloy by carbothermal reduction and subsequent aluminum metal extraction by soluble anode electrolysis. However, metal impurities in the alloy have important effects on the product purity. In this study, anodic dissolution of the coarse Al–Si alloy and cathodic electrochemical reduction of metal impurity ions in the electrolyte were investigated. The phases, element distributions, and compositions of the anode, electrolyte, and products were investigated by X-ray diffraction, scanning electron microscopy, and inductively coupled plasma atomic emission spectrometry. When using an aluminum wire of diameter 2 mm as reference electrode, the order of anodic metal dissolution is Mg > Ca > Al > Fe > Si > Ti > Mn, and that of metal impurity ion reduction in the electrolyte is Fe > Si > Al > Mg > Ca. Mg and Ca dissolve into the electrolyte before aluminum does, but they have little effect on the product purity because of their high decomposition voltages. Fe and Si in the alloy anode begin to dissolve at electrode potentials of 0.4 and 0.7 V, respectively. If keeping the electrode potential lower than 0.3 V, the Al purity reaches 99.9%.