Search

The preparation of coarse Al–Si alloys by carbon-based electrothermal reduction is a viable means of recycling scrap aluminum on an industrial scale to allow the high-value utilization of this resource. However, the presence of impurities on the cathode can have significant effects on the product purity. The present study explored the behavior of impurity elements on the cathode and the reasons for the decreased purity of aluminum deposited at the cathode with increases in electrolysis time. X-ray diffraction, scanning electron microscopy and inductively coupled plasma-atomic emission spectroscopy were used to study the compositions of the molten salt electrolyte and of the cathode product, as well as the phases and element distribution on the working electrode. With increasing cell voltage, the elements added as impurities were found to precipitate in the order of Fe > Al > Si > Mn > Ti > Mg > Ca. Increasing the concentration of these elements in the molten salt electrolyte was determined to increase the cell voltage, with Mg and Ca having the greatest effect. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

Diagrams of the equilibrium potential E (relative to the standard chlorine electrode) against the activity of oxide ion ( expressed as its logarithm, pO2-) in systems of Ti-O-Cl-M (M=Li, Na, Mg, Ca, Sr and Ba) were plotted to investigate the electro-deoxidation of porous TiO2 pellets in different chloride molten salts, including LiCl, NaCl, MgCl2, CaCl2, SrCl2 and BaCl2. From the diagrams, the reduction pathways of TiO2 in different molten salts are similar; and the applied potential (vs Cl-/Cl2) on the cathode and O2- ion activity influence greatly on the reduction pathway of TiO2 and the deoxidation limit. To test and verify the results of the thermodynamic analysis, electro-deoxidation experiments in different molten salts were done to determine the actual pathways in the electrochemical reduction of TiO2 and the possible deoxidation limits in the molten salts. The results indicated that the thermodynamic analysis is helpful in predicting and understanding the electrochemical reduction process of titanium oxides though the experimental results differ slightly from the thermodynamic analysis in some systems. Low-oxygen Ti can be obtained only in molten CaCl2. [ABSTRACT FROM AUTHOR]